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Date: Tue, 22 Mar 2005 07:43:00 -0500
From: Matthew Williams <williams@mackinfo.com>
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To: Rotary motors in aircraft <flyrotary@lancaironline.net>
Subject: Re: [FlyRotary] water temp sender connections
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If the sensor is a resistive type (RTD, thermistor) then it will require 
an excitation voltage or current.  With two monitors hooked to one 
sensor they will each be trying to provide the excitation energy and the 
result will be unpredictable (or predictably bad).  Hooking two monitors 
to a thermocouple type sensor is theoretically possible but I wouldn't 
trust such a setup.  Much better approach is two sensors; also gives you 
redundancy.

Matt

Paul wrote:
> 
> I may have stumbled upon something that probably making it difficult for 
> me to tune my MicroTech ECU.  The ECU takes into consideration 
> information from the O2 sensor, water temp and air temp to make 
> adjustments to the ignition timing and fuel mixture settings.  I hooked 
> my water temp sender to two units....both my voice annunciating engine 
> monitor and the MicroTech ECU.  While I was running the engine today, I 
> scrolled to a page on the MicroTech ECU handheld programmer that I have 
> not viewed before.  This page provides both engine rpm's and water 
> temperature.  The engine rpm's agreed exactly with my engine monitor.  
> The water temps, however were WAY off.  The engine monitor said the 
> water temp was 180 degrees F and the ECU said the water temps were -15 
> degrees C.  Prior to the engine temps warming up, my engine monitor said 
> 140 degrees F, and the ECU said -24 degrees C.  On various map pages, 
> the cold start enrichment is set to slowly start leaning the mixture 
> after 50 degrees C.  That would put my REAL temps probably around 350 
> degrees F.  Not gonna happen.
>       My question is....has anyone else connected more than one monitor 
> to a single water temp sensor? (I have the stock Mazda sensor located in 
> the water pump housing). I will also check the MicroTech manual again to 
> see if there is any place to calibrate the water temp sensor. (I know I 
> had to calibrate the throttle position sensor initially for idle 
> setup).  Is it possible that one unit would have a correct reading and 
> another connected to the same sending unit would be so far off? 
> Different wire sizes making a difference?
>       My next step will be to disconnect the engine monitor wire from 
> the water temp sending unit, and see if the ECU water temps are more in 
> line with what they should be.  Just wondering if anyone else has 
> connected more than one instrument to a single sending unit.  Thanks in 
> advance for all replies.  Paul Conner
>  

-- 
+----------------------------------------------------------+

  Matthew Williams                 Mack Information Systems
  215-884-8123 x. 111                       25 South Avenue
  215-886-5030 fax                        Wyncote, PA 19095