The discussion centers on the behavior of a series LC resonant circuit, specifically regarding the measurement of current using a clamp-on ammeter. Participants confirmed that while the capacitor cancels out the inductance, some inductance always exists in the circuit, affecting the magnetic field and current measurement. The resonant frequency was established at 250Hz with a capacitance of 500uF and an inductance of 810.56uH, measured using an MTP MS5300 inductance meter. The accuracy of clamp-on ammeters, particularly those rated for 50Hz to 500Hz, was also evaluated in the context of transient responses and steady-state AC power measurements.
PREREQUISITESElectrical engineers, hobbyists working with resonant circuits, and technicians involved in current measurement and analysis using clamp-on ammeters.
sophiecentaur said:As you mention a Clamp-on Ammeter, you are clearly considering pretty low frequencies
Idea04 said:With no inductance in the circuit the magnetic field will collapse.
Idea04 said:In a series LC resonant circuit the capacitor acts to cancel out the inductance of the the circuit. With no inductance in the circuit the magnetic field will collapse. So my question is, with this collapse of the magnetic field will it be be harder to measure the current in the circuit with a clamp on ammeter that measures the current from the magnetic field it develops around the conductor?
Some AC clamp on ammeters are good enough only up to 400-500 Hz. Readings at 1 kHz can be quite off with them. Do you measure circuit at steady state AC power or want to measure its' transient response? What exactly is your circuit and how do you know resonant freq is below 1 kHz?Idea04 said:When calculating the capacitance for the circuit I did include the inductance of the wire. The resonate frequency is less than a kilohertz. I measured the circuit inductance with and inductance meter and the value dropped below the inductance of a single wire. I just wanted to be sure because that the clamp on meter would still be accurate.
What sort of Capacitance are you using in your calculations? Resonant frequency is 1/(2π√(LC))Idea04 said:When calculating the capacitance for the circuit I did include the inductance of the wire. The resonate frequency is less than a kilohertz. I measured the circuit inductance with and inductance meter and the value dropped below the inductance of a single wire. I just wanted to be sure because that the clamp on meter would still be accurate.
Probably you have situation where adding the cap decreases or increases overall impedance/reactance of the circuit. That depends on parallel or series connection of two reactive components with respect to the source. That's a normal thing, your ammeter is OK.Idea04 said:The capacitance in the circuit is 500uF, the inductance of the circuit including the wires is 810.56uH and the resonant frequency is 250Hz. I measured the inductance of the wire to be 13.5uH with a MTP MS5300 inductance meter. The clamp meter I am using is good for frequency from 50Hz to 500Hz. I wanted to make sure that the clamp on ammeter was reading properly because without the capacitor the current output was higher than the supply voltage of the circuit, and with the capacitor the current was much lower than the supply voltage. But the impedance with the capacitor was much lower.
No, that is not quite true. What happens is that a energy flows from current in the inductance to voltage across the capacitor and back again. Since the voltage and current is 90° out of phase, no power is involved. The amplitudes can be quite high, though.Idea04 said:In a series LC resonant circuit the capacitor acts to cancel out the inductance of the the circuit.
But it's true that the Reactance of one will cancel out the reactance of the other at resonance.Svein said:No, that is not quite true. What happens is that a energy flows from current in the inductance to voltage across the capacitor and back again. Since the voltage and current is 90° out of phase, no power is involved. The amplitudes can be quite high, though.