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thermocouple readings off engine block

I am trying to take temp readings from a small engine using thermocouples. One of the readings is off the block of the engine. When running the engine without the ignition (using the dyno) everything is normal but when I turn the ignition on, I get really large spikes in my readings. I think it has something to do with the spark from the ignition causing a potential difference. Is there any way to get rid of this, or is there something else that could be causing the error?
Thanks
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Hi tzj,
 
It seems like what you may need to do is either some signal conditioning in hardware or some signal processing in software. I am not sure as to which hardware you are currently using to take your measurements, but some of our products can be used in conjunction with a signal conditioning block which can help you filter out unwanted signal components. The spikes you see in your reading are made up of high frequency components and therefore, they can be eliminated by choosing a conditioning block with the appropriate low-pass filter. The other method would be to use a digital low-pass filter in software to post-process your readings. If you are using LabVIEW, you can find your filter functions by accessing the Signal Processing » Wfm Conditioning palette. The  Filter express VI would probably the way to go if you are not too familiar with filtering as it is the easiest to use. You can also refer to some of our shipping examples in LabVIEW, which can be found in your Example Finder under Analyzing and Processing Signals » Signal Processing.
 
I hope this helps,
 
S_Hong
 
 
S_Hong
National Instruments
Applications Engineer
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