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Devin Seran

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Vacuum Gauge Series: What is a Thermal Couple Gauge?

Posted by Devin Seran on Mon, Apr 12, 2021 @ 04:02 PM

What is a Thermocouple Gauge?

Vacuum Gauge Series - Thermocouple Gauge Tubes Fun Fact

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.

Teledyne Hastings Gauge Tubes

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.

Vacuum Gauge Tube Illustration DV-6R-resized-183

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
Model DCVT-6 Vacuum Gauge

HPM

DV-6R-resized-183 DV-6S-1

Application Example:

Gas Plant Tanks 182395563There 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.

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Tags: vacuum gauges, Thermocouple Gauge Tubes

Introducing our Newest Product - THCD-401 4-channel power supply

Posted by Devin Seran on Thu, Mar 05, 2020 @ 03:51 PM

Figure 1- THCD-401 Teledyne Hastings is proud to announce our newest 4-channel power supply, controller and display, the THCD-401. The THCD-401 provides both ±15 VDC or 24 VDC to power our mass flow controllers, flow meters, vacuum gauges and pressure transducers. Feedback from connected devices is displayed on the bright, front panel LED display in 6-digit resolution, making open and closed channels easily identified at a glance. The THCD-401 can set a relay point for control of other processes and has a high accuracy of ± (0.02% of Reading + 0.01% of Full Scale). Custom configuring our products to customer needs is our specialty. Your THCD-401 can be factory configured to match the gas, range, units and the output of your instruments for out-of-box functionality.

What’s Improved?

In short, the THCD-401 was designed for exceptional user access and control.  The addition of a circular touch pad simplifies navigation through the unit’s various menu options, while left and right arrow keys allow easy selection of digits to be changed. Calibration is no longer needed for various levels of input voltage and built-in fuses provide additional surge protection.  Back panel communication ports have been streamlined and a USB-C and Ethernet port for serial communication have been added. 

Ethernet Starburst-1The addition of Ethernet communication provides access to the newest feature that the THCD-401 has to offer; the internal web server! The web server can be accessed by entering the IP address of the THCD-401 into a browser’s address bar (requires static IP address configuration on the network prior to use). While the web server feature works best in Mozilla™ Firefox®, it can be accessed via any browser you choose.  Figure 2 shows the web server interface with applications along the top navigation bar and a live data stream for remote read.

The web server allows you to name channels and adjust the range or units based on your device and the full scale (V) voltage output that it sends. This enables users to see the flow rate of a flow controller or meter, as well as the ability to OPEN/CLOSE all channels at the click of a button. Other applications include linearization, setting of a relay point and finding the total amount of gas that has passed through the device using the totalizer function.
Figure 2 - New web browser interface for THCD-401

It should be noted that while all these advanced features are available via the web server (Ethernet) connection, the THCD-401 also offers direct access to each via the front panel display menus using the circular touch pad.  This allows for quick and convenient setup of the channel’s full scale and range(V) for new devices.

If a relay point has been tripped, it will be indicated to the left of the channel’s name on the THCD-401 display. The display will also show the current mode of the set point, if it is not configured in AUTO mode. In OPEN mode, the set point outputs a voltage greater than the full scale of the device. In CLOSED mode the set point outputs a voltage less than the minimum output voltage of most devices. AUTO mode is dependent on the user defined set point configured through the THCD-401 physical buttons, digital communication or external input. 

More Information:

The THCD-401 was designed to be a highly flexible and multi-featured process display controller that can be panel mounted and capable of interfacing to an assortment of meters, controllers and gauges.  A powerful upgrade from the previous THCD-400 model, the THCD-401 adds digital communications, a bright LED display and a variety of customizable options to an already time-tested platform. To learn more about the
THCD-401 or any of our other vacuum and flow products, contact us at hastings_instruments@teledyne.com, call 1-800-950-2468, or click the button below.

Interested in THCD-401

Tags: Power Supply