T/C reads erronious values from inside runing engine.

[TC_Measurements]

Thermocouple measurements read off by hundreds of degrees when reading through SCXI/LabView (modified version) when T/C is located inside a running gas turbine with a generator.  However, values read correct when T/Cs are plugged into handheld readers.  T/Cs go to SCXI-1102 amp before going to SCXI signal conditioner.  Can the SCXI system be setup to read values steady and correct like the handheld readers?

[devchander]

Hi,

as long as you have configured the channel correctly( that means selected the right  thermocouple type, cjc source and its dependencies, expected minimum and maximum values, units, channel name, physical channels) you should be able to get a pretty stable temperature reading.

check if these are properly configured if you are getting such a large offset in your readings.

a lot of facors can contribute to such large variations apart form these settings.

In fact a lot of discussions have taken place in this forum regarding tc measurements.

just go through all previous posts and you might get clarifications to your query

Regards

Dev

[Conseils]

Could be an earth loop, it's a common problem with connecting things into a P.C.

It's fairly easy to check, if the thermcouple reads steady when physically close to the engine but not touching then get noisy as they touch the case it's likely to be an earth loop.

Suggestions....

  Battery operation for all the aquisition equipment (not always practical).

  Electricaly (mineral or sheathed) insulated thermocouples (not always space / possible).

  Sort out the loop problem by arranging the ground potentials (tricky and time consuming / could be a problem with a PSU).

  Try measuring the voltage between the back of the computer chasis and the turbine earthpoint (you may be in for a bit of a supprise).

[Russ@Davis]

One other specific issue: is the lead from the TC in the same conduit / cable tray as AC electrical wiring?  This will cause an induced voltage and  can create an offset and/or erratic reading.

If the grounding is an issue, you can get TC's probes that are both grounded and ungrounded.  I have had some applications where I was required to use an ungrounded TC.

RS

[smithdb1960]

I use SCXI systems with 1102 and 1303 for making grounded and un-grounded TC measurements in engine test cell without issues. The 1303 when used for grrounded TC measurements will need to have the internal resistor removed.