lml@lancaironline.net Mailing List Archive

Nice work, Brent. I've been in the pressure sensor business for quite a while and I don't know of a commercially-available millivolt output sensor that is environmentally packaged with a "real" connector; so your approach may be the only option. In my opinion, a millivolt output sensor without a fully sealed package, connector and wiring is unacceptable.

Just another comment about loss of oil pressure: It's my understanding (please correct me if I'm wrong!) that if the engine truly loses oil pressure the prop governor will also cease to function, creating an overspeed condition. So a zero oil pressure indication without any change in engine speed is cause for concern and immediate landing, but not panic. On the other hand, I have read a report of an accident where the engine speed started to surge and the pilot assumed the governor was acting up. A minute later the oil pressure went to zero (oil leak caused loss of oil). Turns out if he had recognized the surge as a loss of oil pressure he could have made it to the nearby airport. So my "plan" is to go into panic mode if the engine surges even though there is no oil pressure loss, but not panic if the engine speed is stable but the oil pressure indication goes to zero.. Both, of course require an immediate landing. The guy with the engine surge was flying a fully certified aircraft with NO oil pressure alarm - how can "they" allow such things? I was tempted to install a low oil pressure switch along with the electronic engine monitor, but I didn't. Might be a good idea and I think I'll do it next time.

Gary Casey

I had a similar experience as Bill except it was the oil pressure sensor. Nothing gets you on the ground faster than a zero oil pressure alarm. Happened twice. The first time I replaced the sensor and the second time was about a month later. I figured it must have been a connection of the DPU so I replaced the cable, connections and even removed the DPU to verify proper function. I swapped fuel pressure and oil pressure inputs to be sure it wasn't a flaky A-D channel on the DPU. After weeks of mucking about it turns out that the new sensor was flaky. A call to JP got the "You installed it you bought it" response. My reply? Foxtrot Yankee.

I never much cared for the Media Mate sensors because they used crummy "Faston" spade connections that treat millivolt signals like a junk yard dog so I decided to make something better..

Understand that these types of pressure sensors use strain gages (resistors that vary with strain) in a Whetstone bridge configuration. The output is proportional to the input and the pressure applied, or millivolts per volt of excitation per PSI of applied pressure. If at 50 PSI and 5 volt excitation you get a 5 millivolt output then at 10 volt excitation you would get 10 millivolts at the same applied pressure. VM1000 uses 5 volt excitation.

For the oil pressure I ended up selecting the Honeywell 19C series in 0-100 PSI range (19C100PG4K) http://sensing.honeywell.com/index.cfm?ci_id=140301&la_id=1&pr_id=145986

and machining a backshell out of aluminum to accept a MIL Spec 4 pin connector. (see attached picture of the modeled assembly). You need access to a lathe and a mill for about an hour to make the backshell. The sensor was about $110 and the connector another $20.

The fuel pressure sensor needs to have a 0-50 PSI range so the part number would be 19C50PG4K.

The sensor has been installed for over 2 years without any problem.

Any brave soul that wants to follow my footsteps to make their own backshell, email me and I'll send you a drawing, or better yet, the SolidWorks model.

Regards
Brent Regan

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Sorry wrong picture. Here is the correct one.

Bryan

On Sat, Jun 20, 2009 at 9:13 PM, Bryan Wullner <vonjet@gmail.com> wrote:

My Lancair 360, N127EM, got its pink slip today after 4 years of construction. Its now ready for test flights.
Its a Lancair 360 with MKII tail, outback gear.

Bryan