flyrotary@lancaironline.net Mailing List Archive

Hi Joe,

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.

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.

Tracy

----- Original Message -----

From: Joe Hull

To: Rotary motors in aircraft

Sent: Wednesday, October 26, 2005 10:23 AM

Subject: [FlyRotary] EM2 Calibration

Thanx for all the suggestions on calibrating my EM2 –

I spent 3 hours last night trying to calibrate just the Oil Pressure sender. Only about 30 minutes of that were real calibration tasks – the rest of the time was spent trying to get a positive number instead of a negative number. Anyone know why or how the “Scale Factor” is negative?

If the “Scale Factor” is negative then the derived value, of course, is negative. So, I tried to see if I could get the scale factor to “wrap around” by bringing it to zero – but after hours of holding buttons and countless counts to -63.99% (and or -128) I did nothing but overflow onto the screen buffer and start popping numbers onto screen labels. So, it was the same tedium getting it back to where it was.

There’s got to be an easier way!

Thanx,

Joe Hull

Redmond (Seattle), Washington

Cozy MkIV #991 (working on Engine & Electrical & Finishing)

http://www.maddyhome.com/canardpages/pages/JoeHull/index.html