|
|
In a message dated 3/15/2003 8:39:10 PM Central Standard Time, glcasey@adelphia.net writes:
I have taken apart a Vision fuel probe and was amazed to
find that there was no, and I mean none, EMI protection built into the
circuitry, so that might give one a clue about the protection, or lack
thereof in the rest of the system.
Gary,
I also have the VM fuel probes - Exceptionally accurate and unaffected by EMI/RFI. The probes send a digital frequency as a consequence of the resistance/capacitance circuit at the probe. This differs from the thermocouples that send a small voltage variation to an analog to digital converter. These wires, carrying weak voltage signals, are susceptible to RFI - thus disrupting the conversion. Note that the Rocky Mountain Instrument OAT thermister circuit is not affected.
<<Another thought is just to twist the thermocouple wire pairs along their whole length to make a poor man's shielded wire. >>
The version of EGT and CHT probes are special wires covered with a braid which I believe is shielded by contact with the probe case/engine.
<<Or it could be directly radiated through the face of the display into the box, as that is probably the least well protected part>>
The VM EPI 800 displays and the VM1000 display is connected to the "computer" via ribbon cable which carries all display data and is picked off by the proper device. I doubt that the display is the problem.
I too find it hard to believe the cause is noise on the power lead. Other functions could be affected.
I remain puzzled why some of us have this problem while other VM installations do not.
Scott Krueger
N92EX
|
|