The role of electrical instruments is to measure various electrical parameters, such as current, voltage, period, frequency, electrical power, power factor, resistance, inductance, capacitance, etc. By measuring the values of these electrical parameters, electricians can understand the technical performance and working conditions of the electrical equipment of the circuit, so as to carry out appropriate processing and necessary adjustments to ensure the normal operation of the circuit and the safe operation of the equipment. Therefore, electricians must master the principles and usage of commonly used electrical instruments.
Classification of electrical measuring instruments
It is mainly divided according to the principle of action and use. Everyone just needs to know about it.
According to different uses: it can be divided into voltmeter, ammeter, power meter, watt-hour meter, etc.; it can also be divided into three types: DC meter, AC meter and AC-DC dual-purpose meter according to the type of current. Multimeter for voltage, resistance and other functions.
According to the principle of action: there are four commonly used types: magnetoelectric type, electromagnetic type, electric type and induction type. Others include vibration type, thermoelectric type, hot wire type, electrostatic type, rectification type, photoelectric type and electrolytic type.
According to the measurement method: it can be divided into two types: direct reading and comparison. Instruments that directly indicate the value to be measured are called direct-reading instruments, such as voltmeters, ammeters, power meters, etc.; instruments that compare the measured values with "standard quantities" are called comparative instruments, such as balance bridges, compensation device, etc. The chapter on electrical instruments here focuses on direct-reading instruments.
According to accuracy: it can be divided into seven types: 0.1, 0.2, 0.5, 1.0, 1.5, 2.5, and 5.0. The allowable error of a 0.2-level instrument is 0.2%, and the error of a 0.5-level instrument is 0.5%, and so on. Instruments above grade 0.5 have higher accuracy and are mostly used in laboratories as calibration instruments. Level 1.5, Level 2.5, etc. have lower accuracy, and are generally installed on switchboards and consoles to monitor the allowable conditions of electrical equipment.
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