Introduction to commonly used test instruments for electricians

This article shares the basics of common portable electrical test instruments that must be understood and mastered when engaged in electrical equipment installation, maintenance, debugging, etc.: multimeters, clamp ammeters, insulation resistance meters, oscilloscopes, DC bridges, ground resistance testers, and loop resistance testers. Knowledge.

1. Multimeter

A multimeter is an electrical instrument that every electrical (engineering) practitioner must master proficiently. It is a necessary testing tool for electricians, electronic equipment and instruments during maintenance and production. Its basic function is to measure current (AC/DC) and voltage (AC/DC). and resistance, derived functions include: measurement level (decibel), power, capacitance, inductance and main parameters of transistors, etc. Because of its diverse uses, it is called a multimeter.

There are many types of multimeters with different shapes, but the basic structure and usage are the same. According to its internal structure, commonly used multimeters are divided into two types: pointer type and digital type. An analog multimeter is a multi-functional measuring instrument with a mechanical meter as the core component. The measured value is read by the pointer of the meter. The measured value of a digital multimeter is directly displayed in digital form on the LCD screen, and also has some Voice prompt function. According to the appearance, there are desktop, clamp, handheld and pocket types.

2. Clamp ammeter

The clamp ammeter is a portable instrument specially used to measure the current of AC circuits. Its biggest feature is that it can measure large currents without disconnecting the circuit under test. In actual work, because it is very convenient to use, it is widely used.

If you use an ordinary multimeter to measure the circuit current, you need to disconnect the circuit first, and then connect the multimeter for measurement. In actual operation, if the equipment is in normal working condition, disconnecting the circuit will cause a power outage, which is obviously very inconvenient. , such as power distribution lines in factories, schools, and institutions where power cannot be cut off at will. At this time, a clamp ammeter can be used.

Clamp ammeter is referred to as clamp meter, and its working part is mainly composed of ammeter and through-core current transformer. The iron core of the feedthrough current transformer is made into a movable opening and is in the shape of a clamp, hence the name clamp ammeter. At present, common clamp ammeters are divided into pointer type and digital type according to the display mode; according to the function, they mainly include AC clamp ammeter, multi-purpose clamp meter, harmonic digital clamp ammeter, leakage current clamp meter and AC and DC clamp meter. Ammeter etc.

3. Insulation resistance meter

Insulation resistance meter (commonly known as megohmmeter, megohmmeter) is a test instrument specially used to detect the insulation condition between electrical equipment, household appliances or electrical circuits and ground and phase lines. Since the resistance unit of this instrument is usually megaohms (MΩ), it is often called a megohmmeter. Insulation resistance meters are mainly used to measure the insulation resistance of electrical equipment and electrical circuits.

Insulation resistance meters measure the insulation resistance of electrical equipment, household appliances or electrical circuits to determine whether the insulation of electrical equipment is good or bad, whether there is leakage, etc. Some multimeters can also measure megohm-level resistance, but the voltage provided by the multimeter itself is low and cannot accurately measure the quality of the insulation of high-voltage electrical equipment. For high-voltage electrical equipment, in order to detect the quality of its insulation performance, in addition to using an insulation resistance meter Insulation resistance test, voltage withstand test must also be done.

According to different working and display modes, insulation resistance meters can usually be divided into two categories: hand-operated insulation resistance meters and digital insulation resistance meters.

4. Oscilloscope

Oscilloscopes are mainly used to measure the waveform, frequency, period, phase and other related quantities of electrical signals. The basic structure consists of a display circuit, a Y-axis amplification circuit, an , necessary testing tools during production.

An oscilloscope can simply be thought of as a voltmeter with a graphical display. An ordinary voltmeter has a pointer or digital display that moves on its dial to give a measurement reading of the signal voltage. The oscilloscope is different. An oscilloscope has a screen that graphically displays the change in signal voltage over time, known as a waveform.

According to different signals, they can be classified into analog oscilloscopes and digital oscilloscopes.

5. DC bridge

The DC bridge is a comparative measuring instrument mainly used for testing low resistance resistors.

The DC resistance test of the windings of equipment such as transformers is an indispensable test item after the handover, overhaul and tap changer change of motors, transformers, etc.; when repairing motors, it is necessary to measure the DC resistance of their windings; during line maintenance, the line measurement DC resistance, etc. At this time, the DC resistance can come into use. Commonly used DC bridges include DC single-arm bridges and DC double-arm bridges.

6. Ground resistance measuring instrument

Ground resistance tester, also known as ground megger, is mainly used to measure the grounding resistance and soil resistivity of various types of power distribution systems, lightning protection systems and other system grounding devices. It is divided into digital ground resistance tester and clamp-type ground resistance tester. instrument, hand-operated ground resistance tester.

7. Loop resistance tester

In high-voltage circuit breakers, busbar joints and other departments, contact resistance will increase due to oxidation of the contact surface, poor contact fastening, etc. When a large current flows, the temperature of the contact point will increase, which will accelerate the oxidation of the contact surface and increase the contact resistance. If it continues to increase or continue, serious accidents will occur, so it is necessary to measure the contact resistance frequently or regularly.

The loop resistance tester, also known as the contact resistance tester, uses the principle of Ohm's law and adopts a design method that integrates a switching power supply, a digital ammeter and a microohmmeter to achieve the purpose of measuring microresistance with high precision. It is mainly used for testing the contact resistance and current-carrying conductor resistance of high-voltage circuit breakers and busbar joints. It has the advantages of wide signal output current adjustment range, stable output signal, high test accuracy, and intuitive reading.