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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
All EPT functions have a common internal core that tracks angular position. The supporting internal logic around the
core interprets the incoming crank and cam position pulses according to an expected pattern. Each EPT function
has a Boolean crankshaft and camshaft input. These signals may be connected via any available NI 9411 digital
input source within the DI Driver System. The pattern input signals are named according to the most common
engine applications, such that there is a crankshaft trigger wheel and an optional 4-stroke camshaft trigger wheel.
However, it is also possible to operate with a single trigger wheel mounted to a camshaft of a 4-stroke engine. This
would require routing the physical camshaft trigger wheel sensor signal into the Crank_DigChanAsn of the DI Driver
window description for assigning NI 9411 digital inputs to internal signals.
Digital Signal Filtering
It is often necessary to implement filtering of the crank and/or cam signals prior to entering the EPT function. The
DI Driver System software provides an integrating filter function which rejects positive and negative digital signal
pulses having a pulse width less than the filter time. Refer to the
window description for further
information about filtering the NI 9411 digital inputs.
EPT Pattern Simulation
All EPT functions contain a built in pattern simulation tool specific to the pattern for which the EPT function was
configured. Pattern simulation is turned on simply by setting
button of the
to
TRUE
and
setting the
to an appropriate value for the simulated speed. When simulation is turned on, the
Crank and Cam inputs to the EPT function are internally disconnected and replaced by the internally simulated
counterparts. The simulation feature allows the designer to bench test the DI Driver System functionality at any stage
of the development without the need for external simulation hardware.
Achieving Sync
In order for position tracking (sync) to start, a few conditions must be met. First, some pattern specific values must
be set correctly to the EPT function, such as
(if N-M),
, and
ON
. When
the stall speed (RPM) is exceeded, the
indicator will be set to
Spinning
and the EPT function begins
counting a complete cycle of crank teeth. After a complete engine cycle of crank teeth is received, the EPT function
begins looking for the first occurrence of a unique feature of the crankshaft and camshaft pattern which identifies an
absolute position. For example, if an N-M pattern is being used, the function searches for the occurrence of the M-
tooth gap. This is the moment of achieving sync. When sync is achieved, the
Sync
and the angular position of the crankshaft will be tracked. As sync is maintained,
will show the latest
crankshaft tooth count with respect to absolute 0 position. Each EPT function will have different rules for achieving
and maintaining sync, as well as location for absolute position 0. This information is contained in the EPT Pattern-
Specific Information section below.
Содержание NI DIDS-2103
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Страница 212: ...212 ni com NI DIDS 2100 Series User Manual 14 Connecting General Purpose Solenoids to the PFI Driver LS Channels...
Страница 213: ...NI DIDS 2100 Series User Manual National Instruments 213 15 NI 9411 to Single Ended and Differential Encoder...
Страница 214: ...214 ni com NI DIDS 2100 Series User Manual 16 9066 RS 232 Serial Connector to TDK Power Supply...
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