Measurement instructions for commonly used electrical components
(1) resistance measurement
With the multimeter did not measure the resistance, first of all should be shorted to the pen, twist the zero potentiometer zero, so that the pointer in the ohm zero position. And every time after changing gears also need to readjust the zero potentiometer zero. In the selection of ohm gear, try to select the measured resistance value in close proximity to the centre of the dial resistance reading position, in order to improve the accuracy of the test results; if the resistor in the circuit board, it should be welded open one of the legs can be tested, otherwise the resistor has other shunt devices, the reading is not accurate! Measurement of resistance resistance, do not touch the fingers of both hands, respectively, the meter pen and resistor pins, in order to hinder the shunt of the human body resistance, increasing the error.
(2) Measurement of resistance value to the ground
The so-called ground resistance measurement, that is, the red pen with a multimeter ground, black pen connected to one of the measured components, measuring the point in the circuit resistance value to ground, and the normal resistance value for comparison to determine the scope of the fault. In the measurement, the resistance level is set at R * 1k file, when the measured resistance value of the point of comparison with the normal difference is large, indicating that the part of the circuit there are faults, such as filtering air leakage, open resistance or integrated IC damage.
(3) transistor measurement
Convert the range of the multimeter to the ohm file R * 100 or R * 1K file to measure the diode. Can not use R * 10, R * 10K file. The former for the two a resistance is too small, a resistance is too large, the current through the diode is too large, easy to damage the diode, the latter because of the higher internal voltage, easy to break through the diode with a lower voltage. If the measured resistance is only a few hundred ohms to a few thousand ohms (forward resistance), the red and black pens should be swapped and then measured, if not measured resistance should be a few hundred kilo ohms (reverse resistance), indicating that the diode can be used. When measuring the forward resistance value, the red pen is measured at the end of the diode's negative pole, and the black pen is measured at the end of the diode's positive pole ~ (diode unidirectional conductivity).
By measuring the value of forward and reverse resistance, you can check the diode is good or bad, the general requirements of the reverse resistance than the forward resistance in a few hundred times. That is to say, the smaller the forward resistance the better, the reverse resistance is the larger the better.
(4) AC voltage measurement
We can use the universal DC voltage file and AC voltage file to measure the sunset current and AC voltage value, respectively, is the time to connect the multimeter with the measured circuit in the form of parallel connection. To choose the meter head pointer close to the full scale deflection 2/3 of the range. If the size of the voltage on the circuit is not estimated, it is necessary to use a large range first, and then use the appropriate range after an accurate measurement, so as to prevent damage to the multimeter out of the voltage is too high. In no amount of DC voltage, the multimeter should be the red pen in the measured circuit positive pole, and the black pen to the negative pole of the circuit, can not be reversed ~ in the measurement of higher voltage should pay special attention to the two respectively hold the red, black pen about the edge of the part of the measurements, or first a pen fixed at one end, and then touched the test point.
(5) charging transformer measurements
Can be in the transformer is not energised in the case of a multimeter with the ohm file preliminary estimate of a eye its good and bad. First of all, the multimeter will be selected in the R * 10 file, measure the transformer primary coil DC resistance value, generally in a few hundred ohms to a few thousand ohms, if the measured value is infinity, it means that the coil has been disconnected, can not be used!
Then test the insulation resistance value between the primary coil and secondary coil, should be the larger the better ~ If the resistance value is small, it means that the insulation between the initial level is bad, and can not be used ~ The above measurements, if they are good, you can connect the transformer to the power supply to measure the output voltage value, with a filtering circuit of the transformer should pay attention to the red and black pens should be placed correctly on the positive and negative terminals of the voltage output terminal, if the output voltage is measured is normal, it means that the coil has been broken, and can not be used! If the measured output voltage is normal, the transformer performance is good, this aspect is usually used in mobile phone chargers.
