REFLECTOR: Dynon fuel pressure

[Brian Michalk]

Back in my instrumentation days, the classes taught that "grounding" is 
really a misnomer.  There are two type of common voltage, referred to as 
"ground."
The first is power grounds.  This is for lights, motors, alternators and 
that sort of stuff.  The other type is for instrumentation.  The sensor 
either generates a small voltage potential, or somehow moderates a 
voltage or current.

I hate grounded sensors.  They mix the power return path with my 
sensitive acquisition system that I take great pains to keep noise 
free.  When the mfg. provides these, they contaminate all sorts of 
things causing ground loops, induced voltage, and possibly injected RF 
noise.

I don't consider temperature probes where the body is grounded to the 
engine case for example to be a problem.  In that case, the acquisition 
sensor checks for a voltage drop across the temperature probe, which is 
a high impedance sensor, and thus does not contaminate my sensitive 
acquisition voltages.  It is still a current loop and that make it 
susceptible to noise because the current that went from the acquisition 
system to the probe, and into the engine case has to magically find its 
way back to the acquisition system somehow.  The problem is that we 
don't know the return path, and that's the problem.

Okay off my sandbox.  Can you put a voltmeter on the sensor?  Do you get 
the same results with everything turned off except the Dynon?

On 4/2/2012 11:43 AM, Scott Derrick wrote:
> I'm having an issue of a false high fuel pressure readingon my Dynon EMS.
>
> I came within minutes of removing the fuel pump to see if the high 
> pressure reg was dirty or the recirc outlet was clogged. A 5 hour job 
> just to uncover the pump?
>
> I happened to be testing the installation of a replacement capacitive 
> fuel probe and noticed the fuel pressure was reading 10 psi and the 
> engine was off! I played around with re-grounding the sensor(Dynon has 
> a serious Achilles heal because they use ungrounded sensors) to see if 
> that would alleviate it but no joy.
>
> Anybody else have this issue?
>
> I'm thinking of switching to a GRT sensor as they are 1/2 to 1/4 the 
> price of Dynon's and most are grounded.
>
> Scott
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