3.15
PLC 500 TROUBLESHOOTING Examples
PROBLEM #1, PLC is not measuring lengths.
POSSIBLE CAUSES
1. Encoder - pinion gear loose on encoder shaft
- bad encoder
2. Encoder Cable - bad connection at encoder or PLC
- open or shorted wire
3. PLC unit - damaged hardware
4. Display unit - no power from PLC unit
damaged hardware
5. PLC has lost ACT LTH (Actual Length) parameter - perform self calibration procedure and enter original ACT LTH
parameter value.
DIAGNOSIS;
a. With the machine in MANUAL mode; bring the shuttle forward to the home position and clear the length display to
read ‘0.000’. Run the shuttle, in slow speed, to the rear then back to home, moving full shuttle strokes.
· Length should accumulate on the display as a positive number when the shuttle moves away from the blade and
should count negative going back. If negative going back, and positive coming toward home, then the green chan-
nel wire and the white channel wire should be reversed.
· If the display alters between 0.000 and 0.001 or 0.000 and -0.001, then one of the encoder channels is not being
recorded correctly.
b. To determine the cause, rst, check the encoder cable connections at both ends to be sure all four wires are con-
nected properly. (See next page for connection / wiring information)
Measure the voltage:
a. At encoder connector;
• Between 0 V pin and 24 V pin. This voltage should be a minimum of 22 to 26 VDC.
If the voltage is incorrect; check encoder cable continuity - if OK, possible PLC problem. If the voltage is
correct, go to step b)
b. At encoder connector;
• Between 0 V and channel A and 0V and channel B. This should be slightly less than supply voltage at
each channel.
If voltage is incorrect at this point, check for proper continuity of these wires and repair as necessary.
NOTE:
When checking the encoder cable for continuity, each wire should also be checked for shorting to ground and shorting to
each other. If voltage to the encoder is correct; go to Step C).
c. At the encoder connection of the PLC; - between 0 V and A&B channels.
With the shuttle moving slowly, voltage should be approximately 10 -13 VDC. Input LED’s X0 and X1 should
icker or go dim with the shuttle moving. If these LED’s show no change with the shuttle moving, the encoder is
likely at fault. Check that the pinion gear is securely fastened to the encoder shaft and that it can rotate along the
rack as the shuttle moves.
If all mechanical components are functioning correctly then the encoder is defective.
If all tests check positive, the problem is in the PLC unit.
To Next Page
Loading...