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Current Measurement: MSP430F4618/2013 EXperimenter kit

sheik abdullah
Intellectual 330 points
Other Parts Discussed in Thread: MSP430F4618, MSP430F5438

Hi,

  I am working on MSP430F4618/2013 EXperimenter kit. In that I am not able to measure the current consumping by MSP430.

  While measuring the current across PWR1, the reading of Multimeter(in DC current mode) always show 0 reading. I tried for different program also.

  First I removed the PWR1 Jumper. And I connect the multimeter serially, the board get the power(tried for both battery and FET power), and the application start executing but the current value are not moving from 0.

  Kindly help me to fix the problem.

 

Regards,

sheik

  • 0
    Guru 227245 points

    I don't know the layout off-hand, but if you do not properly attach the multimeter (or it has a too-high inner series resistance in the low-current ranges), then the MSP is powered by the board through its port pins, as these have a higher voltage than its own VCC. Te supply current then runs 'around' your multimeter. It isn't really healthy for the MSP.

  • 0 in reply to Jens-Michael Gross
    Intellectual 330 points

    Hi, 

     Thanks JMG for your reply.

    The multimeter what I using to measure the current has capability to measure upto 200uA. I tried with MSP430F5438 Exp Board, it is working and, but for F4618 exp board, it showing 0 A.

    FYI , I post the pic.

       kindly help me in this.

    Thanks & regard

    sheik

     

  • 0 in reply to sheik abdullah
    Guru 227245 points

    Good you sent the picture. :)

    The µA/mA range use the same input as the voltage ranges. You plugged the cable into the 10A socket, which is only used for the 10A range (and has a very-low ohm shunt).
    Through this low-Ohm resistor (usually in the range of several milliOhm), the MSP is powered, but you won't see a reading as there is no current through the µA/mA/V input.

    However, the other input in µA mode may have an inner resistance of several hundred ohms (to get a noticeable voltage to measure on this low current). Especially on lower-cost multimeters. So it may still be that you're not seeing all the current because some of it comes through the port pins. if you have a second multimeter, you can measure the voltage drop across the first multimeter that measures the current. If it is below 0.2V, then all is fine.

  • 0 in reply to Jens-Michael Gross
    Intellectual 330 points

    Thanks JMG,

                Then, how can I measure the current consumed by MSP.

    Reagrds,

    sheik

  • 0 in reply to sheik abdullah
    Guru 227245 points

    sheik abdullah said:
    Then, how can I measure the current consumed by MSP.

    After plugging the cable into the other socket, I think it should work, as long as the current doesn't get too high. So unless you start having LEDs sourced by the MSP (which adds the LED current to the MSP current), even a cheap multimiter should be able to measure the µA currents without a voltage drop of 0.2V.
    Usually, 0.2V is exactly the voltage drop at scale end (200µA). Teh reason is that the multimieters measure only voltage, not current. And the voltage is measured often on a 0.2V reference. So the current inputs just have resistors that provide 0.2V voltage drop when the current that flows through them reaches the scale maximum. This would mean that your multimeter will act like a 1kOhm resistor in the current path (200µA*1kOhm = 200mV). And all is well.

    This does, however, mean, that your measuring influences the circuit under test. and one additional kOhm in the current path may make a significant difference.

    However, in your case, it should work as long as the current is well below the 200µA limit.

  • 0 in reply to Jens-Michael Gross
    Intellectual 330 points

    Thanks JMG,

         I got the current information by using low current measurement Multimeter.

     

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