Omron CJ1W-CT021 Operation Manual page 170

Length Measurement
Digital Input Function 11
Reading Captured Value
Measuring length
Digital Output O0 ON
150
To measure the length of objects the pulses of encoder E1 are counted by Linear/
Circular Counter 1 (corresponding DIP switch on the front of the Unit is in the ON-
position). Photo-electric sensor D1 is connected to Digital Input I0. Digital Input I0
controls Counter 1 and is assigned Digital Input Function 11 (Reset, Stop, Capture
and Continue).
Gate Closed
Capture Reset
At the falling edge of Digital Input I0, when an object enters the beam of the photo-
electric sensor, the Counter Value is reset, the gate is opened and Counter 1
starts counting pulses from zero. At the rising edge of Digital Input I0, when the
object leaves the beam of the photo-electric sensor, the Counter Value of Counter
1 is captured and the gate is closed.
By issuing an IORD-instruction from the PLC ladder program the captured Coun-
ter Value is read. The length of improper sized objects is stored in Extended Mem-
ory of the PLC (refer to the ladder program example on the next pages).
The length is measured by Counter 1 and should be ideally 5000. The valid range
for the length of an object is 4900 – 5100. If the length of an object is in Range 0
(4000 – 4900) or Range 1 (5100 – 6000) the object is improperly sized and must
be removed. Digital Output O0, in the Output Pattern of Counter 1, is turned ON
when the Counter Value is within Range 0 or 1.
4000 4900
Range 0
Gate Closed
Gate Open
Object passes
photo-electric sensor
Capture
5000 5100 6000
Range 1
Section 6-2
Gate Open
Object passes
photo-electric sensor
Reset Capture
Counting Range
Circular Counter 1