GI 275 OAT accuracy

the400kid

the400kid

Pre-takeoff checklist
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Sep 2, 2013
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FLAAV8R
I have a new GI 275 ADI connected to a GTP 59 OAT probe. When I look at the OAT on the display, it's always 2 degrees cooler than four other temperature sources that I have (which are all in agreement), including a digital thermometer. I always conduct this test first thing in the morning with the hangar doors closed so that sunlight doesn't influence the readings. My first question is, has anybody else experienced this? My second question is, is there an offset in the -275 setup that would allow me to adjust it upward by 2 degrees?

The OAT needs to be accurate so that the built in air data computer can calculate the true airspeed and wind direction and I'm concerned that these elements are displaying incorrectly, including the crab angle on the GTN.
 
There is no adjustment for the GTP 59. It's a restive probe sensor and could be thrown off by poor crimps or splices in the system... however higher resistance = higher temp, so the fact that you are reading cooler wouldn't really lend credence to that. It's supposed to be accurate to w/in +/- 1.5 C, so it's pretty close to being within tolerance given the other probes have their tolerances as well so there would likely be some overlap there. Could perhaps try swapping another probe to see if it changes, but since they are like $400+ that's a tough sell :)
 
Don't know if it's relevant, but my JPI can be calibrated up to 10 degrees for probe error. Is there any way to calibrate the 275?
 
The location of the temp probe will determine the accuracy of the reading. For that purpose the panel instrument is usually adjustable.
 
MBDiagMan said:
The location of the temp probe will determine the accuracy of the reading. For that purpose the panel instrument is usually adjustable.
Click to expand...

Your statement would be true while flying, but when on the ground and taking a reading before opening the hangar door, the probe should give the same reading as all the others.
 
Yes, but when is the OAT more useful? On the ground before opening the door or in the air?
 
Resistive temperature sensors are nonlinear. It would not surprise me to see a little variance. It may not even be variance in the sensor itself.
 
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