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G3X OAT probe cal.
- Thread starter n700jl
- Start date
Where do you have the probe mounted?
Hello Jon,
The GTP 59 is a very high accuracy TSO'd RTD type OAT probe that doesn't require any calibration. These probes generally either work and work well, or they don't.
I suppose this static reading is in the shade of your hangar where there isn't any pavement heating going on which might influence the air temperature under the wing?
When I power up my avionics in the hangar in the morning I have pretty amazing correlation between OAT, oil temperature (also high accuracy RTD probe), and all the high sensitivity type J CHT probes. The higher range type K EGT probes even agree pretty well.
With everything cold and at ambient in the hangar, how do the oil temperature and OAT probe readings compare?
Thanks,
Steve
Another thing to do is to check for loose or dirty connections all throughout the circuit that connects the GTP 59 to the GSU 73, especially the ring terminal at the base of the probe body. This type of temperature probe is simply a precise resistor whose resistance changes with temperature in a predictable way. Just a few extra ohms can cause a significant temperature offset.
- Matt
- Matt
jthocker
Well Known Member
I was suspicious that my probe was reading High also. Walked into the hangar and fired up the G3X and had solid 60 degrees on all CHT's and EGT's but 62 on the OAT. Removed the probe and scotchbrited the metal under the ring terminal and will check again tomorrow.
Having this problem with OAT probe, never realized that it was off by 4 degree celcius... pickup ice on wings in IFR last week at 4 degree celcius outside, didn't melted, dropped altitude by 1000 ft then ice melted... Tested the probe in icy water at 0 celcius... confirmed it off by 4 degree. Contacted garmin regarding problem and they told me no warranty and i have to change probe....
Really bizarre that there is no offset calibration in configuration mode to adjust it... By the way Aspen and MGL have this kind of calibration available on their products...
Regards,
Louis
Really bizarre that there is no offset calibration in configuration mode to adjust it... By the way Aspen and MGL have this kind of calibration available on their products...
Regards,
Louis
PilotjohnS
Well Known Member
If they add a calibration, someone is bound to screw it up more than 4 degrees
Jetmart
Well Known Member
We can calibrate our fuel tanks but not OAT?
PilotjohnS
Well Known Member
A gallon of water can be accurately measured by most anyone. There are lots of containers around that has a gallon capacity within 1%, not to mention most fuel pumps. Whereas I have yet to see a hangar with a calibrated temperature standard.
RV8JD
Well Known Member
As does Dynon.
Carl Froehlich
Well Known Member
Remember, RV speeds of 170+ knots does start touching into ram air heating (perhaps a degree F or two). I consider ice possible when OAT reaches 34 degrees. Now add the condition of sub-cooled liquid if clipping the top of a build up and you get ice.
I moved my OAT probes to the first bay in the wing as the areas near the tail always read higher than actual.
Carl
Doesn't make any sense i have to change a 600$ probe for something it could be easily integrated in the software and make this working fine. As Garmin's competitors does...
I got the specification sheet from garmin and at 500 Ohms it should be 0 celcius.... tolerance is 499.40 to 500.60.
There is a small text funny to read at the bottom of the spec sheet :
''Note: There are no production tests performed on the probe. Any testing required will be at thediscretion of Quality Assurance, and will be performed as a part of receiving inspection.''
PilotjohnS
Well Known Member
If the specs are that tight, I would look at installation. Make sure ring terminal is clean, no corrosion, and maybe add a ground wire from wing to fuselage. Any resistance more than 0.4 ohms will affect reading it seems. JMHO
Are your (resistantce type) fuel gauges accurate still?
low cost sensor : https://vansairforce.net/threads/temp-sensor-for-gad13-or-gsu25.224929/
and curve for pt500 :
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Ground is only for bounding not for reference to GSU25... my airplane is composite... I already made test with wire connected to ground and no difference...
The probe is off by 6 ohm in regards to the spec sheet... tested with different temperatures and it's off linear...
For your info... my fuel gauge are CIES and no issue at this point...
Before Garmin will make an update on their software regarding this issue, i will test a resistor in parrallel to sensor and adjust the offset to 500 ohm at 0 degree celcius... then verify if it's correlate with different temperatures references.
Regards,
Louis
Ridders
Member
My garmin probe is pretty accurate, I installed it under the wing, it doesn‘t get any heat from the engine exhaust and reads same as the LCD one I have in panel.
One thing to watch for is Mr Magoo fuelers!
I had one of these jokers attach his grounding clip, onto my lovely new garmin temp probe.
- theres two massive exhaust pipes near by for that!
One thing to watch for is Mr Magoo fuelers!
I had one of these jokers attach his grounding clip, onto my lovely new garmin temp probe.
- theres two massive exhaust pipes near by for that!
