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Date: Fri, 03 Aug 2007 00:14:27 -0400
From: Finn Lassen <finn.lassen@verizon.net>
Subject: Re: [FlyRotary] Re: EM2 & builder issues
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To: Rotary motors in aircraft <flyrotary@lancaironline.net>
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That's what I used in my simple set-up, but it does require three wires 
to the sensor: Ground (could be the shield of the cable), +5 Volts and 
Sensor output.

 I had a junction box on the engine side of the firewall which also had 
the EGT chips (amplified the EGT voltages to 0 to 10 Volts -- I forget 
the part number) and then a multi wire cable from there to my EM, with 
only one wire for group, +5, +10 volts and one for each signal. When 
removing the homemade sensors from the oil pan or engine block I would 
disconnect the leads from the junction box (screw terminals), roll up 
the wire and then screw out the sensor housing.

Finn

Wendell Voto wrote:
> Tracy,
> Maybe you shouldn't had said 50th but we won't tell.
> Could the EM2 use LM34 temp sensors?  They give 10mv/deg. F and have 
> very good accuracy (spec is 1 degree but I get less than .1 degree 
> repeatability one sensor to another)and track well, very linear.  They 
> are what I am using, just JB welded into a hollowed out old sensor and 
> plan on using for oil and water temps.
> Wendell
>
>     *Fine points on the EM2:*
>      
>      
>      
>     The default sensors on the EM2 are very low cost automotive types
>     but they are not inherently super accurate.  Usually there in no
>     big down-side for the water or oil temp to be off a few degrees so
>     most builders need not go any further.  If the water temp turns
>     out to be actually 178 instead of  180, no big deal.  Super
>     accuracy can be had with these sensors if you go to the trouble of
>     calibrating the instrument but then you must get into the nitty
>     gritty of the calibration procedures and the troubles can begin.
>      
>     But here is where it does matter.  If you are calculating thermal
>     loads and heat dissipation based on differential temps (let's say
>     water temps in and out of the radiator for instance)  a few
>     degrees of error can make your results meaningless.  In this
>     example, it is not uncommon for the Delta T to be in the range of
>     10 degrees at some power settings.  If the error in temperature is
>     a couple of degrees, the error is huge, especially if the errors
>     are in opposite directions.
>      
>     Bottom line is, if you need very accurate readings, learn to
>     calibrate the EM2 if that is what you are using.  To do this, you
>     need a good reference.  The easiest way is to use a non-contact
>     (infra-red) thermometer.  Harbor Freight and others are now
>     selling inexpensive ones for about $10.00.  No reason for any
>     airplane builder not to have one.   Be sure to paint the test
>     points on the part to be measured with a spot of flat black paint
>     to eliminate emissivity errors. 
>      
>     Tracy  (should I have said 50th?  )
>      
>
>          
>
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