Many thanks to everyone who has responded. I have a better idea now of how
the system functions and a list of things to check when I’m next in the
hangar.
It seems there a few things that could be wrong:
Air in the lines
Sensor heads not working
Bellows stuck
Wiring issues
On the latter point: These are analogue transducers sending a voltage to
the main unit, and the conversion to digital is done in the main unit. If the
voltage range is 0-50 mV full scale, then it is asking for a resolution of 0.5
mV to get 1% FSD accuracy. From the electronics point of view, that is a pretty
tall order without special wiring techniques and cables and connectors.
One thing I think I will do is to rig up a dummy sensor unit, with a knob
that controls the output from 0-50 mV. That would be useful for testing the
wiring and the main unit, and a simple test for a faulty sensor.
Yours,
Nick
Sent: Sunday, March 30, 2014 8:32 PM
Subject: Re: VMS1000 pressure gauges on LNC2
Nick did you purge the lines? We have seen many times on new engines
that the pressures don't come on reliably until the lines have been purged well
of air. I know, the sensors should still be seeing pressure, but it just doesn't
seem to work until you actually get rid of the air in the lines. That might help
fix the oil. Were the wires to the gold anodized box disconnected during your
re-build? Having the wrong wires in the wrong holes, or reversed, can cause some
funky readings on the VM systems.
Tim
Aircrafters
Hello All,
I’ve got a Lancair 320 and we’ve just re-installed the engine and are in
the process of the annual inspection.
Both the fuel and the oil pressure readings on the VMS1000 display are
very strange. The fuel pressure gives a reading when there is no pressure and
the oil pressure reads very low. A quick check with some old steam gauges
suggests the actual pressures are about right. The pressure sensors are both
in the engine bay, fed with flexible hoses.
Is this likely to be the pressure sensors? Do they tend to misbehave? Is
there an easy way to check them? Or could it be in the wiring or the display
unit itself. I can’t see anything in the VMS1000 manual about
calibration.
Any help gratefully received.
Thanks,
Nick