Four kinds of intelligent pressure control

Four kinds of intelligent pressure control

Posted by: Leigh Moyer

From nitrogen purging or filter characterization, through vessel pressure control and leak testing applications, Alicat instruments are versatile and easy to use, while still providing excellent process control. This is because they operate with very fast control response (50-100 milliseconds) and high accuracy.

Our products are easy to program through a display interface, a serial connection or an analog connection, and we are dedicated to fast-turn-around on customized products to meet unique and variable specifications and requirements across industries. Pressure control applications can be enhanced by multivariate, rapid control, as demonstrated with these four examples.

Filter Characterization

An Alicat Pressure Controller can be used to set the pressure drop across the filter by measuring pressure before and after the filter while an Alicat mass flow meter can be used to measure the flow rate required to generate the needed pressure drop. Because mass in equals mass out, the flow meter can be placed upstream of the pressure controller as well.

Filter Test

Diagram 1

Diagram 1 illustrates a filter test using a differential pressure controller to regulate pressures before and after the filter while a mass flow meter measures flow-through at that pressure combination.

Manufactured Component Leak Characterization

Diagram 2

Diagram 2

Using an Alicat Mass Flow Meter and an Alicat Pressure Control Device, the user has a fast, accurate and reliable method for leak checking components. Our mass flow meters have full scale ranges as small as 0.5 sccm with 200:1 turndown ratio, meaning that flows as low as 0.0025 sccm (2.5 sμlm) can be resolved. If plumbed as shown in Diagram 2, the pressure is controlled at the entrance to the Device Under Test (DUT). A constant bleed though the needle valve allows the pressure controller to precisely hold the pressure at the DUT, ensuring that any flow through the meter after the bypass valve is closed is caused either by a leak or due to a cooling of the volume of the DUT. As long as the temperature of the DUT is constant, the flow reported at the meter will be the leak rate of the DUT.

High-Efficiency Helium Leak Testing

Alicat’s Dual Valve Pressure Controller is designed to prevent inefficient off gassing and to save costly gases like helium in closed-volume applications. In one kind of test, the pressure controller first removes all the air out of the test chamber then refills the chamber with helium to the desired test pressure. The gas analyzer records any helium that passes through the test device. The integrated exhaust valve of the pressure controller opens only when needed, so it maintains test pressures without continuously wasting gas through a bleed valve. See Diagram 3.

Helium leak testing using a dual valve pressure controller with pressure sensing to a helium chamber.

Diagram 3

Backpressure Control with Flow Monitoring

Backpressure control using a mass flow controller set to control on pressure.

Diagram 4

Instead of using a dedicated pressure controller and a separate mass flow meter, Alicat’s mass flow controllers (MFC) reduce equipment needs to a single instrument. This can be accomplished by setting the MFC to control for absolute pressure. The instrument will now control pressure while simultaneously displaying flow rates. As illustrated in Diagram 4, the mass flow controller allows pressure inside the system to build, simulating the internal pressure of a tire versus the air compressor that is attempting to fill it.

Conclusions

Specialized application engineering knowledge acquired by Alicat, for measuring and control techniques used in a wide spectrum of pressure and flow control processes, ensures that Alicat can quickly provide the optimum solution to your specific need and application, helping you create the most cost- and time-efficient system.

Reference: click here.

D&D Engineering – “W’ere YOUR Sensor Guys”
3835 E. Thousand Oaks Blvd. Suite 464 Westlake Village, CA 91362  – Voice: (818) 772-8720 Fax: (818) 772-2477 Toll Free: (888) 333-6474
Email: sales@sensorguys.com Website: www.sensorguys.com

Alicat Electronic Pressure Controllers

Alicat Electronic Pressure Controllers

Posted by: Jesse Arenstein

The new Alicat Electronic Pressure Controller (EPC) packs all the analytical stability and accuracy of our standard pressure controller, but in a compact form ideal for installing in high volume original equipment manufacturing (OEM) applications, ensuring that the end product is outfitted with the best components available.

From bioreactors to chemical analysis, quality control to metrology and beyond, Alicat customers are building pressure based OEM systems that require greater and greater levels of accuracy and control stability.

Dual valve pressure control for OEM applications.

Dual valve pressure control for OEM applications.

Sold in batches of 25 units or more, the fully customizable EPC is an economical solution to pressure control in OEM applications. Three varieties of EPC—single proportional valve, dual proportional valve and back-pressure—allow for customized pressure control in embedded systems.

A single valve device is ideal for regulating straightforward applications, like using a pressure regulator to knock down inlet pressure off a gas bottle, or providing volumetric flow control against a calibrated orifice. With control times faster than 100 milliseconds, it adds control stability and responsiveness to any desktop analyzer, lab in a box, reactor or sample preparer for chemical separation processes like gas chromatographs or mass spectrometers.

A dual valve system adds a second valve directly into the component, allowing for real time pressure control of flows into and out of a process, without the waste found in using a single valve pressure controller and a continuous bleed. Dual valve controllers are used to precisely control dome-loaded industrial processes involving high volumes at high pressure—as well as in tiny capillary tubes for cancer cell analysis, where miniscule amounts of fluids are moved around.

A back-pressure controller operates proportionally to increase frictional resistance on the outlet of a fluid control system. By taking advantage of a wide range of orifice sizes, EPC back-pressure solutions vent-down systems with many different flow requirements, while maintaining speed, accuracy and a full range of pressure and vacuum controls. No matter what back-pressure process users are controlling, the Alicat EPC can provide deep resolution and granularity improvements while maintaining speed, accuracy and a full range of back-pressure and vacuum back-pressure control.

The number of applications for pressure control in the scientific and industrial world are staggering and the EPC allows companies to integrate the fastest pressure control meter into products. As the world of technology continues to miniaturize and pack more and more performance into smaller packages, Alicat EPC’s are an invaluable tool for pressure control needs in OEM technologies.

Reference: click here.

D&D Engineering – “W’ere YOUR Sensor Guys”
3835 E. Thousand Oaks Blvd. Suite 464 Westlake Village, CA 91362  – Voice: (818) 772-8720 Fax: (818) 772-2477 Toll Free: (888) 333-6474
Email: sales@sensorguys.com Website: www.sensorguys.com

Reducing fluid control cost, complexity and inventory with Alicat MFCs

Reducing fluid control cost, complexity and inventory with Alicat MFCs

Posted by: Ryan Barner

Controlling multiple pressures and managing differing gases can be critical to getting the data you need but multiple variables often means multiple instruments, adding complication and cost to your system. With one Alicat mass flow controller, you have the ability to simplify process controls—limiting error points—while increasing parameters monitored, and therefore saving you money on your next MFC installation.

Fewer Controllers for Large Flow Ranges

Let’s say you have to control flow over a large range, like 10 SLPM to 1000 SLPM. Most flow control solutions require two or more units to achieve accurate control over this range. Standard Alicat mass flow meters and controllers have a 200:1 turndown ratio. That means that where you normally deploy two MFCs to accomplish high and low range control in a system you might be able to replace those two MFCs with one Alicat MFC. With the turndown ratio of 200:1, a 1000SLPM Alicat MFC can control a range of 1000SLPM down to 5 SLPM. By eliminating a second controller, you reduce programming, and plumbing complexity—and most likely, you save money in the purchase.

Repurpose and Save Costs

With Alicat MFCs, each unit comes preprogrammed with 98 standard gases and gas mixtures, meaning if you need to service a controller, you don’t need an inventory of MFCs for each gas type, you can just keep one Alicat on hand. All you have to do is select the correct gas from the list and you’re good to go. No K factors to deploy, and no extra units to accommodate different viscosity gases—your mass flow rate stays accurate.

Process Insights from Multivariate Data

Alicat MFCs measure and report pressure, temperature, volumetric flow and mass flow. Having all of this information may allow you to eliminate one or two other instruments in your process and thereby reduce your overall instrumentation purchase costs even further. A side benefit to eliminating additional instruments is fewer leak points. And because Alicat MFCs use differential pressure measurement to obtain a mass flow rate, our MFCs can be set to control on pressure and still read mass flow. A single Alicat MFC can replace instrument duplication, providing you with a simpler, cost effective way to meet all your MFC needs.

All the ways

Alicat mass flow controllers simplify your setup while reducing overall instrumentation costs in your system because:

  • The 200:1 turndown ratio gives you a wider measurable control range.
  • One instrument can be repurposed to many gases.
  • Multivariate parameter measurements to obtain temperature, volumetric, mass, and pressure data.
  • Fewer instruments mean a lower cost of ownership cost over the life of the process.

Contact Alicat to build your simple, most effective and cost-saving fluid control process.

Reference: click here.

D&D Engineering – “W’ere YOUR Sensor Guys”
3835 E. Thousand Oaks Blvd. Suite 464 Westlake Village, CA 91362  – Voice: (818) 772-8720 Fax: (818) 772-2477 Toll Free: (888) 333-6474
Email: sales@sensorguys.com Website: www.sensorguys.com

Alicat Mass, Flow and Pressure Instruments Now Offer EtherCAT Protocol

Alicat Mass, Flow and Pressure Instruments Now Offer EtherCAT Protocol

Posted by: Edgar Schrock

Alicat Scientific’s line of mass flow, pressure and liquid instruments can now be ordered with the EtherCAT protocol. Users of Beckhoff PLCs for industrial automation can now connect Alicat devices with the high-speed and robust EtherCAT protocol.

In the chemical, medical, manufacturing and power industries, Alicat instruments rapidly and precisely monitor and control critical process parameters. The speed and reliability of Alicat devices are particularly well suited to vacuum coating processes, such as Atomic Layer Deposition and Chemical Vapor Deposition. All of the mass flow or pressure controller’s data, including: mass flow, volumetric flow, pressure, temperature, selected gas calibration, setpoint, and totalized flow can be output to a central PLC running a compatible automation protocol. Users may also change setpoint or gas selection, and issue other commands remotely.

EtherCAT joins Alicat’s wide offering of industrial automation protocols, which also includes Modbus TCP/IP, Modbus-RTU, EtherNet/IP, DeviceNet and PROFIBUS communication options to fit new or existing systems. For easy drop-in replacement of older industrial units, Alicat instruments are made to fit the same space as common industry mass flow controllers. All Alicat instruments are backed by NIST-traceable calibration, comprehensive technical support and the flow industry’s only lifetime warranty.

Reference: click here.

D&D Engineering – “W’ere YOUR Sensor Guys”
3835 E. Thousand Oaks Blvd. Suite 464 Westlake Village, CA 91362  – Voice: (818) 772-8720 Fax: (818) 772-2477 Toll Free: (888) 333-6474
Email: sales@sensorguys.com Website: www.sensorguys.com

EtherCAT in vacuum and industrial applications

EtherCAT in vacuum and industrial applications

Posted by: Michael Diaz

Manufacturers of Vacuum Deposition systems are increasingly turning to software-based industrial PLCs. These PLCs offer a variety of benefits, including greater productivity, precision performance, cost savings, speed-to-market and the ability to add processes like motion control and machine vision in the future.

Because there are so many different Ethernet fieldbus standards available, it’s difficult to choose one. Adopting the wrong standard can mean unnecessary cost and sacrificing competitive advantage due to slower performance.

MC-ethercat-vacuum-logoFor the control and regulation of vacuum coating processes, data speed and integrity are crucial. EtherCAT has been designed especially for these kinds of applications and meets all demands for fast controls. EtherCAT is a high-performance, low-cost, easy to use Industrial Ethernet technology with a flexible topology. The EtherCAT Technology Group promotes EtherCAT and is responsible for its continued development. EtherCAT is also an open technology, so anyone is allowed to implement it.

EtherCAT is the fastest Industrial Ethernet technology, but it also synchronizes with nanosecond accuracy. This is a huge benefit in applications where the process is controlled via the bus system. The rapid reaction times work to reduce transition times between process steps. In this way, EtherCAT’s performance leads to improved efficiency, greater throughput and lowered costs.

EtherCAT delivers the features of Industrial Ethernet at a price similar to that of a traditional fieldbus system. The only hardware required by the master device is an Ethernet port, eliminating the need for expensive interface cards or co-processors. EtherCAT slave controllers are available from various manufacturers in several formats.

EtherCAT P is a new addition to the EtherCAT protocol standard. It enables not only the transmission of communication data, but also the peripheral voltage via a single, standard four-wire Ethernet cable. EtherCAT and EtherCAT P are identical in terms of the protocol technology, only the Physical Layer differs. By providing the power supply via the communication cable, EtherCAT P offers additional cost benefits and enhances numerous applications.

Alicat now offers EtherCAT compliant Mass Flow and Vacuum Controllers. We have taken the extremely fast response time of the Alicats and paired it with the speed of EtherCAT. The EtherCAT technology has been seamlessly integrated into the product family, along with other Profibus, Modbus and DeviceNet.

Reference: click here.

D&D Engineering – “W’ere YOUR Sensor Guys”
3835 E. Thousand Oaks Blvd. Suite 464 Westlake Village, CA 91362  – Voice: (818) 772-8720 Fax: (818) 772-2477 Toll Free: (888) 333-6474
Email: sales@sensorguys.com Website: www.sensorguys.com

Precision & Repeatability in Fiber Optic Manufacturing

Precision & Repeatability in Fiber Optic Manufacturing

Posted by: Ryan Barner

In the optical fiber industry, manufacturers’ needs center around precision and repeatability. It’s somewhat analogous to archery, where accuracy means hitting the bullseye. If you can hit the same point on the target every time, that’s precision. Repeatability is being able to demonstrate the same precision every time you walk up to the line and shoot. Let’s take a look at how optical fibers are manufactured, and where Alicat fits into the picture.

How Optical Fibers Are Manufactured

The fiber optic manufacturing process begins with the creation of a preform, where layers of very pure glass are built up on a rod. Different types of gases in very specific amounts are used to deposit a new glass layer on each pass, and every layer that is laid down on the base will give the end fiber a different property. A flame uses fuel gases, operated by a mass flow controller, to maintain a certain temperature and ensure the process is running optimally. The layering process sometimes takes place over the course of many hours depending on the size of the preform.

After the preform is created, it is then placed into a drawing tower. As one end of the preform is heated, inert gases are used to keep the heating element from burning up during the process. As the first drop falls from the melted end, a thin fiber is produced and then cools in a cooling tube filled with nitrogen as it descends through the tower.

The thickness is measured, quality is checked, and depending on the end use of the product, a coating process may apply a very thin polymeric or acrylic layer on the outside of the glass. This coating helps to protect the pure glass from environmental conditions and preserve the important properties within the glass fiber itself. Pressure control regulates the flow of this liquid polymer. In an extrusion-like process, it coats the fiber. Flow pressure needs extremely precise and repeatable control to provide a consistent coating over the product. Even a tiny amount of pressure fluctuation could lead to microns of variation in the overall thickness, which could dramatically affect the overall performance of the fiber. During the UV or Thermal curing, the material is keep in a an inert atmosphere to help the curing process. These gases are again controlled by mass flow controllers.

Depending on the size of the preform, it’s possible to run a fiber that spans anywhere from thousands of feet to hundreds of miles. We’re talking about pulling something to the width of a human hair and spooling it at 90 feet per second for hundreds of miles, while still maintaining uniformity. This is why the initial phase of making the preform is so important—to make a uniform product, the mass flow controllers must offer precise, repeatable controls of the gases that are used to deposit the different layers of glass.

Alicat’s Role in Fiber Optic Manufacturing

Fiber optic companies use Alicat products in several different aspects of the preform process and drawing process. During creation of the preform, we can be used for the burner control application, which controls the fuel gases which heat up the preform and help to control the deposition of each thin layer. We can also control the actual gases being used to create the very pure glass being deposited. And our mass flow controllers are used in the drawing process, where argon is being fed into the furnace area to keep the element from burning up. (The end result depends on the shape of the cone.)

About every five milliseconds, signals from our measurement sensors go through our entire processor. Depending on the type of process and operating pressures, the controller will have a control response of 50 milliseconds or less. (Sometimes we can help to tune that number down to sub-50 millisecond timeframes.) For anyone who might have a hard time imagining how fast this is, it takes the average human 300 to 400 milliseconds (thousandths of a second) to blink their eyes. Before you can even blink, our instruments have already obtained hundreds of measurements. To put that into perspective, in one second the gas burners and flow in the cooling tower may be adjusted over 200 times. That’s how we’re able to maintain repeatability and accuracy while a fiber is produced at 90 feet per second.

More Data Collection Means More Insight into the Process

Specialty fibers for high energy applications need to have very specific optical properties, which are shaped by the density and mix of materials. Therefore, depending on the part of the process, engineers want the ability to see as many parameters as possible. With an Alicat, you not only get the mass flow measurement, but also absolute pressure, volumetric flow, and temperature information so that you can refer back to it later. From a quality control perspective, you can use these parameters to determine what changed in the process and correlate that to a run that was rejected because of a defect.

Typically, the signals that provide this information go into some sort of a controller (a PLC) for interpretation. In case of a spike or a zero flow condition, the Alicat controller would send a signal to the PLC, which would then be able to shut down the line. Instead of having hundreds of feet or even miles of unusable product, it gives manufacturers the opportunity to identify that there’s a problem, get it fixed, and start the process again quickly.

Podcast of the interview for this post:

Compensating for Changing Environmental Conditions

Local environmental conditions can drastically affect the optical fiber manufacturing process. Unfortunately, we still find manufacturers that are used to the old way of doing things, where they don’t have the ability to adjust to changes in environmental conditions. For example, a particular manufacturer is located in an area that experiences heavy thunderstorms, which cause changes in barometric (atmospheric) pressure, and that causes an inconsistent product. With a storm in the neighborhood, they might decide not to even begin their 12-hour process, depending on the day’s forecast. Alicat can overcome and compensate for those changing atmospheric conditions and allow the manufacturer to produce high quality fiber—regardless of weather—because we measure flow in the context of pressure changes.

Other glass shaping processes

Mass flow instrumentation is used in many other glass processes besides fiber optics. Container manufacturers use mass flow controllers for regulating the gas flow to their melt process. There are also manufacturers that use mass flow to control the flame used to make fiberglass for structural components. Architectural glass is another huge consumer of mass flow controllers. They have an oven that’s hundreds of feet long, which requires precise temperature control to create a consistent glass product. (These are typically huge sheets of plate glass.) At any given zone of the oven, a specific temperature must be maintained with very precise flow control of fuel. Alicat mass flow controllers are deployed by architectural glass manufacturers to coat the glass to create different properties in the final product.

In the days before industrial automation was available, someone who gained years of expertise could determine the correct temperature just by looking at the color of the flame. They eventually learned how to make slight manual adjustments while walking down the line. What will the company do when those people retire? That’s where digital mass flow controllers come in—automation allows people to focus on developing optimal process conditions and monitoring parameters within the furnaces. Once everything is set up, it’s possible to know exactly what flow rates are needed to maintain the proper temperatures. The process is repeatable, and it provides useful data that can help identify why there may have been an inconsistency in the glass. The end result is greater repeatability, efficiency and a much better product.

Reference: click here.

D&D Engineering – “W’ere YOUR Sensor Guys”
3835 E. Thousand Oaks Blvd. Suite 464 Westlake Village, CA 91362  – Voice: (818) 772-8720 Fax: (818) 772-2477 Toll Free: (888) 333-6474
Email: sales@sensorguys.com Website: www.sensorguys.com

About that Pressure Control Loop feature? It’s so cool

About that Pressure Control Loop feature? It’s so cool

Posted by: Alyssa Jenkins

As an applications engineer at Alicat Scientific, I talk to people in every industry all over the world and learn about how they use our product. One of the most interesting applications I’ve seen is in a chemical reactor, where our mass flow controllers are used to control pressure and make sure that processes are repeatable.

Our flow controllers can be set to control on pressure while measuring mass flow. Our mass flow controllers measure volumetric flow rate, mass flow rate, temperature, and pressure. (It’s possible to control on any of those except temperature.) By controlling on pressure, you essentially have a pressure controller and mass flow meter in a single device. It’s a fairly unique option, and it takes a second to appreciate how valuable it can be.

Most other mass flow controllers don’t provide much flexibility, allowing only for control of mass flow. Take, for example, the pressure decay method to perform a leak check—you’ll use a pressure controller to set the pressure, stop the flow, and wait for pressure to decrease. Then you can perform calculations based on the exact volume and gas used. (This requires you to have extensive knowledge beforehand.) If you have a pressure controller with mass flow measurement, you’ll see the leak rate instantaneously—as soon as the pressure settles. This saves you time, calculations, and physical space, too.

Here’s a 47 second video to help you visualize it:

What is Closed Loop Pressure?

Closed loop pressure is our term for using a feedback loop based on pressure instead of mass flow. A mass flow controller will typically measure the mass flow and adjust the valve open or closed to increase/decrease the mass flow to the desired level. When controlling on pressure, the valve will adjust based on the pressure measurement. For example, let’s say you’re controlling pressure downstream of the Alicat and want to reach 100 psi. If you’re currently at 80 psi, the mass flow controller will open the valve further until the pressure reaches your set point. This is useful whenever you have an application where you want to control pressure and determine the flow rate. It could be leak checking, flow checking, or quality checking where you have a specific flow vs. pressure curve that needs to be met. Here, your end goal would be to keep variation within certain tolerances to make sure that the product meets your quality standards.

Hear Applications Engineer Alyssa Jenkins talk about the Pressure Control Loop feature in depth:

MCD With CLP and Totalizer

MCD closed volumeOur mass flow controller with dual valves, closed loop pressure, and totalizer is a bidirectional controller with three ports (inlet, process, outlet) and two valves: one with incoming flow and another separate exhaust valve. It can control a closed volume of pressure, meaning not only can one valve open or close to increase/decrease the flow rate, but it can also exhaust to atmosphere or vacuum pump if you overshoot the pressure. The totalizer measures the amount of flow that has occurred. There are four different ways to determine the total amount of flow using these bidirectional meters:

  1. Add positive flow and subtract negative, allowing the total flow to go negative
  2. Add positive flow and subtract negative, not allowing the total flow to go negative
  3. Add positive flow and ignore negative flow
  4. Add positive flow and subtract negative flow, resetting when it reaches 0

You’ll know how much is in that specific volume at any given time, which is important if you want to measure the amount of gases going into a system.

Using Alicat With Rotameters

A rotameter has a floating indicator in a graduated tube.

A rotameter has a floating indicator in a graduated tube.

Rotameters measure volumetric flow rate, and they are tuned at a very specific pressure to give the mass flow rate. While they may be marked in standard liters per minute (slpm) or standard cubic centimeters per minute (sccm), this reading is only valid at the pressure for which the rotameter was tuned. An Alicat, on the other hand, is valid at all times because it has a pressure sensor that adjusts the reading when the pressure changes. Comparing rotameters to Alicats is like comparing apples to oranges because they are measuring different things, unless the rotameter is at it’s very specific calibrated pressure. However, since we can control pressure with an Alicat mass flow device, why not control to the pressure to which the rotameter is tuned?

We’re typically talking about the setting the pressure downstream of the rotameter, so it’s simply a matter of placing the Alicat downstream with the valve on the opposite side, so that you are controlling the back pressure from the valve, through the Alicat and the rotameter. Then you can measure the flow directly on the mass flow meter and the rotameter at the same time. Of course, you must make sure that the Alicat has the rotameter’s gas and standard conditions selected. They aren’t adjustable on the rotameter, but they are adjustable on the Alicat. You can choose from hundreds of gases (up to 130, but most standard series have 98 selectable options) along with user-selectable standard temperature and pressure.

Why Choose Alicat?

Solving unique problems is probably my favorite part of being an applications engineer. When it comes to Alicat products, everything can be customized to suit a customer’s needs. If a customer has a unique application that we haven’t seen before, the solution might involve making some small tweaks, like putting a valve in a different place or adding a relative humidity sensor. For instance, right now we’re figuring out how to work with 500 liters per minute of sulfur dioxide. Because it’s highly corrosive, we need to use 316 stainless steel and FFKM. One of my colleagues is also working on making our new IP or NEMA rated instruments more durable. We started a whole redesign of the system based on the input of a couple of customers.

If you have an application that you think might require a customized solution, call Alicat to speak with an applications engineer. We’ll answer your technical questions to the best of our ability and help you figure out if there is a custom solution we can build to meet your needs.

Reference: click here.

D&D Engineering – “W’ere YOUR Sensor Guys”
3835 E. Thousand Oaks Blvd. Suite 464 Westlake Village, CA 91362  – Voice: (818) 772-8720 Fax: (818) 772-2477 Toll Free: (888) 333-6474
Email: sales@sensorguys.com Website: www.sensorguys.com

Customizing mass flow and pressure controllers: brilliant to baroque

Customizing mass flow and pressure controllers: brilliant to baroque

Posted by: Dan Yount

Many customers, even our most loyal ones, don’t realize that we customize just about EVERY Alicat instrument order. That’s because all our instruments are built when you order, and configured and programmed to best suit the application and conditions for which you’re buying them. Customizations can range from having a meter automatically tare itself every 24 hours, to engineering new limits of what our pressure controllers can handle! To give you an idea of how we work out your new requests, here are some simple and helpful customizations we produced on request.

Local Valve Drive Percentage

Resulting from a customization created at a customer’s request, the Local Valve Drive (LVD) option lets you monitor the work your valve is doing—because it can help you assess whether your process is in trouble. The LVD parameter appears on the large, multivariate display screen of an Alicat mass flow controller (or pressure controller), right above the main parameter output in the center. The LVD option reports the proportion of power being applied to the valve to maintain the setpoint. Valve drive percentage is something our devices normally track internally, and is a useful data point in troubleshooting, should you ever need it (our free lifetime support, available by phone or email, can help you with any troubleshooting you need). The value to the customer is that it serves as an indicator of the overall health of their chemical reactor vessel’s inputs and outputs. A significant change in the valve drive may indicate several possible failure conditions. Here’s a quick video showing this simple and smart customization at work:

Our “Local Valve Drive” (LVD) customization allows you to see how much drive is being given to a valve from your controller. One of our customers wanted a quick way to diagnose if their reactor’s output was dropping. Given steady pressures and flow rates, the valve drive will consistently be within a certain range. Our customer knew that at 30 PSIG inlet pressure with 10 SLPM of flow, the valve driver would be somewhere between 35-40% full power typically. If they saw the valve drive creeping much higher than this, then they would know that they were losing pressure differential in the process, since the valve was needing to open the valve wider than usual to create the same amount of flow. It may be that something is clogging the valve, making it open wider to allow flow to pass through. If they saw the valve drive percentage at 100 this would indicate that the valve was 100% open, or it was at least trying to be that way. They’d know that their reactors were creating such little output that it wasn’t possible to generate enough flow to satisfy their setpoint.

Local Valve Drive is now an option you can ask for, if your application calls for it.

Controlling pressurization speed

A customer wanted to use a pressure controller to maintain a certain pressure within a leak test chamber. However, they also wanted to make sure that the chamber would not pressurize too quickly.

MCD-Series bidirectional mass flow controller, shown with IPC option

MCD-Series bidirectional mass flow controller, shown with IPC option

To assure this, we built them a dual-valve mass flow controller in our MCD Series. A dual-valve mass flow controller can be programmed to fill with one valve and vent with a second valve. Like all our standard MFCs, it can be set to control flow based on pressure, rather than mass flow, (while still measuring mass flow!) Our dual-valve mass flow controller is also able to measure mass flowed in either direction. The MCD series of mass flow controller can be perfect for dispensing gases into a closed volume without overshooting or overpressurizing, or as an instantaneous pressurized leak test, with a built-in pressure relief valve for quickly changing the devices under test.

The customer used pressure control mode so that the setpoint was in pressure units, not mass flow units.

Finally, we created a custom software feature: a “Mass Flow Limit” function, configurable through the front screen. This would operate as a governor on the flow rate. It tells the valve to not open any further, once a certain mass flow rate was reached. This effectively limited how quickly the unit was allowed to pressurize their system.

Custom Configuring: a Stainless, IP-rated Dual Valve Pressure Controller

Customization can come in the form of unique combinations of options. Like this PCDS–it’s a dual valve pressure controller with a lot of options added on:

psds-ip65-remotevalve_lr

  • Stainless flow bodies and corrosion-resistant seals for using aggressive gases
  • A remote pressure sensor port (it’s on the backside of the flow body with the display), so that the pressure control will be based on a remote volume, independent of the valve lines.
  • IP-65, a liquid ingress prevention rating, means all the connectors are sealed with gaskets, and the display panel doesn’t have our menu buttons
  • The second valve is remote. The cable is the right length to mount the “relief” valve in a different location of the process flow.
  • Modbus industrial protocol on board. Without interface buttons to program the device, remote commands are necessary. But the display will provide a visual confirmation of the operation of the device for any technicians on the scene.

Altogether, it’s a very unusual device.

What’s your application?

When you place an order, our apps engineers always ask a lot of questions, like “What is the application? What are the operational parameters, and what are you trying to do?” This guides them in recommending things like custom tuning of valves (no extra charge!), or the selection of a particular sensor, or communications options. We do our best to make the device perform at its very best in your hands. Sometimes that means custom engineering, sometimes just custom configuring of existing options. Alicat prides ourselves in our ability to accommodate many custom configurations, or invent a solution!

Reference: click here.

D&D Engineering – “W’ere YOUR Sensor Guys”
3835 E. Thousand Oaks Blvd. Suite 464 Westlake Village, CA 91362  – Voice: (818) 772-8720 Fax: (818) 772-2477 Toll Free: (888) 333-6474
Email: sales@sensorguys.com Website: www.sensorguys.com

How can I take advantage of PID Tuning?

How can I take advantage of PID Tuning?

Posted by: Jas Gill

Alicat flow and pressure controllers use closed loop control algorithms to achieve their highest degree of control stability. The algorithms are a mathematical relationship that dictates the response of the valve to the flow or pressure conditions. It assesses the difference between the set point and the process value—whether it be mass flow, volumetric flow, or pressure—as an error. The degree of error determines what kind of input to send to the valve, reaching the correct value in the quickest time possible. The amount of time expended to minimize the error—and therefore the control response of the controller—depends on what type of loop is being used (PD or PD2I) and what P, D and I values are used.

When you order your controller, we set the Proportional and Derivative values by trying to replicate the application parameters (process conditions) to the best of our ability before we ship it to you. This customization to your system is one reason our controllers are fast.

No worries

If process conditions change, the valve response may change drastically depending on how much you deviate from the conditions the valve was tuned at. You need not worry about erratic response from your controller if the conditions change, since PID tuning can be done in field to get better control at the new process conditions. You can change PID terms through the display panel buttons, or through electronic commands using digital or analog communications.

You’ll get optimal performance from your controller when you select correct values for all three parameters (two in case of single valve controllers). The ‘P’ term opens the valve to achieve the set point, ‘D’ term applies a damping influence to eliminate the overshoot and ‘I’ function helps the system settle to the set point.

A previous blog describes the P, D, I terms:
Achieving Responsive and Stable Valve Control with PID Tuning
Briefly:

  1. Proportional (P): The P term applies power to the valve as it tries to decrease the error between the set point and the process value position to achieve the set point.
  2. Derivative (D): Think of this as a damping term which tries to reduce the rate of change. The larger the D term, higher the damping influence on the valve drive.
  3. Integral (I): Integral in calculus is the area under the curve, it determines the output of the valve as a function of the sum of all the errors. I term takes into account previous readings to reduce the error and correct the process value to the set point.

 

Oscillating around the set point

If your controller shows signs of oscillations about the set point, or is unstable in its control response, it is a sign that the P term is too large. The greater the P value, the greater the range of oscillation. To get rid of the oscillation (settle the controller to set point), you would need to decrease the P term.

Let’s say you have a 10 SLPM controller set to 10 SLPM for Hydrogen. The controller is oscillating between 8 and 12 SLPM. Hydrogen is a low viscosity and a very light gas compared to Air. This being the case, the valve—which is tuned with air—should be re-tuned. So, starting with the factory P value (for example, it may be 1000), try decrements of 10% and keep on going down until you see the controller settle to the set point quickest. Generally, we only touch the D terms after you have altered the P term, so if you still have small oscillations, you can increase the D value with 5-10% increment. This should help the controller become more stable.

PID response shown graphically, by varying P

Excessive P (purple) produces oscillation. Low P (red) slowly rises to the setpoint. Optimal (green) settles quickly.

Delayed setpoint

A second situation is when your controller takes too long to get to the set point or never achieves the set point, but settles to a flow rate or pressure below the set point value. This implies either too small a P value being used or too large a damping influence. Using the analogy of a car, imagine you want to get to 70 miles per hour. but when you start increasing the speed, someone applies brakes which decreases the acceleration of the car. The car may never get to 70 mph if the deceleration is larger than acceleration, and the car may settle at a speed of 60 mph when acceleration = deceleration, or the opposite forces are equal.

In this case, try increasing your P value in 10-15% increments until you see the controller getting close to your set point. Next step would be to decrease the D value to help the controller get to the set point in a quicker time. If you start seeing some oscillations, that means the D value has been set too low.

Control loop adjustment is all about getting a good feel of how the controller responds to changes in the P and D terms. The gas viscosity, inlet pressure, back pressure can greatly influence how the valve responds. Tuning the valve is an art rather than science and the more familiar you get with your controller, the better you’ll be able to tune it.

 

 

 

 

Reference: click here.

D&D Engineering – “W’ere YOUR Sensor Guys”
3835 E. Thousand Oaks Blvd. Suite 464 Westlake Village, CA 91362  – Voice: (818) 772-8720 Fax: (818) 772-2477 Toll Free: (888) 333-6474
Email: sales@sensorguys.com Website: www.sensorguys.com

Alicat Mass Flow Controllers Powers MDC’s XpressStick Gas Delivery Module

Alicat Mass Flow Controllers Powers MDC’s XpressStick Gas Delivery Module

Posted by: Edgar Schrock

Gas connection module benefits from Alicat’s MCE’s high precision flow control

Alicat Scientific’s MCE mass flow controllers have been integrated into MDC Vacuum Products’ XpressStick™ MFC Gas Stick. With precision control of gas flows of up to 20SLPM and onboard display, Alicat’s MCE provides gas programming functionality to the gas connection module, which links pressurized gas inputs to vacuum chambers.

The Alicat MCE accurately controls gas flow rates as low as 0-0.5 sccm full scale or as high as 0-20 slpm full scale. With 20 to 50 millisecond control response times to setpoint changes, the MCE improves vacuum coating end products and helps eliminate target poisoning.

The MCE mass flow controller helps drive precise doses of gases for mixing and purging in vacuum coating systems

The all-in-one design of the XpressStick MFC gas stick eliminates complex hardware specification in processes which include a combination of specialty gases, pressure, precise regulation, and vacuum. Its easy programming and precise gas control system allows users to go from bottle to process in one simple step. Designed to meet ultra-high purity process requirements, the XpressStick is also offered in a stainless steel model for corrosive environments.

With the MCE’s zero warm up time, the XpressStick is ready to control process flows in just one second, with real time mass flow, volumetric flow, absolute pressure and temperature data, fully compensated for temperature and pressure. The gas module is programmed directly through the MCE’s integrated display, with easy changes to gas type using the on-board gas calibrations.

“Fast response time, accuracy, and reliability were all key criteria in choosing an MFC instrument for our XpressStick,” explained MDC Vice President of Engineering & Technology, James Moore. “Based on past experience with Alicat, we knew that they could deliver all three, with an integrated display that enables our all-in-one design.”

Alicat mass flow controllers, pressure controllers and vacuum controllers are used in vacuum coating systems around the world.

Reference: click here.

D&D Engineering – “W’ere YOUR Sensor Guys”
3835 E. Thousand Oaks Blvd. Suite 464 Westlake Village, CA 91362  – Voice: (818) 772-8720 Fax: (818) 772-2477 Toll Free: (888) 333-6474
Email: sales@sensorguys.com Website: www.sensorguys.com