RTD Temperature Spikes and Erratic Readings


Thread Starter

Ahmed Ali Khan

Hello everyone,

We have three CAT 3516C Gas Generators installed in our facility. 2 out of 3 runs under normal operation and third one acts as a standby. Two days ago we observed a tripping of the one of the Gas Generator occurred due to high temperature of Stator Windings of the Alternator. RTDs has been installed for sensing of the temperature in the stator. We considered loose connections in the wiring and thus carried out tightening of all the connections. The temperature was restored to normal values after tightening of connections. This generator was put on standby. Today this generator was in in stop condition and high temperature alarm was actuated and tripping signal was initiated although it was not running. The high value of the temperature reading stayed for around 2 minutes and then it returned to its normal value. The second time around, no rectification activity was carried out and the temperature returned to its normal value on its own. Has anyone ever faced such issue before? Any inputs will be highly appreciated.
As the temp had returned back momentarily means the issue is related to RTDs and its integrity. suggest to interchange the RTD connections to confirm the defective loop.
1) I'm not a generator guy, but I have to believe that the specific point that tripped the high alarm has to be in an error/fault log somewhere. That should point you in the right direction as to which sensor circuit to investigate.

2) An RTD high alarm is caused by a higher resistance at the analog input that the equivalent resistance value for the alarm temperature alarm value.

a) High resistance can be caused by loose wire or a single strand of multistranded (not solid) wire barely making contact, breaking open or coming loose from the connection.

One recent episode had terminal loose connection inside the RTD plug(jack), as shown in the photo here,


The cover piece partially held the wire in place, but the wire would make intermittent contact with the terminal screw. An open circuit is a very high resistance which can trigger an alarm.

As much as I like the convenience of RTD plugs and jacks, I'm always suspicious of others' wiring techniques, which can be pretty awful, so the first thing I suspect is plugs and jacks.

b) I've had RTD's fail internally presumably from vibration. The very thin wires inside the sheath can fail and make or break depending on temperature or vibration.

c) Over the years I recall having found two stripped terminal screws on the old style terminal blocks (my father's style), the dual row of screw connections with the raised bakelite dividers between screw connections.

d) I hate wire nuts for instrumentation wiring, but I run into them here and there. I've found more than one bad connection because the wires were not in contact with each other. Typically, a wirenut sized for three #12's but underneath are two 20g conductors.