Both the engine oil temperature and the air temperature are derived from the same type of sensor. This sensor is a negative temperature co-efficient (NTC) thermistor. This is simply a resistor whose resistance decreases as the temperature increases. The thermistor is connected to ground on one side. A resistor on MyECU connected to 5 volts forms a potential divider with the thermistor and this voltage is connected directly to one of the microcontroller's analog inputs. On My16M, the oil temperature is only to determine whether or not to choke the bike for starting. As the oil temperature increases less choke is applied. The air temperature is sampled continuously and used to do a fine tuning of the amount of fuel that is delivered to the engine. As the air temperature increases, its density decreases, necessitating a leaner mixture.
The data on the right measures resistance versus temperature for both air and oil temperature sensors.
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