we are facing problem on bearing temp. , RTD PT100 reading change too much for rising and falling 70 to 80
we tight the terminations also replace the sensor by new one and same the problem.

also, we observed the reading some times become smooth and straight, the terminal box have all PT100 for the pump and all the reading are fluctuating
we need the recommendations.
Have you tried:

1) Exchanging the non-working RTD for another working RTD on the monitoring system? If so, what were the results? (If the problem "follows" the intermittent RTD to a new channel/input on the monitoring device, then there's something wrong with the interconnecting wiring, and/or the RTD. If the problem remains on the same input channel, then it's the monitoring device that has a problem.)

2) Using a decade box/RTD simulator on the monitoring device input channel the intermittent RTD is connected to? If so, what were the result?(If you connect a decade box/RTD simulator directly to the monitoring device and the signal doesn't drift over time, then it's the interconnecting wiring and/or the RTD.)

3) Disconnecting the interconnecting wiring from the monitoring device and the intermittent RTD and meggaring the wiring? (wire to wire, and wire to ground) If so, what were the results?

4) Have you confirmed the RTD wiring is properly terminated at the monitoring device channel input terminals and the RTD itself? Some monitoring devices are VERY particular about which wire is connected to the power ("excitation") terminal, and which wire is connected to the COMP terminal, and which wire is connected to the sense ("signal") input?

5) Some monitoring devices can use three-wire or four-wire RTDs; some have only three terminals, but a four-wire RTD is used. Are you certain of the terminations (wiring configuration)?

6) It's presumed the circuit is wired using twisted, shielded wiring/cabling, and that the shield drain wires are only terminated at one end. Have you verified the shield drain wire terminations? (Ideally, the interconnecting wiring would be three-wire, twisted, shielded cables, with an over-all foil shield and a bare drain wire (sometimes called a "triad" cable); what wire/cable is usefor the interconnecting wiring at your site?

7) You've said you tightened the terminations; did you check the terminal lugs for tightness? (Sometimes, crimp-on terminal lugs are not properly installed and can become loose over time.)

8) Is there any high-voltage and/or high current device nearby to the pump that starts and runs when the reading difference starts to increase, or that shuts down when the reading difference normalizes? (This would indicate there is some kind of induced voltage/current on the interconnecting wiring leads which is causing a problem.)

Please write back to let us know what you find!