How passive temperature sensors work ??
How passive temperature sensors work ??
(OP)
Hi everybody! Can someone inform me how does passive temperature sensors work (without a supply voltage). It has a resistor in it and the resistance changes according to the temperature but where is the voltage source ? (If I'm not wrong the pull-up voltage in the ECU is only to determine the fault situation of the curcuit - so it cant be the supply v).
Or any websites that gives the fundemantal principles thanks for the info...
Or any websites that gives the fundemantal principles thanks for the info...





RE: How passive temperature sensors work ??
http://en.wikipedia.org/wiki/Thermistor
http://www.thermometrics.com/htmldocs/whatis.htm
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RE: How passive temperature sensors work ??
RE: How passive temperature sensors work ??
The sensor is a two terminal device with a resistance that is a function of temperature. It usually has one terminal connected to ground (return) and the other terminal connected to the ECU. In the ECU, this terminal is connected to a fixed resistor. The fixed resistor's other terminal is connected to a voltage supply. The circuit formed is a voltage divider. So, for example if the sensor's resistance, at a certain temperature, is equal to the fixed resistor's value, the voltage measured at their junction is exactly half the supply. In the ECU, the junction voltage is measured with an A to D converter.
For fault detection, if the sensor or cable is open, the junction voltage goes to full supply voltage. If the sensor or cable is shorted to ground, the junction voltage goes to zero. Since either voltage extremes are illegal, the ECU can declare a fault.
How this helps.
RE: How passive temperature sensors work ??
CODE
|
Rf
|
------ECU
|
Rv
|
Ground
Operation:
Current flows from Batt+ to Ground through both resistors. As Rv changes with temp, the voltage seen at the ECU node changes. This voltage is read by the ECU and translates it to a temperature.
Dan - Owner
http://www.Hi-TecDesigns.com