Reliance electric PSC7000, Руководство по эксплуатации

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10-2
10.1.2 Latch Variable
Three types of latch variables can be captured by the respective counters. The latches
are Z pulse, mark signal, and origin point signal. The signals entered from the input circuit
pass through the latch control circuit, and the value of each counter is captured to the
latch variables.
In the latch control circuit, logic inversion of the signals (selection of either normal-open
input or normal-close input) and logic selection of the signals (which signal is captured)
are executed from the input circuit of the respective latches (Z, mark and origin point).
See Section 10.1.4 and 10.1.5 respectively.
The present count captured by the latches will be enabled by means of the control output.
The difference between the count with a latch and the count during scanning can be
obtained through the LATCH_READ block of the control block task.
1) Z Pulse Latch Variable (CHn_Z_LATCH!)
This variable captures a count with the Z pulse signal transmitted from the pulse
tachometer. When the pulse tachometer rotates forward, the value is captured on the
rising edge of the Z pulse signal (output of the latch control circuit for input logic). When
the pulse tachometer rotates backward, the value of the counter is captured on the falling
edge of the Z pulse signal. Thus, the origin point of the pulse tachometer can be detected
without a margin of error (+/-1 pulse or less) regardless of rotation direction.
Phase A
Phase B
Z pulse
Counter
Ｎ－１ Ｎ Ｎ Ｎ－１
Z pulse
Ｎ
Latch Ｎ－１
Fig.10-2 Transition of Z Pulse Latch Variable