|
|
Chris,
I don't have an EM2, so I don't know how helpful this info will be.
Calibrating a linear sensor (thermocouples not included since they are not linear) generally requires a 2 point scaling. The display instrument typically converts the input signal (AI) to engineering units (EU) by use of a linear equation - y=mx+b. m is the slope or gain of the equation and b = the y-intercept or offset. For a system to calculate calibration values 2 points are need to determine the gain, then the gain(m) and one calibration point are used to calculate the offset(b.) The two points are generally captured by exposing the sensor to a low standard and sampling the AI, then exposing the sensor to a high standard and capturing the AI. In both cases the instrument must be told what the low and high EU values are. With these 4 values the gain and offset are calculated.
Per your text it sounds like you have only sampled one point. Without the second sample point, gain and offset values will be inaccurately calculated. These inaccurate calibration gain and offset values will improperly compute the EU and may even be a negative value. Your 0 display can be from a negative calculated EU the is clamped at zero (clamped = min or max displayed value, when the EU is out of the clamping range.
Note: thermistors are not truly linear, but for practical purposes most often they are calibrated as linear devices. When a thermistor signal is calculated through a linear equation, its most accurate points will be at the 2 points that were used to calibrate. With that in mind, I would recommend the high calibration point be near the normal operating temperature.
Hope this is useful, in the end your manual should describe the most accurate calibration method.
Joe
----- Original Message ----- From: "Christopher Barber" <CBarber@TexasAttorney.net>
To: "Rotary motors in aircraft" <flyrotary@lancaironline.net>
Sent: Thursday, August 02, 2007 2:18 PM
Subject: [FlyRotary] EM2 question
Shocking....Chris is asking another question about the EM2. Hey, me asking
questions means I am out there trying to make progress......not that I am
defensive or anything <g>
Anyway, since my "buttons" issue the Coolant Temperature on the main screen
has been showing "0". The oil temp is working ok. I figured that I must
have inadvertently set it to 0 when I was having my button problem. I
figured now that the buttons are working properly I could just go and
calibrate it. Figured a good starting point would be to use the cold oil
temp as a guide. However, when I try to calibrate it, it will not change
from zero. I thought that maybe there was not % change from zero and I
tried changing other calibration modes but nothing I have currently tried
has changed it from zero. I admit to very little current understanding of
the calibration feature at this time (even though I really like that it is
included in the EM2....I like options even though they can be a pain
sometimes).
Any direction on how to get this off of zero would be helpful as I am
hesitant to start the dang thing 'till I can know how hot the coolant
is....I know I can get some idea from the oil, but still.
David Staten will probable be much better at figuring this out, but we have
not been able to meet up for actual progress in the last few days. TIA.
All the best,
Chris
Christopher Barber
Attorney and Counselor at Law
5110 Bissonnet, No 418
Bellaire, Texas 77401
Serving the Needs of Senior Texans
281-464-LAWS (5297)
281-754-4168 Fax
www.TexasAttorney.net
--
Homepage: http://www.flyrotary.com/
Archive and UnSub: http://mail.lancaironline.net:81/lists/flyrotary/List.html
|
|