Anyone have a spare windshield OAT gauge

[Stephen]

I posted this in the parts section, but wanted to ping here as well. I have an EDM 900 that is giving me crazy temp readings. I have been working with JPI support on it and am on my second probe, second location (now in fresh air inlet) and still the thing doesn't work. I have to use the full -10 deg to get it to read +1 on field temp then the think slowly climbs in indication so at altitude it is always reading 35 - 45 deg C.       So......while I troubleshoot it; does anyone have a *cheap* but *functional and accurate* round windshield gauge that you may have pulled for your engine monitoring system that I could get and use while I get this mess straightened out? I need something to pinch hit for fall IMC for obvious reasons. 

 

Thanks as always,

 

Stephen

[AH-1 Cobra Pilot]

Are you looking to drill a hole in your windscreen?  I have seen that done on other aircraft, and it seems to work well.  It is also the first place to catch ice, so it makes a good warning.  It would scare me to risk a windscreen crack, though.

Some boob mounted my OAT probe on the aluminum baffle right in front of the right-front cylinder.  (Pun intended.)  I constantly get  readings that I know are too high.  My mechanic suggested relocating it to another location, but what he suggested as easiest also put the probe where it would constantly snag on anyone checking the oil, etc.  Any recommendations as to a new probe location?

[Stephen]

My original probe was through the windscreen. I have the 1st (defective) probe that JPI sent me in it currently to plug the hole, and the active one in the pilot side fresh air inlet intake. I can get pictures for you. I have heard either that inlet or in a wing inspection panel OB of the gear are the best places. Search for OAT under my name and there is a thread there with (generously) donated pictures from the Mooney forum guys.

[RLCarter]

Looking at your other post on issues with your JPI, my guess would be head unit (possible grounding issue) probes do fail but several at the same time is rare, temp probe should be out on the wing so your not reading the heat from the cowl area

[Alan Fox]

Try polarizing the leads , the temp probes can be polarity sensitive , 

[Bob_Belville]

4 hours ago, Stephen said:

I posted this in the parts section, but wanted to ping here as well. I have an EDM 900 that is giving me crazy temp readings. I have been working with JPI support on it and am on my second probe, second location (now in fresh air inlet) and still the thing doesn't work. I have to use the full -10 deg to get it to read +1 on field temp then the think slowly climbs in indication so at altitude it is always reading 35 - 45 deg C.       So......while I troubleshoot it; does anyone have a *cheap* but *functional and accurate* round windshield gauge that you may have pulled for your engine monitoring system that I could get and use while I get this mess straightened out? I need something to pinch hit for fall IMC for obvious reasons. 

 

Thanks as always,

 

Stephen

I have one setting on a shelf in my hangar that was mounted through the left window before I added an Aspen and an EDM 930 each of which reports OAT. I figured 2 OATs that did not quite match was enough so I removed the old mechanical probe. 

I'd be happy to lend it to you. I hope you already have a hole to mount it in! 

Send me a PM

[CWM20f]

I also have one if needed. Just let me know. 

[carusoam]

Getting accurate OAT on a JPI should be an incredibly easy thing to do right.

It would be wasted effort chasing down alternative ways to get the OAT from a different resource.  (A pilot has to do what he has to do)

Expect something goofy has happened with the existing sensor and track it all the way back to the JPI Head.

The OAT sensor is a thermocouple.  Two wires of differing materials generate a temperature sensitive microvoltage at the point they are soldered together.  The JPI is essentiall a voltage meter calibrated in °F.

There are two or three different common thermocouples.  Type J, Type K, and others....

Make sure you have the right type to match your setting in the JPI.

It is probably a Type K thermocouple. Check to make sure. Then check the settings in the JPI.

The JPI manual is available on line and is worth a good read...

Things that can cause a TC to not work...

• Hooking them up with reversed polarity.
• having the wrong setting to match the TC type.
• Wire Extensions not made of the same wire type to match the thermocouple.
• Wire extensions reversed polarity.
• accidental grounding to the airframe.

Think Of It As two wires twisted together at one end running all the way back to the JPI in the panel. Not touching anything else along the way.

The only time you get eronious Numbers is when the sensor is sitting out in the sun or in the warm air stream exiting the cowl.

The factory location for the sensor is under the wing out away from heat sources in the shade.

Is that any help?

For Some reason JPI customer service isn't very helpful.  If you can follow the logic here, you can probably get this worked out without help from JPI...?

PP Thinking only, not a mechanic.

Best regards,

-a-

 

 

 

[Stephen]

On 10/16/2017 at 5:08 PM, RLCarter said:

Looking at your other post on issues with your JPI, my guess would be head unit (possible grounding issue) probes do fail but several at the same time is rare, temp probe should be out on the wing so your not reading the heat from the cowl area

Thanks guys I'll try the polarity and review grounding and the type setting issues. That said I have a hole in my windshield already (original probe from removed system was there); the defective probe from JPI (didn't meet resistance spec) and I need JPI wants it back for RMA.  I figured that I might be able to put a working analog gauge in it to plug the hole and give me a reasonable reading while I figure out the problem. 

[Stephen]

On 10/16/2017 at 9:32 PM, CWM20f said:

I also have one if needed. Just let me know. 

PM sent. 

[Stephen]

On 10/16/2017 at 9:08 PM, Bob_Belville said:

 

I'd be happy to lend it to you. I hope you already have a hole to mount it in! 

Send me a PM

Hi Bob, huge thanks for the offer; I may still take you up on it and will PM if so. I PMd CWF (he's next state over in TX) let me see what the $ scoop is there (if I get the EDM working I may make a permanent windshield plug out of it) . 

[Bob_Belville]

7 hours ago, Stephen said:

Hi Bob, huge thanks for the offer; I may still take you up on it and will PM if so. I PMd CWF (he's next state over in TX) let me see what the $ scoop is there (if I get the EDM working I may make a permanent windshield plug out of it) . 

Stephen, I have since replaced my windows but before I did that I had plugged the OAT hole in the side window with clear silicone. I preferred that patch to having the post of the gauge hanging out, costing me some fraction of a knot!

[Stephen]

On 10/18/2017 at 7:13 AM, Bob_Belville said:

Stephen, I have since replaced my windows but before I did that I had plugged the OAT hole in the side window with clear silicone. I preferred that patch to having the post of the gauge hanging out, costing me some fraction of a knot!

Thanks Bob, I was talking with another mechanic about plugging it with silicone, wondering if it would hold up ok. Sounds like it does. Like you once I am through my EDM teething problems and get OAT back on the black box, I would rather delete the windshield OAT snorkel.  Good call thanks for sharing.

[Stephen]

I went ahead and ordered a basic OAT gauge (scott type) through the windshield to get by for now...so cancel the APB on finding a used one.