Calculating Current from a Function Generator

[Student1008]

I wasn't sure where to post this, but I am a physics student working on a thesis and the experiment I ran involved using a function generator to generate a magnetic field (wire was bent into a loop). I am trying to figure out how to convert the frequency (15 MHz) and Vpp (10V) to current so I can calculate the B-field. I know it's not as simple as V = IR since it's a wave (pulse bursts to be exact). Please help!

 

[sophiecentaur]

Hi
If you want to measure the current through a coil then you can put a small Resistor in series (at the Earthy End would be easiest) and look at the volts across that. The current through your coil will then be I=V/R. If the current is really high then your resistor can be very low and still give you a measurable voltage drop across the resistor. This is just what a DVM does, in fact, when measuring current.
The high frequency involved could be a problem here, though, if the coil has multiple turns and could be self-resonant. This can be detected by varying the frequency and checking that the current is just dropping linearly from 0 to 15MHz - i.e you are off resonance. It would dip sharply at a parallel resonance.

 

[Student1008]

Hi
If you want to measure the current through a coil then you can put a small Resistor in series (at the Earthy End would be easiest) and look at the volts across that. The current through your coil will then be I=V/R. If the current is really high then your resistor can be very low and still give you a measurable voltage drop across the resistor. This is just what a DVM does, in fact, when measuring current.

Is this the only way to measure the current? I was also thinking of trying to formulate a wave equation from the frequency/B-field (I am studying magnetoinductive waves). Would you have an idea of how to do that?

 

[DragonPetter]

You can also use a hall sensor to measure current, assuming your test setup is still in place.

 

[alphysicist]

As a fellow scientist, I understand your dilemma and am happy to provide some guidance on how to calculate current from a function generator.

First, it is important to note that the equation V = IR still applies in this scenario, but we need to consider the time-varying nature of the signal being produced by the function generator. This means that we need to take into account the frequency and pulse bursts in our calculations.

To calculate the current, we can use the following equation: I = Vpp/2R, where Vpp is the peak-to-peak voltage and R is the resistance of the wire loop. However, since the frequency of the signal is 15 MHz, we also need to consider the time component. The equation for calculating current in this case would be: I = Vpp/(2Rf), where f is the frequency in Hertz.

Now, since the signal from the function generator is a pulse burst, we need to consider the duty cycle, which is the ratio of the pulse duration to the total period. This can be represented as a percentage or decimal. For example, if the pulse duration is 1 ms and the total period is 10 ms, the duty cycle would be 10%.

To account for the duty cycle, we can modify our equation to be: I = (Vppd)/(2Rf), where d is the duty cycle.

Finally, to calculate the B-field, we can use the equation B = μ0IN, where μ0 is the permeability of free space, I is the current we just calculated, and N is the number of turns in the wire loop.

I hope this helps you in your calculations and in your thesis. Best of luck with your experiment!