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The Honeywell MediaMate fuel pressure transducer sold by VMS (JP Instruments) utilizes a plug-on Hirshman (right angle) connector which, as Brent points out, is a poor design considering the weak 50 mVDC output signal and potential for voltage drop across the connector. The Measurement Specialties replacement that I recommended employes a permanently connected 2' cable, which virtually eliminates voltage drop; however, it's 2' length is too short and requires a connector to mate with the VMS-furnished four conductor cable (the wires furnished with a new $1,000. Oildyne pump and most FM/CD/MP3 players are also too short and require connectors). Utilize a four-circuit AMP free-hanging connector (Digi-Key p/n A1402/1431) (http://dk3.c.digikey.com/B092/p80221.pdf) and gold-plated pin/socket (Digi-Key p/n A1432/1434 (http://dk3.c.digikey.com/B8092/p80222.pdf)
Bill Rumburg
N403WR (Sonic bOOm)
----- Original Message ----- From: "Brent Regan" <brent@regandesigns.com>
To: <lml@lancaironline.net
Sent: Sunday, June 21, 2009 8:32 P
Subject: [LML] Re: VMS 1000 Fuel Pressure Transducer
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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