A Controller’s "Process" Goes From Wire Out to Wire In

A controller seeks to maintain the measured process variable (PV) at set point (SP) in spite of unplanned and unmeasured disturbances. Since e(t) = SP - PV, this is equivalent to saying that a controller seeks to maintain controller error, e(t), equal to zero.

A controller repeats a measurement-computation-action procedure at every loop sample time. A sensor measures a temperature, pressure, concentration or other property of interest from our process. The sensor signal is transmitted to the controller. The pathway from sensor to controller might include: a transducer, an amplifier, a scaling element, quantization, a signal filter, a multiplexer, and other operations that can change the size, sign, and/or units of the measurement. After all electronic and digital operations, the result terminates at our controller as the "wire in" measured process variable (PV) signal...

There's more. Read the complete article at:

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Please note that this post is a complete rewrite of a previous article of the same title.

Happy New Year!

Doug Cooper

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