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From: "Joe Ewen" <jewen@comporium.net>
To: "Rotary motors in aircraft" <flyrotary@lancaironline.net>
References: <list-2227427@logan.com>
Subject: Re: [FlyRotary] EM2 question
Date: Thu, 2 Aug 2007 18:38:59 -0400
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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/
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