|
-
POSTING RULES

-
Donate yearly (please).
-
Advertise in here!
-
Today's Posts
|
Insert Pics
|

09-02-2011, 06:12 AM
|
|
|
|
Join Date: Mar 2005
Posts: 41
|
|
Dynon sending unit internal wear
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.
Last edited by chckwlsn@yahoo.com : 09-02-2011 at 06:25 AM.
Reason: photo did not come up
|

09-02-2011, 10:06 AM
|
|
|
|
Join Date: Mar 2008
Location: Seattle
Posts: 1,412
|
|
Yep;
Good classroom presentation. 
__________________
Scott Emery
http://gallery.eaa326.org/v/members/semery/
EAA 668340, chapter 326 & IAC chapter 67
RV-8 N89SE first flight 12/26/2013
Yak55M, and the wife has an RV-4
There is nothing-absolute nothing-half so much worth doing as simply messing around with Aeroplanes
(with apologies to Ratty)
2019
|

09-02-2011, 11:52 AM
|
 |
|
|
Join Date: Jan 2005
Location: 57AZ - NW Tucson area
Posts: 10,011
|
|
Interesting wear mark. How was the sensor mounted?
__________________
Gil Alexander
EAA Technical Counselor, Airframe Mechanic
Half completed RV-10 QB purchased
RV-6A N61GX - finally flying
Grumman Tiger N12GA - flying
La Cholla Airpark (57AZ) Tucson AZ
|

09-03-2011, 09:18 PM
|
|
|
|
Join Date: Mar 2005
Posts: 41
|
|
The Fuel pressure sender was firewall mounted on the manifold block supplied from Vans.
|

09-04-2011, 12:06 AM
|
 |
|
|
Join Date: Feb 2005
Location: LSGY
Posts: 3,198
|
|
Very interesting
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)

|

09-05-2011, 06:53 AM
|
|
|
|
Join Date: Jan 2005
Location: Winslow, UK
Posts: 18
|
|
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.
__________________
David
G-RVDG RV-9 (ex 9A)
|

09-05-2011, 07:36 AM
|
|
|
|
Join Date: Jan 2005
Location: Cincinnati, OH
Posts: 1,558
|
|
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.
__________________
SH
RV6/2001 built/sold 2005
RV8 Fastback/2008 built/sold 2015
RV4/bought 2016/sold/2017
RV8/2018 built/Sold(sadly)
RV4/bought 2019 Flying
Cincinnati, OH/KHAO
JAN2020
|

09-05-2011, 08:23 AM
|
 |
VAF Moderator / Line Boy
|
|
Join Date: Jan 2005
Location: Dayton, NV
Posts: 12,256
|
|
Quote:
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!
__________________
Paul F. Dye
Editor at Large - KITPLANES Magazine
RV-8 - N188PD - "Valkyrie"
RV-6 (By Marriage) - N164MS - "Mikey"
RV-3B - N13PL - "Tsamsiyu"
A&P, EAA Tech Counselor/Flight Advisor
Dayton Valley Airpark (A34)
http://Ironflight.com
|

09-05-2011, 08:49 AM
|
 |
|
|
Join Date: Mar 2006
Location: Newport, TN
Posts: 7,496
|
|
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.
|

09-05-2011, 09:47 AM
|
 |
|
|
Join Date: Aug 2006
Location: santa barbara, CA
Posts: 1,682
|
|
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
|
Posting Rules
|
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts
HTML code is Off
|
|
|
All times are GMT -6. The time now is 03:59 AM.
|