REFLECTOR: Odd fuel pressure Problem

[Scott Derrick]

Isn't that "anti-aliasing" or am I backwards???

That's what its called in DSP on the software side of things....

Scott

At 01:28 PM 11/26/2004, Wayne wrote:
>On a digital oscilloscope they call that "ailiasing"
>----- Original Message ----- From: "Ronnie Brown" <romott at adelphia.net>
>To: "Velocity Aircraft Owners and Builders list" <reflector at tvbf.org>
>Sent: Friday, November 26, 2004 2:26 PM
>Subject: Re: REFLECTOR: Odd fuel pressure Problem
>
>
>>A similar problem is occurring with the Blue Mountains/Dynon's with a
>>vibration caused sampling frequency problem.  Attitude indicators are laying
>>over sideways at certain rpms.
>>
>>Since Chuck and others are having a similar problem, I would suggest that a
>>snubber/orifice needs to be added to the fuel pressure sensor line.
>>Digital/computerized instrumentation samples the data instead of having a
>>continuous readout like an analog instrument.  If the pulses from the fuel
>>pump are in sync with the digital sampling frequency, then the read out at
>>certain times could  be sampling the low pressure part of the readings, and
>>hence the indicated low pressure (at certain rpms or other harmonics).
>>
>>My fuel pressure sensor line has a 1/16" orifice - a fitting was filled with
>>silver solder then drilled out with a drill bit.  This should reduce the
>>pulses reaching the sensor and improve the accuracy of the fuel pressure
>>readout.  I have similar orifices on my oil pressure and MAP lines.
>>
>>Incidentally, the fix on the Dynons was a change in the solid state gyro
>>sampling frequency to avoid the offending engine RPM harmonic.
>>
>>Ronnie
>>
>>
>>
>>----- Original Message ----- From: "Jack Sheehan" <j.f.sheehan at larc.nasa.gov>
>>To: "Velocity Aircraft Owners and Builders list" <reflector at tvbf.org>
>>Sent: Friday, November 26, 2004 1:09 PM
>>Subject: Re: REFLECTOR: Odd fuel pressure Problem
>>
>>
>>>Scott,
>>>Here is what I understand. The VM-1000 is a really good instrument.
>>>there have been a lot of installation problems but the readings you
>>>get from the instrument are correct usually. I have had the same
>>>problem with a Lycoming IO-540. It seems that the lycoming fuel pumps
>>>do actually fluctuate in pressure. The tolerance on the alarm of the
>>>VM-1000 sometimes does not trip but sometimes it does. Visionmicro
>>>does have a new software change that permits the delay of the alarm.
>>>They also have a recommended fix for the fuel pressure. They
>>>recommend the installation of a snubber in the pressure line just
>>>before the transducer similar to the one that is in front of the
>>>manifold pressure transducer. For some reason I can almost predict
>>>the low fuel pressure alarm as I climb through 8500 feet.
>>>Seems the digital instruments are telling us things we really didn't
>>>want to know and would never see in an old analog gauge.
>>>If you need more info I suggest you call Visionmicro systems. ask for
>>>Dave he is a really helpful technical support guy.
>>>We used to have to make a decision between JPI or Visionmicro for a
>>>good digital system but now they are the same company or at least
>>>there has been some sort of merger but VisionMicro is still the place
>>>to call.
>>>Why it took so long to happen on your airplane I do not know but I
>>>can also go for weeks without any fluctuation alarms which also does
>>>not make a lot of sense. I suppose temperature,pressure etc make a
>>>difference.
>>>
>>>Jack
>>>N55XL
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>>
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>
>
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