IMC CANSAS - Page 328

328 Properties of the Modules
imc CANSAS Users Manual - Doc. Version 1.9 - 05.12.2014© 2014 imc Meßsysteme GmbH
Hysteresis:
In order to prevent that low-level noise in a not very steep edge causes multiple crossings through the
threshold value, it is possible to enter a hysteresis here. Only once this hysteresis has been crossed,
the edge detector monitors the signal from the other direction. The hysteresis can be stated between
0 V (= no hysteresis) and 40 V.
Signal delay:
If a signal arrives delayed at the edge detector, then it is possible to specify the delay time using this
parameter. The time specified here directly affects how the ignition angle is determined, since
determining it involves observing the ratios of time differences between various pulses. The signal
delays are observed in forming the time differences.
E.g. the following effects can delay a signal:
the original signal itself is already delayed
the sensor causes delay
external conditioning, lines cause delay
(different) conditioning in imc CANSAS-IGN can also cause delay, especially low-pass filters!
a signal's edge is not very steep. The threshold value is in the middle of the edge, not at its start.
Delay times are not always easy to determine. However, an imprecise or incorrectly entered time can
cause significant errors in determining the ignition angle.
The delay time is stated in ms, and may not have decimal places. Even microseconds make a
difference!
The Snapshot mode can help to determine the delay times, particularly with edges which are not very
steep. This is because depending on ow high the threshold value is, there can be a different delay with
respect to the actual start of the edge.
Thus, even with low pass filters (e.g. imc CANSAS-IGN's adjustable 1st order low-pass) it is not easy to
determine the delay time according to the rule of thumb (0.16 / cutoff frequency). This rule of thumb
is only valid with a suddenly jumping input signal, for instance, if the threshold value is about 63% of
the peak height. If the threshold value is different, the delay can be significantly different. Since the
threshold value and the signal shape are relevant, the imc CANSAS software is not able to
automatically correct any delay caused by a configured low-pass filter.
Pull up to 5 V:
A resistor can be switched on at each input to 5 V. If this resistor is switched "ON", then an external
switch (switch to 0 V) can easily be connected. Otherwise, the resistor is not used ("OFF").
This parameter is also effective in Snapshot mode.
Trigger edge:
The edge detector determines the threshold crossing only in the specified edge direction: positive or
negative. In the case of the 4th channel (camshaft), the trigger edge is used in conjunction with the
camshaft pattern.
Coupling:
AC- or DC-coupling can be selected. With AC-coupling, a 1st order high-pass filter is connected
between in order to eliminate a DC-offset. With DC-coupling, this high-pass filter is not connected
between. The high-pass filtering comes before the optional absolute value formation and thus before
the edge detector.
This parameter is also effective in Snapshot mode.