1. The detection of the color code inductor places the multimeter in the R×1 block, and the red and black test leads are connected to any of the terminals of the color code inductors. At this time, the pointer should swing to the right. According to the measured resistance value, the following three cases can be identified: A. The measured color code inductor has zero resistance and has a short circuit fault inside. The magnitude of the DC resistance value of the B-coded inductor is directly related to the enamelled wire diameter and the number of windings used to wind the inductor coil. As long as the resistance value can be measured, the measured color code inductor is considered normal. .
2, the detection of the transformer in the middle of the week A will dial the multimeter to R × 1 block, according to the arrangement of the windings of the windings of the transformers in the middle of the transformer, check the on and off conditions of each winding one by one, and then determine whether it is normal. B. Insulation performance The multimeter is placed in the R×10k block and tested in the following states: (1) the resistance between the primary winding and the secondary winding; (2) the resistance between the primary winding and the outer casing; (3) The resistance value between the secondary winding and the outer casing. There are three cases in the above test results: (1) the resistance is infinite: normal; (2) the resistance is zero: there is a short circuit fault; (3) the resistance is less than infinity, but greater than zero: there is leakage fault.
3. Detection of the power transformer A. Observe the apparent appearance of the transformer by observing the appearance of the transformer. If the coil lead is broken, de-soldering, whether the insulating material has burnt marks, whether the iron-tightening screw is loose, whether the silicon steel sheet is rusted, whether the winding coil is exposed or the like. B insulation test. Use the multimeter R×10k block to measure the resistance between the core and the primary, the primary and the secondary, the core and each secondary, the electrostatic shielding layer and the secondary and secondary windings. The multimeter pointer should refer to the infinity position. move. Otherwise, the transformer insulation performance is poor. Detection of C coil on and off. Place the multimeter in the R × 1 block. During the test, if the resistance value of a winding is infinite, the winding has a faulty fault. D discriminates the primary and secondary coils. The primary and secondary pins of the power transformer are generally led out from both sides, and the primary winding is marked with 220V, and the secondary winding is labeled with rated voltage, such as 15V, 24V, 35V. Then identify them based on these markers. E detection of no-load current. (a) Direct measurement method. Open all the secondary windings and place the multimeter in the AC current block (500mA, stringed into the primary winding. When the plug of the primary winding is inserted into 220V AC mains, the multimeter indicates the no-load current value. This value should not be It is greater than 10%-20% of the full load current of the transformer. Generally, the normal no-load current of the power transformer of common electronic equipment should be about 100mA. If it exceeds too much, it means that the transformer has short-circuit fault. (b) Indirect measurement method. A 10/5W resistor is connected in series in the primary winding, and the secondary is still completely empty. Turn the multimeter to the AC voltage block. After power-on, measure the voltage drop across the resistor R with two test leads, and then calculate the no-load with Ohm's law. The current I is empty, that is, I empty = U / R. The detection of the no-load voltage of the F. The primary of the power transformer is connected to the 220V mains, and the no-load voltage value of each winding is sequentially measured by the AC voltage of the multimeter (U21, U22, U23). , U24) should meet the required value, the allowable error range is generally: high voltage winding ≤ ± 10%, low voltage winding ≤ ± 5%, the voltage difference between two sets of symmetrical windings with center tap should be ≤ ± 2%. G general low power supply change The temperature rise is allowed to be 40 ° C ~ 50 ° C, if the quality of the insulating material used is good, the temperature rise can be increased. H detection identifies the same name of each winding. When using the power transformer, sometimes in order to get the required secondary voltage Two or more secondary windings can be used in series. When the power transformer is used in series, the same name of each winding participating in the series must be correctly connected, and no mistake can be made. Otherwise, the transformer cannot work normally. I. Power transformer Comprehensive detection and identification of short-circuit faults. The main symptoms after short-circuit faults in power transformers are severe heat generation and abnormal output voltage of the secondary winding. Usually, the more short-circuit points between turns in the coil, the larger the short-circuit current, and the transformer heats up. The more serious it is, the simple way to detect whether the power transformer has a short-circuit fault is to measure the no-load current (the test method has been introduced earlier). The transformer with short-circuit fault will have a no-load current value that is much greater than 10% of the full-load current. In severe cases, the transformer will heat up quickly within a few seconds after no-load power-on, and the iron will be touched by hand. Hand feel. At this point you can not measure the load current transformer short circuit judge points exist.