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XMS4 - What Temperature Sensor To Use | Application Note : AN 7


Perfect Power Application Notes.


Application Note : AN 7

This note describes the use of engine temperature sensors with the XMS4 system, and how to adapt an existing temperature sensor to the XMS4.



The engine temperature is important, and apart from the ECU measuring it, it is very often displayed on the dashboard. It would be nice if the existing, or any other sensor, could be used with the XMS4.



The XMS4 system requires a NEGATIVE TEMPERATURE COEFFICIENT (NTC) sensor. Most engines use it. A NTC reduces its resistance as the temperature rises. This can be measured on the workbench with a multimeter, reading its resistance at room and at some elevated temperature. The resistance at the HIGH temperature must be SMALLER.


If the temperature sensor is not connected to any other device, then the sensor needs a "PULLUP". This is done internally in the XMS4 range.


XMS4 Stand Alone Unit - Engine Temperature Sensor Connection




The XMS4 can be calibrated to read the engine temperature in DEGREE C of F. The process is described in a different application note. In short, it requires a TWO POINT calibration, which tells the XMS4 :


  • If it is a high or low point you are specifying
  • At what step of the XMS4 temperature scale the point is
  • The display temperature (C or F) at this point




With the above provisions, any sensor can be used, and calibrated. The practical calibration is explained in another application note.