Pressure and temperature measurement at extremely low ambient temperatures

Standard pressure gauges and thermometers generally deal with ambient temperatures down to -40 �C. But what must be the 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� for example. This 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 monitoring of pumping stations and pipelines.
Minus 40 �C ? this value is often exceeded faster than one thinks. That is demonstrated with a turn 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 must be observed:
For pressure measurement at extremely low ambient temperatures only available with filled case: The WIKA pressure gauge model PG23LT.
1. Forever filling
A measurement at extremely low ambient temperatures requires filled-filled measuring instruments. The liquids useful for this protect the instrument from condensation formation within the case caused by temperature fluctuations. They thus avoid the window from frosting, so the measured value can still be read safely.
However, nearly all silicone oils used for this purpose commence 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’t be ensured.
Therefore, for the POLARgauge� series a special low-temperature silicone oil has been specified. This oil remains in circumstances that allows correct measurement and measured value display, even at -70 �C.
The case of the POLARgauge� model PG23LT (r.) compared to a typical version (l.): It has no elastomers.
2. The elastomers
Elastomers are found in all mechanical pressure gauges or thermometers. They offer a secure sealing between your individual components. At length, they are the flat gasket at the window, and with pressure gauges and also the blow-out device on the trunk of the case and the vent valve for pressure compensation.
However, the sealing materials used in standard designs cannot durably withstand very 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 the window and case is made of a special material. It really is adapted to extremely low ambient temperatures. The vent valve has a stainless steel cap.
Summary 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, a suitable variant is available for almost any application. Do you want to buy differential pressure gauge models? Inside our WIKA online-shop you will discover some of our standard designs. Assuming you have any more questions, your contact will gladly assist you to.

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