A process transmitter typically "measures" a process variable - flow, level, temperature, pressure - and produces an output in response to changes in the input variable. Most transmitters incorporate a sensor that measures the input variable and provides an output of which 4 - 20mA is common.
Critically important to the performance of a transmitter is a concept called damping. As the input variable changes, the transmitter output must be updated and changed accordingly.
Damping is the amount of time required, in addition to the update time, for the transmitter output to reach 63.2% of its final value after a step change has been applied to the input. A typical damping response curve for a process transmitter is shown below:
The transmitter's damping is adjustable from 1 to 32 seconds. Damping reduces the effects of electrical noise and any other insignificant transient noise that may influence the transmitter's output signal. It is often used to stabilize control circuits and prevent false triggers.
In the absence of electrical or transient noise, damping may not be necessary in processes that are slow and have an inherent delay time, for example, temperature control loops. Damping should be minimized under conditions of rapid process change.
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