A digital megohmmeter is composed of medium to large scale integrated circuits. This meter has a high output power, high short-circuit current value, and multiple output voltage levels (each model has four voltage levels).
The working principle is that the DC high voltage generated by the internal battery as the power source is converted by DC/AC from the E-pole to the L-pole through the tested product, thereby generating a current from the E-pole to the L-pole. After I/V conversion and division by a divider, the measured insulation resistance value is directly displayed on the LCD. Suitable for measuring the resistance values of various insulation materials and the insulation resistance of transformers, motors, cables, and electrical equipment. The outer shell is made of high-strength aluminum alloy, and the machine is equipped with an equipotential protection ring and a fourth-order active low-pass filter, which can effectively shield the external power frequency and strong electromagnetic field. No manual work required, powered by batteries, with automatic range switching. The clear panel operation and LCD display make measurement very convenient and fast.
The digital megohmmeter generates high voltage during operation, and the measuring object is electrical equipment, so it must be used correctly, otherwise it will cause personal or equipment accidents. Before use, the following preparations should be made:
1. Before measurement, the power supply of the tested equipment must be cut off and the device must be short circuited to ground for discharge. It is never allowed to conduct measurements with the equipment live to ensure personal and equipment safety.
2. For equipment that may induce high voltage, this possibility must be eliminated before measurement can be carried out.
3. The surface of the measured object should be clean to reduce contact resistance and ensure the accuracy of the measurement results.
4. Before measurement, check whether the digital megohmmeter is in normal working condition, mainly checking its "0" and "∞" points. Shake the handle to reach the rated speed of the motor. The digital megohmmeter should point to the "0" position during a short circuit and the "∞" position during an open circuit.
5. When using a digital megohmmeter, it should be placed in a stable and sturdy place, and away from large external current conductors and external magnetic fields.
After completing the above preparation work, the measurement can be carried out. During the measurement, attention should also be paid to the correct wiring of the digital megohmmeter, otherwise it will cause unnecessary errors or even errors.
There are three terminals for a digital megohmmeter: one is the "L" terminal, one is the "E" terminal, and the other is the "G" terminal (also known as the protective ring). Generally, the measured insulation resistance is connected between the "L" and "E" terminals. However, when there is severe leakage on the surface of the measured insulator, the shielding ring or non measurable part of the measured object must be connected to the "G" terminal. In this way, the leakage current flows directly back to the negative end of the generator through the shielding terminal "G" to form a circuit, instead of flowing through the measuring mechanism (dynamic coil) of the digital megohmmeter. This fundamentally eliminates the influence of surface leakage current. It is particularly important to note that when measuring the insulation resistance between the cable core and the outer surface, the shielding terminal "G" must be connected properly, because when the air humidity is high or the cable insulation surface is not clean, the surface leakage current will be large. To prevent the impact of leakage on the internal insulation measurement of the tested object, a metal shielding ring is generally added to the outer surface of the cable, Connect to the "G" end of the digital megohmmeter.
When using a digital megohmmeter to measure the insulation resistance of electrical equipment, it is important to note that the "L" and "E" terminals cannot be reversed. The correct connection method is to connect the "L" terminal to the conductor of the tested equipment, the "E" ground terminal to the equipment casing, and the "G" shielding terminal to the insulation part of the tested equipment.
If "L" and "E" are reversed, the leakage current flowing through the insulation body and surface will flow through the casing and converge to the ground, and then flow into the measurement coil through "L", causing "G" to lose its shielding effect and causing significant measurement errors. In addition, because the insulation degree between the internal leads of the "E" end and the casing is lower than that between the "L" end and the casing, when using a digital megohmmeter on the ground and using the correct wiring method, the insulation resistance between the "E" end and the instrument casing and the casing to ground is equivalent to a short circuit and will not cause errors. However, when the "L" and "E" are connected in reverse, the insulation resistance between "E" and the ground is parallel to the measured insulation resistance, resulting in a smaller measurement result, Bringing significant errors to the measurement.
It can be seen from this that in order to accurately measure the insulation resistance of electrical equipment, it is necessary to use the digital megohmmeter correctly, otherwise, the accuracy and reliability of the measurement will be lost.
Product features:
1. Prompt sound output: When the instrument generates high voltage, there is a prompt sound output.
2. Automatic discharge: Equipped with a residual high-voltage discharge circuit, it can automatically discharge the residual high-voltage on the tested equipment after testing.
3. Multi purpose power supply: AC/DC dual-purpose, equipped with rechargeable battery and AC adapter.
4. Portable and convenient: The instrument adopts a portable design, which is easy to operate in the field.
5. Strong practicality: The high-voltage short-circuit current is ≥ 3mA, making it an ideal testing instrument for measuring the insulation resistance of large transformers, transformers, generators, high-voltage motors, power capacitors, power cables, lightning arresters, and other equipment.
6. Scope of use: This table is suitable for measuring the grounding resistance of various devices in departments such as power, postal and telecommunications, railways, communications, mines, etc., as well as measuring the resistance value of low resistance conductors; This table can also measure soil resistivity and ground voltage.
Kvtester Electronics Technology Co.,Ltd. is a high-tech enterprise specializing in power testing, testing, research and development, production, and sales of testing equipment. It has been engaged in the electrical testing industry for many years, and its products are of high quality. We welcome customers to come and purchase. Service hotline: 0086-27-81778799, to learn more, visit the official website: www.kvtester.com
