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 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 utilizing the WIKA POLARgauge� as an example. The product family has been designed specifically for measurement at extremely low ambient temperatures 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 frequently 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 will be operated in 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. 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, so that the measured value can be read safely.
However, the majority of silicone oils used for this purpose begin to solidify at temperatures below -40 �C. The movement then no longer works, or may also freeze. Application-aligned tabs on the parameters (e.g. process pressure) can’t be ensured.
Therefore, for pressure gauge น้ำ ¿½ 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.) compared to a standard version (l.): It does not have any elastomers.
2. The elastomers
Elastomers are found in all mechanical pressure gauges or thermometers. They provide a secure sealing between the individual components. In detail, these 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 found in standard designs cannot durably withstand very low ambient temperatures. They become brittle as time passes and lose their sealing properties. This results in the case filling escaping. This, in turn, leads to the formation of condensation and the frosting of the window.
Therefore, in the development of the POLARgauge� series, elastomers have been eliminated in all critical points. The seal between the 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.
Summary 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, a suitable variant is available for almost any application. Do you want to buy differential pressure gauge models? In our WIKA online-shop you will discover some of our standard designs. Assuming you have any further questions, your contact will gladly help you.

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