Mitsubishi MELSEC Q Series Programming Manual page 549

(b) The contact instruction prior to the CHK instruction does not control the execution of the
CHK instruction, but rather sets the check conditions.
Advance end sensor (X0)
turns ON at the detection
(c) A ladder such as the one shown below can be created to perform a cycle time over
check for the system shown above:
T0
X000
X004 X005 X000
Y050
X005 X004 X001
Y051
Y050 X000
Y051 X001
(d) The following points should be taken into consideration when creating a ladder for use
with the CHK instruction:
1) The contact numbers for the advance edge detection sensor and the retract edge
detection sensor (X ) must always be continuous. Further, the contact number (X )
for the advance edge detection sensor should be lower than that for the retract edge.
2) Controls for the advance edge detection sensor contact number (X ) and output with
the identical number (Y )
When advance operation is in progress .... turn ON
When retract operation is in progress........ turn OFF
*1: Output (Y ) is treated as an internal relay, and cannot be output to an external device.
Advance
Retract
Retract end sensor (X1)
turns ON at the detection
When T0 is OFF, program jumps to the instruction
CHKST
next to the CHK instruction.
Executes CHK instruction when T0 is ON.
CHK
Y050 Advances conveyor 1.
SET Y000
Turns ON the internal relay used for failure detection.
Y051
Retracts conveyor 1.
RST Y000 Turns OFF the internal relay used for failure detection.
K100
T0
Cycle time
check timer
*1
are as follows:
CHKST,CHK
Advance command (X4)
Advance operation
(Y50)
M
Retract operation
(Y51)
Retract command (X5)
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