IMPULSE•G+/VG+ Series 4 Technical Manual
November 2022
Page 204
6.2 Troubleshooting Encoder and Brake Faults and Alarms
The faults and alarms in this section may involve the encoder feedback or motor brake system. During system
startup, these faults and alarms are often caused by parameters that need to be adjusted. However, if the system
has been running for some time, this usually indicates a problem with the physical system and adjusting the
parameters should only be done after the physical system has been inspected.
6.2.1 DEV–Speed Deviation Fault
Definition
A Speed Deviation fault means that the VFD output is not able to follow the commanded speed reference. This is
possible if there is not enough torque available to follow the internal speed reference. Therefore, speed deviations
may occur when the VFD is at its programmed torque limit. In addition, if the VFD receives erratic, or missing,
encoder pulses, speed deviations are also possible. If the initial VFD tuning and start-up of the system was
successfully completed and the crane has been in operation without any faults, then the occurrence of this fault
most likely indicates that something mechanical with the system has changed or VFD parameters were changed
(i.e., failed encoder, load snag, crane overload, change in acceleration or deceleration times, etc.).
Corrective Action
1. Do
NOT
continue to operate the hoist.
NOTE:
Continued attempts to operate the hoist with speed deviation faults can result in loss of control of the load.
2. As a precaution, the Load Float Time (C08-10) should be set to zero until the source of the speed deviation
fault has been determined and corrected.
3. Verify if the load has snagged or if there is a load on the hook that exceeds capacity.
4. Check the alignment of the encoder pulse wheel and sensor head, or the encoder shaft coupling. If the pulse
wheel is misaligned or the shaft coupling is loose, the VFD may get erratic pulse signals or no signals at all
causing a Speed Deviation or PGO fault. Make repairs before attempting to operate the hoist.
5. The encoder cable should be checked for damage.
•
Each of the encoder wires should be checked for continuity, and visually checked for damage.
•
The wires should be checked for shorts between any two wires, including the shield or ground.
6. If the encoder feedback system checks out mechanically and electrically, then check for something in the
mechanical system that might be resisting normal operation. One example may be the brake is not opening
fully and drag is preventing the system from operating at commanded speed.
7. If the encoder feedback system checks out and no other mechanical problems can be found, then something
must have changed in the control system.
•
Check if the accel or decel times have been changed (B05-01, B05-02, C01-02, C01-04, or C01-05).
•
Check if a function that provides an alternate acceleration or deceleration rate has been enabled or
changed (Quick Stop, Reverse Plug Simulation, Accel/Decel Time 2).
If one of these times is too short, causing a torque limit, then the times should be extended.
8. If none of the above steps has identified a valid problem(s), only then should the speed deviation detection
levels be adjusted.
NOTE:
The reaction time necessary to stop a load is limited to the lift of the hoist and the response time of the hoist
brakes. It is desirable to have as fast a fault reaction time as possible without causing nuisance faults.
9. Increase Encoder Speed Deviation Level to no more than 30% (F01-27).
10. After the corrective action has been taken and the fault no longer occurs, set the Load Float Time (C08-10)
back to its initial value.
