If undesired temperatures are applied to a pressure gauge, readings can be distorted and in some cases even damage the gauge. This is where temperature compensation comes into play, which ideally eliminates temperature-related changes.
What influence does temperature have on pressure gauges?
In a pressure gauge, the Bourdon spring deforms elastically under pressure, which is what enables a measured value to be read. The Bourdon spring is temperature dependent due to its elasticity. This leads to measurement errors when the temperature changes. Materials that trigger temperature-related changes during measurement are also used in piezoresistive pressure transducers. In both cases, zero offsets and span errors are the result.
Standard measuring devices are usually no longer usable at over 100°C.
Solution
Pressure gauges can be optimized for different temperatures. Additional cooling elements, heat-resistant materials and temperature compensation are used here.
Good results can be achieved with pressure transmitters using temperature compensation. However, if the pressure transmitters are optimized for operating temperatures of 0 – 70°C but operated at 100°C, measurement inaccuracies are to be expected. Measuring devices that are compensated for a specific temperature range must not leave this range.
The temperature compensation
Passive temperature compensation
With passive temperature compensation, temperature-dependent resistors (passive elements) are switched into a so-called Wheatstone measuring bridge. The resistance elements have a fairly linear temperature behavior.
Only errors of the first order can be compensated with this.
Active temperature compensation (polynomial compensation)
Active temperature compensation involves placing the meter in a warming cabinet and subjecting it to different pressures at different temperatures. This results in coefficients that are stored in the measuring device so that it can independently compensate for temperature errors.
Additional cooling elements
a) Temperatures up to 150°C
In order to distance the electronics from the application, a cooling fin is used between the measuring cell and the amplifier.
b) temperatures above 150°C
From 150°C the pressure connection should only come into contact with a cooled medium. Cooling fins are screwed directly in front of the pressure connection.
c) Temperatures up to 250°C
At extreme temperatures, an upstream diaphragm seal system with a cooling section can theoretically be used. Apart from the dimensions, this method leads to incorrect measurements.