Multimeter
The multimeter is an electrical instrument that every electrical practitioner must be proficient in. It is a necessary test tool for electricians, electronic equipment and instrument maintenance and production.
Its basic function is to measure current (AC/DC), voltage (AC/DC) and resistance. Other functions include measurement level (decibel), power, capacitance, inductance and main parameters of transistors, etc. Because of its variety of uses, this is why it is called as multimeter.
There are many types of multimeters with different shapes, but the basic structure and method of use are the same. Divided according to its internal structure, there are two types of commonly used multimeters: pointer type and digital type.
The pointer multimeter is a multi-functional measuring instrument with a mechanical head as the core component. Its measured value is read by the pointer on the head.
The value measured by the digital multimeter is directly displayed in the form of numbers by the LCD screen, and it also has some voice prompt functions.
Divided by shape, there are desktop, clamp, handheld and pocket and so on.
Clamp ammeter
Clamp ammeter is a portable instrument specially used to measure the current of AC circuit. Its biggest feature is that it can measure large current without disconnecting the circuit under test. It is widely used because of its convenient use during working.
If you use an ordinary multimeter to measure the circuit current, you need to disconnect the circuit first, and then connect the multimeter to measure. In actual operation, if the device is in normal working condition, disconnecting the circuit will cause a power outage, which is obviously very inconvenient. For example, the power distribution lines of factories, schools, and institutions cannot be powered off at will, and a clamp ammeter can be used at this time.
The clamp ammeter is mainly composed of an ammeter and a feed-through current transformer. The core of the through-type current transformer is made into a movable opening and is shaped like a clamp, so it is called a clamp ammeter. At present, the common clamp ammeters are divided into pointer type and digital type according to the display mode. According to the function, there are mainly AC clamp ammeter, multi-purpose clamp ammeter, harmonic digital clamp meter, leakage current clamp meter and AC/DC clamp ammeter, etc.
Insulation resistance meter
Insulation resistance meter (commonly known as megger) is a test instrument specially used to detect the insulation status of electrical equipment, household appliances or electrical lines to the ground and between phase wires. Since the resistance unit of this instrument is usually megohm (MΩ), it is often called a megohmmeter.
The insulation resistance meter measures the insulation resistance of electrical equipment, household appliances or electrical lines to judge whether the insulation of electrical equipment is good or not, whether there is leakage, etc.
Some multimeters can also measure megohm-level resistance, but the voltage provided by the multimeter itself is too low to accurately measure the insulation of high-voltage PCBs of 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 for insulation resistance testing, a withstand voltage test must also be done.
According to different working and display methods, insulation resistance meters can usually be divided into two categories: hand-operated insulation resistance meters and digital insulation resistance meters.
Oscilloscope
The oscilloscope is mainly used to measure the waveform, frequency, period, phase and other related power of the electrical signal. The basic structure is composed of a display circuit, a Y-axis amplifier circuit, an X-axis amplifier circuit, a scanning synchronization circuit, and a power supply circuit. It is a necessary test tool for the maintenance and production of electronic equipment and instruments.
An oscilloscope can simply be thought of as a voltmeter with a graphical display. An ordinary voltmeter is a pointer or digital display that moves on its dial to give a measurement reading of the signal voltage. Oscilloscopes are different. An oscilloscope has a screen on which it can graphically display the change in signal voltage over time, known as a waveform.
According to different signals, it can be classified into analog oscilloscope and digital oscilloscope.
DC bridge
The DC bridge is a comparative measuring instrument, mainly used for testing low-value resistors. The DC resistance test of the windings of transformers and other equipment is an indispensable test item for motors, transformers after handover, overhaul and change of tap changers.
When repairing the motor, it is necessary to measure the DC resistance of its winding. When the line is overhauled, measure the DC resistance of the line. Then, the DC resistance can be used at this time. Commonly used DC bridges include DC single-arm bridges and DC double-arm bridges.
Ground resistance tester
The ground resistance tester, also known as the ground shaker, is mainly used to measure the connection resistance and soil resistivity of the grounding devices of various power distribution systems, lightning protection systems, etc. It is divided into digital ground resistance tester, clamp ground resistance tester, and hand-cranked ground resistance tester.
Loop impedance tester
For high-voltage circuit breakers, busbar joints and other components, due to contact surface oxidation and poor contact fastening, the contact resistance will increase. When a large current flows, the temperature of the contact point will rise, which will accelerate the oxidation of the contact surface and further increase the contact resistance. Even worse, it might lead to serious accidents. So it is necessary to measure the contact resistance frequently or periodically.
The loop impedance tester, also known as the contact resistance tester, uses the principle of Ohm’s law, adopts the design method of switching power supply, digital ammeter and micro-ohmmeter, and achieves the purpose of measuring micro-resistance with high precision.
It is mainly used for testing the contact resistance of high-voltage circuit breakers and bus joints and the resistance of current-carrying conductors. It has the advantages of wide adjustment range of signal output current, stable output signal, high test accuracy and intuitive reading.