I am new in the automation industry, and now I am focusing on learning how to wire correctly analog inputs in detail, since last time I tried I damaged the module input because of wrong wiring.
Here I have several questions about analog input wiring. They may seem pointless to you but I need these answers to fully understand analog input concept. It would be appreciated if you answer these questions.
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When using 2 or 3 wire 4 – 20 mA current transmitter, does analog output wire (4 – 20 mA) always produce a current referenced to the power supply common? I mean, can we think this transmitter as a fixed voltage source and a variable resistor so the minus side of the voltage source is always linked to power supply common?
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When using a 2-wire 0 – 10 V voltage transmitter, if the input module and transmitter are fed by same power supply, will just wiring the + terminal of transmitter to the + terminal of module be enough (by wiring " – " of the module and " – " of transmitter to common)? I'd like to know if the voltage produced by transmitter is always referenced to ground or can be any floating value.
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The second question is valid for also for a 4 – 20 mA 4-wire transmitter. If both input module and transmitter are fed by same power supply, will just wiring + terminal of transmitter to the + terminal of the module be enough (by wiring " – " of module and " – " of transmitter to common)? It seems to me that a 4 wire transmitter output can be any floating value but what happens if we use same power supply for the module and the transmitter ?
Best Answer
With regard to your multiple questions...