Teledyne Hastings Instruments Blog

As we say good-bye to John Glenn, it is a good time for Teledyne Hastings to recall with pride our company’s and our city’s connection to this great American hero. Now, many people know that John Glenn was the first American to orbit the earth. But most people don’t know that the original seven Mercury astronauts, including John Glenn, received their original spaceflight training in 1959 at NASA-Langley in Hampton Virginia which is also our home for Teledyne Hastings.

The Hampton Roads area of Virginia has memorialized several landmarks to commemorate Project Mercury. There are several bridges in the city of Hampton which are named for the astronauts. “Military Highway” was renamed to Mercury Boulevard. And, in Newport News, the Denbigh branch of the Newport News Public Library System is the “Grissom Library”.   

NASA was formed in late 1958 when NACA operations were converted over. Previously, NACA (National Advisory Committee for Aeronautics) was established in 1915 and built Langley field in Hampton. Now in doing some background reading for this blog, I found it interesting to learn that NACA was created out of fear that the U.S.A. might be falling behind the Europeans in aeronautics and that NASA, in turn, was created out of fear that the U.S.A. was falling behind the Soviets in the Space Race.

In a book entitled The Story of Hastings-Raydist, Carol Saunders points out that NACA did not hire many engineers during the first part of the Great Depression. But, in 1935, NACA accelerated hiring and they brought on Charles Hastings as a “Junior Scientific Aide”. In 1939, a newly hired mathematician named Mary Comstock was hired and placed in an office across the hall. The two were married and together created Hastings Instruments in 1944.

And speaking of mathematicians at Langley, there is a movie “Hidden Figures” (released December 25, 2016), which tells the story of three female mathematicians who were part of the computer pool. Which brings us back to John Glenn. In the early days of computers, engineers did not always trust the results of the electronic data processors. The computer pool, in other words, human mathematicians, were used to crunch through complex calculations. Before his historic flight in 1962, Glenn requested that one of these computer pool women, Katherine Johnson, verify the results of the computer. The contributions of these women to the space program was remarkable.

For more information on Teledyne Hastings Instruments click the button below or visit www.teledynehastings.com

The following books were referenced in the writing of this blog:

Hidden Figures by Margot Lee Shetterly

Hampton - From the Sea to the Stars edited by James T. Stensvaag

The Story of Hastings-Raydist by Carol Hastings Saunders  

Teledyne Hastings is proud to release our newest, most advanced, line of digital flow meters and flow controllers - the 300 Vue. In this blog, we will discuss the three types of Input/Output (I/O) that can be used with the 300 Vue. These are: Analog, Digital, and Touchscreen Display.

(1)   Analog

The 300 Vue is very flexible. The instrument can be configured to give and receive analog signals. For example, the 300 Vue can use 0-5 VDC, 0-10 VDC, 4-20 mA, or 0-20 mA.

Let’s take a look at a 300 Vue flow controller which has been setup to have a full scale flow rate of 100 sccm and has 0-5 VDC I/O. In the case of a flow controller, there are two analog voltage signals that we need to understand. The first is the flow output signal. In our example (0-5 VDC), 5 VDC corresponds to 100% of the full scale of the flow controller. The relationship between the voltage output signal and flow rate is linear. So, if we have an output of 1 VDC from the 300 Vue, then we would have a flow rate of 20% of full scale which corresponds to 20 sccm (20% * 100 sccm = 20 sccm).

Correspondingly, in our example, the 300 Vue will accept an analog command signal between 0 and 5 VDC. Again, 5VDC corresponds to 100% command signal. The command signal tells the flow controller how to set the flow rate. So, if we wanted the flow rate to be 75 sccm, we would provide a 3.75 VDC command voltage  (75 sccm* (5 VDC/100 SCCM) = 3.75 VDC).

One last comment before we move on. Analog I/O is still used in many applications. Older flow power supplies and PLC’s often utilize analog I/O. The 300 Vue flow instrument makes it easy to integrate into these systems.

Interested in more information on the Vue? click here

(2)      Digital

The 300 Vue can provide digital I/O via RS232 or RS485. Connection to the digital port is made via the micro USB connector or the small bayonet-style connector. Let’s take a quick look at an RS232 command for the 300 Vue. If we send “F”, the 300 Vue will respond with the flow rate.

f <cr> <lf>

25.889 sccm

Simple - right? Now in the case of a flow controller, we will want to be able to send a command signal to tell the flow controller how to set the flow rate. One way to do this is to use V5, the “Setpoint”. The Setpoint Command is simply the flow rate expressed as a percent of the flow controller’s full scale. So, “V5=100” will set the flow rate to 100% of full scale. You can also use V4 which sends the command in the given units, as opposed to % of full scale.

Digital communication with the 300 Vue can be utilized in a few different ways. First, you can use our free user software which can be obtained from our website. If you want to see all of the capability (including flow data logging) you can watch this short “How To” video.

Next, many of our digital flow controller users write their own code using LabView. By working with the “F” and the “V5=  “, or “V4=  “ commands, the user can easily read and control the flow rate in their application.

Here at Teledyne, we often use TeraTerm for communicating with our digital flow instruments. Click to visit TeraTerm website for more information.   

TeraTerm is nice because it is open source (free) yet it is very powerful. I also like the fact that TeraTerm allows the user to save and restore a communication set up file. In other words, once you have a TeraTerm “ini” file working, you can save it so that you don’t have to reconfigure the settings each time you start up the program. If you have TeraTerm and would like a copy of my setup file for the 300 Vue, just send me an email. 

Interested in more information on the Vue? click here

(3)      Touchscreen Display

Ok, we’ve talked a little bit about analog I/O and digital communications. Now, let’s explore the coolest feature of the 300 Vue – the color touchscreen display. With the touchscreen display, it is very easy to see and control the flow rate. First, we should point out that the 300 Vue flow instrument is very easy to power up; you just plug in the connector and you are in control.

Once the flow instrument is powered, the flow rate is observed as shown in the picture below:

Now, to change the flow setpoint or command signal we touch Setpoint and we see the numeric keypad screen as shown below.

Changing the setpoint is easy… you just type the value you want and hit ENTER. The display then returns to showing the flow rate.

The 300 Vue is very flexible with respect to Inputs and Outputs. If you have questions about I/O, our applications engineers are always standing by and ready to help. You can reach us at hastings_instruments@teledyne.com or by calling 1-800-950-2468.

One of the goals of these blog postings is to give readers knowledge about vacuum and mass flow technology. The Society of Vacuum Coaters has established a foundation (SVCF) with a similar goal. Dr. Don McClure (Acuity Consulting & Training) has created “The Vacuum Wizard Video”. Dr. McClure worked at both IBM & 3M and has been teaching for over 20 years about vacuum coating onto flexible substrates.

As stated on the SVCF website, “The Vacuum Wizard Video brings to life the fundamentals of vacuum and vacuum coating technology through an informal and thought provoking presentation using non-technical jargon and filled with live demonstrations.

The Vacuum Wizard Video seeks to raise awareness of students and educators about the fascinating world of vacuum and vacuum coating technology. The only prerequisite is a curiosity about this amazing technology.

The Vacuum Wizard Video can be a useful training tool in the corporate world for personnel who require a basic understanding of vacuum technology. Sales representatives, customer service personnel, field service and maintenance technicians, lab technicians, and engineers with no vacuum technology background, can all benefit from the Vacuum Wizard Video.”

(Check out the Teledyne Hastings’ Vacuum Model 2002 Vacuum Gauge on the table)  Click the button below to request an evaluation sample of the 2002 Vacuum Gauge

You can get more information about the SVC Foundation and the video series by visiting:

http://svcfoundation.org

Click to see a sample of the Vacuum Wizard Video 

This is part two of a two-part blog on Thermal Mass Flow sensors.  In part one, we described the desired characteristics of a thermal mass flow sensor.  In part two, we will discuss the operation of the 300 series flow sensor (Patent #6,125,695) and how its design addresses the desired traits.

In our previous blog, we showed a cutaway of a thermal mass flow meter.  Now let’s take an inside look at the 300 series flow sensor:

When gas is flowing through the bypass shunt, a small pressure drop is developed which will direct a fraction of the flow through the arced / semi-circular capillary tubing in the flow sensor. On the outside of the capillary tube, there are two resistive wire coils which are tightly wound and in excellent thermal contact with the tube. These two identical windings are referred to as:

• Upstream Heater Coil (1)
• Downstream Heater Coil (2)

Associated with each of the two heated coils is an ambient coil. The ambient coil is in excellent thermal contact with the aluminum ambient block.  Aluminum has a very high thermal conductivity which ensures that both ends of the sensor tube and the two ambient coils (3 and 4) will be at the same temperature.

Two identical Wheatstone resistance bridges are formed from the two pair of coils (see image on right).

The circuit shown in the image on the right is designed to ensure that the heated coils (upstream and downstream) are maintained at a constant temperature (ΔT) above the corresponding ambient coils.

Next, we calculate the power (W) required to maintain ΔT by:

This power will be calculated for both the upstream bridge and the downstream bridge. It can be shown that:

So, by maintaining both heaters at the same ΔT above ambient, the mass flow rate is directly proportioned to the difference in power (W) between the two bridges. For example, when no flow is passing through the capillary sensor tube, the power needed to maintain ΔT will be the same (i.e. ṁ = 0)

As gas flow increases in the tube, heat is transferred from the upstream heater to the gas stream.  This will force the upstream circuit to use more power to maintain ΔT. In turn, the gas will transfer heat to the downstream heater which will cause the downstream circuit to use less power to maintain ΔT.

Now, here is the best part: the mass flow rate is directly proportional to the power difference. In other words, LINEARITY!

In our previous blog, we discussed how excellent linearity leads to improved accuracy. And, not only does the 300 series sensor give excellent linearity, the circuit shown on the right reacts very fast to changing flow. Thus, the 300 series has excellent responsive time.

One last note, we have designed the 300 series to use relatively large diameter tubing.  This larger tubing allows flow meters to be designed with lower pressure drop than many mass flow meters on the market.  

Visit our website for more information on Teledyne Hastings 300 series Flow Meters.

Teledyne Hastings' Thermal Mass Flow Sensors are used worldwide.  Download our application note on High Throughput Leak Detection to learn about improving lead testing precision and throughput and how to reduce testing time.  

Be sure to visit our website for additional information on Teledyne Hastings Mass Flow Controllers and Mass Flow Meters

Note: The content of this blog was updated February 4, 2023 to provide more information for the reader.

The applications engineers here at Teledyne Hastings discussed topics for our blog. We all agreed that one of the more frequent questions fielded, involves the units used to measure vacuum levels. We find that the technicians who use their vacuum system daily often seem to develop a sixth sense about the “health” of their systems. They know something isn’t quite right when the base vacuum pressure (or rate of pressure change) is not what they expect. So, when vacuum pressure measurements are inconsistent from batch-to-batch, that is the time when the user stops to ask the meaning behind the data that their vacuum measurement instrumentation is providing.

Measuring Vacuum Pressures

A vacuum exists when there is negative pressure, or when there is system pressure that is less than atmospheric pressure. Manufacturing processes generate different levels of vacuum when operating at peak efficiency for a given vacuum application that are measured using a vacuum gauge. Absolute vacuum is the absence of all matter. Atmospheric pressure, also known as barometric pressure, is the pressure due to earth’s atmosphere. Atmospheric pressure is 760 Torr or 14.696 psia at sea level and changes with altitude. The vacuum pressure scale is book-ended by absolute vacuum pressure in the “ultra-high” vacuum range and atmospheric pressure at the “rough” vacuum range. It should be noted that absolute vacuum, or perfect vacuum, is never truly attained.

Most users know that vacuum is commonly measured using units of pressure. There are a few different systems of pressure measurement, and this blog will discuss those most used. In Armand Berman’s book, Total Pressure Measurements in Vacuum Technology, pressure unit systems are divided into two categories: “Coherent Systems” and “Other Systems”.

Common Units of Vacuum

“Coherent Systems” of units are based on the definition of pressure (P) as the force (F) exerted on a chamber wall per unit area (A). P = F/A. The International System of Units, or SI units, is commonly used for pressure measurement. http://physics.nist.gov/cuu/Units/units.html The SI unit for pressure is the Pascal (Pa), and it is interesting to note that NIST (National Institute of Standards and Technology) published papers are always required to use SI units. Again, the SI unit for pressure (force per unit area) is the Pascal. 1 Pa = 1 N /m2.

As a unit of pressure, the Pascal is not always convenient to use because vacuum systems often operate in pressure ranges where collected data results in large numbers. For example, near atmospheric pressure, we would measure approximately 100,000 Pa. So, a more convenient unit, the bar, was developed. (1 bar = 100,000 Pa)

Moving lower in pressure, it is very helpful to then use the mbar (1 mbar = 0.001 bar), which has become the predominate unit of measure in Europe, as the basis for describing pressure levels. As a specific example, look at the base pressure specification of a turbo pump, which will typically be given in terms of mbar (e.g., Base Pressure < 1 x 10^-10 mbar).

“Other Systems” of units include the Torricelli system, which is based on an experiment (shown in the diagram below) conducted by the Italian scientist, Evangelista Torricelli. In this experiment, the pressure exerted on the mercury can be shown to be P = hdg, where h is the height of the mercury column, d is the density, and g is the acceleration due to gravity.

By measuring the mercury column height, the pressure can be determined. The Torr unit (named after Torricelli) has been defined as 1 millimeter of mercury (1 Torr = 1 mmHg). This unit, as well as the use of the mTorr unit (1 mTorr = 0.001 Torr), is commonly used in the United States. Historically, pressure was sometimes described in terms of “microns”, which simply meant a mercury column height of one micron (1x10^-6 m). Note that the micron and the mTorr are the same.

Lastly, it should be noted that occasional confusion arises between the use of different, but seemingly similar, units of pressure. As explained above, the mbar and the mTorr are not the same. One mbar has the same order of magnitude as one Torr (1 mbar = 0.75 Torr).

Unit Conversions

The table below gives some conversion values between various commonly used units of pressure and vacuum. A useful website for conversions:

http://www.onlineconversion.com/pressure.htm

Absolute Pressure and Gauge Pressure

In conclusion, keep in mind that vacuum measurements can be referenced to ambient pressure, gauge pressure measurement or absolute pressure measurement (perfect vacuum). An absolute pressure measurement is referenced with respect to absolute vacuum. Absolute pressure will often be designated by the letter “a” after the unit of measure; “psia.” ​As an example, an absolute pressure reading of 30 psia (pounds per square inch absolute) is a pressure that is 30 psi above vacuum. It is important to understand that there is no negative absolute pressure. There are some

Gauge pressure measurements are measured relative to the ambient atmospheric pressure. Relative, or gauge pressure, will often be designated by the letter “g” after the unit of measure; “psig.” As an example, 30 psig is a gauge pressure that is 30 psi above ambient atmosphere (typically 14.7 psia at sea level). In this example the gauge pressure, 30 psig, is equal to an absolute pressure of 44.7 psia.

What is a vacuum system?

A vacuum system can consist of multiple a vacuum pumps and vacuum gauges attached to a tank that is designed to measure below atmospheric pressure. The vacuum pumps reduce the air pressure inside of the tank to the pressure range that the vacuum pump is rated for. Different vacuum pumps bring the vacuum pressure to different levels depending on the strength of the vacuum pump.

Attached to the tank is usually at least one vacuum pressure gauge. An application may require another type of vacuum gauge to measure a different pressure point. An example of this would be using a piezo pressure gauge and a Pirani pressure gauge to have a larger range of the vacuum pressure measured. A piezo vacuum gauge would be used to measure the rough vacuum range around atmosphere and the Pirani could be used to measure below 1 Torr in the mTorr range. There are vacuum gauges that use technologies from different vacuum gauges to create a combination vacuum gauge to measure vacuum pressure across a wider pressure range. Teledyne Hastings combines both the Pirani and piezo technologies to make the HVG-2020B vacuum pressure gauge.

Vacuum Gauges Poster

Vacuum Gauges Free Poster Unit Conversions and More

Original Content posted Sept 22, 2014

FAQ Corner - Units for Vacuum Measurement
an overview of units used to measure pressure

Earlier this year, the applications engineers here at Teledyne Hastings discussed topics for our blog. We all agreed that one of the more frequent questions that we discuss with folks involve the units used to measure vacuum levels. We find the technicians who use their vacuum systems daily often seem to develop a sixth sense about the “health” of their systems. They know something isn’t quite right when the base pressure (or rate of pressure change) is not what they expect. So, when pressure measurements are not consistent from batch to batch, that is the time when the user stops to ask the meaning behind the data that their vacuum measurement instrumentation is providing.

Now, most users know that vacuum is commonly measured using units of pressure. There are a few different sets of pressure units, and this blog will discuss the more commonly used ones. In Armand Berman’s book, Total Pressure Measurements in Vacuum Technology, pressure unit systems are divided into two categories: “Coherent Systems” and “Other Systems”.

Coherent Systems of Units are based on the definition of pressure (P) as the force (F) exerted on a chamber wall per unit area (A). P = F/A.  The International System of Units, or SI units, is commonly used for pressure measurement. http://physics.nist.gov/cuu/Units/units.html  The SI unit for pressure is the Pascal (Pa). It interesting to note that at NIST (National Institute of Standards and Technology), published papers are always required to use the SI set of units. Again, the SI unit for pressure (force per unit area) is the Pascal. 1 Pa = 1 N /m².

Now, the Pascal as a unit of pressure is not always the most convenient because vacuum systems are often operating in a range of pressures where we would need to collect data using large numbers. For example, near atmospheric pressure, we would measure approximately 100,000 Pa. So, a more convenient unit, the bar, has been derived. (1 bar = 100,000 Pa)

Moving lower in pressure, it is very helpful to then use the mbar (1 mbar = 0.001 bar). So many vacuum users, especially in Europe, use the mbar as the basis for describing pressure levels. As a specific example, look at the base pressure specification of a turbo pump, it will be given in terms of mbar (e.g. Base Pressure < 1 x 10^-10 mbar).

Another system of pressure units is based on the Torricelli experiment (shown in the diagram). In this experiment, the pressure exerted on the mercury can be shown to be P = hdg, where h is the height of the mercury column, d is the density, and g is the acceleration due to gravity.

By measuring the mercury column height, the user can determine the pressure. The Torr unit (named for the Italian scientist Torricelli) has been defined to be 1 millimeter of mercury (1 Torr = 1 mmHg). This unit is very common, especially in the United States. It is also common to use the mTorr (1 mTorr = 0.001 Torr). Many years ago, pressure was sometimes described in terms of “microns”, which simply meant a mercury column height of one micron (1x10^-6 m). Note that the micron and the mTorr are the same.

One last word about the units used to measure vacuum: on occasion, there is confusion between pressure units. As we have seen above, the mbar and the mTorr are not the same. One mbar has the same order of magnitude as one Torr  (1 mbar ≈ 0.75 Torr).  The table below gives some approximate conversion values. A useful website for conversions:

 http://www.onlineconversion.com/pressure.htm

Douglas Baker is the Director of Sales & Business Development of Teledyne Hastings. Antonio Araiza prepared the Torricelli experiment drawing. Antonio is the head of Technical Documentation at Teledyne Hastings (and is among the best soccer referees in the Commonwealth of Virginia).