Measurement of commonly used components with multimeters
(1) Measurement of resistance
When using a multimeter to measure resistance, you should first short-circuit the test leads and turn the zero-adjusting potentiometer to zero so that the pointer is at the ohm zero position. Moreover, the zero-setting potentiometer needs to be readjusted after each shift. When selecting the ohm level, try to select the resistance value to be measured close to the resistance reading in the center of the dial to improve the accuracy of the test results; if the resistor is on the circuit board, one of the legs should be soldered open before testing. Otherwise, there are other shunt devices in the resistor, and the reading will be inaccurate! When measuring the resistance of a resistor, do not touch the test leads and the pins of the resistor with the fingers of both hands respectively to prevent the shunting of the human body's resistance and increase the error~
(2) Measure the resistance value to ground
The so-called resistance value measurement to the ground is to use the red test lead of the multimeter to connect to the ground, and the black test lead to one of the points of the component being measured, measure the resistance value of the circuit to ground at that point, and compare it with the normal resistance value to determine the scope of the fault. When measuring, the resistance range is set to R*1k range. When the resistance value of the measured point is greatly different from the normal value, it means that there is a fault in this part of the circuit, such as filter circuit leakage, open circuit or integrated resistance. IC damage etc.~
(3) Measurement of transistors
Convert the multimeter's range to the ohm range R*100 or R*1K to measure the diode. R*10 and R*10K files cannot be used. In the former case, if one resistor is too small and the other resistor is too large, the current passing through the diode will be too large and the diode will be easily damaged. In the latter case, the diode with lower withstand voltage will easily break down due to the higher internal voltage. If the measured resistance is only a few hundred ohms to several thousand ohms (forward resistance), you should swap the red and black test leads and then measure again. If the resistance value is not measured at this time, it should be a few hundred kiloohms (reverse resistance). resistor), indicating that this diode can be used. When measuring the forward resistance value, the end measured by the red test lead is the cathode of the diode, and the end measured by the black test lead is the anode of the diode ~ (one-way conduction characteristics of the diode) ~
By measuring the forward and reverse resistance values, the quality of the diode can be checked. Generally, the reverse resistance is required to be several hundred times higher than the forward resistance. In other words, the smaller the forward resistance, the better, and the larger the reverse resistance, the better~
(4) Measurement of AC voltage
We can use the universal DC voltage range and AC voltage range to measure the voltage values of DC and AC respectively. Then connect the multimeter and the circuit under test in parallel. To select the range where the meter pointer deflects close to 2/3 of the full scale. If the voltage on the circuit cannot be estimated, use a large range first, and then use a suitable range after precise measurement. This can prevent the multimeter from being damaged due to excessive voltage. When not measuring DC voltage, touch the red pen of the multimeter to the positive pole of the circuit being measured, and touch the black pen to the negative pole of the circuit. Do not do the reverse. When measuring relatively high voltages, special attention should be paid to the two points. Hold the red and black test leads by their edges to measure, or first fix a test lead at one end, and then touch the tested point ~
(5) Measurement quantity of charging transformer
You can use the ohm setting of a multimeter to make a preliminary estimate of whether the transformer is good or bad when the transformer is not powered. First, select the multimeter to R*10 and measure the DC resistance value of the transformer's primary coil. It is generally between a few hundred ohms and several thousand ohms. If the measured value is infinite, it means that the coil has been broken and cannot be used!
