Clamp voltmeter principle
The ammeter is made by the action of the magnetic field force of the conducting conductor in the magnetic field. The internal current meter with a permanent magnet, magnetic field generated in the electrode, a coil in a magnetic field, the coil ends are respectively provided with a spring, a spring is connected to each terminal current meter, connected by a rotating shaft of the spring and the coil, the shaft relative to the front end of the current table, there is a pointer.
When the current passes through, the current flows along the spring and the rotating shaft through the magnetic field, and the current cuts the magnetic induction line, so that the coil is deflected by the force of the magnetic field, and the rotating shaft and the pointer are deflected. Since the magnitude of the magnetic force increases with the current, the magnitude of the current can be observed by the deflection of the pointer.
This is called magnetoelectric ammeter, which we use in our laboratory. The ammeter is connected in series with a large resistor. When measuring parallel to be measured between two points, will not change the characteristics of the original circuit, current meter display value is proportional to the measured point voltage: internal resistance of ammeter Ro is very small, can be neglected, the external resistor R, so according to Ohm's Law: I = U/ (R Ro) = U/R is current meter using a current carrying rectangular coil made by principle of moment rotation in a magnetic field. A voltmeter can be understood as a ammeter in series with a large resistor
