Hitachi HSC-2100 Hardware Manual page 162

Case 2 -- the count value is abnormal:
Input pulse signal frequency exceeding its
specification limit
Excessive pulse input due to noise
Relay contact make and break operations not
counted
None of the above
Case 3 -- no comparison output is produced:
External power not supplied
External power supply voltage too low
External wiring incorrect
None of the above
Check item
Check item
Lower the frequency to 20 kHz or less if
the module used is LWC400 or LWC401.
If it is LWC402, lower it to 100 kHz or
less.
Take a noise reduction measure.
Replace the relay contact with a transistor
contact.
Replace the pulse counter module with a
new one.
Supply power to the external power
source.
Apply rated voltage (20 to 28 VDC) to the
pulse counter module.
Correct the wiring.
Replace the pulse counter module with a
new one.
6-13
6 MAINTENANCE
Remedial action
Remedial action