Dear Sir,

Please let me know what are the probable root causes for the failure of a Aanlog Input Module. In our plant its been observed that frequent failure of Channel faiure.

Please find an issue which i have attended in our plant, likewise observed for different water plant systems.
what will be the reson behind that, one observation was the two wire tranmitter instrument earth no where connected to earth terminal. please guide me on the same.

Issue:
PW-II/DS-05/HMI-01 system Heater inlet temperature reading continuously showing as 159.8 degC on the HMI display irrespective of the process conditions.

Verification checks performed:
- Wire continuity test all the way from Power supply to Transmitter to PLC– Found OK
- Measured RTD (Radix make) Sensor Output – got 115 ohms = 39.96 degC – Found OK
- Transmitter Working condition- by connecting it to the other working channel of the PLC card – Found OK , please let me know if there is any other way to verify trasmitter is working or not?
- Measured loop current b/w Power supply  TransmitterPLC– measured 0.4 milli amps – found NOT OK. Should be measured in b/w 4 to 20 milli amps as per RTD output resistance 115 ohms.
- 4 to 20 milliamps source applied to directly to PLC card IN2+ & IN 2- Terminals– No response from the PLC, on and the reading still showing on the HMI as 159.8 degC – concluded PLC Analog input channel gone bad.

Root Cause:
Analog input card channel IN2+ and IN2- terminals are gone bad.

Solution:
AI card Model: IF4 & Make: Allen Bradley shall be procured , escalated the same to Mr.Ashok.
Note: Currently no SPARE available in the PLC system.

- please let us know what is the instrumentation grounding importance and what are instrument earth grounding rules while we hook up two wire or 4 wire transmitter? Thanks in advance

Hey, Chandra recently I had also faced this issue 2 analog input cards got burnt. I checked and found that there was no proper grounding available to the modules. I have given the grounding properly and neutral grounded too then no problem repeated.

Yes, grounding is a must in such critical parts of our control system.

I think Mr. Scott will be more helpful to explain this in detail, waiting to get some more info on that.

Mr.Kumar

can you please share us the rough drawing how you implemented it. if possible share me the real field installation pictures.
what cable you have used ? whether shielded cable or 3 wire cable ?
whether you have terminated ground on the both the ends , i mean instrument side as well as PLC side (TB side) or at one side only?
How much resistance/volts we have to get if its properly grounded?
Kindly share you knowledge mate

My mail id [email protected]

Thanks in advance