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Chapter 14: Inputs- Using
RPM Adapter Input
General notes on wiring the RPM adapter input (secondary way of measuring RPM)
‘RPM Adapter’ input is for an optional direct engine RPM input (main RPM input is via DYNertia3’s sensor) and requires
switching (pulsing) to ground so DYNertia3 can determine the RPM.
NOTE: DO NOT directly connect to an ignition system due to the high voltages involved. An ‘RPM Adapter’ unit must be
used to turn any high voltages or analogue voltages from a VR sensor (like an ABS wheel speed sensor) into suitable
pulses.
Hall sensors are ‘switching’ style sensors and can be directly connected to the ‘RPM Adapter’ input as these provide the
correct signal characteristics. They are available to sense from a rotating iron object (such as the common ‘Honeywell
1GT101DC’ sensor shown below) or magnets.
Using a DTec ‘RPM adapter’ for the RPM adapter input
The DTec ‘RPM adapter’ is designed to turn signals from many different sources into a suitable signal for connecting to
digital devices such as DYNertia3’s ‘RPM Adapter’ input.
It can be connected to the ignition coil switching terminal (inductive and CDI systems), VR sensors (also known as
‘inductive’) that generate an AC voltage (like ABS wheel speed sensors), digital coil drive signals (such as on ‘coil on
plug’ systems) or it can even pick up RPM by placing a wire alongside the spark plug lead.
There is a Hi voltage input (up to 600V) and a low voltage input (up to 120V). The low voltage input provides good
sensitivity for VR sensors and digital coil drive signals, the high voltage is designed for direct connection to the coils
switching circuit (coil primary circuit, not secondary spark plug voltage)
The unit provides full isolation to the device connected to it i.e. the internal ‘switching’ circuit that connects to DYNertia3
is isolated from the inputs for protection (full optical isolation).
When probing an unknown system use the Hi voltage input first and watch the tacho display (Setup/Sensor
Calibration/Show Data Stream) for a suitable reading. Inputs have been designed to be almost indestructible to allow for
this ‘try and see’ approach. Just do not allow spark plug voltage to enter the unit, this is potentially tens of thousands
of volts and will cause damage.
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