First, the voltage tester Voltage resistance tester is also called electrical insulation strength tester or medium strength tester. A prescribed AC or DC high voltage is applied between the live and non-charged parts of the appliance (typically the enclosure) to check the withstand voltage capability of the insulation of the appliance. In the long-term work of electrical appliances, not only to withstand the role of the rated voltage, but also to withstand the short-term over-voltage action than the rated operating voltage caused by the operation process (over-voltage value may be several times higher than the rated operating voltage value) . Under these voltages, the internal structure of the electrically insulating material will change. When the over-voltage intensity reaches a certain value, the insulation of the material will be broken down, and the electric appliance will not be able to operate normally, and the operator may get an electric shock and endanger personal safety. 1, the voltage tester structure and composition (1) Boosting section The voltage regulator transformer, the step-up transformer, and the step-up part of the power supply are turned on and off. 220V voltage through the switch, cut off the switch to the regulator transformer voltage regulator transformer output connected to the step-up transformer. Users only need to adjust the regulator to control the output voltage of the step-up transformer. (2) Control section Current sampling, time circuit, alarm circuit. When the control section receives the start signal, the instrument immediately powers up the boost section. When the received loop current exceeds the set value and an audible and visual alarm is issued, the boost circuit power supply is cut off immediately. Shut off the boost circuit power supply when a reset or time-out signal is received. (3) Display Circuit The display shows the boost converter output voltage. The current value displayed by the current sampling portion and the time value of the time circuit are generally counted down. (4) The above is the structural composition of a traditional voltage tester. With the rapid development of electronic technology and single-chip, computer technology; program-controlled voltage tester has also developed rapidly in recent years, program-controlled voltage tester and the traditional pressure meter is mainly different from the booster part. Programmable pressure gauge high pressure boosting is not regulated by the voltage regulator through the mains, but through a single computer control to generate a 50Hz or 60Hz sine wave signal and then amplified through the power amplifier circuit boost, the output voltage value from the single Tablet computer control, the other part of the principle and traditional pressure meter is not much difference. 2, the selection of voltage tester The most important thing in selecting the pressure resistance meter is 2 indicators. The maximum output voltage value and the maximum alarm current value must be greater than the voltage value and alarm current value you need. In general, the test product standard specifies the application of a high voltage value and an alarm determination current value. If the higher the voltage is applied, the larger the alarm judgment current is, the greater the power required by the voltage tester step-up transformer is, and the general step-up transformer step-up transformer power is 0.2kVA, 0.5kVA, 1kVA, 2kVA, 3kVA, etc. The maximum voltage can be up to tens of thousands of volts. The maximum alarm current 500mA-1000mA and so on. Therefore, you must pay attention to these two indicators when selecting a pressure meter. Too much power will cause waste, and the selected low pressure test will not be able to correctly determine whether it is qualified or not. According to IEC414 or (GB6738-86) in the selection of the power method of pressure meter, we think it is more scientific. "First, the output voltage of the pressure meter is adjusted to 50% of the specified value, and then the test object is connected. When the observed voltage drop is less than 10% of the voltage value, the power of the pressure meter is considered to be sufficient. "That is, if the voltage test of a product is 3,000 volts, first adjust the output voltage of the voltage tester to 1500 volts and then connect it to the test object. If the voltage drop of the pressure tester at this time is not greater than At 150 volts, the power of the pressure meter is sufficient. There is a distributed capacitance between the charged part of the test object and the shell. The capacitor has a CX capacitive reactance. When an AC voltage is applied across the CX capacitor, it will induce a current. The magnitude of this current is proportional to the capacity of the CX capacitor and the applied voltage value. When this current is large or exceeds the maximum output current of the pressure meter, this pressure meter cannot correctly determine whether the test is qualified or not. Second, insulation resistance tester The insulation performance of electrical products is one of the important signs to evaluate the quality of insulation. It is reflected by the insulation resistance. We measure the insulation resistance of a product, which refers to the insulation resistance between the live part and the exposed non-charged metal part (case). According to different products, apply a high current, such as 100V, 250V, 500V, 1000V, etc., to specify a minimum Insulation resistance value. Some standards stipulate that the insulation resistance is not less than 1MΩ per kV. Currently, in home appliance product standards, only the thermal insulation resistance is usually specified, and the insulation resistance value under normal conditions is not specified. The insulation resistance value under normal conditions is set by the enterprise standards. If the normal insulation resistance value is low, there may be some hidden trouble or damage in the insulation structure. For example, if the insulation resistance of the motor winding to the housing is low, it may be due to damage of the winding's mean-transistor insulation during the inserting process. In the use of electrical appliances, due to sudden power-on or cut off the power supply or other reasons, the circuit generates over-voltage, resulting in a breakdown in the insulation damage, resulting in personal safety or threat. 1 ã€Insulation resistance meter structure and composition Insulation resistance meter, also known as megohmmeter, shake table, Meg. The insulation resistance meter is mainly composed of three parts. The first is a DC high voltage generator for generating a high voltage in a straight line. The second is the measurement loop. The third is the display. (1) DC high voltage generator Measuring the insulation resistance must apply a high voltage at the measuring end. The high voltage value is specified in the national standard of the insulation resistance meter as 50V, 100V, 250V, 500V, 1000V, 2500V, 5000V... There are generally three ways to generate DC high voltage. The first type of hand crank generator. At present, about 80% of megohmmeters produced in China are using this method (source of shake name). The second type is boosted by the mains transformer and rectified to obtain DC high voltage. The method used for general utility meters. The third method is to use a transistor oscillation type or a dedicated pulse width modulation circuit to generate DC high voltage, which is generally adopted by battery-type and utility-type insulation resistance meters. (2) Measurement loop In the above-mentioned megger (Megohmmeter), the measurement loop and the display part are combined into one. It is completed with a flow ratio meter, which consists of two coils with an angle of 60° (left and right). One of the coils is connected across the voltage, and the other coil is in the measurement loop. middle. The deflection angle of the head pointer is determined by the ratio of the current in the two coils. Different deflection angles represent different resistance values. The smaller the measurement resistance, the greater the coil current in the measurement loop and the greater the deflection angle of the pointer. . Another method is to use a linear ammeter as a measurement and display. The flow ratio meter used in the front is non-uniform due to the magnetic field in the coil, when the pointer is infinite At a large point, the current coil is exactly in the place where the magnetic flux density is the strongest, so although the measured resistance is large, the current flowing through the current coil is very low, and the deflection angle of the coil will be larger at this time. When the resistance to be measured is small or 0, the current flowing through the current coil is large, and the coil has been deflected to a place where the magnetic flux density is relatively small, and the deflection angle caused thereby will not be large. This achieves a nonlinear correction. The resistance of a typical megohmmeter header needs to be several orders of magnitude. However, when directly using a linear current meter to directly enter the measurement loop, the scales at the time of high resistance are all squeezed together and cannot be distinguished. In order to achieve nonlinear correction, nonlinear elements must be added to the measurement loop. In order to achieve a small resistance value when the shunt effect. The shunt does not occur at high resistance, so that the resistance display reaches several orders of magnitude. With the development of electronic technology and computer technology, the digital display gradually replaces the pointer type instrument. Insulation resistance digital measurement technology has also been developed, in which the pressure ratio meter circuit is one of the better measurement circuits, and the pressure ratio meter circuit is composed of a voltage bridge circuit and a measurement bridge circuit. The signals output by these two bridges are directly converted into digital values ​​through A/D conversion and then processed by the SCM. 2 , the selection of insulation resistance meter Insulation resistance meter is mainly used to measure the voltage value, the other is the range that needs to be measured, whether it can meet the needs. If the measurement is frequent, it is best to select the alarm setting function. Sulfentrazone Herbicide,Dismiss Sulfentrazone,Sulfentrazone Crabgrass,Sulfentrazone Fmc Jiangsu Hanlian Biological Technology Co.,Ltd , https://www.hanlianbio.com