REFLECTOR: Dynon fuel pressure

[Brian Michalk]

Oh.  Actually we love the same thing.

Yes.  I agree.  For any sensor you give me, it needs a minimum of two 
wires.  One for voltage reference (ground) the other for signal.

Using the chassey for signal return is asking for trouble.

On 4/2/2012 4:20 PM, Scott Derrick wrote:
> 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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>