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NI EDIDS-2400 Series User Manual | © National Instruments | 169
teeth rising edges each engine cycle. The
EPT Encoder function can be configured to
track 360 or 720 degrees. When tracking 360
degrees, the reference tooth is located on
the crankshaft, yet is directed to the CamSig
input of the EPT function. When tracking
720 degrees, the reference tooth is located
either on the crankshaft or on the camshaft.
When located on the crankshaft, then an
additional cam phase signal must be present
in order to mask (using EncZMask ) every
other crank reference, such that every other
crank reference is allowed to pass through to
the CamSig input of the EPT function. This
would cause the crank encoder pattern to
effectively generate twice the teeth between
each reference tooth seen by the EPT function.
Table 4.11.a, Supported EPT Patterns
Brief Glossary of EPT Function Terms
CAD: Crank Angle Degrees. There are 360 CAD per two stroke cycle or one crankshaft rotation. There are 720 CAD
per 4-stroke cycle, or two crankshaft rotations. In a 4-stroke engine, the camshaft completes exactly one rotation per
two rotations of the crankshaft. There are two strokes of the piston (up and down) within the cylinder during a single
rotation of the crankshaft. A single stroke of the piston covers 180 CAD.
EXTRAP: The single numerical digit suffix of each EPT function selection refers to the level of EPT Position
Extrapolation. This is a fixed power of two by which the angular resolution of tracked crankshaft position is improved
over the physical teeth alone. For example, if the EPT function has a fixed extrapolation level of 7, then the crank
angle resolution between each physical tooth is improved by a factor of 2^7 = 128. Each individual extrapolated
angle unit between the physical crank teeth is called a Crank Angle Tick (CAT)
CAT: Crank Angle Ticks. Single unit of angular measure of the EPT function. Reported as a power-of-two angular
ticks of crank position travel, having a resolution dependent on EXTRAP and the number of physical teeth per
crankshaft rotation. For example, if using the N-M EPT VI, which has an extrapolation of 7, the number of CAT per
crank tooth would be 2^7=128, and angular position would be evenly incremented by 128 CAT from one physical
tooth to the next. If a 60-2 pattern were used, the maximum number of CAT per crankshaft rotation would be
60*128=7680. If the engine was a 4-stroke, the total number of CAT per engine cycle would be 2*60*128=15360.
MAX_CAT: Maximum Crank Angle Ticks per engine cycle.
EPT Function Commonality
EPT Input Signals