Current measurement over hours

Discussion in 'The Projects Forum' started by vaka85, Dec 9, 2014.

  1. vaka85

    Thread Starter Member

    Aug 21, 2014
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    Hi all,

    I'd like to record (with a PC maybe it would be easier) the current consumption of a DC motor.
    The motor is mounted on a machine and he will perform his movements continually for hours, so we can see its power consumption.
    Since I want to see the exact trend of the signal, I need to record it with a scope.

    I know there are other tools to do this current log, but I want to buy a scope also for other uses, so I take two birds with one stone :)

    So could you give me some advice to understand which model is suitable for my needs?
    And also: to measure corrent is ok a normal amperometric clamp connected to the scope?
    Requested features:
    - it should be connected to a pc in order to log some hours of data.
    - 4 channels
    - bandwidth could be low..
    - current measurement clamp to connect to the scope.

    Thanks
     
  2. wayneh

    Expert

    Sep 9, 2010
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    I'd use data acquisition for this. My tool is a LabJack U3-HV, but there others such as Dataq. These inexpensive solutions presume you have a computer to dedicate to the task.

    I'd also consider the Kill-o-watt. Not sure it has the details you want.
     
  3. MikeML

    AAC Fanatic!

    Oct 2, 2009
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    Can you break one of the wires going to the motor to insert a low resistance shunt? If so, monitoring a time-varying DC motor current then just requires a simple current monitoring IC, typified by the ZXCT1009 and its brothers.

    Use a PC USB data logger to sample the voltage out of the ZXCT1009, and pick a sampling interval sufficiently fast to catch the details of the motor current dynamics you are interested in.
     
    Last edited: Dec 9, 2014
  4. MaxHeadRoom

    Expert

    Jul 18, 2013
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  5. Alec_t

    AAC Fanatic!

    Sep 17, 2013
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    If you've got a deep pocket you can buy a DC clamp Ammeter/logger with a USB/Bluetooth interface for a PC.
     
  6. vaka85

    Thread Starter Member

    Aug 21, 2014
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    Thank you all for the replies
    this is very interesting! Thank you!
    The motor can absorb up to 30A.
    If I put 1 ohm shunt resistor, in the worst condition, the current across the resistor will be about 30 A, and the voltage across 30 V.
    I need to find some current sense amplifier more suitable for my values.

    Regarding the other replies: I need a scope also for other measurements, so I take two birds with one stone. So for sure I will by one, but since this will not happen in a short time, in the meantime I can try the current monitoring IC..
     
  7. GopherT

    AAC Fanatic!

    Nov 23, 2012
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    1 ohm is not low.

    0.001 ohm is low. Monitoring 30 mV is easy.
     
  8. MikeML

    AAC Fanatic!

    Oct 2, 2009
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    Yes, the ZXCTxxx series is intended to be use with current shunts that are typically a few milliOhms or less. 30A through 1mΩ produces a voltage drop of only 30mV.
     
  9. vaka85

    Thread Starter Member

    Aug 21, 2014
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    yes, but not so easy to find into my collection of resistors :)
    I found some 1 ohm 10 W resistors, I'll put some of them in parallel..
     
  10. vaka85

    Thread Starter Member

    Aug 21, 2014
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    I will use some 1 ohm resistors put in parallel.. 10 W each. It should be enough
     
  11. MikeML

    AAC Fanatic!

    Oct 2, 2009
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    Accurate Current Shunts are a special component made for the purpose. They have a four point connection scheme to preserve accuracy.
     
    vaka85 likes this.
  12. vaka85

    Thread Starter Member

    Aug 21, 2014
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    even more interesting!
    Thank you Mike, your answer are always very useful
     
  13. ErnieM

    AAC Fanatic!

    Apr 24, 2011
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    I get shunts like that from China off EBay for a fifth the price.
     
  14. vaka85

    Thread Starter Member

    Aug 21, 2014
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    yes, but with 40 days delivery time to Italy ;)
     
    Last edited: Dec 12, 2014
  15. ErnieM

    AAC Fanatic!

    Apr 24, 2011
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    Then you better place the order today. :rolleyes:
     
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