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

Totalizer Averaging Smooths Out the Data in Flow Measurements

Posted by: Alyssa Jenkins

Alicat’s optional totalizer feature is a great way to meter the total flow through a system. Adding a totalizer to a controller means you can dispense fluids in set quantities. We call it batch mode: set a total mass desired, set a flow rate, and the controller stops when the delivery amount is reached.

Totalizer averaging adds another number to your totalizer screen—the average flow rate during the metered period.  Calculating the average after the sample has finished is simple, but real time averaging can be tedious and require additional programming.  Why not just have it on the screen?  Not only does totalizer averaging appear in the screen, it also appears in the serial data stream—right next to the totalizer value. Now you can easily streamline your existing communication programs.

tot-avg-screen_highlighted_800

Totalizer averaging can be extremely helpful during leak checking or flow characterization.  Using a mass flow device to control the pressure on a device under test and while measuring the flow rate is a compact solution essentially including two devices in one.  For smaller flow rates and volumes, minute changes in pressure will force changes in flow rates—which in turn change the pressure.  This can lead to an oscillation of both pressure and flow rate.  While the oscillation is natural, it can make it difficult to determine a single number to report.  With totalizer averaging, the average flow rate can easily be seen and recorded in real time rather than waiting until the process is complete to calculate.

Alicat devices have always had a flow averaging feature available to help minimize noise, since we sample in milliseconds. For users who are unaccustomed to a fast-responding sensor, the totalizer averaging can be easier to read, and helps to correlate our flow measurements to results from slower-responding instruments.  Totalizer averaging gives the ability to average flow measurement data over variable periods—from milliseconds to hours—extending the possibilities.

If the totalizer software is already on your device, the totalizer averaging feature can be added easily in the field via serial communication.  For those who are familiar with serial communication, simply add 1024 to the current number in register 88.  (Need a little help getting set up for serial communication?  Our applications engineers can help you out). The totalizer option itself is described on the product options page.

Here’s a video that shows how easy it is to use the Totalizer Options:

The totalizer option and totalizer averaging can be added to most Alicat mass flow and liquid devices ordered since 2003. Contact our applications engineers for more information about how to upgrade your unit today—get your serial numbers handy.

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

Gas Chromatography’s mobile phase and mass flow control

Posted by: Joe Ancona

It’s safe to say that a Gas Chromatograph is one of the most important tools one will see in an analytical chemistry laboratory. Chromatographs are the workhorses of the analytical trade. When it comes to separating, analyzing, verifying purity, or determining concentrations of various chemical concoctions, the “GC” as it is commonly known, can provide a quick, accurate, and repeatable result for a large cross-section of known compounds. Of course, to have precision in analyzing means all the components in the system must work as expected. A clean ‘column,’ appropriate for the substances being separated, a properly prepared sample, diligent injection methodology, and a stable mass flow rate of the inert carrier gas are all required.

Basically, a modern gas chromatograph is designed to take a sample in the form of a ‘slug’ and pass it through a long ‘column’, as carried by a steady flow of inert gas. While the sample moves through the column in a computer-controlled oven, it’s heated to various temperatures, and its output is fed to the detector array. The sample and carrier gas are eventually vented out as waste.

The key measurement function of the GC is centered on timing. As the components of the sample are separated in the column, they emerge at different times and in rising and then falling intensities. The detector simply plots the peaks against time (retention Rt) and strength (peak area). Based on known chemistry, the components and concentrations of the original sample can be determined with amazing accuracy.

Misnomers and misconceptions

If you’re unfamiliar with how a gas chromatograph works, let’s dispel a couple of misnomers and incongruities. First, there is no traditional vertical ‘column’ inside the GC! (The decades old classic ‘column chromatography’ process does in fact use an actual glass tube, up to several feet tall. The column effects the purification of individual chemicals through a powder or slurry, using the principals of partition equilibrium.) Although the over-arching concepts are very similar, the modern GC’s column is now a very thin, coiled capillary tube. These fine quartz or fused silica tubes have only 0.1 to 0.53 millimeter internal diameters, but are cut to 12 to 100 meters in overall length! Modern capillary tube columns are internally coated with a thermally stable, high molecular weight polymer. This extremely thin polymer layer (0.1 – 10 thousandths of a millimeter) is referred to as the ‘Stationary Phase’.

A second common misconception comes from the word “Chromatography” itself. When you see ‘Chroma’ you might think ‘color’. When you see ‘-graphy’ you would normally assume there is some type of written or printed result. Just as the ‘column’ sub-component name has carried over from traditional separation techniques, so has the ‘chroma’ element. In the early days of thin layer chromatography (circa 1900), it was the actual colors of the various compounds in plant materials spread across the paper stationary phase which gave the Chromatography process its name.

Lastly, there isn’t a universal gas chromatograph for every compound. Some aspects of the sample to be tested must be known in advance, so that the right kind of GC is used. Different chemical groups need different columns, tailored to their properties. Certain volatile compounds need to be vaporized, and kept that way, meaning oven heating schedules must be selected for the best separation resolution. Most importantly, there are many different types of detector heads to match the appropriate selectivity of the test sample. Detector technologies include flame ionization, thermal conductivity, electron capture, photo-ionization, conductive, and so on… A majority of the detection technologies are dependent on steady state mass flow rates.

Timing is everything

As the various chemical compounds move through the capillary via the flow of inert gas—called the Mobile Phase—each will effectively ‘stick’ to the walls of the column at varying levels of adhesion and therefore will elute through the tube and into the detector head at different times. This happens regardless of the steady flow rate of the carrier gas, since the compounds all have a unique—and therefore identifiable—affinity to the stationary phase coating inside the capillary. All of the compounds make it through eventually; but it’s how fast they make it through that distinguishes one from another. Because of this, it is imperative for the carrier gas flow rate to be constant; otherwise flow rate would become a seriously disruptive variable to the detection of a particular chemical compound.

Imagine a sturdy wooden ramp in your backyard, used to roll different types of balls across a freshly cut patch of grass. Starting at the top of the ramp, a bowling ball rolls down, and across the yard. It’s barely slowed by the friction of the grass. A Bocce ball has a similar result, but doesn’t quite make it as far as the bowling ball. A soccer ball falls someplace in between the two. A whiffle ball hardly goes a few feet past the end of the ramp, and a ping pong ball is stopped within inches. Obviously, each ball has its own mass, diameter, angular momentum, rolling resistance, etc., but within reason, one could determine which ball is which, just by how far it rolled on the grass; once the norms were established. This assumes of course that the uniform grass surface (think: polymer coating in column) isn’t swapped out for a rocky dirt lot (a contaminated column), and that the fixed wooden ramp (a.k.a. the steady carrier gas flow rate) isn’t raised or lowered randomly during testing (unstable gas flow).

Minimizing the Variability of Flow

The effectiveness of a gas chromatograph relies heavily on stability and repeatability. Whether it be the method of injection of the sample, the computer controlled oven temperature profile, the use of a clean ‘blank’ (just ask any DUI lawyer about that one!), or the steady state flow of the carrier gas, the only variable in the process should be the sample itself.

Alicat Scientific, Inc. specializes in both precision mass flow control and high speed/high accuracy pressure control; each of which can be used to deliver exacting inert gas flows to your GC column. Even in low flow regimes, our mass flow controllers can provide stable flow from zero to full scale within tens of milliseconds. Each MFC has the ability to measure and control up to 98 default (common) gases and gas blends; changeable on-screen, or via digital control. No matter what inert carrier is being used for a particular test (N2, He, Ar, CO2), you can use the same Alicat MFC for each, so long as it is set to the gas being flowed.

If the GC uses a fixed orifice that requires stable pressure control, Alicat produces a wide range of electronic pressure controllers (both standard and OEM electronic pressure regulators) which can be custom tailored to just about any flow rate/pressure condition/speed, achieving the best result possible.

For verifying flows in a particular gas chromatography system, or to calibrate the gas delivery components within a GC, use one of our portable calibration flow meters to quickly establish proper carrier gas operation:

Our flow measurement technology has been used and trusted for over 25 years by some of the leading gas chromatograph manufacturers in 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

7v Firmware Update Makes Interface More Intuitive for Alicat Flow and Pressure Instruments

Posted by: Danielle Adams

We’ve just made it easier to use your Alicat mass flow meters and pressure controllers from their front panels. This post has all the details on our 7v firmware update, which features a more intuitive user interface.

If you’ve been with Alicat for very long, you’ve seen us add new menu selections to our flow and pressure instruments from time to time. We incorporated these features into a set of “Miscellaneous” menus (MISC1 and MISC2) in order to preserve the existing interface. However, after filling up MISC1 and MISC2 with new functions, we decided it was time to give the entire menu system an intuitive update.

Alicat mass flow controller showing new basic configuration menu

Alicat mass flow controller showing new basic configuration menu

Here to explain the motive behind these changes is Brian Clandenon, Alicat’s Senior Software Engineer:

“As Alicat has added more functionality to our instruments, the idea was to make minimal changes to existing buttons in the menus. While this was reasonable for each small change, so many changes built up over the past few years that some related functions became scattered across multiple menus. This made the menus more challenging to navigate and to remember.

Alicat mass flow controller showing new advanced setup menu

Alicat mass flow controller showing new advanced setup menu

One goal of a good menu system is to make settings easy to find, so it became time to review the overall structure of the menus. We endeavored to organize the settings in ways that would be more intuitive to new and existing users alike, so that the changes would outweigh the inconvenience of learning the new locations.”

The following FAQ describes the changes to Alicat’s menu structure in the new 7v firmware.

Which instruments are affected by this change?

All Alicat-branded instruments manufactured on or after May 22, 2017, will ship with 7v firmware, with the exception of no-change customers who have not yet approved this update.

Can I update my existing instruments to 7v?

Alicat’s 7v firmware update is compatible with most Alicat instruments that have serial numbers of 135,000 or higher. Some instruments with serial numbers between 80,000 and 135,000 may also be compatible with 7v. Upon request, we can update your firmware to 7v during your instrument’s next annual recalibration at no charge. Alternatively, we can update instruments outside of the recalibration process for a firmware update bench fee of $80 (USD).

Will my new 7v Alicat communicate the same as my existing 6v Alicats?

Yes. Communications protocols and commands have not changed in the move from 6v to 7v, so your command set will remain the same, no matter which protocol you have been using.

Which changes will I notice?

Alicat mass flow controller showing new main menu

Alicat mass flow controller showing new main menu

The new menu map is reproduced on the following page. Below, you will find a listing of changes to the menu structure. Please see your new operating manual for more details.

  • A new BASIC CONFIG menu allows easy access to GAS SELECT, DEVICE UNITS and STP/NTP options. The GAS menu option also displays the currently selected gas.
  • A new TARES menu gives you access to flow and pressure tares, plus AUTO TARE.
  • A new ABOUT menu collects DEVICE INFO, DEVICE STATE and MFG INFO in one place.
  • The contents of the old MISC, MISC1 and MISC2 menus can now be accessed via the ADV SETUP menu, with the exception of STP/NTP, which is now in BASIC CONFIG.
Feature New Menu Location (7v Firmware) Old Menu Location (6v, 5v or 4v)
AUTO TARE MENU > TARES MENU > CONTROL SETUP
CONTROL SETUP MENU > CONTROL MENU > CONTROL SETUP
DEVICE UNITS MENU > BASIC CONFIG MENU > MISC
DIAG TEST MENU > ABOUT > DEVICE STATE MENU > MISC > MISC2 > DIAG TEST
FLOW AVG MENU > ADV SETUP > SENSOR SETUP MENU > MISC > MISC1
GAS SELECT MENU > BASIC CONFIG > GAS MENU > GAS SELECT
LCD CONTRAST MENU > ADV SETUP > DISP SETUP MENU > MISC > MISC1
MFG DATA MENU > ABOUT > MFG INFO MENU > MFG DATA
MODEL INFO MENU > ABOUT > DEVICE INFO MENU > MFG DATA > MODEL INFO
PRESS AVG MENU > ADV SETUP > SENSOR SETUP MENU > MISC > MISC1
ROTATE DISP MENU > ADV SETUP > DISP SETUP MENU > MISC > MISC2
RS232 COMM MENU > ADV SETUP > COMM SETUP MENU > RS232 COMM
STP/NTP MENU > BASIC CONFIG MENU > MISC > MISC2
TARE P w/BARO MENU > TARES > TARE PRESS MENU > MISC > MISC2 > TARE P w/BARO
ZERO BAND MENU > ADV SETUP > SENSOR SETUP MENU > MISC > MISC1

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

The RS-232 Communication Protocol and your Alicat instrument

Posted by: Joe Ancona

The 55-year-old RS-232 protocol is the default method of talking to Alicat devices. Aside from RS-232, you could configure your instrument with RS-485, Profibus DPV1, ModBus RTU, DeviceNet, and Ethernet IP protocols. For the bulk of our customers however, the tried and true RS-232C communication standard will remain the go-to method for commanding and reading Alicat devices.

The Not-So-Standard RS-232 Standard

One of the main reasons that RS-232 has survived for over five decades is that it is a useful, but low level and rudimentary signal, with fairly loose operational guidelines. In 1962, the sole application for the RS-232 communication standard was connecting electromechanical typewriters and their host mainframes/modems, commonly known as ‘Teletype’ systems.

When more advanced electronic machines were developed subsequently, proprietary adaptations led to nonstandard pin assignments, connectors and signal voltage levels. For example the original specification called for a DB-25 connector, but in the last 30 years most RS-232 products have adopted a DB-9 connector (technically called DE-9M).

The ‘data’ being sent on RS232 lines are simply positive (+) and negative (-) voltage pulses relative to a ground reference. A group of +/- pulses sent by one device are carefully timed by the receiving device and decoded into whatever the hardware settings deem to be data bit packages. In other words, the RS-232 standard only defines a relatively loose general electrical framework to transmit and receive electrical pulses. What one does with all these pulses is ultimately up to the connected hardware. Things like character encoding, spacing, start bits, stop bits, bit order, error detection, bit transmission rate, etc. are not the responsibility of the RS-232 scope, and are established by the user’s connected circuitry, usually in the form of a serial communication port and its associated chips and transistors.

db9-pins

It’s the COM Port’s job to make sense of the pulses on behalf of the attached computer or peripheral. For reference, an RS-232 system must transmit from one device (sent on its Tx pin), to a receiving device (received on its Rx pin), and vice-versa. Do not try to connect Tx to Tx or Rx to Rx in an RS-232 three wire system! The only pin that is connected directly is the ground pin, which gives both ends a common reference point to measure the pulses from. Each RS-232 driver uses inversion logic and employs a single ended, bi-polar output voltage to feed to a UART (Universal Asynchronous Receiver/Transmitter). Because the system has three wires and two distinct channels of communication, it is considered a “Full Duplex” system. Data can be transmitted at the same time as it is being received.

RS-232, the Alicat Way

Understanding how loose the RS232 “standard” really is, you might be wondering how Alicat uses it. Alicat does offer the ubiquitous DB-9 or the “standard” DB-25 connector, but we can provide RS232 communication on any connector that is offered, such as DB-15, 6 pin industrial locking connectors, and of course the default 8 pin miniDIN jack.

Alicat RS-232 Specifications

However, our real departure from the standard, is how Alicat has exploited signal levels and allowed for multiple units to work on the same COM Port. Because Alicat devices neither accept nor produce negative voltages, a traditional +/- 15V RS232 is not possible. Fortunately, a positive only pulse of +5V can be made to replicate an RS232 waveform (logic high ‘mark vs. logic low ‘space’), readable by 99% of all UARTs used today.

Once UART serial ports went out of fashion in the early 2000’s, USB to serial converters took their place; most today use the FTDI chipset to replicate the COM Port. Alicat’s unique signal profile is also fully compatible with these devices.

In addition to bending the rules for signal level and polarity, Alicat has also designed a clever work-around for being able to use up to 26 units at once on a single serial COM Port. The technical term for this capability is called ‘Multi-Drop’ communication, and is supported by all Alicat units equipped with serial communication (whether RS-232, or the differential signal based RS-485). Through multi-drop communication, every device on the line is configured to have a unique identifying letter (A-Z), and every unit listens to the commands that have been sent. However, even though each device ‘listens’ to each command, a particular unit will only accept and respond to the command if the instruction begins with that instrument’s unique ID letter.

So you can read the current flow rate on unit “A”, give a new setpoint to the MFC “B”, and reset the totalizer on unit “C”; all while being hooked together on the same three wires (electrically in parallel).

Even though the RS-232 communication ‘standard’ itself is old enough for a place at the Smithsonian Institution, it is still heavily used today for all types of computer based systems that talk to various peripheral components. Employing the universal ASCII (American Standard Code for Information Interchange) character set as our language, Alicat instruments will continue to be sold with the robust, universal, and reliable RS-232 system for the foreseeable future. For basic connection and terminal examples please see our video and instructional here:

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

Customer Experience: Ethernet/IP

Posted by: Michael Hodges-Owen

Most customers don’t call us for our razor-sharp wit, or our slightly eccentric social skills. Instead, we know with certainty that whenever a customer comes to us, they have a problem that needs to be solved. While Ethernet/IP™ is not required for every process, some customers insisted on it. We recently added Ethernet/IP to the list of available communication protocols that can be configured on any mass flow, liquid, or pressure device. We wondered what the most significant benefit was for choosing it. So we reached out to a few companies who have already implemented it into their process to find out why they chose this option.

For perspective, consider that most Alicat devices are configured with an analog input/output connection. The connection requires individual signal wiring for each unit, which can get messy if there are a lot, and it only provides information on one or two parameters in the process. Our instruments are also normally configured with RS-232 (or RS-485) connections–those require reliable drivers, written for the specific, proprietary formats with which you’re communicating. It was important to one of our customers to acquire near real-time process information for control and diagnosis, to include setpoint, mass flow, volumetric flow, absolute pressure, temperature, and valve position. Using Ethernet/IP, which supports 10 and 100 Mbps bandwidths, gave them the capability to talk to multiple Alicat units over a redundant network that was easy to implement into their process.

eip_mc-d_600

Not only did the Ethernet/IP option fulfill their requirements, the versatile configuration options clinched their decision to go with Alicat. Most standard features–such as the multivariate front panel display, or selection from 98+ gases with full accuracy–come with Ethernet/IP equipped devices too. However, the devices don’t have an analog output, or support Power over Ethernet (PoE). The units are equipped with two RJ45 connectors to provide the redundancy that is expected within an automated control system. Alicat’s Ethernet/IP has been certified in conformance by ODVA®, the standards body for Ethernet/IP.

Ethernet/IP is rapidly growing in popularity.

 

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

Custom Part Number Decoder

Posted by: Edgar Schrock

Because Alicat instruments are so highly customized, our part numbers get quite long and confusing. Customers often want to reorder a similar instrument or to find out what options are included in a particular one so they can repurpose it. The part number, printed on the silver manufacturer’s label on flow body of your Alicat instrument can tell you a remarkably large amount about what the factory settings were when we shipped it.

Senior Applications Engineer Mike Owen has put together a very concise way of decoding the settings and options embedded in your part number. It’s a one-page PDF you can find in our site navigation menus under accessories or support. Just look for the “Part Number Decoder” link.

An unexpected benefit of the decoder is that you can use it as a quick reference on whether or not we offer an option as a standard addition. If you don’t see the option you need, you should still contact us, because custom engineering solutions are a big part of what we do, every day.

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

3 reasons why Alicat is the fastest flow controller company in the world

Posted by: Jas Gill

Building the fastest mass flow meters/controllers and pressure equipment in the world is both a point of pride for us and a unique factor for which our customers select Alicat instruments. The question is, ‘fastest’ in regards to what? Having started working at Alicat Scientific recently, I’ve found these three things which help make Alicat the fastest flow controller company in the world.

Reason #1. Fast Sensor Response Times

Alicat devices have the fastest response time compared to any other flow device manufacturer. The frequency of sampling means the sensor takes close to one thousand readings in a single second. Through a PID loop, which regulates responsiveness, a valve then controls the flow rate to the set point. The control response time for valves is 50-100 milliseconds–adjustable through PID tuning. If we apply the chemical kinetics analogy to this system, the rate determining step (RDS) or the rate limiting step would be the valve adjusting its position according to the difference between the set point and the flow reading. The sensor itself is very fast, detecting changes in pressure every millisecond. Thermal sensors, which are relying on the absorption and transmission of heat information, take longer to detect flow changes—it’s physics. This is one reason why our patented laminar flow differential pressure mass flow devices are quicker than thermal flow devices.

More about control speed of response

Reason #2. Me! (Also known as) Fast Technical Support

We don’t have separate phone extensions for technical support and new applications. You won’t have to wait to be put through to the right department, everybody is available immediately.
When you call us to specify a product or to troubleshoot your flow process, one of our applications engineers—like me—helps you with technical queries, troubleshooting or applications. Virtually every instrument we ship is customized in some way to the customer’s application, and our application engineers help you do that.
When you send in an email (be it new orders, service requests or general inquiries) to us, we try to respond within an hour—we’re even opening international service offices and coming in early to cover more time zones around the world.
With Alicat, you can expect the fastest customer service.

3. Convenient features that make you faster

Alicat devices have a built-in Gas Select feature that’s different from all the others. Many other brands offer gas changing on the instrument, but with some big drawbacks: you suffer from reduced accuracy, and you may need to calculate and program in K-factors to your process. For customers who are unable to accept reduced accuracy, the actual result is weeks of delay while the instrument is recalibrated at the factory, or down time while an instrument is replaced from spares.
Alicat devices change gases without losing calibrated accuracy, and they do it ultra-fast, at the touch of a button. The standard line of mass flow controllers have 98 different gas calibrations, the stainless steel MS/MCS series devices have 131 calibrations, including corrosive gases. Using Alicat devices gives you the flexibility of instantly repurposing an instrument for a different gas without delays in reconfiguration.

There are certainly other ways in which Alicat is fast. What’s your favorite?

 

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