Teledyne Hastings Instruments Blog

What is a Thermocouple Gauge?

Teledyne Hastings was founded in 1944 as “The Hastings Instrument Company” by Charles and Mary Hastings. The introduction of thermal sensing technology in late 1940s at the young company offered potential for a variety of new technologies and quickly became the foundation for many early Hastings’ instruments. Early products included air velocity indicators, thermal mass flow meters, stack emission monitors and, of course, the thermocouple vacuum gauge tube.

By 1964, Hastings Instruments had grown into one of the leading vacuum and thermal mass flow instrument companies in America. Today, our popular Thermocouple Vacuum Gauge Tube product lines, including the DV-4, DV-5, and DV-6, are trusted globally where repeatable, rugged, and dependable pressure measurement is needed. Based in Hampton, Virginia for over 75 years, the highly-skilled employees at Teledyne Hastings are dedicated to delivering thermocouple vacuum gauges of exceptional quality.

How does a thermocouple gauge tube work?

The physics behind how a thermocouple vacuum gauge tube functions is simple. For example, let’s look at the DV-6R thermocouple vacuum gauge tube, which is capable of pressure measurements within the range of 0 – 1000 mTorr. The DV-6R can be seen in the image below, along with the representative schematic.

A thermocouple consists of a junction of two dissimilar filaments that are soldered together. Three thermocouples are shown (A, B, and C) in the DV-6R diagram, and many thermocouple gauge tubes use multiple thermocouples to form a thermocouple array. At each junction, there is a small voltage (on the order of a mv) which is a function of temperature. When the gauge tube is in operation, thermocouples A and B are resistively heated inside the gauge tube’s housing. Because each filament connected to both A and B thermocouples is exposed to the gas in the vacuum, thermal energy is transferred away from the array at a rate which is dependent on the number of collisions between the gas molecules and the filament wires.  This transfer of thermal energy is, in turn, dependent on the pressure inside the tube. In essence, by measuring the rate of thermal energy transfer, the pressure inside of the tube is indirectly determined!

To understand the concept more fully, let’s consider two extremes. In high vacuum, where the pressure is very low, there will be fewer gas molecules to collide with each filament and the tube’s voltage output will be relatively high. Higher temperature corresponds to higher thermocouple output. As we approach near atmospheric pressure (760 torr), there are more gas molecules, resulting in more thermal energy transferred away from the filament. Consequently the thermocouples run at a lower temperature resulting in a relatively low output. The varying output produced by the thermocouple gauge is dependent on the thermal conductivity of the gas in the vacuum system, which is then used to measure pressure.

Thermocouple vacuum gauges are “indirect gauges”, meaning they accomplish pressure measurement by measuring a physical property, such as thermal conductivity or ionization rate of gas molecules, to determine the pressure in a vacuum system.

How to use a thermocouple vacuum gauge tube:

Teledyne Hastings’ vacuum gauge tubes are manufactured to the highest quality and tested to be extremely repeatable from one gauge tube to another to ensure accurate process control. Thermocouple vacuum gauge tubes are physically installed on a vacuum system and then used to measure various pressures across the tube’s full scale range. When the filament inside the tube is excited, the output is then converted to a pressure measurement.

An example gauge tube installation would consist of a DV-6R thermocouple vacuum gauge tube connected to a DCVT-6 panel meter or HPM-4/5/6 handheld meter. Both the DCVT-6 and HPM-4/5/6, are factory configured to work seamlessly with DV-6R gauge tubes, out of the box. The output from the gauge tube is then monitored by the DCVT-6 or HPM-4/5/6 and the level of vacuum displayed.

In the case of the DCVT, two contact relays are available for process control, and the dual relays will independently toggle according to user-defined setpoints, when the vacuum setpoint has been crossed. This demonstrates how the factory-tested repeatability of our gauge tubes results in consistent and repeatable process control! The DCVT also provides serial communication (RS232), LabVIEW™ drivers and linearized analog output options (0-1 VDC, 0-5 VDC, 0-10 VDC, 4-20 mA).

Related Products

Teledyne Hastings' Vacuum Products
DCVT-6	HPM 4/5/6	DV-6R	DV-6S

Application Example:

There are numerous, diverse vacuum applications and different vacuum systems can require specific thermocouple vacuum gauge tubes. At the most basic level, vacuum systems can be installed in a variety of environments including outdoor with exposure to weather elements, indoor industrial and laboratory conditions in which exceptionally high cleanliness standards are required.

A good example of how a thermocouple vacuum gauge tube meets the requirements of a specific application, is presented in the vacuum insulation or vacuum jacketing field. The technique of using a vacuum guard or barrier to thermally insulate a cryogenic or refrigerant tank is straightforward: by removing the air from around an object, conductive heat transfer is eliminated. The better the vacuum attained, the higher the level of vacuum insulation. To effectively measure pressure below the 1 Torr range, a vacuum dial gauge is simply not sensitive enough; a thermocouple vacuum gauge tube is required.

To obtain vacuum readings from DV-6 gauge tubes, a dedicated electronic display or handheld battery-operated readout is used. The Teledyne Hastings’ DCVT provides continuous monitoring via an easy to read LED display. For periodic vacuum monitoring of one or more tubes, the hand-held HPM 4/5/6 is recommended because of its portability (9V battery power) and its ability to be quickly connected to a DV-6 tube and obtain an accurate reading with fast response time. To ensure the most accurate measurement, the DB-20 Reference Tube can be used to validate the electronic calibration. This can assist in determining if the thermocouple vacuum gauge tube requires replacement by ensuring that it is producing an accurate reading.

Teledyne Hastings has created a detailed application note on vacuum jacketing insulation at this link.

For more information about any of our thermocouple sensor series or vacuum gauges, we are here to help. In addition to LiveChat on our website, you can contact us at hastings_instruments@teledyne.com or call 757-723-6531 (800-950-2468) or click the button below.

We at Teledyne Hastings Instruments are pleased to introduce the newest member of our vacuum measurement portfolio, the HVG-2020A.  The HVG-2020A is a piezoresistive vacuum sensor with an optional touchscreen display that reads from 0.1-1000 Torr.  The sensor uses 316 Stainless Steel as the wetted material and provides a gas independent pressure measurement, meaning your measurement will be accurate no matter what gas species is being used.  The HVG-2020A features an excellent accuracy rating of ±(0.1% of Reading + 0.5 Torr).  This rugged sensor comes in a number of system connections for ease of installation: 1/8” NPT, 1/4” VCR®, 1.33” Mini-CF, 2.75” CF, KF-16, KF-25, 1/2” Weld Stub, and 1/2” VCR. Let’s talk about some of the powerful features that allows the HVG-2020A to stand out.

Analog I/O: The HVG-2020A has a 9 pin D-sub connector on top of the assembly that allows an analog output signal to be measured amongst other features.  The selected linear analog output signal is proportional to the full scale range of the sensor (1000 Torr). Available outputs are 0-1 VDC, 0-5 VDC, 0-10 VDC, 0-20 mA, and 4-20 mA.  The sensor will come configured from the factory with one of these outputs active, but can be easily changed by the user should output requirements change.  Through the touchscreen display, there is a menu that allows the user to cycle through the available output options.  If the HVG-2020A was configured without a touchscreen, the analog output can be changed via digital communications, which we’ll talk about in the next section.  In addition to the analog output, the 9 pin D-sub will have Hi & Lo set points.  The Hi set point is active when the pressure is above the set value and the Lo set point is active when the pressure is below the set value.  Finally, the 9 pin D-sub has a pin for input power.  The HVG-2020A can accept 12-36 VDC for power.  In the event, the user doesn’t have 12-36 VDC to send via the 9 pin D-sub, there’s a 24 VDC input connection port that’s compatible with a bayonet-style power supply.

Digital I/O:  As mentioned earlier, the HVG-2020A has a few different methods digital communication can be established.  First and easiest is the micro-USB port on top of the gauge.  This will allow the instrument to be directly connected to a computer without the need for adapters or extra wiring.  There is also a 4-conductor TRRS jack on top of the instrument.  This port can be used for daisy-chaining gauges together with RS485 or a standard RS232 communication connection.  Finally, the 9 pin D-sub will have two pins designated for TTL serial communication. These digital communications (with the exception of TTL) can be connected to a PC and used with our Free Windows software for the HVG-2020A.  The software has a number of features including data logging and customization/configuration of the gauge.  Digital communication also allows for command syntax to be sent manually to the instrument. These commands are especially important if the HVG-2020A was ordered without a touchscreen display.  Through digital communication, the user can issue commands that change the analog output, adjust set point values, stream pressure readings, or change pressure units, just to name a few.

Touchscreen Display:  The most powerful feature of the HVG-2020A is the touchscreen display.  The intuitive display allows for quick visualization of the current pressure without needing to have a separate power supply or remote display. There are five available views to choose from (shown left to right below): Pressure View, Pressure & Temperature View, Set Point View, Bar Graph View, and Pressure over Time View.  The pressure is always displayed on each of these five screens.

There is also a menu button which will allow the user to cycle through a number of sub menus.  Through these menus the user can change the screen orientation should they mount the gauge in a position other than vertical, set the zero (this should only be performed if the system pressure is known to be well below 0.1 Torr), view device information such as serial number and firmware levels, change the analog output, cycle between RS232 or RS485 and a number of baud rates, and finally restore the configuration of the gauge back to the original factory setup.  The touchscreen display makes reading vacuum pressure as clear as 20/20 Vision!

LED Status Lights:  Lastly, the HVG-2020A features two LED lights on top of the instrument.  These are extremely helpful in getting a general idea of the current pressure and status of the vacuum gauge. The chart below explains each combination of Status & Vacuum LED.

The HVG-2020A vacuum gauge is ideal for many applications requiring rough vacuum measurement.  The picture on the right shows a simple lab set-up using a diaphragm vacuum pump & an analog needle gauge.  The HVG-2020A would be a perfect fit for this set up.  With the local touchscreen display, extensive wiring and configuration is not needed.  Simply supply the gauge power and you are reading pressure. It’s easy to See why the “2020” is the vacuum gauge for the job! 

To learn more about the HVG-2020A or any of our other vacuum and flow products, contact us at hastings_instruments@teledyne.com, call 757-723-6531 (800-950-2468), or click the button below.

VCR® is a registered trademark of Swagelok Company.

Teledyne Hastings is working to expand our throughput so that we can better serve our customers by meeting increased demand while decreasing lead times. Over the last several months, we have added and improved calibration systems in both our vacuum and flow production areas. We have also purchased a new vacuum furnace which increases our production capacity. In this blog, we will describe what a vacuum furnace is, how it functions, and how we use it.

A picture of our newest vacuum furnace is shown below.  The three major components of the vacuum furnace, from left to right, are the high-speed diffusion pump, the vacuum chamber with a high temperature hot zone, and the control cabinet. The diffusion pump is capable of pumping 180,000 lpm.  While the pumping speed may seem unnecessarily high for the given volume, keep in mind that the gas load, at high temperature, can be very high. The diffusion pump is connected to the hot zone chamber via a large right angle vacuum valve. The diffusion pump is backed by a rotary vane vacuum pump. Pressures in the foreline can be monitored by using a Teledyne DV-6R vacuum gauge tube. The base pressure of the system, with the heat zone at room temperature approaches 1 x 10^-6 Torr.

 Leon Whitehead at the controls of the new vacuum furnace.

The hot zone is the heart of the vacuum furnace. A picture showing the inside of the hot zone is shown below. The effective hot zone size is 12”w x 12” h x 24” d. The molybdenum rod elements inside the hot zone are resistively heated once the system has reached sufficient vacuum. Under vacuum, the hot zone can reach temperatures exceeding 1300°C (2372°F).

Inside the hot zone. Note the series of Molybdenum rod elements.

The vacuum furnace is controlled by a touchscreen panel with PLC. The operator can select and execute a pre-programmed temperature/time profile for a given task. In addition, pressure and temperature at various locations on the system are monitored and displayed. The control cabinet also includes the transformers, contactors, and fuses. 

Teledyne uses our vacuum furnaces for both fusing and brazing operations - all while precisely controlling the environmental conditions within the hot zone. In a typical schedule, the system is pumped out to its base pressure and then the hot zone is brought up to 800°C. After reaching this temperature, the hot zone is held for a period of 20 minutes. Next, the hot zone is slowly ramped to 1100°C, which takes about an hour. The hot zone is then held there for up to 1 ½ hours.

Teledyne Hastings Instruments is an ISO 9001:2008 certified manufacturer and we produce a complete line of instruments for precise measurement and control of vacuum, pressure, and gas flow. Our vacuum furnaces and the corresponding Quality Work Instructions deliver consistent results, which in turn provide our customers with high quality instrumentation. For information on Teledyne Hastings and our Mass Flow Meters and Controllers or Vacuum Gauges, please visit www.teledyne-hi.com or click the button below.

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 

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).