Pyrometer circuits are sensitive instruments that amplify uV/mV signals into something the gauge can read...Electrical noise, grounding issues, partial circuit failures can all be to blame.
I would start troubleshooting in this order.
1.Change the ground/check the ground.
2. Look for things in the wiring that can give off noise and give your pyro a fit. If you see something obvious move the wires or install some chokes on the line to help suppress noise. in this instance, near the gauge would be better.
3. if all else fails ask the manuf if it's possibly a bad gauge.
I would start troubleshooting in this order.
1.Change the ground/check the ground.
2. Look for things in the wiring that can give off noise and give your pyro a fit. If you see something obvious move the wires or install some chokes on the line to help suppress noise. in this instance, near the gauge would be better.
3. if all else fails ask the manuf if it's possibly a bad gauge.
