Allen Bradley 1734-IE2C Analog Input Problem

jjdizon17

Member
Join Date
Dec 2016
Location
Taguig City
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6
We had encounter a problem regarding on our Allen Bradley 1734-IE2C, When we connect 1734-IE2C, to CompactLogix (L18ER), the PLC does not function,but when we remove IE2C, it will going to function. What we should do so that PLC can function properly .

Note: Our analo Input contains Pressure Transmitter and VFD signal and if we remove 1 (Hardwire), the PLC wil function. We measure the mA and its over 90mA, what should we do in order to bring it down to 4-20 milliamps? Thanks :)
 
Last edited:
Welcome to the forum!

You'll probably need to provide a little more information about what you mean by the PLC "does not function". Does it fault, or does the logic just not perform the operation you expect it to?

As to the wiring problem you describe, you will need to provide some more information as well - part numbers and a wiring diagram would help out, otherwise all we can do is take wild guesses.
 
If you have measured 90 mA of current into an Input point on an 1734-IE2C, then either you have mis-wired the input or the module is defective.

Either one of these possibilities might cause the controller to fault or its power supply to shut down.

If double-checking your wiring does not solve the problem, then you must replace the 1734-IE2C module.
 
The AI might have been damaged at 90mA, but the root cause is not necessarily the AI.

If 90mA is measured while disconnected from the AI, then the fault is field related.

2 wire, 4-20mA loop powered field devices, like (most) pressure transmitters are supposed to regulate the field current to 20mA under normal conditions, 21-22mA under fault conditions. Active powered analog outputs (found on some VFDs) are current regulators as well.

Failure to regulate loop current to those limits is either
- a catastrophic failure in the field instrument/analog output
- a wiring fault that bypasses the field instrument/analog output and leaves the analog input without a current regulator
- a wiring fault involving a ground loop that is using the AI's input connection-to-ground to "equipotentialize" grounds at different potentials.
- theoretically electrical interference could increase a current signal, but in 35 years I've never seen a DC current level of 90mA from 'noise'.
 

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