Sensors

Sensors measure physical properties, and convert their measurements into electrical signals to be captured by the data logger and used for running the vehicle, diagnosing the vehicle, verifying that the vehicle is running properly, and/or helping to tune the vehicle.

Common Sensors

Sensing location/movement of vehicle

These sensors are used to tell where the vehicle is, and how it is moving. Dataloggers often have some or more of these sensors built in. With these sensors, where they are mounted on the car may change how useful the data is. For instance, you may find that you want to mount them as close to the center of gravity as possible.

Accelerometer

Measures its acceleration in one or more axes. This may or may not be the actual acceleration of the vehicle, depending on how it's mounted.

Gyroscope

Measures its angular velocity (change in an angle over time) on one or more axes. Again, you'll probably want these axes to line up with those of the vehicle.

Magnetometer

Measures the strength and direction of the magnetic field. Useful for measuring the yaw of the vehicle.

IMU

Standing for Inertial Measurement Unit, it measures orientation, velocity, and acceleration in all three axes, utilizing accelerometers, gyroscopes, and magnetometers.

GPS Receivers

Obtains GPS data. This is usually used for logging the position of the car, so that you can see where the car is going and compare lines through corners.

Sensing Movement of a Single Component

Hall Effect Sensors

Detect the presence of a magnetic field. These are typically switches, that are either on or off (i.e., not analog). These are most commonly used to detect and measure rotation, e.g. of a gear. Unlike a VR sensor, they require an external magnetic force.

Variable Reluctance Sensors

Known also as VR sensors, they detect a change in the magnetic field. Unlike hall effect sensors, they do not require an external magnetic field, so many OEMs use them for cam and crank position sensors.

Potentiometers

Variable resistor ladders that measure movement. The can be used as driver controls (e.g., for adjusting radio volume), or in linear form for measuring shock travel (among other uses).

Rotary Position Sensors

These act as more accurate rotary potentiometers. Often they are contactless, meaning they last much longer and for many more cycles than potentiometers do. These are useful as pedal position sensors and steering angle sensors.

Knock Sensors

Sensors that detect engine knocking. These will bolt directly to the engine block, and will usually come with the engine.
there are a buncha different kinds of knock sensors - i'll try to get something sketched out here this week -simon

O2 Concentration Sensors

O2 sensors measure how much oxygen is in the exhaust. This allows you to figure out the air-fuel ratio of the engine. Narrowband O2 sensors can only tell you if you are rich, lean, or at the stoichiometric efficiency of the engine, whereas wideband O2 sensors tell you your air-fuel ratio within a much broader range. Narrowband O2 sensors are usually used by the OEMs for troubleshooting catalytic converters, but most racecars use wideband O2 sensors to help when tuning the engine.

Signal Types

Digital Sensors

Pulsed

Pulsed sensors send a series of digital pulses where the frequency of the pulses represents the measurement value. Commonly seen in shaft speed sensors.

PWM

PWM sensors vary the width of pulses at a fixed frequency to represent the measurement value. A simple analog filter can allow a PWM sensor to be approximated into an analog signal.

Serial

Some "smart" sensors transmit their measurement value(s) over a communication protocol such as CAN Bus, I²C, or SPI. This allows multiple values to be transmitted without additional wiring.