Today's Message Index:
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1. 12:24 AM - Re: VM1000 Oil Pressure (Vanremog@aol.com)
2. 03:24 AM - Re: VM1000 Oil Pressure (Greg Fuchs)
Message 1
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| Subject: | Re: VM1000 Oil Pressure |
All-
In the spirit of documenting problems for posterity here is my story on a
recent problem with the Oil Pressure circuit of the VM1000 system. The oil
pressure system uses a transducer (50 mV full range 0-100 psig).
During my last flight in cruise, I developed a low oil pressure reading.
It was low across the board (both at cruise and idle). Taught to believe
my gauges, I aborted the flight and cautiously returned to the field.
I did normal troubleshooting by following the VM documentation and was
unable to identify any significant anomalies in the wiring. I removed the oil
pressure transducer (Vision Microsystems P/N 3010018, Honeywell M/N
MM100PG1QA, Honeywell Data Instruments P/N 9302904) and connected it up on the
bench to a 5 VDC supply voltage across pins 2 and 4 and screwed it into a
manifold along with a 0-100 psig mechanical (steam) gauge. Playing with
compressed air I was able to check the output of the transducer across pins 1
and 3 over the range 10-80 psi and all was smooth and well. This transducer
is designed to put out 0.5mV/PSI, so 30 psig=15 mV, 40 psig mV and so on.
I put it all back together and all is now well, so here is my analysis.
The low output of this transducer system is okay as long as your terminals
(in this case they are all Tin plated) are good and clean. After 12 years
of being on the engine side of the firewall they may have oxidized a mite or
gotten a little bit of oil on the terminals dropping a little bit of that
already low mV. A gas tight connection is a good connection, but these are
just slip-on quick-disconnect terminals. The more environmentally
resistant Hirshmann connector equipped version of this transducer (change
Honeywell M/N suffix from QA to HA) is probably much more resistant to this
situation and is probably a good option going forward. I think that the newer
VM
systems ship with the Hirshmanns. My VM was bought back in 1996. Removal
of the terminals burnished the connections removing the voltage drop and
all is now functional.
Probably would be a good idea to check and reseat these periodically.
N1GV (RV-6A Flying 936TTAE Silicon Valley, CA)
Message 2
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| Subject: | VM1000 Oil Pressure |
Oxidation is the scurge of connections. Maybe throwing a little dielectric
grease into the terminals of the sensor probably wouldn't hurt, either. It
might eliminate most upkeep, since it keeps the air off of them. As you may
know already, it is considered an insulator, so it should not effect any
readings, in fact it will help keep stuff off the terminals that might
affect the readings, such as oil, water, etc. For ease of obtaining, it
should be able to be found at most automotive outlets, most probably. Just
a thought.
Greg Fuchs ...hope to get back to the bird soon, from almost a 6-month
break....time seems to fly even faster if not working on her
_____________________
...
After 12 years of being on the engine side of the firewall they may have
oxidized a mite or gotten a little bit of oil on the terminals dropping a
little bit of that already low mV. A gas tight connection is a good
connection, but these are just slip-on quick-disconnect terminals. The more
environmentally resistant Hirshmann connector equipped version of this
transducer (change Honeywell M/N suffix from QA to HA) is probably much more
resistant to this situation and is probably a good option going forward. I
think that the newer VM systems ship with the Hirshmanns. My VM was bought
back in 1996. Removal of the terminals burnished the connections removing
the voltage drop and all is now functional.
Probably would be a good idea to check and reseat these periodically.
N1GV (RV-6A Flying 936TTAE Silicon Valley, CA)
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