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Rvator
12-03-2014, 12:26 PM
i noticed on last flight the OAT was reading 103 F at 3000 Feet which was totally incorrect as airfield temp was only around 8 degrees centigrade.

Aircraft is a RV7 with a dual AFS 3000 installation not built by me. I have located the OAT sensor under the left wing root and it looks undamaged before I investigate further does anyone know the best way to test whether the sensor is faulty?

Rob Hickman
12-03-2014, 04:40 PM
What is it reading on the ground?

What are your OAT calibration values?

Is this a new problem?

Rvator
12-04-2014, 10:06 AM
Hi Rob

Checked out the following today, to be honest I am unsure whether this is a new issue in as much as it was cld outside when I last flew and a reading OAT value of 103 F at 3000 feet was clearly not right!

I powered up the EFIS which showed a OAT value of 57 F.

By the time I found a pen and paper and then opened up the instrument calibration mode and selected OAT settings it showed:-

Configuration OAT 19.5 deg C / 67.0 deg F

1. Instrument OFF/ON OFF
2. Units FAHRENHEIT
3. Shift Adjust 0.0
4. Num Cal Points 2

AD_VALUE : 10144

Display. (deg F) AD VALUE
32.0 9571
66.0 10202


What stood out was the instrument showed 'OFF'. I changed that to ON and units to Centigrade and pressed 'Save' and exited back to the main display however this still showed a value of 67 F so I repeated the changes and ensured save was selected however when back to the main EFIS display this still showed a Fahrenheit reading but now 57 degs

The EFIS displays are AF-3000 Series Software Version 7.3.7-MVIS

The temperature in the hanger taken from a aircraft type OAT gauge was 6 degs C which should show a value of at least 42.8 degs F

Rob Hickman
12-04-2014, 10:27 AM
1. The F / C change is done from the EFIS > SETTINGS >OAT C/F main menu so you can switch it in flight.

2. Your calibration numbers look about right.

The software does a linear interpolation between the calibration points, using your numbers:


AD-VALUE : 10144
32.0 9571
66.0 10202

It should be showing 63F

Are you sure you are not getting heat from the engine on the probe when in flight?

Have you checked for loose OAT connections?

You might want to try replacing the probe.

Rvator
12-04-2014, 12:56 PM
Thanks rob for your info.

I will checkout the C/F selection from the Settings > OAT menu.

The OAT sensor is mounted underneath in the left wing root area so ought to be out of the engine exhaust.

You say the Instrument Calibration points appear right and that 63 F should be showing on the EFIS display is that suggesting then that the AD-VALUE of 10144 is being read as an input from the sensor by the software? If so that would imply the sensor is faulty as the temp in the hanger was more like 42 F.

Rob Hickman
12-04-2014, 02:26 PM
Adjust the second calibration point to the current temp and AD value and see what happens when you fly it.

Rvator
12-05-2014, 09:39 AM
Okay Rob I'll do that and let you know although I'm a little confused as to how I will know what the current AD value is going to be or does that get computed automatically when the second calibration temp which in this case is currently showing as 66.0 F is changed?

Rob Hickman
12-05-2014, 10:25 AM
The AD_VALUE in yellow in the OAT calibration menu is the current digital reading from the sensor

Rvator
12-05-2014, 11:45 AM
Okay Rob I will make some changes and feed back in due course what happens as it might be a while before I can do an air test.

Rvator
12-06-2014, 10:27 AM
Hi Rob - had a session at the airfield

Followed up on your advice and made some OAT configuration changes.

I determined from a thermometer today's temperature in the hanger was 10 degs C / 50 degs F

There are two EFIS displays in this RV7, on the screen at pilots side the existing configuration values were:-

Instrument Calibration
19.8 deg C / 67.6 deg F

1. Instrument OFF/ON ON
2. Units CELSIUS
3. Shift Adjust 0.0
4. Num Cal Points 2

AD_VALUE: 10747

DISPLAY (degF) AD_VALUE
32.0 9571
66.0 10202

After a bit of trial and error the following changes were made to the first calibration point setting only to get the actual Instrument Calibration values at the top to be 10.0 deg C / 50.0 deg F

DISPLAY (degF) AD_VALUE
50.0 11448


Confusingly the AD_VALUE: which started out at 10757 changed during the process to become 11448. Once the changes were completed the AD_VALUE: number fluctuated which I assumed was in response to temperature variations at the OAT sensor.

The changes were saved and returning to EFIS display the OAT value now showed up as 10 C

Given that the two EFIS units are the same and connected I had expected the changes made to be synchronised onto the second EFIS but this did not happen and it was necessary to make similar changes to the OAT configuration on that unit.

On the second unit the changes were made again only to Calibration Point Number One in order to get the Instrument Calibration values at the top to be 10.0 deg C / 50.0 deg F and to achieve this the actual AD_VALUE: became just 42 and once saved the OAT value on the EFIS screens also showed up as 10 C.

I did not undertake an air test so I have no idea whether the OAT value is going to remain static or change in line with the current outside temperature on the ground or what it will be when airborne.

Rob is what I have done the correct way to configure the OAT?

Why is there the need for a second calibration point and what will be the impact of making no changes to the settings given for that calibration point?

Why is there such a difference between the numbers of the two AD_VALUES: on either EFIS and also why don't they synchronise?

Rob Hickman
12-08-2014, 10:41 AM
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?

Rvator
12-09-2014, 09:23 AM
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?

Rob Hickman
12-09-2014, 06:40 PM
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.

Rvator
12-14-2014, 12:56 PM
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.