• Excellent linearity, no calibration needed
  • Fully compensated analogue output (or I2C)
  • Standard tubing
  • Pressure range 100mBar to 5 Bar
  • Temp range 0-50 ᵒC
  • Media: clean dry air and non-corrosive gasses.


  • CPAP, Spirometers, Ventilators
  • HVAC, filters (∆P control)
  • And many more

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
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The SMT172 by Smartec

The SMT172 is a three terminal integrated temperature sensor with a duty-cycle output. Two of the terminals are used for the power supply (2.7 -5.5 Volts) and the third terminal carries the output signal.
A duty cycle modulated output is used so that the output can be read by a microprocessor, while the  analogue information is still available.

The sensors are available in a number of encapsulations: TO18, TO92, TO220, SOIC-8L, SOT223, HEC and in a 7 mm ss. probe with 5 mtr cable. The SMT172 can be supplied as a naked die as well.

For quick design-in, a lot of applications are available on the web and for those who want plug and play, we have designed a Smart Temperature Acquisition System for 4 or 8 Smartec temperature sensors. It was designed to get the best possible temperature measurement results with the SMT172 temperature sensors (absolute accuracy 0.1 °C, noise <0.0001 °C), at low cost. We offer  an application to connect the board to an Excel  application. In this way, a low budget , high accuracy measurement system can be built.

The SMT172 has an overall accuracy of 0.1 °C in the range from -20 °C to +60 °C and an accuracy of 0.4 °C from -45 to +130 °C. This makes the sensor especially useful in all applications where human conditions (climate control, food processing etc.) are to be controlled.

The CMOS output of the sensor can drive cable lengths up to 20 meters. This makes the SMT172 very useful in remote sensing and control applications.

Datasheet of the SMT172

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Alicat absolute pressure controllers enable direction of cryogen pressures ensuring precise temperature.

by Mic Chaudoir

Neil Hartmann, CTO

Alicat absolute pressure controllers enable direction of cryogen pressures ensuring precise temperature.

Cryogens are loosely defined as gases which liquefy at or below 120°K under standard pressure (760 Torr).1 Cryogens are used for applications including cryopreservation, superconductivity and superfluidity. All of these applications share a need for temperatures under the previously mentioned 120°K temperature at standard pressure (760 Torr)

Liquid Nitrogen is a commonly used cryogen which is near the upper end of the cryogen temperature spectrum. Helium is perhaps the most well-known of cryogens, renowned for its proximity to absolute 0 (0 degrees Kelvin – Helium is typically 3-4 °K, depending on isotope and pressure).2

Figure 1: Graphs showing the interdependence of temperature and pressure for commonly used Cryogens.  Graph 1 shows an overview, while Graph 2 shows an expanded view of lower pressures

Pressure:100 torr760 torr1,000 torr10,000 torr
Helium-42.64 °K4.21 °K4.53 °K
p-Hydrogen14.99 °K20.27 °K21.23 °K
Neon 27.10 °K28.04 °K39.36 °K
Nitrogen63.49 °K77.36 °K79.76 °K108.39 °K
Argon 87.30 °K89.98 °K121.73 °K
Oxygen74.45 °K90.19 °K92.90 °K124.76 °K
Methane91.72 °K111.67°K115.11 °K155.69 °K

Table 1: Table showing the equilibrium temperatures at low, medium and high pressures for common Cryogens

Back Pressure Control

In systems where cryopreservation is the goal, researchers are concerned with maintenance of cryogen volumes as evaporation occurs. However, fluctuations in the atmospheric pressure can be the driving source of changes in Dewar pressure, as these are typically not fully closed systems. In an extreme example, boiloff from propellant storage tanks was estimated to cost $625,000 ($4.1M/year in inflation adjusted dollars) at NASA’s John F. Kennedy Space Center.3

Here, we analyze a more common volume; a 100L Dewar of liquid helium. Atmospheric pressure often fluctuates, commonly changing by +/- 25 Torr. In the case of a decrease in pressure, this will result in the vaporization of 0.874 Liquid Liters generating 25 standard cubic feet (or ~700 Standard Liters) of Helium gas. This translates to approximately $25 worth of liquid Helium.4Given the current supply shortage of Helium, it’s unlikely that these prices will decrease in the future. Over a period of years this may amount to thousands of dollars in unnecessary loss. An Alicat Absolute Pressure Controller can be used to maintain a constant absolute pressure in the head space of a Dewar, ensuring minimal loss of cryogens. In addition to controlling the pressure, Alicat Mass Flow Controllers and Meters can measure the actual gas lost while controlling the pressure of the head space. Alicat’s totalizer function can also directly measure the mass escaping over time. This technique also allows the amount of cryogen remaining in the vessel to be inferred.

In the case where a Helium recovery system is utilized, the exhaust port of a back pressure controller would be connected directly to the recovery manifold (as opposed to venting to atmosphere). This system configuration is desirable for its low cost and simplicity, while allowing for precise back pressure control of cryogens.

Figure 1:Diagram of a typical system using an Alicat back pressure controller to control headspace cryogen pressure 

Active Headspace Pressure Control

Faster, more flexible control of cryogen pressure and temperatures can be achieved using an active headspace pressure control scheme. Using the technique outlined above, the only source of positive pressure is boiloff due to heating of the cryogen itself. Therefore, utilizing pressure changes to control temperatures is dependent on the time to boiloff the necessary amount of cryogen, which is typically a slow process. Some users speed this pressure increase (and warming) with the use of a pressure builder coil. These coils expose a greater surface area of liquid cryogen, causing faster gas formation and pressure buildup.

Greater speed and control can be achieved by attaching a positive pressure source of warm gas, as well as a vacuum system to a Dual Valve Pressure Controller (PCD). This configuration allows for rapid introduction of warm gas, increasing system pressure. This in turn is assisted by an increased rate of boiloff as the cryogen shifts its equilibrium conditions. This rapidly increases cryogen temperature while maintaining precise control. Conversely, the pressure of the system can be lowered by venting to atmosphere or a vacuum. As the pressure decreases, cryogen temperature will decrease as well.

Figure 2: Diagram of a typical system using an Alicat differential pressure controller (PCD) to actively control headspace cryogen pressure 

Some of these advanced techniques utilize an Alicat Mass Flow Controller’s multi-parameter measurement features, also found in Alicat’s unique Bidirectional Mass Flow Controllers.  All Alicat Mass Flow Controllers simultaneously measure mass flow, volumetric flow, absolute pressure and temperature over 1000 times/second. As implied by the diagrams shown, we recommend the use of heat exchangers to maintain the gas temperature at the control valve above 263 °K. Alicat’s very low temperature and pressure span shift means that even with a large temperature difference, accuracy is not compromised (See our paper on this topic for more information)

The vapor pressure of any liquid is a function of temperature.  Conversely, the temperature of a liquid in thermal equilibrium with its saturated vapor is a function of its absolute pressure.  Therefore absolute pressure control = absolute temperature control.

To summarize, an Alicat Mass Flow or Pressure Controller or Meter can be used in many scenarios that benefit from cryogenic temperature control:

  • Monitoring of cryogen loss from closed volumes
  • Control of back pressure in cryogenic storage containers
  • Maximizing efficiency of cryogen recovery systems
  • Temperature control of cryogenic experiments via absolute pressure control


1. Quick reference for common Cryogens with temperature conversions between Kelvin, Celsius and Fahrenheit.

Cryogen Boiling Point (°K)Boiling Point (°C)Boiling Point (°F)

2. “Cryogenics.” Wikipedia, Wikimedia Foundation, 12 Dec. 2019, https://en.wikipedia.org/wiki/Cryogenics#Industrial_applications.

3. Salerno, L. J., et al. “Terrestrial Applications of Zero-Boil-Off Cryogen Storage.” SpringerLink, Springer, Boston, MA, 1 Jan. 1970, link.springer.com/chapter/10.1007/0-306-47112-4_98.

4. “Helium Users Grapple with Supply Crunch.” American Institute of Physics, 9 Apr. 2019, www.aip.org/fyi/2019/helium-users-grapple-supply-crunch.

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

Shaping a Paint Stream Using Mass Flow Pressure Controllers

by Alyssa Jenkins

Automatic paint sprayers, like those used in the automotive industry, require a constant flow of gas and paint to evenly apply a coat of paint to a surface. While atomizing the paint, the amount gas and paint supplied to the electric field can be adjusted to shape the stream of paint. This creates a consistent, quality finish.

Consistency between runs of the robotic painting system is vital. Different paint colors have differing properties, like weight, therefore different pressures and flow rates are needed to achieve the same shape. Repeatability and consistency of the flow rate are critical to ensure an even coat in all colors.

Alicat mass flow controllers have a repeatability of ± (0.1% of reading + 0.02% of full scale). They are also calibrated against a NIST traceable standard to ensure that every device is within our stated accuracy of ± 0.6% of reading.

With protocol choices like EtherNet/IP and EtherCAT, it’s easy to automate the process of changing colors without changing the shape of the stream.

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
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Alicat has recently announced our newest mass flow controllers with dramatic improvements in precision, response time and operating range.

by Mic Chaudoir

File:Saguaro Sunset.jpg

The 2020 Winter Conference on Plasma Spectrochemistry is coming to Tucson, Arizona from January 13-18 at the El Conquistador resort. This conference will feature the latest developments in plasma spectrochemical analysis utilizing inductively coupled plasma, DC plasma, microwave plasma, glow discharge and laser sources.

Alicat has recently announced our newest mass flow controllers with dramatic improvements in precision, response time and operating range. These upgraded units provide unmatched controllable range and incredible accuracy for low-mid range mass flow control. Alicat also has a full line of products for high flow rates, liquid flows, pressure control and other specialized flow control needs.

Alicat also shares the organizer’s passion for inductively coupled plasma (ICP). We will be bringing our new Fusion Flow line of gas mixers, suitable for precise control of plasma gases. Alicat will also have samples of our corrosion resistant product line suitable for aggressive gases and demanding applications.

Alicat is a local Tucson company and we are happy to support the 2020 Winter Conference on Plasma Spectrochemistry. Visit us at booth #6 to learn more about how the world’s fastest flow control company can help improve your plasma.

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

Specially designed SAE to Tri-clamp® adapters allow for easy adaption of Alicat BIO Mass Flow Meters and Controllers to customer control systems.

by Mic Chaudoir

SAE 4 and 8 tri-clamp adapters

Specially designed SAE to Tri-clamp® adapters allow for easy adaption of Alicat BIO Mass Flow Meters and Controllers to customer control systems. 

Alicat, the world’s fastest flow controller company, now offers adapters designed to adapt BIO series Mass Flow Meters and Controllers to the popular Tri-clamp® system. The Tri-clamp® is popular in food, beverage and biopharmaceutical industries. These adapters allow for gases to flow without giving potential contaminants crevices to evade removal or sterilization. The Tri-clamp® design also allows for easy installation and removal without the use of tools.

These adapters are stocked in SAE 4 to ½” Tri-clamp® and SAE 8 to 1” Tri-clamp® sizes (other combinations available upon request). All adapters include an appropriate O-ring and use only certified USP VI/FDA grade elastomers. These adapters are manufactured from 316L stainless steel to ensure the highest purity and corrosion resistance.

These adapters complement Alicat’s innovative BIO series of Mass Flow Meters and Controllers. The BIO series is the world’s first gas flowmeter designed especially with the needs of the bioprocessing industry in mind. These meters and controllers utilize BPE-compliant materials, a process water resistant design and unmatched 10,000:1 controllable range to make bioprocess gas flow control more robust and efficient.

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 (and others) are effected by temperature and pressure.

The Effect of Temperature and Pressure on Flow Measurement

Mass Flow Comparison- rev23

Mic Chaudoir, Ph.D. Kevin Gudenkauf, MSc

 2 of 12ALICAT.COMThe Effect of Temperature and Pressure on Flow MeasurementMic Chaudoir, Ph.D.Market Managermchaudoir@alicat.comDr. Chaudoir obtained his degree in Cell and Molecular Biology from Northwestern University in 1997.He has led product development and marketing at a number of scientific instru- ment companies including Leica Microsys- tems, Photometrics and Fiberguide Indus- tries. He joined Alicat Scientific in late 2018 and currently leads Alicat’s efforts in the bioreactor and optics markets.Kevin Gudenkauf, MScTest EngineerKevin@alicat.comMr. Gudenkauf obtained his Bachelor’s of Science in Physics from the University of Arizona. He went on to obtain his Masters of science in Physics from The Ohio State University in 2012. He has since helped advance Alicat’s differential pressure tech- nology and has held positions in applica- tions engineering and test engineering. His latest projects include testing and validation of Alicat’s industrial protocols and refinements to the Alicat flow mea- surement models for improved accuracy and reliability.
Analysis of Temperature and Pressure Conditions on Flow MeasurementMass flow measurements have achieved never before seen levels of accuracy and precision. But how do you know what level of precision you need? And further, how does this information relate to your unique application or system? This white paper gives a comprehensive overview and comparison between mass flow meters representing a variety of manufacturers and technolo- gies. This information will equip you to make the most of your existing instruments and intelligently evaluate new instrumentation for your particular system. Get the latest information on why specifications matter and what impact this will have on your mass flow measurements!The Effect of Temperature and Pressure on Flow Measurement ALICAT.COM 3 of 12


Mass flow control for gases is a topic which has been studied and defined for several centuries –dating back to the 1600s.1 Given this level of time and attention, the principles behind mass flow are very well understood. Commercial methods for controlling and measuring mass and volumetric flow universally publish specifications which give prospective users the ability to accurately assess the suitability of the instrumentation for their re- quirements. Despite being straightforward theoretically, the ability to evaluate systems based on their published specifications can be confounded by several factors:

  • Differing levels of flow error inherent to a device under standard calibration and use conditions
  • Differences from the manufacturer’s standard cali-bration conditions and the conditions under which the mass flow measurement is actually madeIn this analysis, we set out to make comparisons of mass flow accuracy using the published specifications of many commonly used mass flow devices and com- paring them to Alicat’s MC models. We will first assess the error inherent in the flow measurement under stan- dard calibration conditions. We then look at the effect of common flow control applications where the flow rate measurement may be affected by variances from the standard calibrated temperature and pressure. This involves a discussion of temperature and pressure coeffi- cients and their effect on mass flow, an often overlooked topic, but one which can be critical for proper prediction of system performance.1 “Gases and Gas Laws/Boyle’s Law Lab.” Wikiversity, en.wikiversity.org/wiki/Gases_and_gas_laws/Boyle’s_law_lab.

Apparatus for transference of gases and pressure gauge Credit: Wellcome Collection


4 of 12 ALICAT.COM The Effect of Temperature and Pressure on Flow Measurement

Accuracy (% Full Scale)
% Reading 0.6 0.5 1.0 0.5 0.9 1.0 0.5 0.5
 Repeatability (% Full Scale) 0.02 0.2 0.01 0.04 0.2 0.2 0.2
% Reading0.
Temp coefficient (% Full Scale) 0.01 0.05 0.3 0.02 0.05 0.04 0.05 0.025
% Reading (per °C)
   Pressure coeffient % Full Scale 0.00068 0.01 0.2 0.0 0.01
% Reading (per PSI)0.00680.20.01030.
Stated Controllable Range 10,000 200 1,000 150 100 50 50 50 100Table 1: Published specifications and models for all of the devices used in this comparison. In the case of Alicat specifications we have measured and confirmed these specifications in our test lab. When specifications were unavailable, the space is crossed.Comparison of Mass Flow MetersWe began by obtaining published specifications for mass flow instrumentation from various manufacturers.2 Our method was to compare devices from a wide range of manufacturers utilizing a variety of technologies, in order to obtain a comprehensive evaluation. The goal was to gain insight into the differences in accuracy be- tween these devices. Note that in many cases, there are a very wide range of devices available from the same manufacturer–in some cases in excess of 6 units overlapping in features and function. For the purposes of clarity we chose the most accurate non-Coriolis device and utilized the best published specifications from each manufacturer. When a manufacturer offered a higher precision calibration option (often referred to as “high accuracy” or “high performance”) we utilized the specifications for that option. For Alicat devices, we used standard versions for these purposes; high accuracy versions would display even greater flow rate2 See appendix for the actual datasheets used.accuracy. Comparisons between differing mass flow technologies and manufacturers are not necessarily readily available. There have, however, been a number of publications where existing MFCs are used a standard to compare against new processes or technologies (ref 3-5). Specifications between units are often expressed using different units and/or standard conditions. To fa- cilitate comparison we converted all specifications to a standard format, based on commonly use units (°C and Pounds per Square Inch (psi)). All specifications used in this paper are summarized in Table 1.The analysis carried out will be most useful when ap- plied to a hypothetical device used in a wide range of conditions. For this scenario, we analyzed a 100 Sccm device flowing air under the manufacturer’s stated calibration conditions, one of the most common con- figurations that we see in use.Figure 1 shows a comparison of flow rate uncertaintyThe Effect of Temperature and Pressure on Flow MeasurementALICAT.COM 5 of 12


M Series


DPC 17


MFM 2120 RS-232 low flow


EL-FLOW prestige








SmartTrak 100


Red-Y High Performance

(standard cubic centimeters per minute) for all of the meters analyzed at flow rates between 0 and 100 Sccm (full scale). We generated a flow model which takes into account the specifications given and calculates flow rate uncertainty at actual flow rates. In general, the flow rate uncertainty scales with flow rate. We make a more detailed explanation of the lower flow rates, where this is not necessarily the case, later on in this analysis. In Figure 1, lower values indicate that the unit is measuring with less uncertainty/more accuracy. The differences between specified mass flow error at the top and bottom of these accuracy graphs is large. The topmost graph in Figure 1, for example, specifies flow rate error of ±1 Sccm at 60 Sccm flow rate. The best specified meter demonstrates an error of ±0.35 Sccm, a 65% change in error between the two measurements.Using the data presented one notices that several manufacturers’ devices (including Alicat) display a step change in error rates near the bottom of the flow range. As these graphs display uncertainty/error in flow rates, lower numbers indicate better performance. It’s notewor- thy that in every case, Alicat’s Mass flow measurements are shown to be more accurate than other devices, displaying a lower flow uncertainty. At higher flows, Brokhurst EL-Flow Prestige units are able to achieve similarly high levels of performance.An interesting outcome from accurately measuring the flow rate error happens when looking at lower flow rates. This level of detail in measurement is carried outby Brooks Instruments and Alicat Scientific. At higher flow rates, there are multiple sources contributing to the error in reading (including things like sensor noise, linearity, et cetera). However, below a certain point, the predominant noise factor becomes uncertainty in the zero point setting. As this error does not change with flow rate, it results in a straight line. While the actual flow rate uncertainty is invariant, the error still grows as a percentage of measure with increasing turndown. Table 2 shows how the percent error in reading will still grow at lower flow rates, despite the invariance of the error.An extreme example can be seen by the comparison with the Sierra SmartTrak 100. For example, at a flow rate of 10 Sccm, the Alicat displays uncertainty of 0.1 cc. This means that actual flow at 10Sccm would range between 9.9–10.1 Sccm – a 1% error at a turndown of 10:1. The Sierra unit specifies a flow rate uncertainly of 1 Sccm, or 10 fold higher under the same conditions. Looking at only 1 Sccm, the Sierra now displays uncertainty equal to the measured value – 1 Sccm, ±1 Sccm (with the error equaling the flow rate). Even at a turndown of 100:1, the Alicat device would still produce a useful measurement: 1 Sccm ±0.1 Sccm.The main takeaway is that most of these meters perform reasonably well in the middle or top of their flow range. But as turndown increases, the accuracy becomes much more important. As turndowns exceed 100:1, the usability of the measurements may be dra- matically affected by the accuracy.6 of 12 ALICAT.COMThe Effect of Temperature and Pressure on Flow Measurement

Figure 1: Uncertainty Comparison: Flow Rate Error vs. Flow Rate for 100 sccm MFCs 1.4

1.3 1.2 1.1 1.0 0.9 0.8 0.7 0.6 0.5 0.4 0.3 0.2 0.1 0.0

Figure 2: Percent Uncertainty vs. Flow Rate for Alicat 100 sccm MFCs 12

10 8 6 4 2 0

Sierra SmarttraK BrookS G40 axetriS mFm 2120 MkS mF1

aalBorg dPc 17 BrookS SlamF BronkhorSt el-FloW alicat m


0 20 40 60 80 100

Flow rate in Sccm


0 20 40 60 80 100

Flow rate in Sccm

The Effect of Temperature and Pressure on Flow Measurement ALICAT.COM 7 of 12

Percent uncertainty Uncertainty in Sccm

Brand & ModelUncertainty at 200:1 turndown (0.5 SccM) in SccM per % of measured flow
Alicat M0.1 SCCM per 20% of measured flow
Bronkhorst EL-Flow Prestige 0.1025 SCCM per 20.5% of measured flow
Brooks SLAMf0.18 SCCM per 36% of measured flow
MKS MF1 0.2025 SCCM per 40% of measured flow
Aalborg DPC 170.2025 SCCM per 40.5% of measured flow
Axetris MFM 0.205 SCCM per 41% of measured flow
Voegtlin Red-Y0.3025 SCCM per 60.5% of measured flow
Brooks GF40 0.355 SCCM per 71% of measured flow
Sierra SmartTrak 1000.5 SCCM per 100% of measured flow
Table 2: Comparison of flow rate uncertainty at 200:1 turndown on a 100SCCM flow meter.Table 2 demonstrates this by comparing flow rate uncertainty at higher turndown (200:1) for the meters we compared.Precise use cases always vary by application, but in most scenarios an error rate in excess of 20% means that the uncertainty can meet or exceed the actual flow. For example, at a calculated 40.5% error, and a flow rate of 0.5 Sccm, the Aalborg units can actually be flowing between 0.7025 to 0.2975 Sccm (at a desired flow rate of 0.5 Sccm).Adding the pressure and temperature coefficients allows for a more real-world look at performance, since actual measurement conditions rarely match calibration conditions. For example, high pressure leak testing is a common application for flow and pressure meters and is carried out at pressures in excess of 100psi. Vacuum leak testing by comparison, is carried out down to 10-9atm-cc/sec. Chemical engineering reactors can use hot gases, sometimes up to 100 ̊C. High-temperature gases are also used in preform manufacturing and other applications requiring input compounds that are liquid or solid at room temperatures.While the terms “pressure coefficient” and “tempera- ture coefficient” are commonly used on the specification sheets, it is worth discussing their precise definitions.Pressure coefficient is usually expressed as follows:Mass Flow Span Shift =∆% Reading(1 atmosphere + ∆ atmospheres)Temperature coefficient is usually expressed as follows:Mass Flow Span Shift = ∆% Reading (25°C + ∆ Temperature in °C)The implication of this equation is that as tempera- ture shifts away from the calibration conditions, error in reading increases. The temperature coefficient then, defines the increase in error due to temperature shift away from the standard temperature.While units expressed differ, one example from the Alicat specification sheet reads:Mass Flow Span Shift: ±0.01% Reading per °C from 25°CThe graphs shown in Figure 3 utilize a heat map to fa- cilitate exploration of the additional effect of temperature and pressure on flow rate measurements. An analysis of these heat maps shows an increase in error happens at the extremes of temperature and pressure. As units are routinely calibrated at standard atmospheric pressure, but operated at much higher pressure, the Y axis is of8 of 12 ALICAT.COMThe Effect of Temperature and Pressure on Flow Measurement

Figure 3: Heat Maps Showing Uncertainty in Flow Measurement for Various Manufacturers






160 Aalborg DPC

140 120 100

80 60 40 20

Alicat Meter

Axetris MFM 2120 160

140 120 100 80 60 40 20


Bronkhorst EL-FLOW




ks GF40†

Sierra SmartTrak 100

Brooks SLAMf




120 100 80 60 40 20



120 100 80 60 40 20

160 140 120 100

80 60 40 20

160 140 120 100 80 60 40 20 0



Vogtlin Red-Y High Performance 0



-10 0 10 20 30 40 50 60 -10 0 10 20 30 40 50 60 -10 0 10 20 30 40 50 60

potentially greater interest. These graphs also visually demonstrate that pressure has a much greater impact than temperature: as one approaches pressures of 150 psi for example, accuracy can drop off dramatically. This effect is noticeably more pronounced than at the extremes of temperature (−10 to 60° C). It’s noteworthy that some units (Such as the Brooks SLAMf) that perform adequately near calibration conditions, suffer greatly degraded performance at increased pressures and temperatures. Also noteworthy is the amount of change demonstrated by the Alicat mass flow meter under high pressure and temperature; even at the extremes,

the change in reading error remains well below 2% of reading. Put another way, an Alicat meter reading 50 Sccm under calibration conditions, would still read 50 ±2 Sccm at 0°C and 150 psig. This demonstrates the relative insensitivity of the Alicat units at the extremes of temperature and pressure.

As it is unusual to take the temperature and pres- sure coefficients into account, this should be sobering information for most users. It is not only the flow rate error under calibration conditions that matters – but the flow rate error at operating pressure and temperature conditions as well.

The Effect of Temperature and Pressure on Flow Measurement

ALICAT.COM 9 of 12

Temperature (°C)

† We were unable to obtain complete published specifications for the Brooks GF40.

Uncertainty in percent at 100 Sccm Pressure (0–160 PSIG)


Modern mass flow meters and controllers offer unprece- dented levels of accuracy and precision, even compared to devices from less than a decade ago. This is primarily due to advancements in sensing and signal processing technol- ogies, which benefit mass flow measurement as a whole. All manufacturers listed do an admirable job of measuring and reporting the specifications for their various devices. In this white paper, we evaluated the results of a compari- son between various mass flow control devices using their published specifications. These specifications are extensive enough to allow for predictions of measurement accuracy under various temperatures, pressures and flow rates.

When comparing Alicat’s differential pressure based mass flow measuring instruments to other technologies and systems, Alicat units generally specify better mass flow accuracy. This is despite using the best available units with the highest performing options from other manufacturers. Under certain conditions, some other meters can measure with accuracy close to the current Alicat flow meters. In no incidence, however, do competitors outperform the standard current model Alicat flow meters and controllers.

While comparisons are normally made under calibration conditions and flow rate errors calculated under these same conditions, we have taken the additional step of evaluating performance under temperature and pressures outside of these standard calibration conditions. These conditions differ from standard calibration conditions and are more likely to match those under which the flow measurement is actually performed. We presented this data utilizing heatmaps to facilitate visualization of the differences between units. Un- der these more realistic conditions, the gap in performance between Alicat meters and competitors widens even further.

This comparison set out to evaluate the accuracy of flow measurement for various mass flow meters. Using published specifications, the results show that Alicat manufactures the most accurate non-coriolis mass flow instruments currently available, under the conditions modeled. The authors hope that this comparison is useful and welcome commentary and discussion.

10 of 12

ALICAT.COM The Effect of Temperature and Pressure on Flow Measurement


The Alicat 1-SLPM meter


The Effect of Temperature and Pressure on Flow Measurement ALICAT.COM 11 of 12

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Email: sales@sensorguys.com Website: www.sensorguys.com

Biosphere 2 – Using Flow Measurement to Glimpse the Future

by Carol Schumaker

As the Earth’s climate changes, it is expected that ecosystems around the world will be subjected to increased water stress and/or drought. It is difficult to forecast the range of impacts climate change will have on soil, air, and water quality. In 2019, a group of interdisciplinary scientists from around the world came together to conduct a highly-controlled experiment to measure the effects of water stress on a rainforest ecosystem.

This unique experiment took place in a man-made structure called Biosphere 2. Biosphere 2 is a multi-million dollar facility that was built in the 1980’s to simulate a fully contained Earth ecosystem. The facility is now used for research, education, and tourism.

Figure 1 Biosphere 2, located in Arizona

Biosphere 2, located in Arizona

In October 2019, Biosphere 2’s tropical rainforest biome was closed to the public and about $12,000 worth of carbon dioxide, spiked with an isotopic tracer called Carbon 13, was released into the system. Carbon 13 is an isotope that occurs relatively infrequently in nature, so it was used as a tool to track and measure changes in soil, water, and air systems.

That’s where Alicat came in.

Director of Biosphere 2, Dr. Laura Meredith, had experience using Alicat controllers in other experiments during her time at the University of Arizona Landscape Evolution Observatory. Dr. Meredith was pleased with the accuracy and repeatability of the Alicat controllers, so reached out in search of a partnership.

Alicat Mass Flow Controllers in Biosphere 2

Alicat Mass Flow Controllers in Biosphere 2

Alicat was excited to be part of this important and unique experiment. The company provided the project team with nearly 30 mass flow controllers that were used for a variety of applications, including accurately controlling the release of Carbon 13.

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

RS232 and RS485 are some of the most popular. Even with dozens of new serial interfaces these are still the go to for many of our mass flow applications.

by Sam Miller

There are many different serial interfaces but both RS232 and RS485 are some of the most popular. Even with dozens of new serial interfaces these are still the go to for many of our mass flow applications.

Which interface is best for my application? 

The important differences between the two interfaces have to do with distance of operation, number of devices being used, level of electrical noise, and network topology.

Communication distance. 

The maximum cable distance for RS232 should be 50ft according to the EIA/TIA-232-F specification. It can be difficult to maintain signal entirety beyond this.  RS485 on the other hand has an upper limit of 4,000ft.

Number of devices.

RS232 is intended to be used as point to point communication. This means a single master and a single slave device. Now because we are Alicat, we can be flexible in order to help our customers. Rarely, we have set up a multidrop communication, but this is uncommon and many other manufacturers do not use this set up, so don’t mix and match.

RS485 was designed to work with up to 32 other devices.

Electrical noise and ground reference variations. 

RS232 is voltage based and uses ground as its reference point. This means that if you see some electrical noise on your ground line this can be interpreted as a part of the signal.

RS485 on the other hand has higher noise immunity. It is based off of a differential voltage system and is more suitable to high noise environments. This is done is by using two wires both referenced to each other. If ground shifts both signal lines shift in the same direction keeping the same relative distance from one another.

Network topology and data speed.

Care must be taken setting up a RS485 network. Unlike RS232, RS485 requires the use of a daisy chain topology and will likely cause issues if setup in a star. Termination resistors are also required at the first device in the chain and on the last device in the chain to help with reflections. The data speed allowed is dependent on the length of cables / topology.

In general, RS232 is beginning to fall out of favor because it is being replaced by USB for short distances even though it takes a bit more number crunching power of the processor. While most modern PCs have phased out the RS232 serial port in favor of USB setting up a network is much simpler. USB to RS232 converters are also readily available online.

Figure 1 Comparison Table

Interested in more communication options? Visit our Alicat Software and Drivers page to learn more.

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

Improved Accuracy Specifications on Alicat Mass Flow Meters & Controllers

 by Bill Nick

Alicat’s latest product release (2019) introduces an unprecedented new level of flow accuracy for mass flow meters and controllers. Through improved temperature and pressure compensation our flow measurements are even more resistant to the effects of changing temperature and pressure, and a fully redesigned circuit board has increased our signal to noise ratio and enabled higher resolution for raw sensor data sampling. These augmentations have transformed the already-outstanding Alicat mass flow instruments into one of the most accurate differential pressure-based flow measurement systems on the market.

Alicat devices are now more accurate & maintain accuracy to a significantly lower level than ever before

Alicat mass flow instruments’ have been dropped to ±0.6% of reading or ±0.1% of full scale, whichever is greater (with the high accuracy calibration specification dropping to ±0.5% of reading or ±0.1% of full scale)

Over our old flow accuracy specifications of ±(0.8% of reading + 0.2% of full scale) for standard calibration and ±(0.8% of reading + 0.2% of full scale) for high accuracy calibration.

Increased turndown ratio and resolution specifications from 200:1 and 4 total digits to 10,000:1 and 5 total digits and compensation refinements have increased the flow resolution specifications by a factor of ten.

Replace multiple ranged thermal MFC’s with a SINGLE Alicat

Our usable range is significantly higher than competitors;  You may be able to use one MFC in your system where two were needed because of the flow range limitations of your current MFCs. For example, if you need to control the flow of O2 between 100 SLPM and 100 SCCM, one Alicat MFC can provide accurate, repeatable control over the entire range.  Most thermal based MFCs would require you to have two or more MFCs to complete this same task. This ability leads to:

  • Lower overall build cost
  • Lower cost of operation
  • Less money tied up in inventory for spares/back up units
  • Eliminate gas dependent equipment: Select 98+ preset gases with no recal. Less spares required.
  • Less complicated setup
  • Easy drop-in replacement

Improved Accuracy Means Process Improvements:

  • More accurate gas mixing resulting in less wasted gas
  • More accurate measurements for R&D leading to better decisions when scaling to production
  • Even higher accuracy to perform calibrations of other instruments to a higher standard
  • Improved resolution means finer control:  sensitive applications like bioreactors, pharma, laser, etc can rely on the finer control of an Alicat.

Improved Resolution Means Finer Control:

  • Sensitive process applications like bioreactors, pharma, laser, etc can rely on the finer control of an Alicat Instrument

Example Calculations

To calculate Alicat’s accuracy using the new specification, you’ll need to know the full scale of a flow instrument and its reading.

Let’s assume an M-series Mass Flow Meter with a standard calibration has a full scale of 10 SLPM and it is reading 5 SLPM of flow. For standard calibrations, 16.7% of the full scale is the point at which the error transitions between being greater when calculated with the full scale component of accuracy and greater when calculated with the reading component of accuracy. Since the flow reading is above 16.7% of the full scale, the accuracy calculation is based on the flow reading:

Accuracy = ±0.6% of Reading = (0.006)(5 SLPM) = ±0.03 SLPM

If the flow reading on the mass flow meter is below 16.7% of full scale, e.g. 0.5 SLPM, then the accuracy calculation would look like this:

Accuracy = ±0.1% of Full Scale = (0.001)(10 SLPM) = ±0.01 SLPM

For high accuracy calibrations, the error dominance transitions between reading and full scale at 20% of full scale. With the same full scale and readings as the previous example, the calculations would be as follows:

Accuracy = ±0.5% of Reading = (0.005)(5 SLPM) = ±0.025 SLPM
Accuracy = ±0.1% of Full Scale = (0.001)(10 SLPM) = ±0.01 SLPM

Helpful Terms

 Full Scale:  The maximum calibrated reading of the device.  For bidirectional devices, see the associated specification sheet for an explanation of the full scale.

Resolution: Granularity of variables that are read/controlled

% of Reading:  Portion of the accuracy that depends on the reading.  This is independent of the full scale.  Multiply the stated % of Reading by the actual Reading to get the accuracy at a specific Reading.

% of Full Scale:  Portion of the accuracy that depends on the full scale.  This is independent of the reading.  Multiply the stated % of Full Scale by the calibrated Full Scale of the device to get the accuracy of a specific device.  Note that bidirectional devices might have a different Full Scale.  Please see the individual specification sheets for more information.

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