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# Analog amperemeter or Clamp amperemeter - which is true ?

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#### anotherbrick

##### Full Member level 4
hello dear forum,

I have 28 KHz inverter which is driving LC circuit of a matching inductor in series with ultrasonic piezos

I want measure the current drawn from the lines

the analog amperemeter shows 5 amperes

( analog amperemeter is 10 amperes max )

where clamp amperemeter shows 4 amperes

( clamp meter is not true RMS - 20 Ampere range)

I wanna ask which is true ?

thank you

Hi,

Maybe both.

Maybe the one shos true RMS and the other average current.
What current do you need to know?

If you want to calculate the power dissipation of a resistor you need RMS.
If you want to calculate the power dissipation of a LED you need average current.

Klaus

Klaus

anotherbrick

### anotherbrick

Points: 2
If the clamp meter is based on an iron transformer it is unlikely to be accurate at such a high frequency and will read low. Check its manual.
Frank

anotherbrick

### anotherbrick

Points: 2
hello again ,

is it possible that the analog ammeter reads the vector sum of active and reactive currents ?

thank you

the schema of my circuit

The ammeter can not differentiate the currents as it has no voltage phase reference into it.
Frank

anotherbrick

### anotherbrick

Points: 2
The ammeter can not differentiate the currents as it has no voltage phase reference into it.
Frank

hello chuckey , sorry I ask again ( I am not good anymore at circuit theory - my EE diplom dates back to 1989 )

does the analog ammeter shows only active current that the circuit draws from lines ?

or is it the absolute value of vectoral sum of both ( active & reactive ) ?

I want calculate the power output of my circuit
thats why I want to clear this problem

thank you

It measures the absolute value. ie. the vectorial sum of real and reactive currents.

Frank

anotherbrick

### anotherbrick

Points: 2
It measures the absolute value. ie. the vectorial sum of real and reactive currents.

Frank

Please check the specifications of both ampere meters. I do not think any of them can measure current at 28 kHz.
The best way to know the real current is to use small resistors like 0.1 Ohm to 1 Ohm on the current-carrying lines, and an oscilloscope to read corresponding voltages at 28 kHz. A two-channel scope can read the phase between two current lines. But it may be difficult to prevent induction coupling between test lines to the scope. Use screened cables and be ready to experiment.

anotherbrick

Points: 2