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Is it the noise from VFD?

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  • Is it the noise from VFD?

    I have a HPU system of which the 3 phase AC motor connected to a Baldor VS1SP415-1B inverter. The HPU generates about max 2,700psi and there is 4-20mA pressure transducer in the system to read the pressure.

    the problem is that once the motor is on, there is high frequency noise in 4-20mA signal, which is much larger than the real signal. Since this is the feedback of my PID control of the HPU system, high noise level can not be tolerated.

    The way of my system grounding is that green wire (ground of the 3 phase power supply) of the motor power cable is connected to the motor enclosure, the ground of the single phase power supply, which is from different breaker, of the control system is wired to the control box enclosure. I can measure the ohm is relatively small between the motor enclosure and control box enclosure.

    Any way that the noise can be removed from the system? This is my first time working on eliminating noise from motor drive and here are my questions about it:
    1. the cable being used between VFD and motor is non conduit and unshield cable is about 60-70fts, there are two power socket in between, one is just outside of the VFD and another one for extension cable. Is it the bad thing to do so?
    2. I am not sure if there is line reactor or load filter in the VFD, I assume not. Does adding a line reactor or load filter help in my application?
    3. Since the speed control of the motor is not a requirement for my project, will that be better if I plug the motor directly to the power socket on the wall to bypass the VFD? Is a starter needed in this case?
    4. Is there any issue in the current grounding?

    Thanks for your help in advance.

  • #2
    Your grounding is causing a ground loop.

    It should be Main ground wire from the earth ground to the invertor incoming ground.

    The motor ground wire should have a place on the invertor as well to attach to.

    See page 4-1 and 4-10 of the manual: http://attachments.temcoindustrialpo...ter_Manual.pdf
    If you have an urgent issue, please contact AutomationDirect's Technical Support team. Technical Support: 1(800) 633-0405 or (770) 844-4200 Email Tech Support


    • #3
      What about the shield on the 4-20ma cable. It should only be grounded on 1 end. It is a shield and not a conductor. It is connected at only 1 end so it can drain the noise from the shield. Some cables have 2 shields, the shields should not touch and one shield is connected at each end.


      • #4
        With that cable length, definitely use a shielded motor cable. Also, all grounds should terminate very close to the same place. Lastly, use a shielded signal cable and try only grounding one side of the shield.

        This would work fairly well for a motor cable:


        • #5
          How about routing? Keep the transducer and vfd wiring apart as much as possible. Perhaps mount the pressure transducer on another location? VFD cable in steel conduit or VFD shielded cable is recommended.
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