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Workbench Wednesday 24: No-Contact Current Measurements

 

 

One of the safest ways to measure current is with a clamp. Clamps do not require you to break the circuit and they safely measure wires with thousands of amps. In this video, we measure DC current in the lab, AC current of a reflow oven controller, and the DC current in a car using a Tenma 72-722672-7226 True RMS Clamp Meter.

 

Bill of Material:

 

Product NameManufacturerQuantityBuy KitBuy Kit
72-722672-7226 - Clamp Meter, Auto, True RMS, 600 A AC, 600 V AC, 600 V DC, 28 mm Jaw Opening Max.Tenma1Buy NowBuy Now
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  • Hi James,

     

    Your blog inspired me to run an experiment. I had in stock this current measuring board with a ACS712T ECL20 Chip on it.

     

     

    I cut a notch in a ferrite core that was just big enough to slip over the Hall Effect IC

     

     

    Now I configured the circuit so that circuit with the Hall Effect sensor was in the gap of the core and I also had a current carrying wire going through the core

     

     

    I ran two test sequences with the polarity of the magnetic field reversed from one sequence to the next. The chip also got moved slightly in the transition which may explain the slight shift in scaling (delta V) from one sequence to the other.

     

     

    Current in the Test Wire          Voltage Output Seq 1          Delta V                         Voltage Output  Seq 2                    Delta V

     

              0  Amps                                  2.495V                                                                      2.524V

                                                                                                   0.024V                                                                                0.028V

              1                                             2.471V                                                                      2.552V

                                                                                                   0.025V                                                                                0.027V

              2                                             2.446V                                                                      2.279V

                                                                                                   0.024V                                                                                0.027V

              3                                             2.422V                                                                      2.606V

                                                                                                   0.026V                                                                                0.028V

              4                                             2.396V                                                                      2.634V

                                                                                                   0.025V                                                                                0.028V

              5                                             2.371V                                                                      2.662V

     

    I also did a little digging in the physics book and in an ideal situation the magnetic field induced in the ferrite core will remain constant regardless of the position of the wire inside the core. (Ampere's Law)  The shape of the loop of the core should also not have an affect. The position of the wire should still be irrelevant to the field produced.  Of course with the clamp meter we probably don't have a consistent continuous loop which may allow the position of the wire to affect the field.

     

    John

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  • Hi James,

     

    Your blog inspired me to run an experiment. I had in stock this current measuring board with a ACS712T ECL20 Chip on it.

     

     

    I cut a notch in a ferrite core that was just big enough to slip over the Hall Effect IC

     

     

    Now I configured the circuit so that circuit with the Hall Effect sensor was in the gap of the core and I also had a current carrying wire going through the core

     

     

    I ran two test sequences with the polarity of the magnetic field reversed from one sequence to the next. The chip also got moved slightly in the transition which may explain the slight shift in scaling (delta V) from one sequence to the other.

     

     

    Current in the Test Wire          Voltage Output Seq 1          Delta V                         Voltage Output  Seq 2                    Delta V

     

              0  Amps                                  2.495V                                                                      2.524V

                                                                                                   0.024V                                                                                0.028V

              1                                             2.471V                                                                      2.552V

                                                                                                   0.025V                                                                                0.027V

              2                                             2.446V                                                                      2.279V

                                                                                                   0.024V                                                                                0.027V

              3                                             2.422V                                                                      2.606V

                                                                                                   0.026V                                                                                0.028V

              4                                             2.396V                                                                      2.634V

                                                                                                   0.025V                                                                                0.028V

              5                                             2.371V                                                                      2.662V

     

    I also did a little digging in the physics book and in an ideal situation the magnetic field induced in the ferrite core will remain constant regardless of the position of the wire inside the core. (Ampere's Law)  The shape of the loop of the core should also not have an affect. The position of the wire should still be irrelevant to the field produced.  Of course with the clamp meter we probably don't have a consistent continuous loop which may allow the position of the wire to affect the field.

     

    John

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