System Trouble-shooting

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Thread Starter

Enahore

There is system installed where field sensors communicate with an HMI in the control room. Now all the field datas are no longer available in the HMI. I am thinking that the 2-core signal cable from the field devices to the control room HMI is bad. How do i determine, using a multimeter, whether the cable is bad or still good? A step by step understandable procedure will be appreciated.

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bob peterson

What does "no longer available" mean?

How did you come to decide the cabling was bad? That would be one of the last things I would suspect, especially if multiple sensors were involved.

It is doubtful the sensors are connected directly to the HMI. Likely they pass through some kind of I/O modules first, which are read by a PLC or DCS, and than just the data is transmitted to the HMI.

It seems most likely that the data transmission to the HMI has been interrupted somehow. I would start there.

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Bob
 
What is the 'system'? a DCS? a PLC?

Brand name? model?

Is all the analog and/or discrete data collected remotely and forwarded via a digital communications?

Which digital comm protocol? Profibus? DeviceNet? DH+? Modbus RTU? HART? Foundation
Fieldbus?

How many field devices are off-line? 2? 5? 10? 20?

Are the field instruments still powered up and functional, as indicated in their local displays on the instruments, or are the field instruments dead?

What power supply do they use? Is it a common power supply? Are all power supplies for these
devices still functional?

Is the field device wiring fused/circuit breakered/switched? Are the fuses/circuit breakers/switches OK and in the 'operating' position?

Does the wiring for these field devices use RTP (remote termination P's) terminal blocks with multipair cable that connects to the I/O modules? Are the RTP's connected properly? Are the RTP's fused?

Are fuses intact?

Is wireless involved in any fashion?

Did the plant experience a recent lightning strike? power fluctuations? Brown-outs?

What sort of maintenance or upgrades were performed in that I/O panel recently?

How many junction boxes does that 2 wire cable go through between the control room and where the
I/O is?

How old is the wiring? 2 years? 5 years? 10 years? 20 years? 30 years?

Is your climate temperate, frozen, desert, or tropical ?

How much of the cabling is subterranean (underground)?

When you look out the door of the marshalling panel room where the cable comes in. looking towards the I/O area, how many construction vehicles can you count along that line of sight? Vehicles like excavators, front loaders, back hoes, trenchers, or pile drivers?

Is the I/O that handles the data powered up?

Which LED's are blinking on the I/O controller?
Which LED's are blinking on the I/O modules?
Which LED's by the communciations connection are blinking?

David
 
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