Mitsubishi MELSEC-Q/L Programming Manual page 443

(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
always be continuous. Further, the contact number (X
lower than that for the retract edge.
2) Controls for the advance edge detection sensor contact number (X
*1
(Y ) are as follows:
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
) for the advance edge detection sensor should be
CHKST, CHK
Advance command (X4)
Advance operation
(Y50)
M
Retract operation
(Y51)
Retract command (X5)
) and output with the identical number
1
2
3
4
4
6
7
8
) must
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