Haltech E8 - Manual (Page 155)

Haltech E11/E8 Instruction Manual
conjunction with the internal reluctor adaptor or an optional external reluctor adaptor. A reluctor adaptor
converts the sine-like wave signal from the reluctor sensor to a square wave signal. The actual value of
this ‘high’ voltage is not important because it is the transition from ‘low’ to ‘high’, or ‘high’ to ‘low’ that is
used to trigger the ECU. This transition is referred to as the Trigger Edge and will be shown in the
following illustrations as an upward or downward facing arrow. An upward facing arrow would indicate that
the trigger edge is the transition from low to high and this is called a Rising Edge trigger. If the trigger edge
occurs on the transition from high to low, it will be shown as a downward facing arrow, and would be
called a falling edge trigger. See Figure E.1.
Figure E.1
In order for the ECU to operate correctly a trigger edge must be generated. This edge must occur a fixed
number of degrees before top dead centre (BTDC) and must not change. The position of the trigger is
given in crankshaft degrees and is called Trigger Angle. In addition there should not be any variation in
the trigger angle between cylinders. The ECU can be set by the user to have its trigger edge occur
between 60° and 100° BTDC.
In the example shown in figure E.2 the trigger occurs on a rising edge at 70° BTDC. This assumes that
you are using a Standard Trigger pattern with one pulse per ignition event. The second transition, from
high to low, could occur any time after the rising edge. In some installations the second transition will
coincide with 10° BTDC or TDC itself, or it could happen as close as a few degrees after the trigger edge.
This second edge will have no effect on the correct operation of the ECU. It is only the position of the
triggering edge that is of importance.
Figure E.2
In the previous examples the trigger edge has been shown as the first edge of the trigger pulse. The
trigger does not necessarily have to be the first edge of the trigger pulse. Consider the example shown in
figure E.3. In some trigger devices the pulse given for cylinder one would be a different width than the
pulses given for all the other cylinders. If the first, in this case, rising edges were used as the trigger edge
then there would be a variation of 20° between the trigger for cylinder one and all other cylinders. This
would lead to cylinder one being 20° more advanced than all the other cylinders and obviously this would
be unacceptable. The solution in this case would be to set the trigger point so that it is at a falling edge
and to have the trigger degrees set to 60° BTDC.
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