How do you monitor performance of instrument loops in your plant or facility? Instrument loops can be trip and control loops which can be in a large number from several hundreds to thousands. Even in a small plant like our ours, there are 300 to 400 loops with one or two engineers looking after them. So how to priortize the monitoring exercise and maintenance/testing works on them? How to identify which loops start to show performamce deteriorations and to rectify as soon as possible? appreciate your comments. TQ

Josh -

This is not my area of expertise but I was just at a paper plant and they had an awesome program called Instrument & Electrical Precision Maintenance. They took the structure and lessons from a mechanical PdM program.

They said 90% of control loop problems could be fixed by resolving and improving - Precision Control Valve Performance (50%) - Precision measurement (20%) and Precision tuning (20%).

As you state there a too many control loops to launch a program around 100% of the population so the key is to identify "critical loops" in each area.

Also need to establish precision standards for maintenance work practices, upgrade to precision calibration tools and implement Lambda Tuning methods.

They did warn that this is no quick fix and required a high level of commitment, training, training and more training, making it an integral part of planned work (in the CMMS).

I had never seen such a comprehensive program and needless to say - I left the plant very impressed.

I plan to learn more and hopefully will be bring more knowledge resources to Reliabilityweb.com and hosting learning zone sessions at IMC in the future.

I am working on getting permissions to share more soon.

Good luck and I hope others will post some of the "secrets" they know as well.

Terry O

Josh,
Components in instrument loops may degrade just as mechanical components do the same. Here you generally run calibration PM's to monitor and trend the degradation.


Take Vibration instrumentation as an example.
I once worked in facility where they had all the vibration monitoring equipment labeled as "NPCR" (No periodic calibration required).
The racks were wired to the trip circuits as well. On first pass I found 17 out of 34 sensor loops bad.

How much do you suppose it cost them in false trips? What kind of reliability do you think they had?

Our monitoring method was that we wrote a calibration procedure and assigned it to a PM schedule. The procedure checked the sensor and instrumentation response to the manufacturers calibration curves and performed a functional test of the entire loop at different frequencies with a portable shaker(NIST traceable of course).

In Nuclear Power Plants your In Service Inspection equipment calibrations must be checked quarterly and fall within the prescribed limits. This was one of the jobs of the PdM Engineer/Tech.

Digital control systems should be able to proivde some means of detecting or capturing changes in the instrumentation that could trigger a Condition Based PM event similar to the one desribed above.

Regards

We do have PM fo calibration, validation, control valves, trip & control loop testing etc.
However this is human-dependent and subject to inconsistency. Thus, we are looking for a computer-based program to monitor all the instrument loops by itself & periodically give reports which give the top-ten problematic loop performance. The control engineer can prioritize his action to those top ten loops using those precision maintenance tools mentioned. Perhaps you could elaborate more on the usage of the digital control systems for this purpose. TQ

Josh,
I don't know of any such systems that exist other than features that may exist in a controls system such as a PC based SCADA or something similar. Analog equip. would have to have some interface to capture and digitize the data. Probably an expensive project but not impossible.

What we did is put data sheet in the cal. procedure that captured the info. We then sat dow nand eneed it into excel and trended it. Long an laborous but effective.

I have done what you want to do the past and will help you if you want.

Regards

Actually I'm looking for somebody to share experience in using Matrikon ProcessDoctor or equivalent. I came to know about it after reading PTQ. Tq