Forwarded from the bounce bin. Message is from
"Dave Simpson" <davesimpson@londonweb.net>
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Dear David,
If the error is constant and the readings are not leaping about, then it is
probably a calibration problem . If you send the tacho back to Skydrive,
they will calibrate it for you; they have a proper calibration set up for
tachos. There have been batches in the past which have had large errors,
but the pot can normally cope, even with 10%
01926 612188. Tell 'em I sent you.
If the error is one of variable readings over a short period, then the
problem may lie in the signal cleanliness being supplied into the
instrument. Pick-up from spurious signals from the regulator (it is a
switched mode regulator which can generate large voltage spikes if not
properly supressed), RF from radio transmissions or other avionics could
also be the problem. In this case, you should first experiment with small
value capacitors across the back of the instrument between signal and
ground. Try 0.1 microfarad first.
The tachos work by converting frequency to voltage which is then used to
drive the meter. Simply potting down the voltage will have a small effect
in some part of the range, but will not provide a calibration solution I'm
afraid.
The right way to check the tacho in service from time to time is to use an
optical tacho on the prop. Skydrive sells these, or you could borrow mine
if you're near and skint.
Good luck.
Dave Simpson
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