Pressure and temperature measurement at extremely low ambient temperatures

Standard pressure gauges and thermometers generally deal with ambient temperatures right 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 can 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 utilized in crude oil and natural 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 a few regions. For mechanical instruments which will be 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 useful for this protect the instrument from condensation formation within the case caused by temperature fluctuations. They thus avoid the window from frosting, in order that the measured value can be read safely.
However, nearly all silicone oils used for this purpose begin to solidify at temperatures below -40 �C. The movement then no longer works, or can even freeze. Application-aligned tabs on the parameters (e.g. process pressure) can’t be ensured.
Therefore, for Sure Fire ¿½ 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 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, sufficient reason for 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 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 all 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.
Overview of the WIKA POLARgauge� series
Note
You can get further information 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 every application. Would you like to buy differential pressure gauge models? Inside our WIKA online-shop you will find some of our standard designs. In case you have any more questions, your contact will gladly help you.

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