Something not right
here. The scale factor should not be negative. The default value
for oil pressure channel as shipped is +9.349. Making the EM2 user
calibratable so that a variety of sensors can be used is obviously a mixed
blessing and there is a limit on just how far from the default sensor you
can go. Are you using the recommended sensor or something else? Try
to stay with the 10 - 180 ohm (low to high) VDO pressure sensor family.
Trying to calibrate with an inverse sensor (low pressure = high resistance) is
theoretically possible using negative scale factor but can be devilishly tricky
to do.
Yep, I’ve got the VDO pressure
sensor that came with the EM2. I
measured it’s resistance at zero pressure and it was 9.97 – 9.99 ohms,
so it’s right where it should be on the low end (I didn’t measure
resistance at the high end yet). I’m
not sure how the calibration factors/offsets got so far off – this is
really my first shot at calibrating – e.g. the low-end offset was 750-ish
when I started.
Anyway – any ideas on getting the
scale factor positive? E.g. if I
sit for 2 more hours and ratchet it up to 65,500 will it turn over? It’s always shown a negative
pressure from the day I turned it on – albeit an obviously wrong number
even without the negative.
On temp sensor
calibration, do not use a low value (like ice water) as the low end calibration
point. Automotive gauge sensors are not linear or accurate down
there. I typically use 100 - 130 deg. F as the low end and boiling
water as the upper point. Al's suggested use of an infrared temp gauge to
calibrate is a good one.
Yep, I read the manual and understood that
point. I’m going with a thermometer in a glass of hot water –
working my way via microwave to 212. I like the idea of an infrared gun –
but it’s hard to heat and cool the engine rapidly for repeated checks and
fine tuning of the factors.
Thanx for all you do for us Bozo’s (at least for this Bozo!)