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NI EDIDS-2400 Series User Manual | © National Instruments | 173
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 = 2-
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 Stroke = 4-STROKE.
2-Stroke Applications:
Position 0 and tooth 0 coincide with the first tooth following each crank tooth gap. The CamSig input is ignored.
CrankCount will increment from 0 to NumberOfCrankTeeth - 1. During crank tooth gaps, CrankCount will
continue to increment at the location of each missing tooth. For example, if NumberOfCrankTeeth (N) = 60 and
NumberOfMissingTeeth (M) = 2, then CrankCount would increment from 0 to 59, such that teeth 58 and 59 would
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 CamSig input is TRUE.
The CamSig is only used for achieving initial sync. Once sync is achieved, it is maintained according to the location
of each gap. However, CamSig is still monitored to report whether the signal is normally alternating high and low at
each gap. The CamHistory indicator of the EPT tab reports whether the signal is “Normal”, “Always High”, “Always
Low”, or an unexpected pattern reported as “Error”. CrankCount will increment from 0 to 2*NumberOfCrankTeeth - 1.
During crank tooth gaps, CrankCount will continue to increment at the location of each missing tooth. For example,
if NumberOfCrankTeeth (N) = 60 and NumberOfMissingTeeth (M) = 2, then CrankCount would increment from 0
to 119, such that teeth 58 and 59 would correspond to the two missing teeth while CamSig is FALSE. Teeth 118
and 119 would correspond to the two missing teeth while CamSig is TRUE. Tooth 0 would correspond to the tooth
following missing tooth 119.
It is allowed for CamSig to have more than one pulse per cycle, as long as the signal is high and low during the
correct crank tooth gap for the correct phase of the engine. In some applications CamSig may only be a single short
pulse which is not high during either crank tooth gaps. In this case, the CamOffset and CamExtension parameters
may be used to move the cam signal forward by a specified number of crank teeth and extend the CamSig for
a specified number of crank teeth in order to cover one of the gaps. The Cam Offset function results in the cam
signal width being equal to one crank tooth period; therefore, the extension function is required to extend it over the
appropriate gap.
N+1 Patterns
Pattern Description:
N+1 patterns have N evenly spaced teeth and a single additional tooth (Plus1), placed between two evenly spaced
teeth, on the crankshaft trigger wheel. There are two different sub-configurations within this pattern type, specified
by the Plus1Location button. An advanced Plus1 tooth must be positioned such that it is advanced from the midpoint
between two evenly spaced teeth. The amount of advance must be at least ¼ of the normal tooth spacing. A
retarded Plus1 tooth must be positioned such that it is retarded from the midpoint between two evenly spaced teeth.
The amount of retard must be at least ¼ of the normal tooth spacing. N is stated in terms of evenly spaced teeth, as
if there were no additional teeth. For example, a 6+1 pattern would consist of 6 physical evenly spaced teeth and an
additional physical tooth placed between two evenly spaced teeth. EPT N+1 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