gauge accuracy

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Dana

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How accurate should I expect an engine gauge be? 1%? 2% 5%?

Never had any trouble with the oil temp gauge in my Hatz until yesterday, when it maxed out at 150° on a hot day when it should have been at least 190°, as it was on the previous flight. Can't think of any scenario that would make my engine run 40° colder than normal, so the gauge is kaput. It's an old Aircraft Spruce branded "Arrow" gauge that may be original to the plane.

A year ago the oil pressure gauge went and I replaced it with a Bosch automotive gauge with no problems. Today I bought the matching temp gauge, figured I'd check it in boiling water, it read 205° or slightly less when it should have been exactly 212°. So, around 3% low. I could exchange it for another one... which might be better... or might be worse.

I know, just remember the offset and mark the redline appropriately. I'm just spoiled by the lab grade gauges I use at work.
 

TFF

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I think that it trends correctly makes the error less of a problem. If it was on and off or had a progress reading, I would be more worried. How much money do you want to pay? You can get turbine quality gauges at a couple of thousand each.
 

TiPi

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Looks like it is pretty close to Standard in his part of the world today:

For some reason 3% sticks in my mind as being the norm for automotive aftermarket gauges.
That would be QNH, you need the QFE (density altitude) to calculate the boiling point.
I live at 750m (2,500’) and on a normal day, the boiling point is around 97deg C eg 3% less.
 

Dana

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Well, I'm close to sea level and the pressure right now is 30.02, so that's not it. An electronic thermometer (also unknown accuracy) read 212-213.
 

Skippydiesel

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How can you expect, your off the shelf , relatively (to laboratory & "master" gauges) cheap aircraft or automotive gauges to be accurate?

Laboratory equipment;
  • Is subject to routine calibration tests/adjustments to maintain accuracy/accreditation.
  • May cost many thousands more (per gauge) than those found in light aircraft/cars/trucks/etc due to the quality of materials, the standard of build, etc
  • Operate in "known" environments/conditions of temperature, pressure, vibration (lack of) orientation, etc
Master gauges also have many of the above characteristics, usually to lesser extent .

The best you can expect from a light aircraft gauge, is that they are reasonably (subjective assessment) close to accuracy when first purchased - this will almost certainly degrade over time (operational hours) to the point of failure.

Pilots should view gauges as indicative. Regularly log readings (I do this after every service & randomly between) so as to establish a "normal"/reference reading. By doing this it may be possible to make a judgement call - is the read out (gauge and/or sender) itself changing or is it the engine system????
 

Dana

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When I buy a gauge for industrial use, I expect to have the accuracy given in the specs. Of all the temp gauges I looked at on the aircraft spruce website, only one (a Westach electric gauge) listed the accuracy as 2%. But as @TFF pointed out, repeatability is more important than absolute accuracy (within reason).
 

reo12

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Decades ago we found that many of the non-certified CHT and EGT gauges to be inaccurate. We had quite a number CHT's that were indicating temps that were over 25 degrees and even over 50 degrees in error. Some were using copper wire as extension leads but some were using the proper extension leads. EGT's - some folks were reporting easily 75 to 100 degrees in error.

I seem to recall there being some discussion of this in one of the UL magazines - possibly Ultralight Flying.

I actually bought low melting point metal with a specified melt temperature to use for testing my CHT temperature gauge. Once that was established as being accurate, I spent a day doing ground testing of spark plug colors and CHT/EGT indications at various sustained throttle settings.
 
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