National Instruments NI DIDS-2103 User Manual page 115

Troubleshooting
Achieving reliable, clean crank and cam signals can sometimes be a trial and error process. It is National
Instruments' experience that reliable sync is often not achieved with the first attempt at running the engine over the
entire speed and load range. Even though sync may occur successfully at low engine speeds, it does not always
mean that sync will be consistent at high speeds or loads due to trigger wheel imperfections, sensor placement
distance from the trigger teeth, ignition or injection radiated noise, or camshaft position lash or stretch with respect to
the crankshaft. The system engineer should take care to check that external signal shielding and routing are optimal
and that there is plenty of signal-edge margin for cam belt or chain stretch.
The EPT Diagnostics tab can be used to capture the crank and cam signals for diagnosing post-filter problems with
extraneous pulses or pulse alignment. The
then be stopped for analysis. The signals can be captured upon a loss of sync trigger to look at the crank and cam
signals captured before the loss of sync.
EPT Pattern-Specific Information
N-M Patterns
Pattern Description:
N-M patterns have N evenly spaced teeth and M missing adjacent teeth (gap) on the crankshaft trigger wheel. M
is limited to 1 or 2 missing teeth. N is stated in terms of evenly spaced teeth, as if there were no missing teeth. For
example, a 60-2 pattern would consist of 58 physical teeth followed by two missing teeth. EPT N-M function can be
configured to track 360 or 720 degrees depending upon an optional camshaft input. When tracking 360 degrees
for 2-stroke engines, the camshaft input is ignored. This is designated by configuring the function with
STROKE. When tracking 720 degrees for 4-stroke engines, the camshaft input signal must be TRUE during every
other crank tooth gap. This is designated by configuring the VI with
2-Stroke Applications:
Position 0 and tooth 0 coincide with the first tooth following each crank tooth gap. The
CrankCount will increment from 0 to
continue to increment at the location of each missing tooth. For example, if
NumberOfMissingTeeth
correspond to the two missing teeth and tooth 0 would correspond to the tooth following missing tooth 59.
4-Stroke Applications:
Position 0 and tooth 0 coincide with the first tooth following the crank tooth gap while the
The CamSig is only used for achieving initial sync. Once sync is achieved, it is maintained according to the location
of each gap. However,
each gap. The CamHistory
Low", or an unexpected pattern reported as "Error".
During crank tooth gaps,
if NumberOfCrankTeeth
to 119, such that teeth 58 and 59 would correspond to the two missing teeth while
and 119 would correspond to the two missing teeth while
following missing tooth 119.
It is allowed for CamSig
correct crank tooth gap for the correct phase of the engine. In some applications
pulse which is not high during either crank tooth gaps. In this case, the
may be used to move the cam signal forward by a specified number of crank teeth and extend the
a specified number of crank teeth in order to cover one of the gaps. The Cam Offset function results in the cam
EPT Diagnostics
NumberOfCrankTeeth
(M) = 2, then CrankCount
CamSig is still monitored to report whether the signal is normally alternating high and low at
indicator of the EPT tab reports whether the signal is "Normal", "Always High", "Always
CrankCount will continue to increment at the location of each missing tooth. For example,
(N) = 60 and NumberOfMissingTeeth
to have more than one pulse per cycle, as long as the signal is high and low during the
tab can continuously display crank and cam signals and
Stroke
- 1. During crank tooth gaps,
would increment from 0 to 59, such that teeth 58 and 59 would
CrankCount will increment from 0 to 2*NumberOfCrankTeeth - 1.
(M) = 2, then
CamSig is TRUE. Tooth 0 would correspond to the tooth
CamOffset
NI DIDS-2100 Series User Manual | © National Instruments | 115
= 4-STROKE.
CamSig input is ignored.
CrankCount
NumberOfCrankTeeth
CamSig
CrankCount would increment from 0
CamSig is FALSE. Teeth 118
CamSig may only be a single short
and CamExtension
Stroke = 2-
will
(N) = 60 and
input is TRUE.
parameters
CamSig for