The conveyor starts in reverse or produces an overload when forward operation is expected. Follow the command from the operator request through the PLC or switch, the drive digital inputs, the configured direction logic, and finally the motor conductors. Correct the first point where the commanded and observed states diverge; an overload may be secondary to the unintended reverse command.
What path carries the conveyor run request?
Identify the control path before changing wiring or parameters. The request may originate at a selector switch or pass through PLC logic and an output. That signal then reaches a drive input such as DI1 or a dedicated reverse input. The drive interprets the active inputs according to its parameter set and commands the motor.
| Path point | Address or terminal | Expected state | Proof |
|---|---|---|---|
| Operator command | Read from the electrical print | Forward selected | Input or contact changes once |
| PLC logic, if fitted | Read the input and output addresses from the PLC program | Forward request produces the intended output | Monitor both addresses online |
| PLC output or switch contact | Read from the electrical print | Output follows the command without chatter | Measure the signal at the source |
| Drive terminal |
DI1, reverse input, or terminal named by the print |
Only the intended input becomes active | Read the drive input monitor and measure at the terminal |
| Drive direction command | Drive status display | Forward | Direction status agrees with the request |
Record the actual address and terminal at each hop. The path is proven when a forward request produces one stable forward state at the drive without activating the reverse function.
Are the control wires and jumpers correct?
Layer one first. Isolate power according to the machine procedure, then tug-test the control conductors at both ends. Look for loose terminals, broken strands, and wire whiskers that can bridge neighboring inputs. Inspect the source end as closely as the drive end; a secure drive terminal does not rule out a loose PLC output terminal or switch contact.
Compare the two conveyors conductor by conductor only if the machines are intended to operate identically. One observed difference was a possible missing jumper between the reverse function and DI1. Do not install that jumper from appearance alone. Confirm its purpose against the wiring diagram and the input assignments because bridging a reverse input can create the exact unwanted command being diagnosed.
| Physical check | Fault it can create | Acceptance check |
|---|---|---|
| Loose conductor | Intermittent run or direction state | Conductor passes a tug test |
| Stray strand or whisker | Two digital inputs active together | No exposed strand reaches an adjacent terminal |
| Missing or extra jumper | Input state differs between conveyors | Jumper matches the approved drawing |
| Defective PLC output or switch | Incorrect or unstable command | Source voltage and drive input indication change together |
Restore control power and operate the command without running the motor where the drive permits it. This stage passes when the drive input monitor matches the measured terminal states.
Do the two drives interpret their inputs the same way?
Matching wires do not guarantee matching behavior. Compare the complete input-function assignment and direction-related settings between conveyors, using the machine prints or approved parameter record as the reference. A terminal labeled DI1 identifies a physical input, not necessarily its programmed function.
| Setting group | Comparison | Possible symptom |
|---|---|---|
| Digital input assignment | Function mapped to DI1 and the reverse input |
Forward wiring invokes reverse |
| Command source | Terminal, PLC, or local control selection | Drive ignores the expected source |
| Input polarity or logic | Active and inactive state | Direction remains asserted with the contact open |
| Reverse speed reference | Compare with the approved baseline | Unexpected reverse speed |
| Acceleration profile | Compare forward and reverse behavior | High current during an aggressive transition |
Do not copy every parameter blindly from the neighboring drive. First confirm that motor data, conveyor mechanics, and control intent are the same. The parameter check passes when identical input states produce the intended direction status and reference on both drives.
Where does the forward command become reverse?
Monitor the path while issuing one start request. Watch the PLC input, logic result, physical output, drive input bits, direction status, frequency or speed reference, and current indication. Record state changes in sequence rather than checking them at unrelated times.
| Observation point | Before start | Start transition | Running |
|---|---|---|---|
| Forward request | Inactive | Changes once | Stable active |
| Reverse request | Inactive | Remains inactive | Remains inactive |
| Drive direction status | Stopped | Forward selected | Forward |
| Motor current | Stopped value | Record the displayed rise | Stable for the load |
If the PLC output becomes reverse, troubleshoot the logic and its field inputs. If the PLC output is correct but the drive terminal state is wrong, repair the output device, contact, or wiring. If the terminal state is correct but drive direction is wrong, correct the input assignment or direction parameters. The test passes when the first incorrect state has been isolated to one hop.
How should the direction fault be corrected?
- Back up or record the existing drive parameters before editing them.
- Repair loose conductors, stray strands, or incorrect jumpers using the approved wiring diagram.
- Replace or correct a PLC output or switch contact only after proving that its electrical state differs from the commanded state.
- Set the drive command source and digital input functions to the approved machine configuration.
- Compare reverse speed and acceleration settings if reverse motion coincides with the overload indication.
- Jog or test at the lowest practical operating condition permitted by the machine procedure, with the conveyor clear.
Separate command direction from motor rotation. If the drive reports forward while the shaft physically turns backward, the output phase sequence or mechanical interpretation of forward is wrong. For a compatible three-phase motor installation, exchanging any two motor conductors reverses rotation, but perform that change only with power isolated and only when the drive and motor documentation permit it. Never exchange conductors while energized, and do not use input rewiring to conceal incorrect PLC logic.
The correction passes when the drive reports the requested direction and the unloaded motor or conveyor moves in that same direction.
Does the overload remain after direction is corrected?
Treat the overload as a separate fault only after removing the unintended reverse command. Reverse travel can drive material into a stop, tension the conveyor incorrectly, or apply an unsuitable reverse speed or acceleration profile. Any of these can raise motor current.
- Clear the mechanical path and check that the conveyor turns freely in the intended direction.
- Confirm that the displayed direction and speed reference match the command.
- Compare the active acceleration profile and reverse speed settings with the approved values.
- Run unloaded and record drive current during acceleration and steady operation.
- Add the normal load and repeat the current observation.
- If the overload returns, read the exact drive fault indication and inspect the parameter or diagnostic record associated with that event.
The end-to-end test passes only when repeated start, run, stop, and direction commands reach the correct drive inputs, physical motion agrees with drive status, and no overload recurs under the normal load.
FAQ
Can I copy every parameter from the working conveyor drive?
Only after confirming that the conveyors, motors, wiring, and control intent are equivalent. Compare input assignments, command source, reverse speed, and acceleration settings against the approved parameter record.
Does a forward PLC command prove the drive received forward?
No. Monitor the PLC output, measure the field signal, and read the drive input and direction status; a failed output, loose terminal, or wiring bridge can interrupt the path.
Can a missing jumper make the conveyor run in reverse?
It can change the digital-input state if the design uses that jumper, but install nothing from visual comparison alone. Verify the connection between the reverse function and DI1 against the approved wiring diagram.
Does swapping two motor wires fix a reverse command?
No. On a compatible three-phase motor it changes physical rotation, but it does not correct an erroneous PLC output or drive direction command. Use it only when drive status is correct and physical rotation is opposite.
Can I reset the overload and return the conveyor to service?
First prove the command path, correct the direction fault, and test unloaded. Then repeat start, run, stop, and direction commands under normal load while confirming correct input states, matching physical rotation, stable current, and no recurring overload.