Dynon sending unit internal wear

[chckwlsn@yahoo.com]

Have you ever wondered what happens when the sending unit on your Fuel Press/Oil Press/Oil Temp/ etc goes bad? On our Dynon unit when the resistance on the unit drops, the reading on the engine monitor goes to the highest reading (and so does your blood pressure). We have had a fuel pressure reading that started to be inconsistent, and then would stay at 99PSI when the boost pump was on or the engine was running.
Trouble shooting the unit, I found the readings to be accurate near the low end, but then as the pressure rose to the normal levels, the indication was high. This was confirmed with an ohm meter at the sending unit. The high pressure reading was basically ?open?, the same as if the ring terminal was removed from the post.
A spare sending unit was installed and it appears all is normal. Have you ever wondered what breaks down as the unit wears? Here is the photo of the sending unit with the cover cut off:
http://i54.tinypic.com/ejc3mb.jpg

Take special note of the small wear mark on the resistive material to the right of the ?pointer?. This is evidently where the fuel pressure normally runs at 25PSI on our injected engine. It also is why once the ?pointer? moves to the left of the wear spot, the resistance goes to zero and the engine monitor displays 99psi.
Hope you find this interesting.

[SHIPCHIEF]

Yep;
Good classroom presentation.

[az_gila]

Interesting wear mark. How was the sensor mounted?

[chckwlsn@yahoo.com]

The Fuel pressure sender was firewall mounted on the manifold block supplied from Vans.

[rv8ch]

I never knew what was inside those things, thanks for opening it up. I have a couple of spares, now I'm obliged to have a look inside. (Included a smaller version of your pic below)

[DaveG]

I have to replace mine every 2 years. The normally steady reading of 28psi starts to become a bit inconsistent such as dropping to 25psi for a second then back up to 28. Gradually this becomes worse and the readings jump from low to high. Mine is also mounted on the firewall with the vans manifold block. I now keep a spare.

[Scott Hersha]

Thanks for the picture. Very interesting and also an unbelievably crude mechanical device. With all the elecronic gizomos around these days, isn't there some solid state sensor the size of say, your fingernail, that will sense this pressure and last 2 lifetimes? I built a Rocky Mountain 'micro encoder' on my first airplane (from a kit), that measured temperatures and pressures (airspeed and altitude). They were solid state - no moving parts - and once tested, were very accurate and in theory would last practically forever. Probably not a lot of money in pressure senders.

[Ironflight]

Originally Posted by Scott Hersha

Thanks for the picture. Very interesting and also an unbelievably crude mechanical device. With all the elecronic gizomos around these days, isn't there some solid state sensor the size of say, your fingernail, that will sense this pressure and last 2 lifetimes? .

Yes - Garmin supplies them the G3X system - compact, light, accurate...and they have real connectors on them!

[Brantel]

These type of sensors are used all over the place with different brands of EFIS/EMS systems not to mention millions of land based vehicles. Not exclusive to Dynon and I doubt any EFIS/EMS maker manufactures their own sensors.

It would be nice to have solid state alternatives though.

The problem is that the EFIS/EMS needs to either be able to be calibrated to or have the sensor profile embedded in the setup options to be able to make the switch.

I think at least one EFIS/EMS maker is providing SS sensors for their EMS.

[erich weaver]

My fuel pressure sensor from GRT has a small form factor that is very different than the picture posted, so I suspect it is solid state. Curiously, my oil pressure sensor is like the picture, so not sure what gives there.

Erich