Observed SJ100 FM Output Difference
Two nominally identical SJ100 drives produce different PLC readings. Unit 1 varies its voltage from 0 to 10 V and produces counts from 0 to 32000. Unit 2 produces only 0 to 42 counts and its output does not vary as expected. Both drives have C23 set to 00, so that setting alone does not explain the difference.
Evidence and Unknowns
| Check | Unit 1 | Unit 2 |
|---|---|---|
| Measured output behavior | Varies from 0 to 10 V | Does not vary as expected |
| PLC count range | 0 to 32000 | 0 to 42 |
| C23 | 00 | 00 |
The evidence does not identify the PLC input type, wiring terminals, command source, scaling configuration, drive firmware, or the operating variable assigned to the output. These items must be compared before treating the fault as a drive-parameter problem.
Troubleshooting Procedure
- Measure each drive output directly with the same meter and operating command. Record the voltage at equivalent stopped, intermediate, and maximum operating points.
- Move the Unit 1 signal wires to the PLC channel used by Unit 2, if the process permits. If that channel then reports 0 to 32000 counts, the PLC input and scaling are working and the difference remains with Unit 2 or its wiring.
- Move the Unit 2 signal to the known-working Unit 1 PLC channel. If it still reports only 0 to 42 counts, inspect Unit 2 wiring, reference connection, and output configuration.
- Compare the complete relevant parameter sets rather than C23 alone. Confirm that both outputs are assigned to the same monitored quantity and are tested under the same operating state.
- Inspect terminations and continuity. A missing reference connection, incorrect terminal, or wiring fault can produce a small count change without the expected 0-to-10-V swing.
Verification and Decision Path
If Unit 2 measures the same 0-to-10-V signal as Unit 1 but the PLC remains at 0 to 42 counts, troubleshoot the PLC channel configuration, scaling, and field wiring. If Unit 2 does not generate the voltage swing when measured directly, compare its full output configuration and operating conditions with Unit 1. If configuration, commands, and wiring match but the outputs remain different, the available evidence supports investigating a hardware difference or fault; it does not identify a specific failed component.
FAQ
Why does one SJ100 show 0 to 32000 PLC counts while the other shows only 0 to 42?
The evidence does not establish one cause. Directly measure both outputs, swap PLC channels, and compare wiring and the complete output configuration to separate a drive-side problem from PLC scaling or input-channel configuration.
Does setting C23 to 00 guarantee identical SJ100 FM outputs?
No conclusion can be drawn from C23 alone. Both reported drives use C23 = 00 yet produce different voltage and count ranges, so additional configuration, wiring, operating-state, or hardware checks are required.
How do I verify whether the SJ100 or PLC input is causing the low count?
Measure the drive output directly and test Unit 2 on the known-working PLC channel. A correct 0-to-10-V measurement with only 0 to 42 counts points toward the PLC channel, scaling, or wiring; a missing voltage swing keeps the investigation on the drive side.
