Pressure and temperature measurement at extremely low ambient temperatures

Standard pressure gauges and thermometers generally cope with ambient temperatures down to -40 �C. But what should be the top features of a mechanical measuring instrument that works perfectly well in polar climates with even lower temperatures? This could be explained using the WIKA POLARgauge� as an example. The product family has been designed specifically for measurement at extremely low ambient temperatures right down to -70 �C. The instruments are mainly used in crude oil and gas processing; for example, in the local pressure and temperature tabs on pumping stations and pipelines.
Minus 40 �C ? this value is frequently exceeded faster than one thinks. That is demonstrated with a look to Russia. There, tables with standard temperature values even indicate more than -60 �C for some regions. For mechanical instruments which is operated such ambient conditions, two critical points should be observed:
For pressure measurement at extremely low ambient temperatures only available with filled case: The WIKA pressure gauge model PG23LT.
1. The case filling
A measurement at extremely low ambient temperatures requires filled-filled measuring instruments. The liquids used for this protect the instrument from condensation formation within the case resulting from temperature fluctuations. They thus prevent the window from frosting, so the measured value can still be read safely.
However, nearly all silicone oils useful for this purpose begin to solidify at temperatures below -40 �C. The movement then no more works, or can even freeze. Application-aligned monitoring of the parameters (e.g. process pressure) can no longer be ensured.
Therefore, for the POLARgauge� series a special low-temperature silicone oil has been specified. This oil remains in a state that allows correct measurement and measured value display, even at -70 �C.
The case of the POLARgauge� model PG23LT (r.) in comparison to a standard version (l.): It does not have any elastomers.
2. The elastomers
Elastomers are found in every mechanical pressure gauges or thermometers. They offer a secure sealing between the individual components. In detail, they are the flat gasket at the window, and with pressure gauges additionally the blow-out device on the rear of the case and the vent valve for pressure compensation.
However, the sealing materials found in standard designs cannot durably withstand suprisingly low ambient temperatures. They become brittle over time and lose their sealing properties. This results in the case filling escaping. This, in turn, leads to the forming of condensation and the frosting of the window.
Therefore, in the development of the POLARgauge� series, elastomers have already been eliminated in every critical points. The seal between your window and case is made from a special material. It really is adapted to extremely low ambient temperatures. The vent valve includes a stainless steel cap.
Likely of the WIKA POLARgauge� series
Note
You can get more info on the POLARgauge� series on the WIKA website via the following links. The merchandise family currently comprises four instrument types: The Bourdon tube pressure gauge model PG23LT, the differential pressure gauge models 733.51, 733.31 (filled versions of the models 732.51, 732.31), the bimetal thermometer model 55 and the gas-actuated thermometer model 73. Thus, the right variant is available for almost any application. Would you like to buy differential pressure gauge models? Inside our WIKA online-shop you will find a few of our standard designs. When you have any more questions, your contact will gladly help you.

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