Active Compensation of the Temperature Sensor with Diaphragm Seal Systems

Dr. Thomas Köster (LABOM Head of R&D)
Add to MyDirectIndustry favorites

Innovative pressure measurement technology reduces temperature error by 90%

Pressure measurement with diaphragm seals

Diaphragm seals are frequently used in the process industry for pressure measurements to protect the measuring device against aggressive media or – for example in the pharmaceutical industry – to create a gap-free process connection. The process is separated from the measuring device by means of a thin metal diaphragm. A pressure transmission fluid behind the diaphragm transmits the process pressure to the actual pressure sensor.

A solution can be found for almost any pressure measurement task using diaphragm seal systems.

Measurement errors caused by the influence of the process temperature

A drawback is that the diaphragm seal is not completely non-reactive. A measurement error caused by the influence of the process temperature can occur depending on the design. The pressure transmission fluid expands as a result of the process heat and deflects the separating diaphragm. This generates a restoring force depending on the rigidity of the latter, which is received as an error in the pressure measurement.

Approach: Active correction using the sensor and diaphragm seal temperature

LABOM has developed and implemented a further compensation process to eliminate the disadvantages of the existing processes. The temperature of the pressure trans¬mission fluid is recorded with an additional temperature sensor with the ATC technology (ATC = Active Temperature Compensation). This sensor (a Pt100 element) is positioned as close as possible to the separating diaphragm. The sensor thus records the temperature of the liquid behind the separating diaphragm with good accuracy.

The great advantage of the additional temperature measurement is its significantly faster response time compared to the pressure sensor temperature. The additional sensor records changes in the process temperature much faster. The resulting measurement errors can therefore also be mathematically corrected much faster.

The method is much more robust against changes in the ambient conditions because the temperatures of the significant amounts of fluid in the system (behind the diaphragm and in front of the sensor) are known. The correction can therefore be set so that the measuring error is fully compensated in a stationary state.

The influencing factors on the temperature stability of the pressure signal are thus limited to the manufacturing tolerances of the diaphragm seal and the achievable precision when filling the diaphragm seal. Studies have shown that errors can be reduced by 80-90% with small diaphragm seals in a stationary state.

Summary

LABOM has made a quantum leap in the temperature stability of diaphragm seal systems with the ATC technology. High-precision pressure measurements can thus be carried out together with the high accuracy of the pressure measuring device.

Fig.4 Comparison of ATC technology
Fig.4 Comparison of ATC technology

Associated Trend items