How to use a multimeter to measure whether the components are good or bad and whether the circuit is working properly
I. Off-line measurement
Do not hibernate with the working circuit to do any connection, alone on the component measurement, belongs to the off-line measurement. The following types are briefly described.
1. Inductance, such as 1W ~ 500W power transformer 220V end, DC resistance are generally in a few KΩ ~ tens of Ω, the larger the wattage of the lower resistance. Electromagnetic relay coil resistance is also roughly in this range; in addition to the transformer used in the switching power supply, DC resistance is relatively low, generally in the zero point a few tens of Ω between. The higher the power and frequency, the lower the DC resistance. The DC resistance of small finished inductors is also within this range.
Inductance measurement has a common point, that is, regardless of the positive measurement, reverse measurement, or with a pointer meter, digital meter of any gear, the test results are the same.
2. Measurement of semiconductor devices: measurement of diodes, forward resistance will generally be a few Ω ~ hundreds of Ω between different tables, different gear test results will be different. The reverse resistance will be very large, usually in the megabytes to ∞ between, but germanium tube will be smaller, generally in the hundreds of KΩ above. If the diode with a pointer meter Rx10K gear test regulator value below 9v, there will be forward and reverse resistance are very low, is a normal phenomenon. Measurement of NPN or PNP-type triode, you can b and c, e are understood to be two connected diodes, with the above method of measurement can be. For the triode special gear table, the gear can be used to measure directly.
3. Capacitance measurement
For the digital table, you can directly use the capacitance file measurement. If it is a pointer meter, it can be used to measure the capacitance above 100μF with Rx1 or Rx10, and the capacitance below 100μF with Rx1K or Rx10K. Pointer swing (the larger the capacity of the larger swing) back to the origin is good, otherwise there is a leakage or exchange the pen and then measured, because the electrolytic capacitor in the addition of reverse voltage, leakage will increase. For just removed from the circuit on the capacitor, be sure to discharge the measurement, in order to prevent damage to the multimeter.
4. Rough measurement of integrated circuits
This should have a good integrated circuit for reference. For any two feet of the forward and reverse resistance, are compared against each other. If the resistance between a foot and a good integrated circuit, compared to a large difference, you can initially judge that the integrated circuit has been damaged.
II. Online measurement
Online measurement belongs to the charged measurement. Do this work should first understand the normal voltage or current is measured. Measurement of voltage is best to use the high internal resistance of the digital table to reduce the impact of the measured circuit operating state, otherwise the credibility of the test data will be greatly reduced. Measuring voltage online is an important means of determining whether a circuit or component is good or bad.
Measurement of current, should first be disconnected from the point under test in the case of power failure, serial multimeter, and will be dialled to a slightly larger gear than the current position of the point under test, and then powered on the test can be.
