DP cell Impact of Operating Environment 

All of the sensors described in this module are widely used in control and instrumentation systems throughout the power station. Their existence will not normally be evident because the physical construction will be enclosed inside manufacturers packaging. However, each is highly accurate when used to measure the right quantity and within the rating of the device. The constraints are not limited to operating.pressure. Other factors include temperature, vapour content and vibration. 

Vibration 

The effect of vibration is obvious in the inconsistency of measurements, but the more dangerous result is the stress on the sensitive membranes, diaphragms and linkages that can cause the sensor to fail. Vibration can come from many sources. Some of the most common are the low level constant vibration of an unbalanced pump impeller and the larger effects of steam hammer. External vibration (loose support brackets and insecure mounting) can have the same effect. 

Temperature 

The temperature effects on pressure sensing will occur in two main areas

The volumetric expansion of vapour is of course temperature dependent. Depending on the system, the increased pressure exerted is usually already factored in. The second effect of temperature is not so apparent. An operating temperature outside the rating of the sensor will create significant error in the readings. The bourdon tube will indicate a higher reading when exposed to higher temperatures and lower readings when abnormally cold due to the strength and elasticity of the metal tube. This same effect applies to the other forms of sensors listed. 

Vapour Content 

The content of the gas or fluid is usually controlled and known. However, it is mentioned at this point because the purity of the substance whose pressure is being monitored is of importance whether gaseous or fluid especially, if the device is used as a differential pressure device in measuring flow of a gas or fluid. Higher than normal density can force a higher dynamic reading depending on where the sensors are located and how they are used. Also, the vapour density or ambient air density can affect the static pressure sensor readings and DP cell readings. Usually, lower readings are a result of the lower available pressure of the substance. However, a DP sensor located in a hot and very humid room will tend to read high.