# Measure AC magnetic field strength between 100kHz and 300 kHz

I have tried to find in the webpage some answers about measuring AC magnetic field strength in the range above 50 kHz and more with no luck. Sorry, but if someone could help me will be great.

I need to measure intensity or strength of the magnetic field (1 to 50 mT) between 50khz to 300khz aprox. I have some like "induction heater", with different LC ! L= workcoil., Radius = 2 cm copper tube.

I have used a sensing coil in the middle and i have a strong signal, but iI don't know how to calculate the mT i have. The small sensing coil is 10 turn of awg32 cooper wire with radius = 2,5mm. The voltage is about 0.5 volt, and I can see the out put in the osciloscope(sine wave), I cannot measure the currrent of the sensing coil, and at this frequency my ammeter does not work.

• you mean using something like these magneticsciences.com/magnetic-field-sensors – JIm Dearden Jan 1 '17 at 19:48
• Thank Jim, you are right, but these sensor give 1 mV/mG or V/G, and i have more than 10 mT in my circuit. About 100V output. – Guillermo Jan 2 '17 at 8:49

As with any coil, induced voltage is N$\dfrac{d\Phi}{dt}$.
• I'm not sure why you are confused, the formula is easy enough and you don't need to measure current - a change in flux induces a voltage in a coil and the number of turns (N) magnifies that voltage by N times. So calculate $\frac{d\Phi}{dt}$ based on voltage and N. Then you need to turn this to total flux by using frequency. Then turn to flux density knowing the area of the coil. – Andy aka Jan 2 '17 at 16:58
• At the peak of your voltage, flux rate of change is maximum. If the frequency were 1 rad/sec there is no conversion factor; with ten turns and (say) 500 mV peak, the flux also hits a peak of +50 mWb when the voltage waveform rises through zero and hits a trough of -50 mWb when the voltage waveform falls through zero. But your frequency is a lot bigger than 1 rad/sec hence the peak flux has to be proportionally smaller. So, you get your peak flux (in webers) and divide that by the area of your coil in sq metres to get flux density in teslas. Then your RMS flux density is peak/$\sqrt2$. – Andy aka Jan 3 '17 at 21:31