Originally Posted by SCVJeff
I have a SPMA9575 Altimeter just installed on my Hex, but there is little information as to how it calibrates itself? If I set the Hex in the yard and power it up, it starts off lo, but creeps up to ~10-12' (the yard is 1505' AMSL). So, I assume it's attempting to zero itself at the current AMSL? Nevertheless as I watch it, even on the ground it will wander up as high as 25'. What can I expect the true verticle accuracy of these to be?
Also, is there a way to calibrate the TM1000 voltage monitor that's .2V off? My Hex doesn't glide on a low battery, it drops
The altimeter calibrates itself when it powers on.Barometric altitude is a tricky one to keep calibrated.This thing is extremely sensitive.If you power it on and it zeros(AGL) and then moves into much warmer air or the airtemp locally around the sensor goes up the air becomes less dense and the sensor interprets it as a gain in altitude.This is an inherent physical property of air.The sensor is reading the pressure and it doesnt know if it is purely an altitude gain of if it is simply moving into less dense air at the same altitude.
Try to initialize it when it is acclimated to its actual flying environment as best as possible.If its nice and cool in the shade and your going to fly in the direct sun sit it in the sun for a bit and then initialize it.
Ive had a TM that was slightly out of calibration.It got that way when I forgot to unplug the lead from my balance tap(where I tap the lead into) and left power to it for a day.After that it read .2 volts at actual zero.I marked it and just put a "fudge factor" into my alarm settings and my brain interpretation of the number on the screen.
It is what it is.Understanding how it works helps getting your brain to workaround these small variations.Its a free solution to some compromise it just requires a bit of brain engagement.
Im sure all this stuff could be designed and built to maintain mil-spec accuracy/tolerances in all conditions but we likely wouldnt be able to afford it.Even if we could there there would still be deviations.