Pointer multimeter structure schematic diagram
A set of cylindrical iron cores is embedded inside the circular magnetic steel, and the outer part of the cylinder is a movable aluminum frame. The aluminum frame is wrapped with a coil made of fine enameled wire, and the coil has pointed needles, a balance spring, and a zero adjustment rod at both ends. Its flexibility determines the sensitivity of the watch head, just like the pendulum of a watch. The two ends of the coil are a positive terminal and another negative terminal, represented by a red line for positive+and a black line for negative 1. It is an aluminum frame that can rotate around an axis, and the axis of the aluminum frame is equipped with two flat coil springs and a pointer. The two ends of the coil are respectively connected to these two coil springs, and the measured current enters the coil through the springs. The two poles of the horseshoe shaped magnet each have a pole shoe with a cylindrical inner wall, and there is a fixed cylindrical iron core inside the aluminum frame. The function of the pole shoe and the iron core is to ensure that the magnetic induction lines between them are evenly distributed along the radius and circumference.
When a coil moves in a magnetic field, regardless of its position, its plane is parallel to the magnetic field lines. When current passes through a coil, both sides of the coil parallel to the axis are subjected to magnetic field forces, which cause the coil to rotate. When the transformer head coil rotates, the coil spring is twisted, generating a force that hinders the rotation of the coil. Its torque force increases with the increase of the coil rotation angle. When this hindering effect increases to the point where it cancels out the rotational effect of the magnetic field force, the coil stops rotating. According to the principle of repulsion of the same sex and attraction of the opposite sex in magnetic fields, once the magnetic field of a microampere coil is reversed, the magnetic field it generates will become the opposite magnetic field and interact with each other to deflect in the opposite direction. Furthermore, the current acting through the coil is proportional to the current, so the larger the current in the coil, the greater the rotational effect of the magnetic field force, and the greater the angle of deflection between the coil and the pointer. Therefore, based on the size of the pointer deflection angle, the strength of the measured current can be known. When the direction of the current in the coil changes, the direction of the magnetic field force will also change, and the direction of the pointer deflection will also change accordingly. So, based on the deflection direction of the pointer, the direction of the measured current can be determined.
There is no reverse bias in AC voltage measurement, while for DC voltage measurement: place one of the conversion switches of the multimeter in the appropriate range of DC voltage gear V, and connect the "+" probe (red probe) to the high potential and the "-" probe (black probe) to the low potential, allowing current to flow in from the "+" probe and out from the "-" probe. If the probe is connected in the opposite direction, the pointer of the multimeter will deflect in the opposite direction, making it easy to bend the pointer.
When measuring DC current, place one of the conversion switches of the multimeter in the appropriate range of 50uA to 500mA. The selection and reading method of the current range is the same as that of the voltage. When measuring, the circuit must be disconnected first, and then the multimeter string should be sent to the tested circuit in the direction of the current from "+" to "-", that is, the current flows in from the red probe and out from the black probe. If the multimeter is mistakenly connected in parallel with the load, it may cause a short circuit and burn out the instrument due to the low internal resistance of the meter head. The reading method is as follows: actual value=indicated value x range/full offset.
