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Vacuum Gauge Series: Thermocouple Gauge Tubes

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

Vacuum Gauge Series - Thermocouple Gauge Tubes Fun FactTeledyne Hastings was founded in 1944 as The Hastings Instrument Company by Charles and Mary Hastings. The late 1940s saw the introduction of thermal sensing technology at the young company which became the foundation for many early Hastings instruments such as air velocity indicators, thermal mass flow meters, stack emission monitors and, of course, the thermopile vacuum sensor.

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 around the world where repeatable, rugged, and dependable vacuum measurement is needed. Based in Hampton Virginia for over 75 years, the highly skilled employees at Teledyne Hastings are dedicated to delivering the highest quality thermocouple vacuum gauge tubes.

How does a thermocouple gauge tube work?

How a thermocouple vacuum sensor works is simple! As an example, let’s take a look at the DV-6R, shown in the diagram to the right, along with the representative schematic.

There are three thermocouples shown (A, B, and C) in the diagram. Now, an individual thermocouple consists of two dissimilar metals which are joined together at a junction. At the junction, there will be a small voltage which is a function of temperature. During operation of the gauge tube, thermocouples A and B are resistively heated inside the gauge tube’s housing. Now, since the wires connected to A and B thermocouples are exposed to the gas in the vacuum, thermal energy will be transferred away from the wires at a rate which is dependent on the number of collisions between the gas and the wires and thereby depends on the pressure inside the tube.

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

Let’s consider two extremes. In high vacuum, where the pressure is very low, there will be fewer gas collisions with the wires and the tube’s voltage output will be relatively high. (Higher temperature corresponds to higher thermocouple output). Now, towards high pressures, more gas results in more thermal energy being carried away from the wires and the thermocouples run at a lower temperature and so give a relatively low output.

 

How to use a thermocouple vacuum gauge tube:

To use a thermocouple vacuum gauge tube, you must connect the gauge tube with an instrument that correctly excite the tube’s wires and also converts the output of the gauge tube to the correct pressure measurement. Note that new gauge tubes from Teledyne Hastings are manufactured to the highest quality and are tested to be very repeatable from tube to tube.

So let’s take, as an example, the use of a DV-6R vacuum gauge tube with a DCVT-6 panel meter or HPM-4/5/6 handheld meter. Both the DCVT-6 and HPM-4/5/6, out of the box, are setup to provide the correct activation to the DV-6R. The output from the gauge tube is then monitored by the instrument and the correct vacuum level is displayed for the user.

In the case of the DCVT, two contact relays are available to the user for process control. The user can simply dial up the desired setpoints and the dual relays will independently toggle when the vacuum setpoint has been crossed. You can now easily understand how Teledyne repeatable gauge tubes will lead to repeatable process control! The DCVT also provides serial communication (RS232) and linearized analog output options (0-1 VDC, 0-5 VDC, 0-10 VDC, 4-20 mA).

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 many applications where a thermocouple vacuum gauge tube is an excellent choice. One example we will briefly discuss in this short blog is vacuum insulation or vacuum jacketing. The technique of using a vacuum guard or barrier to thermally insulate a cryogenic or refrigerant tank is straightforward: remove the air from around an object and eliminate conductive heat transfer. The better the vacuum is then the better the vacuum insulation. To effectively measure pressure in the mTorr range, a vacuum dial gauge is simply not sensitive enough.

A vacuum reading can be obtained from any of the DV-6 tubes using either a dedicated electronic display or handheld battery-operated readout. The Hastings’ DCVT provides continuous monitoring with an easy to read LED display. For periodic vacuum checking of one or more tubes, the hand-held HPM 4/5/6 is recommended. For convenience, it is powered by a 9V battery and can be connected to any DV-6 tube for an instant reading. To ensure the most accurate measurement, the DB-20 Reference Tube (with NIST Traceable calibration) can be used to validate the electronic calibration.

If you would like to learn more about vacuum jacketing click here.

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