�ǳ�web Knowledgebase - CPC

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How to Plumb �ǳ�web's Cordis Pressure Controller for Vacuum

Rachel Desenberg — Wed, 28 Jun 2023 18:52:16 +0000

Category:

�ǳ�web's Cordis Series Electronic Pressure Controller can be calibrated anywhere from full vacuum to 150 psi. In this video, �ǳ�web Product Manager Doug Paynter explains how to properly plumb the Cordis CPC series when working with vacuum.

Video filmed at �ǳ�web in Cincinnati, Ohio

VIDEO TRANSCRIPT:

Hi everyone, let’s talk about how to plumb the Cordis CPC Series up for vacuum and vacuum through positive pressure.

The Cordis CPC Series can be calibrated anywhere from full vacuum to 150 psi. We have a multitude of sensors to choose from and can map them out to provide you with the best-fit calibration while still maintaining the accuracy, resolution, and repeatability your complex applications require. Let’s hone in on how to properly plumb the Cordis CPC Series when working with vacuum.

The Cordis CPC is a fill-and-bleed electronic pressure controller. One proportional valve is dedicated to filling (inlet), and one proportional valve is dedicated to bleeding (exhaust). As you can see, we have three primary ports: supply, exhaust, and outlet.

When working with vacuum, we leave the supply inlet port open to atmosphere and place the vacuum supply source on the exhaust port. So if I have a 0 to -15 psi or 29” Hg output calibration to a 0-10 VDC command signal, a 10v command will equal full vacuum.

The exhaust proportional valve becomes the primary valve, which allows the vacuum supply to draw pressure through the outlet port from the downstream work area. This vacuum pressure is monitored via an onboard or external sensor that enables the comparative circuit to accurately close the loop around the downstream vacuum.

If my command changes to reduce the level of downstream vacuum, say from a 10v signal to a 5v command, the comparative circuit will open the inlet valve, which allows atmosphere into the downstream work area, which reduces the level of downstream vacuum to the actual calibrated range.

But what do you do when the application calls for both vacuum and positive pressure through the same Cordis unit? Simple—you now apply positive supply pressure to the inlet port. The comparative circuit controls the proportional valves to maintain the proper downstream pressure. So using a 15 psi differential sensor enables the Cordis to provide complete pressure control between full vacuum and 15 psi—two ranges out of one unit.

If you liked this video, please give it a thumbs up and subscribe to our YouTube channel for more. As always please give us a call to discuss your application needs. I am Doug Paynter, Proportional Product Manager here at �ǳ�web. Thank you for your time.

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Products That Provide Proportional Control of Vacuum

Rachel Desenberg — Fri, 25 Feb 2022 20:28:13 +0000

Category:

Learn more about some of the different options available for electronically controlling vacuum in this quick video from Doug Paynter, �ǳ�web's Proportional Product Manager.

Video filmed at �ǳ�web in Cincinnati, Ohio

VIDEO TRANSCRIPT:

I am Doug Paynter, Proportional Product Manager here at �ǳ�web. Today we want to talk about electronically controlling vacuum. Here at �ǳ�web, we have the ability to provide all types of levels of products that help you control vacuum. Valves can be tested and shipped with as little a leak rate at
10^-11 utilizing our clean room helium gas detector system.

Now let’s talk about �ǳ�web’s EVP and DVP proportional valves. The more current that I apply to the valve, the more of an orifice I create. So I’m able to vary the amount of flow I let into the chamber or let out of the chamber.

We also offer our unique stepper-driven proportional valves that work with vacuum very well. The Eclipse, being designed with low-flow applications in mind, utilizes a ceramic material as the wetted parts. And so, very inert, and you can run different types of hostile gasses or fluids through it. And if you need higher flows, we offer the SCPV stepper-controlled needle valve. Both of them provide significantly higher resolution and work very well with vacuum.

For closing the loop, �ǳ�web can take a vacuum sensor and work with a comparative circuit to give you closed loop vacuum control. With the Cordis, we utilize an onboard micro controller, a specific transducer that we can interface with, whether it’s pressure or flow, and our own EVP, DVP proportional valves. The Cordis can now provide you accurate, repeatable, high resolution control of your Venturi circuit, direct vacuum, or your vacuum break applications utilizing either a digital or analog command.

The Cordis pressure controller can now be calibrated to pretty much any calibration within the application of vacuum control to whatever the application really calls for. Whether it’s in millibar or torr, or inches of water column, inches of mercury, negative to positive pressure or differential, or simply absolute pressure calibrations, the Cordis can now provide you closed loop control of your vacuum circuit.

For more information on how �ǳ�web can help you better control your vacuum applications, give us a call. Be sure to subscribe to our YouTube channel so you can see more riveting videos like this one. Thank you.

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DNA Sequencing

Rachel Desenberg — Wed, 13 Oct 2021 19:58:55 +0000

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Did you know? �ǳ�web products are used in DNA sequencing to help enable early detection of diseases and better, more advanced treatments.

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NIV

Flow Cytometry Application

Rachel Desenberg — Wed, 13 Oct 2021 19:28:58 +0000

Category:

Did you know? �ǳ�web products are used in flow cytometry to help provide early detection of blood-related cancers such as leukemia and lymphoma.

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Pressure Driven Flow Control

Rachel Desenberg — Wed, 04 Aug 2021 18:46:35 +0000

Category:

�ǳ�web pressure and flow control components make for an ideal solution for precise control of critical gases in bioprocessing applications and are a smart alternative to syringe and peristaltic pumps. Smooth acceleration and stable, pulsation-free, bidirectional flow of liquids are achievable, minimizing the damaging effects of acceleration, pressure surges, shear, and impact forces on sensitive media.

A �ǳ�web Cordis Electronic Pressure Controller is precisely maintaining the headspace pressure of a reservoir. The very fine resolution capability of a second Cordis is actively controlling differential pressure to smoothly accelerate the flow of the liquid media to a stable, pulsation-free rate into and out of the reservoir. The piloted pinch valves allow use of the same pressure controllers to control multiple flow paths, in both directions and at differing flow rates.

Watch a video of a similar demo:

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Cordis Electronic Pressure Controls	Cordis Electronic Flow Controls

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Mechanical vs. Electronic Pressure Regulators: A Detailed Comparison

Rachel Desenberg — Wed, 14 Jul 2021 20:32:37 +0000

Category:

Subscribe to �ǳ�web's YouTube Channel

Pressure regulators are essential components in many systems, tasked with maintaining consistent pressure despite fluctuations in input or downstream demand. The choice between mechanical and electronic pressure regulators can have a significant impact on performance, and understanding the strengths and weaknesses of each type is crucial for selecting the right one for a given application. The decision often boils down to controllability, accuracy, dynamic performance, and cost.

Mechanical Regulators

Mechanical regulators have been around for a long time and are widely used due to their simplicity and reliability. These devices rely on physical components like springs, diaphragms, and orifices to maintain a steady pressure. Once set, they are largely "set it and forget it" devices, ideal for stable systems with minimal fluctuations.

Electronic Pressure Regulators

Electronic regulators, on the other hand, use sensors, processors, and electronically controlled valves to regulate pressure more dynamically. They are more complex but offer superior precision and adaptability, making them ideal for applications that require real-time adjustments and integration with other systems. These devices rely on physical components like springs, diaphragms, and orifices to maintain a steady pressure. Once set, they are largely "set it and forget it" devices, ideal for stable systems with minimal fluctuations.

Video filmed at �ǳ�web in Cincinnati, Ohio

Controllability: A Clear Advantage for Electronics

In terms of controllability, electronic regulators far outpace mechanical regulators. Electronic systems are designed to adjust pressure in real-time, based on feedback from integrated sensors. This feedback loop allows for constant monitoring and precise adjustments to the system’s pressure, even when conditions change.

Electronic Pressure Regulators	Mechanical Pressure Regulators
Their ability to interface with other systems and adjust on-the-fly makes them highly versatile. Systems can be automated, and pressure can be fine-tuned based on varying inputs or external factors.	A mechanical regulator, by contrast, is controlled by a fixed adjustment screw. Once set, it stays at that level until manually adjusted again. There is no real-time adaptability or integration with other systems, making it less suited for dynamic environments.

Accuracy: Fixed vs. Dynamic Precision

When it comes to accuracy, electronic regulators offer greater potential for precision.

Electronic Pressure Regulators	Mechanical Pressure Regulators
These systems take advantage of internal sensors and processors that monitor pressure continuously. This allows for dynamic adjustments to ensure pressure remains within the desired range, even in systems with fluctuating demands or inlet pressures. This real-time feedback enhances accuracy, particularly in systems that require precision under varying conditions.	The accuracy of a mechanical regulator is determined by its design—specifically, the diaphragm size, orifice size, and spring tension. While the performance is predictable and consistent, once set, there’s no way to adjust or compensate for fluctuations in real-time. Accuracy is generally fixed based on the model’s design.

Dynamic Performance: Flexibility for Changing Conditions

Dynamic performance refers to how well a regulator handles fluctuations in pressure. This is another clear advantage for the electronic regulators.

Electronic Pressure Regulators	Mechanical Pressure Regulators
Electronic pressure regulators can adjust quickly to changes in both inlet pressure and downstream demands. This is crucial for systems where conditions are constantly changing, such as in high-performance manufacturing or medical applications. Their ability to make quick adjustments ensures stable operation even in fluctuating environments.	In contrast, mechanical regulators are designed for more static environments. Once set, they are less adaptable to changes in system conditions. For stable, low-demand systems, mechanical regulators work well. However, if the pressure fluctuates or if dynamic changes are frequent, a mechanical regulator may struggle to keep up.

Cost: Weighing Performance Against Price

Cost is often a deciding factor when choosing between mechanical and electronic regulators. While electronic regulators offer enhanced performance and flexibility, they also come at a higher price.

Electronic Pressure Regulators	Mechanical Pressure Regulators
The additional complexity of sensors, processors, and feedback loops means that electronic regulators are generally more expensive. However, the added cost is often justified in high-demand applications where precision and adaptability are crucial. For example, industries such as aerospace or robotics benefit from the advanced capabilities that electronic regulators provide.	Mechanical regulators are simpler and therefore more affordable. They are ideal for applications that don’t require constant adjustments or advanced features. For systems that operate in stable conditions and have straightforward pressure control needs, a mechanical regulator offers a reliable, cost-effective solution.

Choosing the Right Regulator for Your Application

The choice between mechanical and electronic regulators depends largely on the specific needs of your system. Here's a quick breakdown to guide your decision:

Electronic Pressure Regulators	Mechanical Pressure Regulators
Choose an electronic regulator if... • You need real-time adjustments or dynamic control • Your system requires high accuracy and adaptability • Integration with other systems or automation is needed • The cost is justifiable due to the need for enhanced performance and flexibility	Choose a mechanical regulator if... • Your system operates in a stable, low-demand environment • You need a simple, reliable solution without the need for constant adjustments • The cost needs to be minimized while still maintaining good performance

Both mechanical and electronic regulators have their place in engineering applications, and the right choice depends on balancing factors like performance requirements, cost, and system demands. Ready to select a pressure regulator for your system? Contact us today for expert advice, or click here to locate your nearest �ǳ�web distributor.

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MAR-1

DR-2

Resolution in Proportional Control Applications

Rachel Desenberg — Wed, 07 Jul 2021 17:42:40 +0000

Category:

What is resolution, and why is it important? Doug Paynter, �ǳ�web's Proportional Product Manager, explains all about it in this quick video—including why most proportional controllers don't publish resolution specifications.

Video filmed at �ǳ�web in Cincinnati, Ohio

VIDEO TRANSCRIPT:

Hi everyone, I’m Doug Paynter, proportional product manager here at �ǳ�web. Today I want to talk about resolution. What is it, and why is it important?

Resolution in Proportional Control Applications

Resolution in proportional control applications is better understood when discussing in the context of controllability. For sensors or input devices, resolution is the smallest measurement change of a unit that is detectable by the device. For example, 0-100 psig pressure transducers may detect pressure fluctuations of 0.1 psig within an electronic pressure controller. The sensor resolution would be 0.1% of full scale.

The problem is that this is only on the input side of the proportional controller. Few proportional controllers can claim to be high resolution devices, simply because of their mechanical means to achieve a satisfied proportional control - the valves.

A proportional pressure controller defines resolution as the smallest value of command change that affects actual pressure response. It bases resolution on the greater of both input and output of the device. So, if a proportional controller has a sensor of 0.1% of full-scale resolution, the unit may only be able to respond to 0.5% because the 100 psig proportional valves only have a resolution of 0.5% of full scale.

The Cordis Proportional Microcontroller

The Cordis proportional microcontroller employs �ǳ�web proportional valves and proprietary algorithms to achieve ≤5 mV resolution. For example, if I take a Cordis proportional pressure regulator and put the calibration of 0-10 volts = 0-100 psig, with that type of calibration I would be able to see - and change - pressures down to 0.05 psig, throughout the whole entire range. That is phenomenal resolution.

Why Most Proportional Controllers Don't Publish Resolution Specifications

The reason most proportional controllers in today’s market do not publish resolution specifications is because their internal proportional valves only achieve steps of 25 mV, and most digital valves—on/off valves—step in the 50 mV, or even worse, resolution. �ǳ�web’s Cordis series proportional control products offer a control ratio of 200:1, signifying 200 steps of resolution for every 1 volt increment.

Understanding How Resolution is Defined

Understanding how resolution is defined in proportional control applications is one of many specifications needed to be considered when choosing the right product. While some applications do not require the high resolution proportional control, no process is going to suffer for better resolution. We do find in a lot of cases in these type of applications, high resolution control yields a significantly better result in the customer’s application.

Be sure to subscribe to our YouTube Channel. I am Doug Paynter, Proportional Product Manager here at �ǳ�web and an all around good guy. Thank you very much for your time.

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Cordis Series Electronic Pressure Controls

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White Paper: Resolution in Proportional Control

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Pressure Sensor Ranges for the Cordis CPC Series Electronic Pressure Regulators

Rachel Desenberg — Fri, 09 Apr 2021 19:04:17 +0000

Category:

�ǳ�web’s Cordis proportional regulator has the unique ability to hone in with high resolution and pressure regulation to give you phenomenal control, linearity, accuracy, and repeatability. Check out this quick video to learn more about the pressure sensors and the types of calibration they enable.

Video filmed at �ǳ�web in Cincinnati, Ohio

VIDEO TRANSCRIPT:

Hi everyone, I’m Doug Paynter, Cordis Product Manager here at �ǳ�web. Today I want to discuss the pressure sensor ranges that we have available for the Cordis CPC series electronic pressure regulators. The CPC series controllers utilize our own manufactured EVP and DVP proportional valves. This allows us to control pressure very smoothly and proportionally in both the filling and relieving directions.

With our unique control specifications, our proportional valves, our internal proportional solenoid valves, and a wide variety of pressure sensors to work with, we can now provide truly high resolution pressure regulation and maintain a good resolution of less than or equal to 5 mV.

Because of our unique microcontroller and proportional valve design, we are now able to maintain that high resolution pressure regulation in both static and dynamic conditions. This means I don’t need a bleed orifice. For the Cordis, that means you can run different types of inert gases through this product and not have to worry about it bleeding expensive gases out to atmosphere.

Our command capabilities are 0 to 10 VDC, 4-20 mA, and 3.3 volt serial. 3.3 volt serial is available on all Cordis products. This allows you the ability to talk to and manipulate the onboard microcontroller. Let’s say you want to manipulate the proportional or integral settings, or you want to get more in-depth and actually change code. With a wide variety of pressure sensors to choose from, you can now configure your command and output to be as specific as possible in your application requirements.

Twenty three pressure sensors allow us to give you any type of calibration within full vacuum to 150 psig. Whether it’s gauge absolute, bar, millibar, or inches of water column, inches of mercury, millimeters of mercury, tor, etc. and so on, now the Cordis proportional regulator has the unique ability to truly hone in with high resolution and pressure regulation to give you phenomenal control, linearity, accuracy, and repeatability for your application success.

There is a twenty fourth remote sense option. This allows you to utilize an external source of feedback. For example, if you already have a pressure sensor that you’ve been working with and you want to run that back as a primary to the Cordis unit. Or, you would rather interface with a higher resolution transducer. This provides a lot more flexibility for you in your application, however, you are going to need to contact the Cordis team to discuss this option a little bit further.

I’m Doug Paynter, Cordis Product Manager here at �ǳ�web. Thanks for watching and please subscribe to our YouTube channel for more videos.

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Video: The Proportional Valves at the Heart of �ǳ�web's Cordis Series

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The Proportional Valves at the Heart of �ǳ�web's Cordis Series Electronic Pressure Controller

Rachel Desenberg — Fri, 09 Apr 2021 18:50:07 +0000

Category:

What's inside your pressure controller? Check out this quick video to learn more about the proportional valves that help make �ǳ�web's Cordis series electronic pressure controls so unique.

Video filmed at �ǳ�web in Cincinnati, Ohio

VIDEO TRANSCRIPT:

Hi everybody, I’m Doug Paynter, Cordis Product Manager here at �ǳ�web. Today, I want to talk to you about the EVP and DVP series proportional valves that we manufacture and utilize internally to the Cordis CPC series proportional regulators. The CPC series is a very unique electronic pressure regulator. Not only does it have an onboard microcontroller and it has a host of different pressure sensors to work with, but it also incorporates our own manufactured EVP and DVP series proportional valves.

The EVP series, better known as the purple cap valve, has been utilized in countless applications around the world for years. It is a very reliable valve that has been utilized in small flow, whether it’s static or dynamic applications, any application where my critical volume is going to be sub 1 cubic inch, I need to be able to do finite pressure control in, it’s the ideal valve.

Now, when I need more flow, I’m going to go with the DVP series valve which was designed to provide more flow in a proportional condition.

The best part about this whole thing is that we manufacture everything. We manufacture the CPC series product. We also manufacture both proportional valves. This gives �ǳ�web the ability to be very versatile in what we provide you as a proportional regulator. We can provide specific calibrations, custom configurations, quick turnarounds—the possibilities are endless because we control what we’re providing you.

This is a great product for your applications. As I said, it’s a high resolution proportional regulator utilizing our own manufactured proportional valves. If you have any questions with what I’ve just said, give us a call. I’m Doug Paynter, Cordis Product Manager. Thanks for watching and please subscribe to our YouTube channel for more videos.

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Video: Pressure Sensor Ranges for the Cordis CPC Series

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DVP

How to Precisely Control Head Pressures of Liquids with �ǳ�web's Cordis Series

Rachel Desenberg — Thu, 25 Feb 2021 20:40:04 +0000

Category:

In this video, Doug Robertson, Director of Research, provides a demonstration of how �ǳ�web's Cordis line of electronic proportional pressure controllers are an ideal choice for precisely controlling the head pressures of liquids for either static or dynamic systems.

Video filmed at �ǳ�web in Cincinnati, Ohio

VIDEO TRANSCRIPT:

Hi, I’m Doug Robertson, Director of Research at �ǳ�web and I’m going to share with you how the �ǳ�web Cordis line of electronic proportional pressure controllers are an ideal choice for precisely controlling the head pressures of liquids for either static or dynamic systems with volumes as small as 4 mL, up to greater than 10 mL, and a variety of pressure ranges from vacuum up to 1 psig, 15 psig, 30 psig, even greater than 150 psig depending on your application. In the following video demonstration one Cordis controller is being used, along with �ǳ�web pinch valves, to control the feed and harvest drive pressure of two separate liquid channels into and out of a 200 mL system. A second Cordis controller is being used to accurately maintain the head pressure over that 200 mL system at 1 psig, even while media is being fed or harvested from the system by the drive controller. As you watch the upper left syringe barrel, a pinch valve has been opened in the channel, then the Cordis pressure controller to the left is creating differential drive pressure so that we’re slowly accelerating the feed of the fluid to a peak flow into the 200 mL system.

If we stop the video briefly, you’ll notice that the drive pressure shown on the left gauge has ramped to 1.5 psig, while the head pressure shown by the center gauge continues to be held steady at 1 psig, providing 0.5 psig of steady differential drive pressure to feed fluid into the 200 mL system barrel. Next, you’re going to see the same drive controller to the left smoothly ramp drive pressure down to 0.5 psig, reversing the differential drive pressure, and begin harvesting fluid back out of the 200 mL system through the same channel it just fed. And then finally, by actuating a different pinch valve, the same drive controller is being used to control harvest pressure from a second channel in the system and transfer additional liquid from the 200 mL system into the barrel down on the lower left. Again, you can see that the system head pressure being shown by the center gauge continues to be held accurately at 1 psig.

Thanks for watching and remember, for precise control of system head pressures, or for applications requiring precision pressure-driven flow control, contact us at �ǳ�web or your local �ǳ�web distributor to learn more about the capabilities of our Cordis line, or visit us at clippard.com.

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6 Ways �ǳ�web's New Cordis EPR is Revolutionizing Electronic Pressure Control

Rachel Desenberg — Sat, 21 Mar 2020 19:55:29 +0000

Category:

The future of proportional control has arrived—and it's digital! The �ǳ�web Cordis is a revolutionary microcontroller primed for escape velocity from a proportional control market that has grown stagnant. In this video, learn about the performance and flexibility of the Cordis, including what differentiates it from similar products and how it solves a variety of application challenges.

Still using an analog pressure controller? Although analog devices have long been the traditional choice for pressure regulation, digital proportional control provides significant advantages for many applications. Learn more about the revolutionary new Cordis EPR.

#CordisEPR

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�ǳ�web's CMO & COO Discuss New Cordis Series

Rachel Desenberg — Fri, 08 Nov 2019 19:43:33 +0000

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Rob �ǳ�web, Chief Marketing Officer, and Ernie Doering, Chief Operating Officer, discuss �ǳ�web's new Cordis electronic pressure controls (EPC) and how this product fits strategically with �ǳ�web's long-time mission of providing customers with fast, efficient service.

Video filmed at �ǳ�web in Cincinnati, Ohio by Fluid Power World

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Fluid Power World Video Interview: Cordis Electronic Pressure Regulators

Rachel Desenberg — Fri, 08 Nov 2019 19:31:38 +0000

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In this video interview, Mary Gannon of Fluid Power World talks with �ǳ�web's Matt Larson about the new Cordis line of digital pressure controls (EPCs).

Video filmed at �ǳ�web in Fairfield, Ohio by Fluid Power World

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Key Differentiators of �ǳ�web's Cordis Electronic Proportional Pressure Controls

Rachel Desenberg — Thu, 31 Oct 2019 15:26:06 +0000

Category:

Learn more about the key differentiators of �ǳ�web's new Cordis high resolution electronic proportional pressure controls (EPCs) in this new video from Ernie Doering, Chief Operating Officer.

Video filmed at �ǳ�web in Cincinnati, Ohio by Fluid Power World

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Cordis Pressure Controls Selection Guide

Rachel Desenberg — Wed, 17 Jul 2019 17:08:27 +0000

Category:

Troubleshooting


Configure Online	clippard.com/part/configure/CPC

Type	Card Unit or Housed Unit Housings are ideal for exposed units when protection is recommended. IP65 housing is translucent so LEDs are visible. Housing also comes with an 8-pin connector. Wire harness not included with either unit.

Porting	1/8 NPT or G1/8

Signal / Command	0 to 10 VDC or Serial

Pressure Range	0 to 150 psig VDC or Serial What is the min/max pressure in your application? This is critical to verify for proper valve selection.

Min. Volume / Flow @ Max. Pressure	≤0.25 in3 / 2.7 l/min ≤0.50 in3 / 6.7 l/min ≤1.00 in3 / 25.0 l/min ≤2.00 in3 / 65.0 l/min

Small Orifice + Large Critical Volume
= Slow Response, Very Stable

Large Orifice + Small Critical Volume
= Fast Response, Unstable

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Gas Chromatography

Rachel Desenberg — Thu, 11 Jul 2019 19:49:54 +0000

Category:

Gas chromatographs can be found in labs all over the world. They are designed to identify compounds based on the measured speed each takes to reach the detector. All gas chromatographs require stable flow control to ensure valid measurement and Identification. In this drawing, precise pressure is controlled to a known and fixed orifice. If pressure remains stable to the orifice, flow remains stable throughout the process. The compound sample is injected into the injector valve and then flows through the column while being heated. This process requires excellent resolution and accuracy to ensure stable flow.

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Pressure Control for 3D Bioprinting (Vacuum)

Rachel Desenberg — Thu, 11 Jul 2019 19:33:17 +0000

Category:

Variable vacuum (just below atmosphere) holds the print fluid up in the print head. The bioink fluid is gravity fed from the extruder to 3D print biologic products. High resolution and very fine vacuum control is required to counteract gravity without sucking fluids back into the controller.

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Cordis CPC Electronic Pressure Controller Troubleshooting Guide

Chris Agricola — Mon, 24 Jun 2019 20:48:24 +0000

Category:

If the blue LED is not illuminated:

- The micro-controller has failed

Possible causes of micro-controller failure:

- High frequency AC noise
- Electro-Static Discharge (ESD)
- A signal greater than 3.3 VDC on the serial communication lines (Pin 5 RX
and Pin 6 TX).
- A signal greater than 3.3 VDC could have come from using RS-232 cable which generates 5 VDC to the micro-controller serial inputs.

If red LED is not illuminated:

- Verify 15-24 VDC power and ground are properly hooked up.
- If 15-24 VDC power and ground are accurately installed the device needs
returned to the factory for evaluation.

PID Observations & Solutions:

These scenarios are dependent on downstream volumes and valve orifice size.

Suggested PID increments per valve size can be found in figure 1.

If proportional setting is too low, the output pressure will hunt around the desired set point within the specified tolerance; taking a long time to settle if it ever does.

- Increase the proportional value until the valves ring at a high frequency for
a short period, then lower to the point that the output settles quickly but
ringing is eliminated.

If proportional setting is too high, the valves will ring at a high frequency
for a short period of time when command signals are varied.

- Lower the proportional value until the ringing is eliminated.

If integral is too low, the output pressure could fall outside of the
specification.

It will also become less sensitive to changes in command, and when exhausting to 0% of command, may close the exhaust valve before venting off all of the pressure.

- Increase integral until the output pressure gets to pressure at the desired
speed without spiking pressures/overshooting.

If integral is too high, a change in command will result in an overshoot of set point. Testing has shown as high as 2% spike in pressure when "integral" is too high.

- Begin lowering integral value until overshoot/pressure spikes are
eliminated.

If a command is given to the Cordis device and there is no response:

Confirm the inlet pressure is sufficient. To determine what these pressures should be, refer to the Installation Instructions Guide.

Verify that the PID settings are not set too low.

If PID values are acceptable, use a voltmeter to check the voltages on the inlet valve connector. With a command and adequate supply pressure, there should be a 11.7 VDC on 1 Pin and 0.2 VDC on the other. If these values are adequate and there is still no pressure output, the valve is faulty or the valve wires were not crimped properly.

If the Cordis device is at pressure, but when the command is lowered,
the output pressure does not exhaust:

Verify the integral setting is not too low.

If the PID values are acceptable use a voltmeter to check the voltages on the exhaust valve connector. When the command signal is lower than the monitor signal or output pressure, there should be a 11.7 VDC on 1 pin and 0.2 VDC on the other. If this is the case, the valve is faulty or the valve wires were not crimped properly.

What happens if the filtration is wrong?

If there is insufficient filtering, sealant, thread tape, metal shaving from piping/plumbing it could migrate to the inlet valve causing the supply pressure to leak past the seat and nozzle to the process side. This will cause a slow loping or high frequency compensation from the inlet valve resulting in premature wear and ultimately failure

If the filtration is too constrictive and restricing the flow too much, this could hurt the performance of the Cordis device by not allowing the valves to be the limiting factor of the control system.

What happens if the customer uses the wrong sealant?

The result of using sealant such as thread tape or pipe dope is that it inherently will fragment or flake once it has solidified and can easily migrate into the pneumatic system. If this occurs and proper filtration is not used, it could result in valve contamination.

What happens if the customer uses the wrong media?

If a media that is not a clean, dry, non-corrosive gas is used through the Cordis, damage to the pressure sensor could occur. This damage to the sensor could result in the element being over-pressurized due to hydrostatic pressure of liquid or the element's output value shifting due to corrosion building on the sense element.

What happens if the customer uses the wrong USB to TTL cord type (5 VDC)?

If a 5 VDC USB to TTL cable is used which would apply 5 volts to pins 5 and 6 of the card assemblies, and pins 2 and 7 on the housed assemblies, the micro-controller could fail due to exceeding its 3.3 VDC rating.

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Digital vs. Analog Control in Proportional Applications

Rachel Desenberg — Mon, 24 Jun 2019 20:44:22 +0000

Category:

Pressure regulators are closed-loop mechanical devices that maintain a pressure setpoint in various processes within a system. They are available in mechanical or electronic versions, in digital or analog models. Although analog devices have long been the traditional choice, digital proportional control provides significant advantages for many applications. Here, we will explore what digital versus analog means in terms of electronic pressure controllers, discuss the differences, and highlight some of the many benefits of digital electronic pressure controllers.

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Mechanical vs. Electronic Pressure Regulation

Pressure regulators are available in mechanical or electronic versions. The primary difference between the two is that if a system that uses a mechanical pressure regulator requires a change in pressure setpoint, an operator must make that change manually. An electronic pressure regulator (EPR) also maintains a pressure setpoint, but the setpoint can be selected electronically, allowing a programmable logic controller (PLC), for example, to alter the setpoint as needed. An electronic pressure regulator significantly increases the flexibility and robustness of a system, but many varieties of electronic pressure controllers leave the system designer with some difficult choices. One of the many choices involved in selecting the most suitable electronic pressure regulator for an application is whether to go with a digital or analog model.

Digital vs. Analog

There are at least three elements of electronic pressure regulators to which the terms digital and analog can be applied: the valves, the communication method, and the technology of the controller. Most electronic pressure regulators employ an inlet valve to increase pressure to the regulated volume, another valve to exhaust pressure, a sensor to measure pressure, and a controller to decide what to do. The valves in the electronic pressure regulator can be simple on-off valves (digital), or they can be proportional valves (analog). Typically, electronic pressure regulators with very high resolution and excellent repeatability use proportional valves.

Benefits of Digital Pressure Controls:

Simple Calibration
& Tuning Procedures

Better Security

Less Noise

Lower Energy Costs

Device Pairing Flexibility

Increased Flow Potential
with External Pressure
Transducer

The second element characterized as analog or digital is the communication method used between the controller and electronic pressure regulator. There are many different protocols for communicating a pressure setpoint. However, they all fall into the two primary buckets of analog or digital. The earliest electronically controlled pressure regulators were analog devices called current-to-pressure transducers, or I/Ps (read: I-to-Ps) for short. In these devices, a current signal ranging from 4 to 20 milliamps would tell the I/P transducer to output a pressure ranging from 3 to 15 psig. For example, a 16 mA current signal would result in a 12 psig pressure output. These instruments were not closed-loop, and they were delicately balanced through great effort and could easily fall out of calibration. That said, the 4 to 20 mA protocol is still prevalent today. Modern electronic pressure regulators with analog input tend to use a 0 to 10 volt analog input signal. Voltage signals are easy to generate, available in a wide variety of industrial control devices, and simplify the mapping of voltage to pressure. Analog signals are an easy way to start controlling an electronic pressure regulator, but they are vulnerable to electromagnetic interference.

Much like Morse code, digital protocols employ a series of discrete pulses representing either one or zero bits to transmit information, eliminating potential damage from electrical noise. A wide variety of digital communication protocols exist, from SPI and I²C (I-Squared-C) to RS232 to modern industrial serial protocols like EtherCAT and IOLink. One thing that all of these have in common is their immunity to electromagnetic noise. They also facilitate a much richer command set and feedback on process status information. However, digital protocols are more complex, requiring a steeper learning curve.

Finally, digital versus analog can also refer to a particular device's control technology. Is the circuitry all analog, or is a digital microcontroller managing the operation of the electronic pressure regulator? Can digital devices provide the same control as analog, and are there practical reasons to choose digital over analog? In this paper, we will explain how microcontroller devices can replace analog technology and provide configurable functionality that enables users to specify the dynamic performance of the valve and adapt its characteristics to various application conditions.

Response Time

For the purposes of this discussion, the definition of response time will be the time required for the controller to achieve the maximum power output to the valves in response to a change in command or operating conditions. Generally speaking, an analog controller will react to such changes significantly faster than a digital microcontroller will. So it would be logical to believe that analog electronic pressure controllers have better response time than digital ones. However, the time necessary for the controller to respond is small compared to the time it takes for the valves to respond to the controller or for the volume to achieve the desired pressure. So practically speaking, response time is not a significant factor in deciding whether to choose an analog or digital controller.

Digital vs. Analog Controller Response Times

Contrasting Calibration & Tuning Procedures

Calibrating and tuning proportional controllers requires adjusting PID (proportional-integral-derivative) settings to dial-in valve performance for specific process conditions. With analog devices, this modification is performed manually by rotating potentiometers until the unit achieves the desired behavior. Digital PID parameters install via a software interface and a few keystrokes. Initial application tuning of both technologies invariably requires some trial and error to optimize a valve's performance. However, we will explain how the microcontroller excels when custom calibrations like offsets and inversions are required.

Most proportional controllers receive a calibration of zero to some number indicating a range of pressure, flow, or force to control. This range is proportional to the signal used to command the device. For example, a typical calibration states 0 to 10 VDC equals 0 to 100 psig. In this example, a command of zero volts will cause the pressure controller to bring the output pressure to zero. In some processes it is essential to have some amount of pressure downstream at all times. In such cases, an offset calibration—like 0 to 10 VDC equals 10 to 100 psig—is prescribed. Alternatively, calibration may need to be inverted; for example, 0 to 10 VDC equals 100 to 0 psig. For analog controllers, these calibration changes are laborious and require cutting existing traces, rerouting wires, modifying hardware, soldering, desoldering, and more. Just one of these modifications necessitates a return trip to the factory. However, altering the calibration of digital controllers is as simple as editing a couple of numbers via the software interface. A task easily performed in the field.

Dynamic Process Reaction

Some pressure control applications are static and require only simple pressure control in a closed volume. However, many applications are dynamic with varying inlet pressures, leaks, setpoints, volumes, and back pressures. Finding a set of PID values that keep an analog electronic pressure regulator well behaved across all of these dynamic conditions can be difficult, if not impossible. A digital pressure controller can change its PID values at any time through a technique called gain scheduling where the microcontroller selects different PID values from a preset menu, so to speak, based on real-time changes in operating conditions. In this way, the digital microcontroller can achieve better stability and repeatability over a wider range of operating conditions than an analog controller.

Better Security, Less Noise & Energy Costs

PID security is another advantage of microcontroller operated products. When the factory-tuned PID settings create undesired controller behavior under particular conditions, a person might try to tamper with the analog controller's PID potentiometers. That can often create bigger problems. Once the PID settings are changed, it is difficult to get the unit back to factory calibration. Microcontroller PID changes, on the other hand, require a digital interface that keeps track of all the modifications to the PID settings. Not only does this provide more accountability, it also gives a means to get back to the factory settings if the new PID values do not work as expected.

Additionally, digital proportional pressure controllers can reduce energy costs and audible noise. Most analog proportional controllers require a bleed—a very small downstream flow—to operate well. This constant bleed is what allows the internal valves to achieve high resolution, but it also consumes media and increases ambient noise levels. Some digital controllers employ proprietary algorithms and custom PWM (pulse-width-modulation) frequencies to produce high-resolution control without a bleed orifice. Compressed air is costly enough to produce, but introduce oxygen or helium into a process, and the cost of energy to compress these gases becomes pricey if a constant bleed exists. If the gas is one that cannot escape into the atmosphere, a bleed orifice is out of the question.

Device Pairing Flexibility

Most modern-day proportional controllers can be configured to accept various sensors as direct or indirect feedback, enabling the pressure control apparatus to control flow, pressure, or force at a critical point in the process. For analog controllers, the external sensors must be analog as well, which both limits the options available and exposes the pressure control system to problems with electrical noise. Further, the feedback signals from the external and internal sensors are often in conflict, creating instability and oscillations.

On the other hand, proportional microcontrollers easily pair with both analog and digital sensors using I²C, SPI or other digital protocols. Because of the flexibility of digital control, the external feedback sensor, once paired with the controller, holds complete authority as the reference against the commanded setpoint. This eliminates all potential conflicts with the onboard sensor, resulting in much better stability and accuracy. Also, since there are numerous flow and pressure sensors available with different power demands for operation, a microcontroller can be configured to deliver the precise excitation required from the sensor of choice, adding another layer of adaptability for micro-controlled proportional devices.

So digital controllers give the designer a wider array of external sensors and transducers to choose from—but why are external sensors used, and how can they add functionality to a process?

External Sensors in Proportional Applications

Dispensing is a typical application managed by proportional controllers. Normal operations require precise pressure control of inert gases over various media: liquids, plastics, adhesives, etc. Sometimes, the pressure of the particular media needs to be regulated instead of the gas above it. Since most proportional controller designs only support gases, a compatible transducer is used to measure the pressure of the specific media and provide feedback directly to the controller. The controller actively modifies the pressure of the gas to induce pressure regulation of the media, based on the feedback signal from the external sensor.

Increased Flow Potential with External Pressure Transducer

The valves employed by proportional controllers range in orifice diameter, but most are between 0.009" and 0.100". The size of the orifice directly relates to the maximum flow potential of the device. Flow is critical to every application, and many processes require much higher flow than the maximum orifice size available. Air piloted mechanical regulators increase flow potential for electronic proportional controllers when standalone flow capabilities are ineffective. An analog or digital controller pilots the appropriate sized mechanical regulator by controlling pressure to the dome. The force created above the diaphragm naturally dictates an equal force underneath the diaphragm, which allows for higher-flow pressure control with remote adjustability. However, every mechanical regulator has hysteresis and inaccuracies that result in immediate pressure drop and some percent differential between dome pressure and actual pressure. The signal from an external pressure transducer installed downstream of the mechanical regulator enables the electronic pressure regulator to control the mechanical regulator's output to the desired pressure. With a proportional microcontroller as the pilot, dome pressure becomes irrelevant—increasing and decreasing with the sole intention of satisfying the external sensor.

In conclusion, although analog devices continue to dominate the proportional control market, there are many advantages to digital proportional control that make it a smart choice. Everything from calibration to sensor variety acceptance to future development opportunities is more accessible and less complicated to realize with microcontroller devices compared to analog. If you're interested in learning more about digital proportional control, check out �ǳ�web's exciting new Cordis series of electronic proportional pressure controls, or contact �ǳ�web for more information.

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Cordis CPC Electronic Pressure Controls FAQ

Rachel Desenberg — Mon, 24 Jun 2019 20:23:56 +0000

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Is the output pressure of the Cordis Pressure Controls linear?

A: Yes, within +/- .05% BFSL

How can I electronically control the Cordis?

A: The Cordis can be commanded with 0-10 VDC (standard), serial or current communication. (Capable of 0-5 VDC for specials only)

Are there other plumbing options available?

A: The Cordis Controller is available in 1/8" NPT or G 1/8"

Are pre-made (Card unit) or molded (Housed unit) cables available?

A: Yes. Part numbers are CPCH-CA6 (Card unit) and CPCH-C1 (Housed unit).

Can PID changes be made in the field?

A: Yes. Refer to the IOM for command sets required to accomplish this.

Can Cordis be calibrated 0 to 5.00 VDC instead of 0 to 10.00 VDC?

A: Yes, but under a special part number (Would result in a custom part number.)

Can the output flow of the Cordis be customized?

A: Yes. This would require more application details and a custom part number.

Can flow of the valves be customized?

A: Yes, with more detailed application specifications.

What is the lowest full scale calibrated range of the Cordis?

A: 0-10" H2O full scale is available with a custom part number

Where can the Cordis be purchased?

A: On-line or from your local �ǳ�web Distributor

Does the Cordis EPR require a constant bleed orifice to function accurately?

A: No

Is the housed Cordis unit IP65?

A: Yes

Are the calibrated pressure ranges based on sensor ranges?

A: Yes. There are 7 ranges currently available as a standard product.

Will the Cordis unit be able to have external sensor feedback?

A: The Cordis was designed to work with an external sensor instead of the integrated sensor element on the PCB as a customer specific special. �ǳ�web will need sensor details to qualify the specifications.

Can the Cordis unit work with vacuum?

A: Yes, as a special.

Will the Cordis product have multi-station manifolds available?

A: Multi-station manifold capable as a special.

The Cordis unit's flow capability is based on the capabilities of the EVP and DVP series proportional valves. Is there or will there be an option to increase the flow capabilities?

A: Yes. Cordis will need to be coupled with a larger regulator or booster. Standard accuracy specifications will not apply.

Is there a program available for re-calibration in the field?

A: No. Not at this time.

Will the Cordis unit be capable of performing at higher pressures above 150 psig?

A: Special Orders

Will there be a digital display option for either the card or housed unit?

A: Not at this time.

What is meant by "serial communication"?

A: Serial communication is the process of sending data one bit at a time, sequentially, over a communication channel or computer bus. (Digital communication)

Can the calibrated output range be inverted?

A: Yes. Specials only.

Can the Cordis unit be used with water type media?

A: No. Clean, dry, inert gases only.

Can the Cordis unit switch between Static and Dynamic flow and still maintain control and stability?

A: Yes, to a certain level of flow. This is valve and application dependent.

Will there be a traceable calibration document per unit?

A: Yes. Each unit will be calibrated before release. Please contact us if you would like the calibration document. Please have your serial # on hand when contacting us to retrieve this record.

Are there any mounting or vibration concerns with the Cordis unit?

A: No for mounting. Vibration will need to be tested.

Will the online configurator help me configure a special calibration, or what is the process for this?

A: For specials, please contact �ǳ�web or your local �ǳ�web Distributor.

What types of materials are available for the Cordis manifold?

A: Aluminum is standard. All other materials are specials.

What is the recommended filtration for the Cordis unit?

A: 40 micron on the supply side.

What is the recommended supply pressure to the Cordis unit?

A: Inlet pressure needs to be 10% higher than the maximum calibrated range of your Cordis. Refer to the Operating Instructions for max. inlet pressure per calibrated range.

Is there a preferred sealant to use when applying fittings?

A: Preferred is Loctite 545 or equivalent.

Is the exhaust port threaded?

A: Yes. CPC-C has #10-32 port. CPC-H has a 1/8" NPT (G1/8)

What is the resolution of the Cordis unit?

A: The Cordis can respond to command signal changes of 5 mV.

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Resolution in Proportional Control

Rachel Desenberg — Mon, 24 Jun 2019 20:03:30 +0000

Category:

(1) https://en.wikipedia.org/wiki/Cytometry

Proportionally controlling the pressure or flow of gasses and fluids to perform various functions is prevalent in laboratories and manufacturing environments. Often, it is imperative to use products that provide the best resolution. But what is resolution, what does it indicate in proportional control, and what might it mean for your application?

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What is Resolution?

Resolution in proportional control applications has context when distinguished from accuracy. Most proportional controllers offer higher resolution than accuracy, but few can claim to be high-resolution devices. Resolution defines the smallest measurement change detectable, while accuracy expresses the deviation of the measurement from the actual value. For example, a pressure transducer may detect pressure fluctuations of 0.1 psig, but the accuracy of the sensor may only be ±2.0 psig. If we record measurements of 99.9 and 100.0 psig, we confirm a pressure change of 0.1 psig, but the sensor's accuracy indicates real pressure to be somewhere in the range of 98.0 to 102.0 psig.

�ǳ�web's high-resolution Cordis series defines resolution as the smallest value of command change that impacts actual pressure response. The Cordis proportional microcontroller employs �ǳ�web proportional valves and proprietary algorithms to deliver 5 mV resolution or better. For instance, a Cordis calibrated 0 to 10 VDC equals 0 to 100 psig realizes pressure changes of 0.05 psig throughout the entire range. With a resolution of 0.05%, the Cordis offers a control ratio of 200:1, signifying 200 steps of resolution for every 1-volt increment. The reason most proportional controllers in today's market do not publish a resolution specification is because their internal proportional valves only achieve steps of 25 mV, and most digital valves step in 50 mV increments or higher.

Why Does Resolution Matter?

High-resolution proportional control for many manufacturing and industrial processes may not be essential. However, applications in life sciences, instrumentation systems, and numerous laboratory processes rely on the subtle nuances produced with high-resolution control. Without the ability to provide a smooth ramp to a process, make tiny changes in pressure and flow or react to subtle dynamic process conditions, many applications would not be possible. High-resolution control delivers the ability to count individual cells; print bio-materials such as bone, skin, and organs; or examine and identify individual compounds in gas mixtures.

For years, the practice of hematology has provided tests that evaluate and diagnose a variety of blood conditions, leading to faster, more targeted treatments. Once a condition is identified, flow cytometry is employed to understand the extent of the condition. By measuring the physical and chemical characteristics of individual cells, flow cytometry furnishes cell size, cell count, morphology, DNA information and the existence or absence of particular proteins (1). These measurements become possible with high-resolution control of the pressurized cell-carrying fluid.

Similar to flow cytometry, gas chromatography requires high-resolution pressure or flow control to provide stable conditions for measurement. The process—also called "GC"—utilizes inert gas (carrier) to move various compounds through "sticky" columns and record the time it takes for each compound to arrive at the detector. The speed at which each element reaches the sensor is the primary metric used to identify the individual compounds. The effectiveness of this process relies heavily on the mass flow rate remaining stable and constant, often during varying temperatures. If the flow rate is not steady, it becomes the most significant variable, obstructing detection of the compound. The dynamic nature of this process demands proportional control that both senses and reacts to the smallest changes in pressure or flow.

Lastly, resolution matters when printing matter. The concept of 3D printing is relatively mature. However, medical 3D printing with biologic material (bioprinting) is just being realized. Everything from blood vessels to skin, bone, and cartilage to the first heart made from human cells has become a bioprinting reality (2). Some of the newest bioprinters employ high-resolution vacuum control to suspend the biomaterial during the printing process. This temporary suspension requires just enough vacuum to overcome gravity until the print head reaches its destination. If too much vacuum is applied, the biomaterial withdraws too far from the nozzle, disrupting the timing and potentially reaching and damaging the controller. Too little vacuum and the excess material destroys the print.

Improving Resolution

A proportional controller's resolution—like its accuracy, repeatability, and stability—are greatly affected by the PID (proportional-integral-derivative) settings driving the device. These settings manage the feedback mechanism and define power distribution and timing to the internal valves in the hopes of mitigating the effects of dynamic process conditions. The PID parameters must be tuned appropriately to the specific application for the best resolution.

Ordinarily, proportional control devices receive their initial PID tuning at the factory during calibration. Some proportional control manufacturers offer excellent application assistance. �ǳ�web is one such manufacturer.

The best way to improve resolution—as well as accuracy and repeatability—is by providing a complete and accurate picture of the specific process. When contacting �ǳ�web technical support, supplying as much of the following details is critical to proper valve operation and setup: downstream volume, minimum and maximum inlet pressures, media, operating and ambient temperatures, minimum and maximum flow requirements, and general process conditions, like static or constant flow. Full application details allow �ǳ�web's engineering team to optimize the PID settings, resulting in optimized performance.

Resolution Resolved

Understanding resolution and its impacts on proportional control applications are just one of the many concepts worth grasping when choosing an electronic proportional controller. While many applications may not require a high-resolution device, no process would suffer from better resolution—and in some instances, unexpected refinements may reveal themselves, elevating your product above the competition.

If you have questions about resolution or want to learn how Cordis can improve your process, locate your nearest �ǳ�web distributor or contact �ǳ�web today.

(2) https://www.livescience.com/65257-3d-printed-heart-human-tissue.html

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Pressure Control vs. Flow Control

Rachel Desenberg — Thu, 25 Apr 2019 18:45:26 +0000

Category:

Product Tips

Pneumatic fluid power is a universal and cost-effective method for delivering energy to instrumentation and industrial processes. In cooling applications, fluid flows past something to carry away heat. In an analytical instrument, the velocity of a carrier gas may be a critical timing mechanism. Gas pressure can mitigate sleep apnea. In each of these cases, fluid is controlled to achieve a particular outcome. The power delivered to these processes requires pressure control or flow control.

How are pressure and flow control achieved? What are ideal products for controlling fluid power and how do they affect the outcome? The answer to those questions begins with a definition of pressure and flow and an understanding of open and closed-loop systems.

Pressure vs. Flow—The Basics

Pressure is force. It acts in all directions, all at once and with the same power. The amount of force a pressure exerts is directly related to the area in which the pressure is contained (pressure = force/area). Pressure does not require directional input, like a hammer on a nail. It merely needs to be routed and contained within a specific operation for reliable power transmission. Pressure can exist in a vacuum (negative pressure) while moving through a conduit (underflow) or deadheaded within a static chamber.

Flow is the movement of pressurized fluids between volumes of varying (differential) pressures. Pressurized fluid always moves from higher pressure to lower pressure. Without a pressure differential, the fluid is stagnant, and the system is absent of flow. Flow (in terms of fluid dynamics) breaks down into two distinct measurable rates: volumetric flow rate and mass flow rate.

All gas has mass. The 3-dimensional space containing gas molecules (mass) is the volume. As temperature and pressure changes, so does the container (volume). The volumetric flow rate measures the space occupied by a particular gas over time. Standard units of measure include liters per minute (LPM) and cubic feet per minute (CFM).

The mass of an object has a finite molecule count. Gasses can compress their mass into smaller and smaller volumes to create pressure. The mass flow rate measures the number of molecules passing through a single point. Standard units of measure are kilograms per minute or pounds per minute.

Open-Loop vs. Closed-Loop Fluid Control

Controlling fluid to a fluid power process infers the ability to set or modify the amount of energy to that process. Numerous techniques and products are available for regulating fluid power. However, they all boil down to one of two concepts: open-loop control and closed-loop control.

A standard faucet is an example of an open-loop system. Adding your hand under the faucet for feedback would make it a closed-loop system.

In open-loop control schemes, a controller provides an input action to generate an output response; the result of the operation is independent and unknown to the controller. It is a cause and "blind" effect relationship. An example of an open-loop system is a standard water faucet. The controller (hand) turns the handle to open a valve (input action). The valve opens and (hopefully) allows water to flow from the faucet. Whether or not water flows is unknown to the valve and the hand (controller). Hence, the system is considered open. For obvious reasons, open-loop systems are less accurate, less repeatable and (generally) less costly.

In closed-loop control schemes, the input action supplied by the controller is dependent on feedback from the process it intends to control. Using the faucet example, assume a person wants to wash their hands at an "acceptable" temperature. The controller (hand) turns both the hot and cold valves to enable water to flow from the spigot. The other hand is placed under the running water to judge (measure) the temperature. The brain interprets the water temperature as too hot or too cold, and this feedback is furnished to the original hand (controller) to modify the input action. Acceptable temperature is now maintained and easily adjusted when changes occur. In the simplest terms, if the output (result) is directly related to the input (action) via feedback, the system is closed-loop, if not it is considered open-loop.

Mechanical & Electronic Flow Control

Flow control valves control the volumetric rate of the fluid that flows through them. Generally, changing the size of the orifice is how the flow rate is set and adjusted. A tapered needle moving in and out of an orifice or opening and closing the gap inside a ball valve changes this rate. Volumetric flow controls are typically used to control velocity—for example, the extension and retraction speed of a cylinder or the rate at which a fluid is sprayed or dispensed.

Mechanical flow control valves are some of the most commonly used fluid control valves on the market. They operate in a wide variety of markets, from everyday household items (such as the water faucet above) to precision medical applications. Some standard industry terms for mechanical flow controls are needle valves, ball valves, and meter-in/meter-out valves, among others. Mechanical flow controls are available with both open-loop and (in some rare applications) closed-loop control.

Propane tanks come standard with open-loop control. Pressurized propane is released when the valve opens, and the rate of flow is directly related to the size of the opening. The flow rate is at its highest when the tank is full. Over time, the pressure in the tank decreases and the differential (between tank pressure and outlet pressure) contracts, reducing flow. Closed-loop mechanical flow controls are uncommon, as it is difficult to send a feedback signal to a mechanical valve. However, a straightforward example would be the flapper valve on a toilet, which closes to allow less flow into the tank as the float rises, ultimately closing when the tank is full.

Example of open-loop control.

Example of closed-loop control.

A medical application where two gases blend at precise ratios for delivery to a patient requires high precision and must be a closed-loop system.

In many instances, the process demand fluctuates, creating instability and making repeatable flow control impossible with mechanical flow valves. In these situations, variable control of the flow using an electrical input becomes necessary. The industry term for these controls is proportional valves. Proportional valves come with a wide variety of actuation methods, for example, a voltage, current, step-input or digital input. They can be designed into a control system that is closed-loop, with feedback from an electronic flow meter, or open-loop. These valves are ideal for applications where the flow requirement is continually changing.

Closed-loop flow control systems generally result from a requirement for precision. A remote-controlled propane fireplace does not require high precision—there only needs to be a noticeable difference between small and large flames—and can, therefore, be an open-loop system. However, a medical application where two gases blend at precise ratios for delivery to a patient requires high precision and must be a closed-loop system. In the case of mixing gases, this may even require a mass flow meter rather than a volumetric flow meter to ensure that the ratios are correct.

Mechanical & Electronic Pressure Control

Pressure control products are designed to control the amount of force produced by a fluid system. Pressure controls are most commonly known as pressure regulators and, like flow controls, are available in both manual and electronic variations. Pressure regulators are not designed to control flow rates. Although pressure regulators used in flowing systems inherently affect the flow by controlling the pressure, they are not designed to act as flow controllers.

Pressure regulators are by nature closed-loop, meaning they must be able to sense downstream pressure (or upstream for backpressure regulators) via a feedback loop that automatically adjusts to maintain setpoint. When the output of the regulator senses that the pressure has dropped below a predetermined point, the regulator opens and allows more pressure though. Once the pressure reaches the setpoint, the regulator closes and no longer allows flow.

Mechanical pressure regulators come in a variety of styles, but every mechanical regulator has three essential elements:

Restriction - A valve that provides an adjustable restriction to the flow, typically a poppet style valve
Load - Part that drives the restriction valve to set the desired outlet pressure, usually a piston or a diaphragm
Reference - Force that determines when the inlet flow equals the outlet flow to provide a constant outlet pressure, often a spring

The use of the reference force is what makes mechanical pressure regulators closed-loop. Without this feedback, the pressure would change every time downstream flow demand changed.

There are two common types of mechanical pressure regulators: piston style and diaphragm style regulators. Piston style regulators tend to be robust and hold up well in applications where ruggedness is a concern. However, they do experience some hysteresis as a result of the friction between the piston seal and the regulator body. They are not for use in applications where the outlet pressure must be held to a tight tolerance. Piston style regulators are excellent for applications where durability is more important than accuracy. For example, if your shop air is 90 psig, but your valve rating is 60 psig, a piston regulator is useful to knock the pressure down so that you do not damage the valve.

If the regulator needs to control low pressures or high precision, a diaphragm style regulator is recommended. Diaphragm regulators employ a disc-shaped diaphragm, usually made of an elastomer, to sense pressure changes, which eliminates the friction experienced by the piston style regulators. The reduced friction results in better precision and accuracy, making these regulators ideal for applications requiring precise, repeatable pressure control; this may include medical, semiconductor, and most applications in life sciences.

Mechanical pressure regulators are an excellent option for applications where upstream pressure and flow see only minor fluctuations and the user wants to "set-it-and-forget-it." However, just like with flow controls, some applications may demand a variable pressure output, remote control, automation, data acquisition or better repeatability, which would require an electronic pressure regulator (EPR).

The most common configuration for an electronic pressure regulator (EPR) is 2 valves and a sensor. One inlet valve, one exhaust valve and an internal pressure transducer actively measuring downstream pressure and continually providing feedback to an analog or digital circuit board. A command signal generator (usually a PLC) is used to supply the EPR with a command setpoint. For example, a 0-10 VDC signal (many options exist) directly equating to the calibrated range of the EPR, in this case, 0-100 psig. A volt command anywhere between zero and ten volts results in the equivalent (as a percentage of full scale) pressure output. For example, with a 5 VDC (50%) command, the inlet valve opens to allow pressure downstream. The inlet valve remains open until the internal sensor says, "Hey, I measure 5 VDC (50 psig), you can close now". If flow increases downstream, pressure drops and the sensor instantly senses the deviation from the 5 VDC command. The inlet valve opens again until the sensor is satisfied. This relationship and automated process extends throughout the full range and is known as linear and proportional closed-loop electronic control.

Choosing the Right Fluid Control

There are many different fluid controls to choose from when designing a pneumatic system. Understanding if you are trying to control force (pressure) or speed (flow) is the first step to selecting the fluid control that is right for you. Additionally, your application dictates whether you can use a mechanical control or if you need electronic control, and whether it can be open-loop or must be closed-loop.

If you have questions about what flow control you should be using for your application, contact tech@clippard.com for additional support.

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Low Pressure Leak Testing

Rachel Desenberg — Mon, 31 Jul 2000 13:57:59 +0000

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Many popular consumer electronic products require strict leak testing to ensure protection from water ingress. Often, these devices are tested at very low pressures. All three of the products in this drawing are pressurized to less than 10 inches of water column (0.36 psig). The pressure is maintained in the DUT while the flow rate is measured. If the flow is anything but zero, the DUT leaks. Most products have a maximum allowable leak rate, so some flow is acceptable.

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Chemical Mechanical Planarization (CMP)

Rachel Desenberg — Mon, 31 Jul 2000 13:55:59 +0000

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The primary material used in the fabrication of integrated circuits is silicon. The quality of the integrated circuit depends directly on the quality of the silicon wafer. A progression of processes is needed to manufacture the highest quality silicon wafers. Perhaps the most critical stage is the Chemical Mechanical Planarization (or polishing) process. CMP is the process of combining chemical and mechanical forces to smooth and flatten silicon wafers. The Cordis high-resolution electronic pressure regulator provides pressure to a pneumatic cylinder which applies force on the wafer against the polishing pad. Cordis is ideal for this process because the dual-proportional valves can maintain exact pressure levels by reacting to subtle changes in force to relieve or exhaust pressure in real-time.

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Vacuum Control (Generator)

Rachel Desenberg — Mon, 31 Jul 2000 13:52:07 +0000

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This schematic shows a vacuum generating application where positive pressure is regulated to a vacuum Venturi to generate and control precise vacuum levels. The Venturi generates vacuum when pressure flows across the internal orifice, this naturally pulls a vacuum. In this example, the Venturi is rated to produce -10 psig with 100 psig input. By adding a vacuum transducer as second-loop feedback calibrated 0-10 VDC = 0 to -10 psig, this process becomes linear and proportional to the commanded setpoint. A command of 5 VDC (50 psig) produces a 5 VDC (satisfied) response when the vacuum level reaches -5 psig.

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Vacuum Control (Inline, Low Flow)

Rachel Desenberg — Mon, 31 Jul 2000 13:51:06 +0000

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This general inline vacuum control schematic shows Cordis controlling vacuum in a static volume. Various flow rates can be achieved based on which orifice is installed on the exhaust side of the Cordis. However, all flow rates will be relatively low and designed for small volumes and/or processes that do not require quick changes in volume.

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Flow Cytometry Pressure Control

Rachel Desenberg — Mon, 31 Jul 2000 13:50:11 +0000

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Flow cytometry employs pressure control of various gases to dispense different chemical fluids through a fixed orifice tube. Based on the rate of fluid flow, lasers mark cells and color code them for precise identification. Because the Cordis unit has superior resolution without the bleed typical in high-resolution electronic regulators, selective grades of gases can be used within the system to dispense the various chemicals. The Cordis unit applies the correct pressure to the vessels so that the chemicals/samples flow through the calibration laser nozzle for molecular identification. The speed of "flow-through" maintained (based on the controlled pressure) ensures accurate identification.

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3D Printing (Positive Pressure)

Rachel Desenberg — Mon, 31 Jul 2000 13:49:16 +0000

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Depending on the media used for printing, positive pressure can be used to dispense fluid to a 3D printer. This drawing shows �ǳ�web's Cordis controlling compressed air above the print fluid, then the rate of flow is varied and controlled from �ǳ�web's Eclipse to the print head. This process is under constant flow and therefore requires very stable and repeatable pressure control to maintain consistent fluid pressure at the inlet of the Eclipse.

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