Analogue sensors are sensors which provide continuous outputs and varying values depending on the state of the system that they are measuring. For example, a driver’s input on the throttle can vary from anywhere between 0% (closed) and 100% (fully open) and therefore the sensor needs to be able to monitor the throttle’s position anywhere throughout the throttle’s entire range.
Most Motorsport analogue sensors usually work on the principal of the sensing element varying its resistance depending on its position within it’s sensing range.
If we supply a stable current to the sensor then, using Ohm’s Law, the varying resistance of the sensing element will mean that the sensor will output a varying voltage depending upon where you are within the sensor’s range.
The data logger can then measure this varying voltage, much like you would with a multi-meter, and we then can calibrate this measured changing voltage against engineering units i.e. pressure in Bar or an angle in degrees etc.
In Motorsport systems most analogue inputs (inputs into the device designed to measure analogue sensors) are designed for sensors that have outputs that vary between 0 volts and 5 volts.
As most car electrical systems are based on a 12-volt battery the actual voltage level will vary throughout the car’s operation on track, based on a number of factors. Due to this constantly varying battery voltage, we can’t just connect sensors to the car’s electrical power circuit, so data loggers have an internal voltage regulator that will supply a constant 5 volts of power, no matter what the actual battery voltage is reading, specifically for use with analogue sensors. A ground wire is required to complete the electrical circuit of the sensor.
Most car’s electrical systems ground through the car’s body and therefore most car mechanics are used to wiring in electronic components by connecting the ground wire to the car body. There’s a number of ways that even small amounts of electrical resistance can build up throughout a car’s body shell (rust etc.) that would affect the sensor’s voltage reading; therefore all good data loggers should also feature a sensor ground pin in order to have its own accurate electrical circuit. Most analogue sensors will therefore feature a 3 pin electrical connector.
It can be common for there to be many more analogue sensor inputs on a data logger than there are dedicated sensor power supply and sensor ground pins. A wiring loom building technique called splicing is used to allow multiple different wires to be grouped together and connected to just one pin on the data logger to accommodate this.
Sensors typically require very little current in order to operate, usually measured in milliamps, and therefore relatively thin wire can be used to build data logger wiring looms, typically between 20 – 24 AWG.