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Thread: Cannot take the reading of the amps

  1. #1
    Join Date
    Mar 2010
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    71

    Cannot take the reading of the amps

    Hello guys,

    I need a little help, because I cannot be able to take the reading of the amps through on clamp multimeter. I can only read the amps on digital multimeter, but not on clamp.


    Here it is the clamp multimeter I have got:
    http://www.bargainhomeuk.com/product...ultimeter.html



    Can you tell me why the clamp cannot take the read of the amps? I guess that they should be able to read either current of AC or DC. If you guess that the clamp multimeter should be able to read, then why I couldn't take the reading and what's gone wrong?



    Any advice would be much appreciate it!

  2. #2
    Join Date
    Jun 2009
    Location
    Fort Worth, TX
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    510
    Are you using a PWM with your setup? If so, the most probably reason is in how the two work. A clamp-on meter works by measuring the magnetic field produced by the wire as current flows through it. The multimeter probably measures current by measuring the very small voltage produced across a small section of wire as current flows through it.

    If you try to measure using a clamp on, and you're using a PWM, the current is changing VERY rapidly. This change in current can screw with the mechanisms that measure the magnetic field(I say CAN... not WILL). A typical multimeter can sample the voltage at a much faster rate, so it should be pretty good.

    All this is ASSUMING you're using a PWM. If not, hell if I know......

    P.S. that meter is intended to measuring HUNDREDS of amps. If you're trying to measure 20A, good luck getting any kind of accurate reading. Just because something CAN measure really high currents, doesn't mean it can measure small currents very well. It's like trying to pick up a B.B. with a crane that's designed to pickup large objects weighing tons. Precision...

  3. #3
    Join Date
    Mar 2010
    Posts
    71
    Yes, I am using PWM for my setup. So I can't see why I couldn't take the reading of the amps for the DC current. When I tried to take the reading of DC and AC current, it said there was no amps in the current. Do you know why I couldn't take the reading?

    I have tried to measure the amps between the battery positive post and the cell positive post, so it said there was no amps. And I have tried to use with the digital multimeter as well which I was on the same boat.

    However, I have changed the wire on a different port on the digital multimeter and I got the reading!

    So the real reason could be why I couldn't take the reading for the amps on the clamp meter, is it could be the wire that has not plugged in the right port on the meter?

    And can you guess that if I could be able to take the reading for the amps of the DC current using with the clamp meter?

    In this case, the site said that the clamp meter I has got can only take the reading of the amps for the AC current. I'm not sure if it could take the reading for the DC current?

  4. #4
    Join Date
    Jun 2009
    Location
    Fort Worth, TX
    Posts
    510
    The way the clamp on meter works, is the current going through the wire makes a magnetic field. If the current changes, it makes a changing magnetic field. This changing magnetic field induces a voltage in the clamp that the meter reads.

    Sounds like you got the traditional AC clamp on meter. They work entirely differently than the newer DC clamp on meters. DC clamp on meters use something called the "hall effect" to directly measure a magnetic field, and extrapolate the current based on that. Sounds like you just wasted some money... You won't be able to get an accurate current measurement if you're using an AC clamp on meter.

  5. #5
    Join Date
    Mar 2010
    Posts
    71
    Yeah, looks like I have wasted some of my money. I doesn't realise that I should always use DC current to measure the DC amps

    Are there any ways to use that clamp meter to measure AC current amps for the circuits?

  6. #6
    Quote Originally Posted by chris0147 View Post
    Yeah, looks like I have wasted some of my money. I doesn't realise that I should always use DC current to measure the DC amps

    Are there any ways to use that clamp meter to measure AC current amps for the circuits?
    Chris, I made the same mistake as you did, and bought a cheap meter from ebay thinking I could measure dc amps.
    Look up the information as how to measure dc current with a shunt arrangement, that will be my next step..

  7. #7
    Chris, I goggled diy for dc shunt and found this youtube site:
    http://www.youtube.com/watch?v=65EiiE4NoDI

  8. #8
    Join Date
    Jun 2009
    Location
    Fort Worth, TX
    Posts
    510
    You'll need some knowledge of electronic circuits in order to build an amplifier to take a tiny microvolts signal, and boost it to volts that you can read accurately.

  9. #9
    Join Date
    Sep 2009
    Location
    Kennedy N.Y.
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    141
    Quote Originally Posted by chris0147 View Post
    In this case, the site said that the clamp meter I has got can only take the reading of the amps for the AC current. I'm not sure if it could take the reading for the DC current?
    You answered your own question... I went and looked at the site you provided, and didn't see any DC AMP specs...
    It only reads AC AMPS....
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  10. #10
    Join Date
    Mar 2010
    Posts
    71
    Thanks for the advice guys, I have learnt my mistake. So what amp meter is the best things for me to buy?


    I want to buy amp meter similar as the clamp meter I has got.



    Thanks!

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