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Wiring Fundamentals: Analogue Temperature

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Analogue Temperature


00:00 - Analog temperature sensors are a type of resistor that change their resistance in response to temperature changes in a predictable way.
00:08 The ECU measures the resistance of this sensor and by comparing this to a calibration table, determines the temperature at the tip of the sensor.
00:15 Overwhelmingly the most common type of temperature sensor you will encounter is a negative temperature coefficient or NTC sensor.
00:23 The resistance of these sensors decreases as their temperature increases.
00:28 NTC sensors have two pins, sensor ground and sensor signal.
00:33 Most ECUs will have dedicated input channels for temperature sensors, which will be described in your ECU documentation.
00:40 The reason most automotive ECUs typically have input channels which are dedicated to temperature measurement, is that they cannot actually measure a resistance value directly.
00:50 What they instead do is compare the unknown resistance value of the sensor to a known fixed resistance value inside the ECU.
00:58 And the calculate what the resistance value of the sensor must be.
01:02 The ECU does this using an internal circuit called a voltage divider.
01:06 And the addition of this fixed known resistance value inside the ECU is the only difference between an analog voltage input channel and an analog temperature input channel.
01:16 It's possible to create a voltage divider circuit within our wiring harness which is external to the ECU, meaning we can turn an analog voltage input channel into an analog temperature input channel.
01:27 This is an advanced technique that often requires generating a custom calibration curve for the temperature sensor and voltage divider and is covered in our advanced motorsport wiring course.