Hi Bill,
Thanks for the info. I think you have done everyone a service and it’s good
to know you have some drop in replacements available at half the price I have
seen them elsewhere.
If you don’t mind, though, I’m going to pursue my ideas a bit further. I
quite like the idea of using off the shelf sensors and using the same one for OP
and FP. There is also the background thinking that the VM1000 is a bit old now
and that rather than building a solution around that, I could devise something
with general applicability.
Over the holiday weekend I did some more investigation. I built a rig in my
workshop to pressurise the old sensors from my air line system* and measure the
resistance changes and the voltage outputs. The two sensors gave the right
voltage changes (50 mV and 100 mV for 100 psi) but with horrendous offsets. The
zero psi values were way out. So they were working, but not actually any
use.
Then I checked the VM1000 panel by injecting voltages on the FP and OP
inputs. That did exactly what was expected, but now I also know what common mode
voltages it will cope with.
Anyway, I have ordered some modern sensors with 0 to 5 V outputs and I’m
going to scale the outputs down to suit the VM1000. I will let you all know how
I get on. If I’m right, then I will have something that should work with any
other monitoring systems that are out there.
Yours,
Nick
*not as easy as it sounds because the sensors are NPT threads and my system
is completely and utterly the way it should be – British Standard Pipe
thread.
Sent: Monday, April 21, 2014 4:43 PM
Subject: [LML] Re: VMS1000 pressure gauges on LNC2
Nick -
The VMS1000 oil and fuel pressures were designed
for the Honeywell MediaMate, which produces 50mV DC full-scale output when
excited with 5VDC. The MediaMate, however, is inferior, antiquated technology
and outrageously overpriced.
A modern, high-quality replacement is the
Measurement Specialties US321. It also produces
50mV DC when excited with 5VDC; hence, it's an electrically-DIRECT replacement
for the MediaMate http://www.meas-spec.com/downloads/US300.pdf
A problem, however, is that the VMS1000's
combination of 5VDC excitation and 50mV DC full-scale output is, apparently,
rarely used in industry; hence, I couldn't locate any US321's -in the needed
pressure range- for sale despite an exhaustive search. I contacted Measurement
Specialties last August and learned that they would manufacture them at a cost
of $140 each, with a minimum order of five. So I ordered five @50 psi (fuel
pressure for fuel-injected engines) and five @100 psi (oil pressure). I ordered
them with four foot pigtails to allow direct routing to the DPU, with no
intermediate connector. Attached is a photo of them installed on my engine. If
anyone is interested, I'm offering the extra's for my price of $140
each.
Bill Rumburg
N403WR (Sonic bOOm)
Hello Everyone,
A few weeks ago we had a discussion about this, and I then went away and
checked my installation. After measuring the voltages I concluded that the
display unit is ok, but both the Oil Pressure and Fuel Pressure sensors are
not behaving.
So then I looked into replacements. There was an interesting post last
September from Bill Rumburg about using sensors from Measurement Specialities;
the originals are Honeywell Mediamates.
Bill was saying the OP and FP transducers are different in their voltage
vs pressure response by a factor of 2 and he was exploring some alternative
devices. But here is another idea. Why not just find a sensor that gives the
correct output for FP? The same sensor will give 2x the reading if used for
OP, but that can be scaled down by 2 with a simple precision resistor
network.
If that is correct, and I’ve followed the previous discussion correctly,
then Digi Key have the very item we need:
What do you think, people?
Yours,
Nick
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