What does a megohmmeter do? What is a megohmmeter?

First, the role of the megohmmeter.

The megohmmeter is a commonly used and indispensable instrument in industrial enterprises such as electric power, post and telecommunications, communications, mechanical and electrical installation and maintenance, and the use of electricity as industrial power or energy. It is suitable for measuring the resistance of various insulating materials and the insulation resistance of transformers, motors, cables and electrical equipment.

Second, the megohmmeter is also called a shake meter. Its scale is measured in megaohms (m). Megohmmeters are composed of medium and large-scale integrated circuits. The meter has a large output power, a high short-circuit current value, and a wide range of output voltage levels (each model has four voltage levels).

3.Product nicknames: Digital Megohmmeter, Pointer Megohmmeter, Insulation Meter, Digital High Voltage Megohmmeter, High Voltage Insulation Resistance Tester, Insulation Resistance Tester, Electric Shake Meter, Electronic Insulation Resistance Tester, High Power High Voltage Megohmmeter.

Four. How it works: A digital megohmmeter is composed of medium and large-scale integrated circuits.

The meter has a large output power, a high short-circuit current value, and multiple output voltage levels (a total of four voltage levels). The working principle is that the battery in the machine passes through the DC DC conversion generated by the DC high voltage, which passes through the product under test from the E pole to the L pole, thus generating a current from the E pole to the L pole. After the IV conversion, the measured insulation resistance value is displayed directly on the LCD via a voltage divider.

The role of the megohmmeter: The megohmmeter is a commonly used and indispensable instrument for the industrial enterprise sector of electricity, post and telecommunications, communications, mechanical and electrical installation and maintenance, and the use of electricity as industrial power or energy. It is suitable for measuring the resistance value of various insulating materials and the insulation resistance of transformers, motors, cables and electrical equipment.

Megger, commonly known as shake meter, is mostly powered by hand-cranked generators, so it is also known as shake meter. Its scale is measured in megaohms (m). It is a kind of measuring instrument commonly used by electricians, mainly used to check the insulation resistance of electrical equipment, household appliances or electrical circuits to the ground and between phases, so as to ensure that these equipment, electrical appliances and circuits work in a normal state and avoid accidents such as electric shock and equipment damage.

Digital Megohmmeter, Pointer Megohmmeter, Insulation Meter, Digital High Voltage Megohmmeter, High Voltage Insulation Resistance Tester, Insulation Resistance Measuring Instrument, Insulation Characteristics Tester, Electric Shake Meter, Electronic Insulation Resistance Tester, High Power High Voltage Megohmmeter.

Digital megohmmeters consist of medium and large-scale integrated circuits. The output power of this meter is large, the short-circuit current value is high, and the output voltage level is many (there are four voltage levels). The working principle is that the DC high voltage generated by the battery in the machine as the power supply through DC DC conversion is from the E pole to the L pole through the tested product, so as to generate a current from E to the L pole, and the insulation resistance value to be measured is directly displayed by the LCD after the I V transformation is completed by the divider.

It is suitable for measuring the resistance value of various insulating materials and the insulation resistance of transformers, cables and electrical equipment. It is used to determine whether the equipment is leaking.

A megohmmeter is an electrical test instrument designed to test extremely high resistance by generating a DC (direct current) voltage of 300 to 15,000 volts, a megohmmeter generates a high-voltage, low-current DC charge that allows it to test the resistance typically encountered in motor winding or cable insulation tests, which are generated by a battery-powered internal circuit or a manually operated generator.

Due to the extremely high resistance common in these applications, testing the winding, grounding, or insulation resistance of electrical equipment, machinery, or devices with conventional ohmmeters may not be accurately achieved, in these cases the resistance can range from a few megaohms to several million megaohms, and the required test voltages are much higher than those used by smaller ohmmeters, megohmmeters use DC voltages of 300 to 15,000 volts to accurately measure these very high resistance values, which are provided at very low rated currents, There is usually no danger to megohmmeter users.

Digital megohmmeters.

There are two basic types of megohmmeters: one is battery-powered and the other uses a hand-crank or motor generator, both megohmmeter models can perform accurate insulation resistance testing on devices and equipment with several megaohms (1,000,000 megaohms) resistance, battery-operated megohmmeters use specialized internal circuitry to convert the low battery voltage to a higher test voltage, these instruments are typically smaller, lighter, and have one-button operation than the generator version, The advantage of one-handed operation and a wide range of operating voltage options, the disadvantage of a megohmmeter for batteries is that the battery life is short and typically only produces a maximum voltage of 5,000 volts.

Generator megohmmeters rely on small internal generators to produce the high test voltages required, these generators are usually operated manually using an external crank handle, but an internal motor drive can be installed, these instruments can produce 300 volts to 15,000 volts without the need to replace batteries, one of the disadvantages of using such instruments is that the operation requires two hands, so the use of clip-on leads or the help of a second person, which are also often bulkier and provide a single test voltage.

When testing electrical equipment, it should always be kept in mind the high voltages generated by these instruments, the dynamometer test voltage should not exceed the operating voltage of the device under test, otherwise irreparable damage may be caused, although the test voltage is provided at a very low amperage, care should also be always taken to prevent electric shock when working with a megohmmeter.

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The megohmmeter, commonly known as the shake meter, is a measuring instrument commonly used by electricians. The megohmmeter is mainly used to check the insulation resistance of electrical equipment, household appliances or electrical circuits to the ground and phases, so as to ensure that these equipment, electrical appliances and circuits work in a normal state and avoid accidents such as electric shock** and damage to equipment and equipment. Most of the megohmmeters are powered by hand-cranked generators, so they are also called shaking meters.

Its scale is measured in megaohms (m).

1.Structure: The two coils are fixed on the same shaft and perpendicular to each other. One coil is connected in series with the resistor R, and the other coil is connected in series with the resistor Rx under test, both of which are connected in parallel to the DC power supply.

See attached drawing. 2.How it works.

When measuring, the current through the coil i1=U (R1+R), I2=U (R2+Rx), where R1 and R2 are coil resistances, and the coil is affected by the magnetic field to produce two opposite directions of torque, t1

k1*i1*f1(α)t2

k2*i2*f2(α)

f1 ( ) and f2 ( ) are a function of the magnetic induction intensity and the deflection angle at the location of the two coils, respectively.

The moving part of the gauge is deflected by the torque until the torque generated by the two coils is balanced.

There is when the torque produced by the two coils is balanced. t1t2

Namely. k1*i1*f1(α)

k2*i2*f2(α)

The above equation shows that the deflection angle

It is related to the ratio of the current in the two coils, so it is called a current ratio meter.

Conclusion:1The deflection angle has a certain functional relationship with the measured resistance rx, so the angle can reflect the size of the measured resistance on the opposite side of the first panicle.

2.The deflection angle of the meter is independent of the supply voltage U, so the speed of the hand-cranked generator does not affect the reading.

The measuring principle of the Megohmmeter Angel can be divided into the following four categories:

Direct measurement of the weak leakage current megohmmeter of the sample.

Current that measures the voltage drop of leakage current across a standard resistor, a voltage megohmmeter, a bridge method, a megohmmeter.

A capacitance charging megohmmeter that measures the leakage current on a standard capacitor for a certain period of time.

According to the measurement method, it can be divided into the following two types:

Comparative measurement method of two-branch voltage ratio or current ratio megohmmeter;

A DC measurement method megohmmeter using the principle of single-branch current and voltage.

According to the test voltage level, it can be divided into the following two types;

Low voltage megohmmeter: 50V, 100V, 250V, 500V, 1000V.

High voltage megohmmeter: 2500V, 5000V, 10000V. For example, Wuhan Huate HT series insulation resistance tester belongs to this kind.

According to the form of information processing, it can be divided into the following two types:

Analog one-pointer indicator. For example, the HT series insulation resistance tester belongs to this category.

2) Analog-to-digital conversion - digital display instrument. For example, the HT series adjustable digital megohmmeter and belong to this kind can be divided into two types according to the grounding form:

The high-voltage positive polarity end button is grounded, and the measurement L terminal is negative voltage;

The input terminal of the measuring circuit is grounded and at a low level, and the output negative high voltage is connected to the test sample. In addition to the above, intelligent megohmmeters have begun to be used abroad.

Megohmmeter. There are several steps when measuring resistance:

1. Selection of megohmmeter: select the voltage of megohmmeter and its measurement range according to different electrical equipment. For rated voltage.

For electrical equipment below 500V, the voltage level should be selected.

A 500V or 1000V megohmmeter. For electrical equipment with a rated voltage of more than 500V, a 1000-2500V megohmmeter should be selected.

2. Preparation before the test: cut off the power supply of the equipment under test before measurement, and short-circuit grounding discharge for 3-5 minutes. Especially the capacitance.

For large equipment, it should be fully discharged to eliminate the error caused by residual electrostatic charge, ensure correct measurement results and the safety of people and equipment. The surface of the DUT should be wiped clean, and the pollution of the surface of the insulator and the humidity of the surrounding environment have a great impact on the insulation test results. The purpose of measurement is to understand the internal insulation performance of electrical equipment, and it is generally required to wipe the measured object with a clean cloth or cotton yarn before measurement, otherwise it will have a greater impact on the purpose of inspection.

Before use, the megohmmeter should be placed smoothly away from the large cracked potato electric source and the place where there is an external magnetic field. Check the megohmmeter itself before measuring, check the open circuit, do not twist the two wires together, shake the generator to the rated speed, and the pointer should point at the " " position; For short circuit check, short the watch pen and slowly turn the generator handle to see if the pointer reaches the "0" position. If zero or infinity cannot be reached.

Explain that there is something wrong with the megohmmeter and it must be repaired.

3. Wiring of the megohmmeter: Generally, there are three binding posts on the megohmmeter, "L" means "line" or "live wire" binding post, "E" means "ground" binding post, "G" represents shielded binding post, in general, "L" and "E" binding posts are connected to the conductor part of the DUT and the shell or other conductor parts of the DUT respectively with a single-phase insulated wire with sufficient dielectric strength (such as interphase insulation).

In special cases, such as the surface of the object to be measured is contaminated and cannot be wiped clean, the air is too humid, or there is an external electromagnetic field.

interference and other lack of interference. It is necessary to connect the "G" binding post to the metal shielding protection ring of the object to be measured; to eliminate the effects of surface leakage or interference on the measurement results.

4. Measurement of megohmmeter: shake the generator to make the speed reach the rated speed (120 rpm) and keep it stable, and the reading after one minute is generally used. When the capacitance of the measured object is large, the time should be extended, and the pointer should be stable and unchanged.

5. Removal of the megohmmeter: before the megohmmeter does not stop rotating and the measured object is not discharged. The object to be measured cannot be touched by hand and the thread removal work must be carried out first, and the object under test must be short-circuited and discharged to the ground first. Then stop the rotation of the megohmmeter to prevent the capacitor discharge from damaging the megohmmeter.

6. Measure the insulation resistance of the motor.

, E terminates the housing of the motor, L terminates the winding of the motor.

Respondent: UHV power.

1.Before measuring, the power supply to the DUT must be cut off and the ground must be short-circuited and discharged. The equipment must never be allowed to be charged for measurement to ensure the safety of people and equipment. Devices that may induce high voltage must be eliminated before they can be measured.

2.The surface of the object to be measured should be cleaned. Reduce the contact resistance and ensure the correctness of the measurement results.

3.Before measuring, the megohmmeter should be tested for an open circuit and a short circuit to check whether the megohmmeter is good. That is, before the megohmmeter is connected to the object to be measured.

Shake the handle to bring the generator to the rated speed (120rmin) and observe whether the pointer is pointing at the "" position of the ruler. Short the binding posts "line (l) and ground (e)" and slowly shake the handle to see if the pointer points to the "0" position of the ruler. If the pointer does not reach the position of the finger, the megohmmeter is faulty.

It should be overhauled before use.

4.When using a megohmmeter, it should be placed in a stable and stable place, and away from large external current conductors and external magnetic fields.

5.It must be wired correctly. There are generally three binding posts on a megohmmeter, of which L is connected to the conductor part of the DUT and the earth insulation, and E is connected to the shell or ground of the DUT.

g is attached to the shield of the object to be measured or the part that does not need to be measured. When measuring insulation resistance, only the "L" and "E" terminals are generally used. However, when measuring the insulation resistance of the cable to ground or the leakage current of the device under test is severe, the "G" terminal should be used and the "G" terminated to the shield or housing.

After the line is connected, you can turn the crank in a clockwise direction. The speed of shaking should be slow and fast, when the speed reaches about 120 revolutions per minute (ZC-25 type), keep the rotation at a constant speed, and read the hail shed after 1 minute. And read while shaking.

Can't stop and read.

Note: When using a megohmmeter to measure the insulation resistance of electrical equipment, it must be paid attention to the "L" and "E" terminals can not be reversed. The correct connection is:

L" wire end button is connected to the conductor of the device under test, and "e" ground end button is connected to the equipment housing. The "g" shield terminates the insulated portion of the device under test. If the "L" and "E" are reversed, the leakage current flowing through the insulator and surface will be collected through the housing to the ground.

It flows into the measuring coil from the ground through "L". The "g" loses its shielding effect and brings a large error to the measurement. In addition, because the degree of insulation between the internal leads and the housing at the "E" end is lower than the insulation between the "L" terminal and the housing.

When the megohmmeter is used on the ground and the correct wiring method is adopted, the insulation resistance of the "E" end to the instrument shell and the shell to the ground is equivalent to a short circuit and will not cause an error, while when the "L" and "E" are reversed. The insulation resistance of "e" to ground is connected in parallel with the insulation resistance to be measured. The measurement results are small, which brings a large error to the measurement.

6.When shaking, the megohmmeter is placed in a horizontal position, and the end button is not allowed to be short-circuited when the crank is rotated. If the pointer is found to be zero, it means that the measured insulator may have been short-circuited, and the handle cannot be continued to shake. In case the coil in the table is damaged by heating.

7.The reading is complete. The device under test is discharged. The discharge method is to use the rhyme ground wire to take off the megohmmeter and short it with the device under test (not a megohmmeter discharge).