REFLECTOR: Oil Pressure

[John Dibble]

Jim, Scott and others, thank's for the help.  I eliiminated the ground
loop on the oil sensor.  I also cleaned the terminals from the battery
to the relay.  The resistance was unchanged at 0.2 ohm.  At my friend's
recommendation I isolated the buss ground.  I had to recalibrate the oil
pressure which read 13 psig with the engine off after these changes.
Today I flew and my oil pressure held solid at 66 psig/88 C.  Also my
fuel pressure read correctly and was stable.  Previously it varied from
2-25  psig.  Also my EGT reading was stable.  It had fluctuated over
several hundred degrees from the day I bought the plane.

John

Jim Agnew wrote:

> John, All instrunments should share a common ground at a single point
> to prevent ground loops.A single point does not imply one connection
> but a local grounding buss to share all the connections. Jim James F.
> Agnew
>
> Jim_Agnew_2 at Yahoo.Com
>
> Tampa, FL
>
> Velocity 173 Elite Aircraft Completed & Flying
>
> -----------------------------------------------------------------------
> From: John Dibble <aminetech at bluefrog.com>
> To: Velocity Aircraft Owners and Builders list <reflector at tvbf.org>
> Sent: Friday, July 31, 2009 8:34:53 PM
> Subject: Re: REFLECTOR: Oil Pressure
>
> My sensor is on the bottom of my oil cooler and has a ground wire
> attached to it.  I
> added a second ground wire which passes through the landing light.
> Would it help if I
> ran the ground wire directly to the battery or to the buss?
>
> John
>
> Laurence Coen wrote:
>
> > John,
> >
> > Your oil pressure transducer is likely grounded at the engine and
> your
> > readout is grounded to your panel buss.  I suspect the ground
> potential at
> > the panel buss changes with change in load but the same thing
> doesn't happen
> > to the engine ground.  You can check the voltage between the engine
> and buss
> > grounds with varying loads.
> >
> > Larry Coen
> > N136LC
> >
> > --------------------------------------------------
> > From: "John Dibble" <aminetech at bluefrog.com>
> > Sent: Friday, July 31, 2009 9:02 AM
> > To: "Velocity Aircraft Owners and Builders list"
> <reflector at tvbf.org>
> > Subject: REFLECTOR: Oil Pressure
> >
> > > At this point I'm pretty sure I do not have an oil pressure
> problem.  On
> > > the return from
> > > OSH, my observant copilot noticed that every time I turned a knob
> the
> > > pressure reading
> > > changed.  So I turned off my radio and the pressure went up 6
> psi.  Then I
> > > turned off the
> > > transponder and the pressure went up another 6 psi, making it 51
> psig
> > > which I am happy
> > > with.  I checked the voltage drop across the relay and it is 0.  I
> checked
> > > the voltage
> > > drop between my RMI monitor ground and another ground.  I varied
> from
> > > 0-0.02 v as I turned
> > > on a few things.  The monitor power voltage decreased from 12.6 by
> 0.1
> > > volt each time I
> > > trurned on something.  I figure that's just the battery voltage
> going down
> > > with increased
> > > load.  What do I need to be looking at?
> > >
> > > John
> > >
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