Maintenance methods for mechanical multimeter and pointer multimeter malfunctions
Pointer system instruments are divided into magnetoelectric instruments and electromagnetic instruments. The current pointer multimeter is mainly magnetoelectric instruments. Due to the low sensitivity of electromagnetic instruments, electromagnetic instruments are generally used in industrial Voltmeter and Ammeter. According to different magnetic circuits, magnetoelectric instruments are divided into three types: internal magnetic, external magnetic, internal and external magnetic, The pointer multimeter with an external magnetic head is easily affected by external magnetic field interference, which can cause inaccurate measurement. Therefore, a metal shielding plate is usually designed on the back cover plate of the multimeter for the pointer multimeter with an external magnetic head. The function of the metal shielding plate is to shield the external electromagnetic field interference, making the measurement of the meter more accurate.
Because the external magnetic meter head is prone to introducing interference from external electromagnetic fields, resulting in inaccurate measurement, a metal shielding plate is installed on the back cover plate of the multimeter to achieve better accuracy in measurement. However, the internal magnetic meter head is generally not designed because it is not easy to introduce interference from external magnetic fields, and the internal magnetic meter head has strong anti-interference ability.
1、 Internal composition of magnetoelectric instruments
There are two parts inside the magnetoelectric instrument: one is the movable part, and the other is the fixed part. The fixed part includes the moving coil, the fixed coil, and the movable part includes the spring spring spring spring, pointer, and damping device. The function of the moving coil and the fixed coil is mainly to generate magnetic field force by applying current, the function of the spring spring spring spring spring is mainly to generate reaction torque to drive the meter needle to deflect, and the function of the damper is to, When the pointer is deflected by the force of a magnetic field, a certain amount of inertia is generated, and the function of the damper is to absorb this inertia so that the pointer can stop at a certain point as soon as possible to achieve rapid reading.
2、 The working principle of magnetoelectric instruments
All mechanical multimeters (i.e. pointer multimeters) are magnetoelectric instruments. Magnetoelectric instruments are divided into three types based on different magnetic circuits: internal magnetic, external magnetic, and internal and external magnetic. Their working principle is that when current flows into the moving coil inside the meter head, a magnetic field force, also known as the rotational torque, is generated. This magnetic field force (rotational torque) drives the spring spring spring inside the meter head, which drives the pointer to deflect, According to the magnitude of the current flowing into the moving coil of the meter head, the strength of the magnetic field force generated varies, resulting in different degrees of deflection of the pointer caused by the hairspring. That is, the greater the current flowing into the moving coil, the stronger the magnetic field force generated. Therefore, the greater the amplitude of deflection of the pointer caused by the spring hairspring, the greater the measured signal. Conversely, the smaller the current flowing into the moving coil, the weaker the magnetic field force generated, So the greater the deviation of the pointer caused by the hairspring, the smaller the measured signal. By using this principle, the size of the measured signal can be achieved.
Similarly, the spring hairspring also generates a torque, which is the reaction torque. Simply put, we know that pointer deflection is caused by magnetic field force (rotational torque), and the pointer is deflected by magnetic field force (rotational torque). However, there must be another torque, which is the reaction torque generated by the spring hairspring, generating a torque that is opposite to the rotational torque (magnetic force) (we call it the reaction torque), When the rotational torque (magnetic field force) and the reaction torque generated by the hairspring cancel out, the pointer stops. If there is only rotational torque (magnetic field force) without the reaction torque generated by the hairspring, the pointer will deflect to its end no matter how large the measured signal is. Therefore, if there is a problem with the hairspring, some faults such as inaccurate measurement signal, large or large pointer deflection amplitude, should be noted.
