REFLECTOR: Dynon fuel pressure

[Scott Derrick]

I love grounded sensors and have used them in instrumentation for years 
in avionics( Space3 Shuttle, B1-B, etc..) and commercial systems.  But I 
expect that what ever I connect the sensor to, will provide me with the 
sensor ground along side the data wire(amp. volt, freq., etc).

I completely agree that using power ground for sensors is B.A.D.

Now Dynon actually provides the ground connections on the EFIS and EMS 
but then provides shitty cheap ungrounded(meaning the ground path is the 
bus(power) ground. Then when you tell them your having problems they say 
your ground path from the engine to the instrument is bad.

I swapped out the crappy Dynon provided ungrounded oil temp sensor which 
was pathetically inaccurate, with a GRT grounded(ground lug on sensor 
run to EMS) and now I get a smooth acurte reading unaffected by voltage 
or amperage changes on the power bus.

VDO is the manufacturer of the fuel sensor sold by Dynon.  They make a 
grounded sensor in the same PSI range, I need to find out if the 
resistance is the same across its pressure range of 80 PSI.   Or install 
a GRT grounded sensor, but that sensor is only rated to 30 PSI and my 
system is capable of producing 32 PSI.  I think that would be OK but???

Scott

-------- Original Message --------
Subject: Re: REFLECTOR: Dynon fuel pressure
From: Brian Michalk <michalk at awpi.com>
To: Velocity Aircraft Owners and Builders list <reflector at tvbf.org>
Date: 04/02/2012 12:49 PM

> 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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