How to measure inductance with a multimeter
Detection of Color Code Inductors
Place the multimeter in R × At first gear, connect the red and black pens to either end of the color code inductor, and the pointer should swing to the right. According to the measured resistance value, there are three specific situations for identification:
The resistance value of the tested color code inductor A is zero, and there is an internal short-circuit fault. The DC resistance value of the tested color code inductor is directly related to the diameter of the enameled wire used for winding the inductor coil and the number of windings. As long as the resistance value can be measured, the tested color code inductor can be considered normal.
Detection of mid cycle transformers
A Set the multimeter to R × First gear, check the on-off condition of each winding one by one according to the pin arrangement rule of each winding of the mid cycle transformer, and then judge whether it is normal.
B Test insulation performance
Place the multimeter in R × 10k gear, perform the following status tests:
(1) The resistance value between the primary winding and the secondary winding;
(2) The resistance value between the primary winding and the casing;
(3) The resistance value between the secondary winding and the casing.
The above test results can be divided into three situations:
(1) The resistance value is infinite: normal;
(2) Zero resistance: there is a short-circuit fault;
(3) Resistance value less than infinity but greater than zero: there is a leakage fault.
3. Detection of power transformer
Check whether there are obvious abnormalities by observing the appearance of the transformer. For example, whether the coil leads are broken, desoldered, whether there are burnt marks on the insulation material, whether the fastening screws of the iron core are loose, whether the silicon steel sheet is rusted, and whether the winding coil is exposed.
B Insulation test. Using a multimeter R × Measure the resistance values between the core and primary, primary and secondary, core and secondary, electrostatic shielding layer and secondary, and secondary windings at 10k gear. The multimeter pointer should be fixed at infinity. Otherwise, it indicates poor insulation performance of the transformer.
C coil on/off detection. Place the multimeter in R × In gear 1, during the test, if the resistance value of a certain winding is infinite, it indicates that there is an open circuit fault in the winding.
Distinguish between 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 often marked with the word 220V, while the secondary winding is marked with the rated voltage value, such as 15V, 24V, 35V, etc. Then identify based on these markings.
E. Detection of no-load current. (a) Direct measurement method. Open all secondary windings, Place the multimeter in the AC current range (500mA) and connect it to the primary winding in series. When the plug of the primary winding is inserted into a 220V AC mains supply, the multimeter indicates the no-load current value. This value should not be greater than 10% to 20% of the transformer's full load current. Generally, the normal no-load current of power transformers for common electronic equipment should be around 100mA. If it exceeds too much, it indicates that the transformer has a short-circuit fault. (b) Indirect measurement method. Connect a 10 Ω/5W resistor in series in the primary winding of the transformer, and all secondary windings are still unloaded. Set the multimeter to AC voltage. After powering on, use two probes to measure the voltage drop U at both ends of resistance R, and then use Ohms
