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Any stationary voltage or current waveform can be decomposed into a sum of a DC component and a zero-mean time-varying component; the DC component is defined to be the expected value, or the average value of the voltage or current over all time. Although DC stands for "direct current", DC often refers to "constant polarity".
A moving coil meter indicates the average (mean) of a varying current through it, [b] which is zero for AC. For this reason, moving-coil meters are only usable directly for DC, not AC. This type of meter movement is extremely common for both ammeters and other meters derived from them, such as voltmeters and ohmmeters.
An electrical meter with integral AC current clamp is known as a clamp meter, clamp-on ammeter, tong tester, or colloquially as an amp clamp. A clamp meter measures the vector sum of the currents flowing in all the conductors passing through the probe, which depends on the phase relationship of the currents. Only one conductor is normally ...
Symbol [1] Name of quantity Unit name Symbol Base units E energy: joule: J = C⋅V = W⋅s kg⋅m 2 ⋅s −2: Q electric charge: coulomb: C A⋅s I electric current: ampere: A = C/s = W/V A J electric current density: ampere per square metre A/m 2: A⋅m −2: U, ΔV; Δϕ; E, ξ potential difference; voltage; electromotive force: volt: V = J ...
Symbol Meaning SI Units of Measure Electric field volts per meter Magnetic field amperes per meter Electric displacement coulombs per square meter Magnetic flux density: teslas or webers per square meter
Transformer or current clamp meter, (suitable for AC current only). Fluxgate sensor , (suitable for AC or DC current). Hall effect sensor (suitable for AC, DC, or pulsating current), a type of current sensor which is based on the Hall Effect phenomenon discovered by Edwin Hall in 1879.
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All meters have a burden voltage (caused by the combination of the shunt used and the meter's circuit design), and some (even expensive ones) have sufficiently high burden voltages that low current readings are seriously impaired. Meter specifications should include the burden voltage of the meter. Resistance in ohms.