Telic Engineering / Field notes / Week 44

Loop checks LM

Week 44Remco Petersen

Sheet 44

Field note, first posted on LinkedIn.

Loop checks start at the sensor. Signal loops from sensors on an aeroderivative gas turbine package through the junction box and control cabinet to the HMI, with six numbered loop check points PACKAGE CONTROL ROOM GAS GENERATOR PT LUBE OIL JB HMI 01AT THE SENSORnot at the terminal 02TAG, RANGE, UNITSsame at card and HMI 03THERMOCOUPLEStype K all the way 04RTD WIRING3 or 4 wire right through 05SPEED, VIBRATIONsignal in at the pickup 06ALARM AND TRIPcheck the action

A loop check is not done when the HMI shows a number.

How I approach loop checks on an LM package:

  1. 1.Start at the sensor, not the terminal. Inject at the field end, so junction box, marshalling and I/O are proven too.
  2. 2.Tag, range and units the same on the card, in the application and on the HMI.
  3. 3.Thermocouples: right extension cable and connectors all the way (type K on the LM2500), polarity checked.
  4. 4.RTD wiring: 3 or 4 wire right through, so lead resistance is compensated.
  5. 5.Speed and vibration: signal in at the pickup end, conditioner matched to the sensor.
  6. 6.Alarm and trip: drive every signal through both. Check the action, not only the reading.

What do you check first in a loop check? And what would you add?

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Remco Petersen
Telic Engineering B.V.
Markenplein 24, 1011 MV Amsterdam
The Netherlands
remco.petersen@telic-engineering.nl
+31 6 51345316
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