Reading engine speed

Engine speed information is required to calculate engine torque and to plot the right RPM scale on dyno report. There are some situations where engine speed doesn’t have constant relation with dyno speed and it cannot be calculated with simple ratio and OBD interface is not available. To get correct engine speed reading in these situation the controller is equipped with specialized Engine speed input, that allows direct readout of the engine speed. Following sensors can be connected to this input:

Variable reluctance sensor, VR sensor

S+First VR sensor wire
S-Second VR sensor wire

Hall type sensor or other digital signal

+Sensor power supply
S+Sensor signal
S-Reference voltage
Sensor return ground

When hall type sensor is used, it is required to connect some external resistors. R1 is usually required for sensors with open collector output. R2 and R3 create voltage divider that supply 2.5V reference voltage to S- input.

PEREK CS1 clamp inductive sensor

CS1 is an inductive sensor designed to read engine speed signal from ignition coil wires (high or low voltage).

+Sensor power supplyWhite wire
S+Sensor signalGreen wire
S-Reference voltageBrown wire
Sensor return groundBrown wire

Any sensor different than mentioned above

+Power supply output to be used by the sensor or reference voltage divider
S+Input signal
S-Reference voltage input
Return ground for sensor or voltage divider

Many sensors not mentioned above could be connected to the Engine speed input. Input circuit analyzes voltage between S+ and S- terminals. Speed signal is triggered when S+ potential drops below S- potential. Circuit rearm voltage is set to 30% of S+/S- peak voltage. When the rearm voltage is crossed, the circuit gets armed to generate next speed signal.

To connect any sensor, circuit must be created which ensures that S+ potential will drop below S- potential every time that speed signal generation is required.