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I have a circa 2013 Seaboard pyrometer in a QSM 770 not reading this season at startup. It has power as it’s lit but the gauge sits at 100, doesn’t move.
what’s changed? Entirely new electronics package and dashboard, engine was heavily serviced including new turbo and exhaust. The sensor was not touched in all of this. Wires look OK, connections look OK.
what’s the easiest and fastest way to isolate whether it’s gauge, sensor or wiring as the problem? Can I leave sensor, wire as is and probe the 4 pin connector with an ohmmeter to isolate the issue?
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I will chime in for anyone else looking for info.
These probes are thermocouples. There are many different types for specific uses and for more accurate reading at lower temps.
I suspect your is a “K” type. which can handle the heat easily but is somewhat less accurate than some others. In this case the K is more than good enough.
They are NOT resistive devices. They are two different metals joined at the points/ends. That join when heated will produce a voltage. As the temperature rises so does the voltage. Those voltages are well documented and are used by the guage or meter to decode and present the temperature.
Yes, resistance can be used to confirm there is continuity but it is NOT always reliable as a test of the thermocouple itself.
There are types that are grounded internally at the probe which can show continuity even though damaged and no longer able to read properly. The joint can be broken but jammed against the probe casing to show continuity yet the ability to produce the needed voltage is gone.
Others, when the cable had been damaged away from the heat source and the conductors pinched together can show continuity.
I have seen both in my work.
When you have problems of course check the connections, plugs and so on. As Tony suggested a torch can be used on the probe end itself to confirm yea or nay. They are not repairable unless it is simply a poor connection as was the case in this thread..
If you need to extend the lead length there is specific wire needed to do so or the voltage can be altered leading to misreadings. To be clear we ignored this requirement and it was still accurate enough for our machines. But in some cases it can cause trouble. Best to order a replacement when needed with more lead length than needed and coil the excess up or trim it back. suspect for exhaust temp reading though a copper wire extension would be acceptable.
JMO
Last but not least and this catches many folk on K. The RED wire is the negative. Do not follow typical wiring practice with the lead colour coding or the polarity will be backwards.
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