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Interference from Van De Graff

  1. Jul 23, 2012 #1
    Hello all I really hope someone can shed some light on a problem I'm having.

    I'm currently researching granular fluid behavior in High voltage electric fields.

    My setup is essentially a 200kV generator placed directly under a glass container with my test medium inside of it.

    The experiments are conducted with an aluminum rod (attached to the grounding port of the generator) inside of the container interacting with the charged bed of particles above the generator.

    In order to control the movement of the aluminum rod in the vertical direction I use a stepper motor setup with a Velmex nf90 controller attached to my computer via serial port.
    The rod is attached to the stepper with a metal and Plexiglas bracket, which at the end is purely Plexiglas; because of this I believe there is not conductivity or transfer of charge from the rod to the motor).

    Before anyone mentions it, YES, I realize the velmex is rather outdated, and clearly no longer supported, but as those of you with limited funding in your research know, if there's something lying around the lab not being used, you jump at the opportunity!

    I have attached a picture of my setup.

    The issue that I have been running into with my tests I believe to be related to an EMF field produced by the generator. When the generator is powered on and fully charged (running at full speed). I am able to control the movement and speed of my stepper motor via my programming, computer controller software (through the Velmex) and manually via a remote. The control though only seems to last for a few seconds (I would guess about 5-8s) until the controller cuts out, locks up, and I no longer have control over the motor.

    Now, the motor is brushless (and therefore susceptible to electronic interference I think?) and when the controller shorts out I hear a steady clicking of some kind coming from the motor and controller. The fuse itself never seems to blow, and if I turn everything off and on again it again works for a short period of time.

    I can't completely contain the setup because I need to be able to use high speed video capture, but I do need the slider and stepper to be able to function continuously.

    Does anyone know how to cut down or eliminate this interference?

    Maybe shielding of some kind?

    I’d really appreciate any help I can get on this. My training and education is mostly mechanical with a small amount of electrical work, but this falls a bit out of my realm of expertise….



    The controller
    http://www.velmex.com/downloads_old_controllers.html [Broken]
     

    Attached Files:

    Last edited by a moderator: May 6, 2017
  2. jcsd
  3. Jul 23, 2012 #2
    The ticking you are hearing is probably arcing.
    Turn all the lights off and look at everything in the dark. Don't rush, it takes several minutes for your eyes to adjust to the dark. Look at everything, arcing can occur in the oddest places.
    The cure for the ticking is to remove any sharp points or edges. Or small wires.
    Aluminum foil is great for making shields.
    Personally I don't like wood with high voltage.
    All metal should be either grounded or connected to the high voltage.
    Good Luck
     
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