If you have a dual screen system each with their own pitot/static and AHRS units, each screen will have its own OAT sensor and calibration. If you have two screens and a single AHRS you should only adjust the screen that is wired to the OAT sensor.
1. Do both of your screens have Pitot/Static connections and AHRS?
2. Was it warming up in your hangar when you did this, or were you touching the OAT sensor?
Rob Hickman
Advanced Flight Systems Inc.
Rob in answer I checked today and there is only one OAT sensor and to confirm there is only one set of Pitot/Static connections and logically these are attached to the EFIS display which is for the Pilot and it is this unit I used to make the OAT calibration changes on.
When I made the initial changes the temperature in the hangar was steady at 10 degs C and yes I did momentarily touch the sensor to see if the OAT value on the EFIS display would rise.
Today on power up the OAT value displayed was 14 degs C however the ambient temperature in the hangar was showing as 12 degs C as measured on a mercury thermometer.
Given that it is probably never going to be possible to get the EFIS OAT value to match the measured OAT temperature I guess a 2 degs C differential is going to acceptable assuming that the error is linear so it is not worth trying to get the OAT calibration to be more accurate.
Can I ask again why is there the need for a second calibration point and what will be the impact of making no changes to the settings that are already entered for that calibration point?
After confirming that there were no Pitot/Static connections onto the second EFIS display then after it had powered up I checked the Instrument Calibration settings for the OAT and saw that the Instrument OFF/ON value was at OFF from this can I assume that there will be no interaction between this unit and the master unit in respect of the other OAT calibration values?
Can I ask again why is there the need for a second calibration point and what will be the impact of making no changes to the settings that are already entered for that calibration point?
It uses both calibration points and if you only adjust one you are only correcting one point. Most people never need to adjust the calibration values. If you have a really old unit you might not have the latest OAT circuit design or yours might have a bad component. If it does not seem accurate send us the screen and we will update it.
After confirming that there were no Pitot/Static connections onto the second EFIS display then after it had powered up I checked the Instrument Calibration settings for the OAT and saw that the Instrument OFF/ON value was at OFF from this can I assume that there will be no interaction between this unit and the master unit in respect of the other OAT calibration values?
Your EFIS without the Pitot/Static and OAT sensor should be getting the calibrated temperature from the other EFIS. If they do not display the same value something is wrong, call me from the plane.
Rob Hickman
Advanced Flight Systems Inc.
Rob have now done an air test with following result.
At initial power up the OAT showed up as +13 C and dropped to +10 C. The area met forecast for the day gave:-
1000 feet +5 C
2000 feet +2 C
5000 feet -4 C
After take off and climb the OAT value increased from +10 C until +14 C at 3000 feet after which I gave up checking as clearly there is an issue!
As the OAT displayed during the air test increased numerically by a number that might have matched the expected temperature decrease with the increase in altitude and assuming that there is not an issue with the sensor itself is there any possibility that the OAT sensor could have been connected in reverse?
In respect of the second EFIS display I can confirm now that there does not appear to be an issue with that unit as the OAT value matched what was being displayed on the main display.
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