What do the symbols on the signal line of the pressure difference relay PDY in the PID diagram mean?
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This post was last edited by LeeMoon0816 on 2021-6-14 at 16:33. I would like to ask the experts here: on the signal line of the pressure difference relay PDY in the PID diagram, do the symbols (+ -) indicate the wiring connections at the relay, meaning that the + symbol denotes connection to the positive terminal and the - symbol denotes connection to the negative terminal? Is that correct?
This probably does not refer to the signal line, but rather to the high-pressure and low-pressure process media that are fed into the differential pressure controller.
The lines with small circles in the diagram represent data links; they are not electrical signals, so + and - do not denote connections. +The two pressures indicated by – form a differential pressure relationship; + denotes a positive pressure data link, while – denotes a negative pressure data link.
That’s probably what you mean. Thanks for the advice!
That’s what you mean; the + and – symbols represent the level of pressure (on a relative basis).
Yes, the △ symbol in the upper right corner (first quadrant) of PDY indicates the algebraic difference of two inputs.