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Motor interference?

  1. Mar 14, 2006 #1
    I have a motorcontroller and a motor and they sit next to each other. The motor shaft has a photointerrupter sensor and the sensor signal is connected to the motorcontroller. The motorcontroller has a feature where it will shuts off the motor whenever it senses a spike in the motor's RPM.

    The problem that i'm having is that whenever I tap into the photointerrupter sensor using a wire, the motorcontroller shuts off the motor like there is an RPM spike. It acts the same way even if the wire i'm taping with is not connected to anything. My theory is that the wire acts as an antenna and it is outputing spikes created by the motor ecm. The motor controller mistaken these spikes as an increase in RPM and shuts off the motor.

    What can I do to overcome this problem??
     
  2. jcsd
  3. Mar 14, 2006 #2

    Danger

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    Stop poking it.

    Seriously, what is your purpose in tapping the sensor? If it's to obtain a signal for some other measurement or something, maybe you could take it from the controller instead?
     
  4. Mar 14, 2006 #3

    chroot

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    You could connect a buffer (op-amp wired in voltage-follower configuration) to the signal, and then look at the signal on the other side of the buffer. This should eliminate the transient phenomena as seen by the motor controller.

    - Warren
     
  5. Mar 14, 2006 #4

    Ivan Seeking

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    You are actually touching the input with the wire while the system is running? If I am understanding you correctly, one might expect this with things running.
     
  6. Mar 14, 2006 #5
    I want to the pulses signal from the sensor. While the motor won't start if I tap into the sensor or it will stop the motor if I tap into while running.

    "You are actually touching the input with the wire while the system is running? If I am understanding you correctly, one might expect this with things running."

    it affects the motorcontroller even if i touch the sensor output with a wire connected to nothing.
     
  7. Mar 14, 2006 #6

    chroot

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    A wire connected to nothing still has capacitance, and still contributes to impedance. I suggest you buffer the signal you're trying to investigate with a suitable op-amp.

    - Warren
     
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