My 590+ drive is displaying a Missing Pulse alarm on the keypad. What should I do?
What is the missing pulse trip?
This trip is triggered when a pulse(s) is missing from the 6-pulse armature current waveform. It is enabled when the motor loading exceeds 1.5 times the DISCONTINUOUS parameter value.
- Connect an oscilloscope across the Armature to verify whether there is a missing pulse.
- Is there a Drive Isolation Transformer for this drive? Is a Line Reactor installed for this drive? Does the missing pulse only occur with other drives running? As these could be affecting the drive.
- Has this system been autotuned?
- Autotune the system if the drive has not been yet. The autotuned procedure can be found in the manual. Use the manual that corresponds with your drive’s firmware revision. Make certain the armature does not move during the autotune.
- Are the SCR connections loose?
- Check the SCR connections between the SCR leads and the trigger board.
- Insure the SCR bridge connections are not loose.
- Is the SCR defective?
- Check the resistance across each SCR in the drive in both polarity. The resistance should be very high. If resistance is low (or 0) the SCR is defective.
- Check the Gate-Cathode resistance of the SCR. The actual resistance is not important. However, the resistance of all the other SCRs must be within 10%.
- Visually check the SCR to make sure it is not damaged. When an SCR faults, it often faults shorted, but occasionally it faults open.
- Is there a defective pulse transformer on the power board or firing board?
- Check the resistance of the pulse transformer winding. The actual resistance is not important. However, the resistance of all the other windings must be within 10%.
- Is there a motor short?
- Check the motor with a megger to check for insulation and continuity issues.
- Use the below document to check the field windings of the motor
- Is there a feedback on the device?
- Check coupling tightness between the motor and the feedback device
- Check connections between the feedback device and the feedback card
- Check the feedback signal to make sure that is no noise in the system
- Are you using the speed loop?
- Check the gains in the speed loop they may be too high and might need to be adjusted (Note that ripple from the speed loop from either the setpoint or feedback can cause unstable current)