How do you measure current in a circuit?

Answer 1

If there is a resistor in the circuit, you can measure the voltage across the resistor with an isolated voltmeter and use the formula:
current = voltage / resistor value

If there is no resistor in the circuit, you must break the circuit (when it is not energized) and insert an ammeter in series (in place of the break, and measure the current directly.
OR
you can insert a very small resistance (1/10th of an Ohm) and use the first method above.

Finally, if it is an AC circuit, and one of the wires is available separate from the rest, you can use an inductive ammeter (also known as an 'amp-clamp'). If it is a DC circuit there are also amp-clamps using Hall sensors that can measure DC without contacting the circuit.

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Answer 2

You add a resistor small enough so that it does not change the way the circuit performs and measure the voltage across it. That's how an ammeter or multimeter measures current

Another way is to use Hall effect devices
a non-invasive clamp on device typically 0 to 30 Amps
DC or AC

is it's AC current then one can use a current transformer
if the turns ratio is large 1mA can represent 1Amp
and the loss in the circuit it's placed in is low if the sense resistor is 100 Ohms ( with the 1mA) then the voltage burden on the primary is 100mV/1000 and the impedance is 100 / 1000000 Ohms

Answer 3

I. AC Current
Wind a coil of wire around the current-carrying wire. Load the coil with a test resistance.
If the coil 1000 turns, then 1000 Amps in the test wire will induce 1A in the coil. The 1A will force a voltage across the test resistance

II. DC Current - Method 1.
Disconnect the current-carrying wire and insert a small test resistance, such as 0.1ohms.
Measure the voltage across the small test resistance. Divide this voltage by the test resistance to find the DC current.

III. DC Current - Method 2
Wind a transformer having two identical core halves with a coil of wire. Open the core and allow the current-carrying wire to pass through the window of the transformer core.
Drive the transformer coil with positive and then negative currents until the transformer core saturates.
The difference between the coil currents needed to saturate the core indicates the magnitude and direction of the unknown current.
This determination requires knowledge of the core properties and some mathematical manipulation.

Answer 4

Use Ohm's Law which is V=I*R V is your Volts, I is current which you are trying to find and R is your resistance in the circuit. To find current take the values you have for V and R and input in equation. Divide R on both sides of the equation which looks like this V/R=I*R/R which results in V/R=I remember R on the right side of the equation cancels out. Hope this helps!!!