Sensor response time

The response of instrumentation is a factor in determining the total SIF response time, which in turn determines the total process safety time of a trip.

The responsiveness of sensors is often described by vendors using a time constant , which is the time for the sensor output to reach 63.2% of a step change. It is dependent on media type, flowrates, emissivity of sensor materials, thermal conductivity of sensor materials, etc.

Where:

• = current sensor reading
• = Initial sensor temperature when it was put into new media
• = Temperature of the new media that the sensor is measuring
• = Elapsed time from the point when the sensor temperature was
• = Sensor time constant

Also see Thermowell Time Constant Estimation.