ParetosFew
Member
System:
Problem: Severe "bouncing" of several different input signals (mV/V and 4-20mA) whenever the drive is active. Only when the drive is told to run, even if at 0 speed. As soon as drive is stopped (but still powered) signals return to acceptable levels.
Things I've tried:
Another thing I may try soon is configuring the drive to not source the 24V for the enable signal. Maybe something in the transformer and power supply internal to the drive is the cause? I've attached photos of the scope measurements although I'm not real confident on them. I think I should have been DC coupling, which I did since and is where I measured the much higher spike values (+/- 2.5 - 3 divs at 5V/div). Unfortunately don't have pictures of latest measurement.
Any Ideas? Also, glad to finally make a post here, I've had many problems solved through google searches that lead to threads here over the past few years in this field. Thanks in advance!
- Drive: Control Techniques - Unidrive SP (Panel Mount)
- Controller: NI cRIO
- Power: Whole system runs off of a 3 phase 480V plug. There is a transformer for 120V that powers a few accessories and a 24V supply. VFD is run directly of the 480.
- May be relevant, entire system is somewhat portable. Panel is on a steel stand that sits next to the machine. All grounding must be through ground prong on 480V plug.
Problem: Severe "bouncing" of several different input signals (mV/V and 4-20mA) whenever the drive is active. Only when the drive is told to run, even if at 0 speed. As soon as drive is stopped (but still powered) signals return to acceptable levels.
Things I've tried:
- Sent signal with process meter - worked fine.
- Signals cables are shielded only on panel side.
- Ran signal cable(4-20mA) completely outside of panel and trays, no change. Moved 24V supply out of panel, laid on floor temporarily, no change. These make me think this is not radiated EMI.
- Because different types of signals are effected, I suspected noise at power supply. Measured huge (>10V) periodic spikes between +24V and 24VCOM.
- No "direct" connection between VFD and 24V system. Only connection is 24V sourced from drive through a Guard Master safety relay contact back to the drive, and chassis ground.
- Moved power supply away from VFD, isolated power supply, tried another power supply all with no change. Seems like power supply is OK.
- Replaced drive enable through safety relay with a jumper (temporarily) so that only thing shared between the drive and the 24V system is chassis ground. Problem persisted.
- This made be suspect noise on chassis ground. Measured between chassis ground and earth ground from a nearby 120V outlet. Spikes still visible, I think confirming that the noise is present on the entire chassis. I definitely think this severe noise on ground would interfere with the cRIO.
Another thing I may try soon is configuring the drive to not source the 24V for the enable signal. Maybe something in the transformer and power supply internal to the drive is the cause? I've attached photos of the scope measurements although I'm not real confident on them. I think I should have been DC coupling, which I did since and is where I measured the much higher spike values (+/- 2.5 - 3 divs at 5V/div). Unfortunately don't have pictures of latest measurement.
Any Ideas? Also, glad to finally make a post here, I've had many problems solved through google searches that lead to threads here over the past few years in this field. Thanks in advance!