322 Properties of the Modules
imc CANSAS Users Manual - Doc. Version 1.9 - 05.12.2014© 2014 imc Meßsysteme GmbH
Zero marking on the crankshaft [degrees before TDC]
The angle specified here will be added to the calculated ignition angle. This parameter accounts for
the fact that, in general, the zero angle marking on the crankshaft is not at the top dead center (TDC),
but a small angle before it. Entered in degrees (-180° to +360°), a positive value indicates degrees
before TDC, while a negative value indicates a zero mark after TDC.
For instance, if the zero mark is +70° before TDC, then enter 70 for this parameter. Conversely, if the
zero mark was 120° after TDC, enter -120.
With incremental encoders having a zero pulse, the zero mark is clearly the position where this zero
pulse occurs. However, rotational sensors which lack a zero pulse, such as a magnetic pickup on a
gear, the zero mark is typically the first tooth (or more precisely, the last edge of the tooth) after the
gap. In other words, if a tooth produces positive pulses, then the first negative signal edge after the
missing tooth is the zero mark.
Aside of TDC offsets, this parameter may be used to introduce any general offset into the angle
calculation if necessary for user specific conditions or site specific standards.
Minimum, Maximum ignition angles
The expected range for the ignition angle is localized here. For instance, to within a range of
-70 .. + 30 degrees.
This contributes to angles incorrectly calculated due to interference being suppressed already in the
device. Thus, the range should be selected to be as narrow as possible.
The range span must be sufficiently small for the number of cylinders. The span is the difference
between the maximum and minimum ignition angle. Example: With a 4-cylinder, 4-stroke engine
there is an ignition every 180 degrees, namely 4 at equal distances over the complete 720 degree
work cycle. If there is an ignition at 170 degrees, then this is 10 degrees before TDC. If there is another
ignition at 350 degrees, this is also 10 degrees before TDC. In this case the maximum span for this
engine is 180 degrees. For engines with higher cylinder counts, this span becomes less.
Furthermore, a 3-cylinder engine responds in this regard like a 6-cylinder one in which only every 2nd
ignition does not occur.
In no case may the span be exceeded when entering the parameters! Incorrect calculation of the ignition
angle would result!
Ignition signal processing
If the ignition signal is to be evaluated, this parameter is set to “active”. This is the normal setting.
Only in exceptional cases where the module is used only for determining the RPMs and no ignition
signal is connected, this parameter is set to “passive”.
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