by bdring » Sat Oct 20, 2012 2:12 pm
The diodes on the relays should always be used and a cap can help a little too in some cases.
You are not giving us much to go on like what drives the relays, what type of sensor it is, how the sensor attaches to the rest of the system or how long the cables are.
You want to use good wiring techniques, like twisting pairs of wires that go to relays and sensors or using shielding wires. You want the shortest lengths possible and separate the sensor from other wires as much as possible.
If the sensor is plugged right into some logic is only takes a tiny noise spike to cause a problem. Temperature is a slow changing thing. You could put a pretty slow R/C filter on the sensor. There are lot of RC filter calculators on the web.
Bart
"If you didn't build it, you will never own it."