Common device measurement of multimeter
Resistance measurement
When using a multimeter to measure the resistance, the test leads should be short-circuited first, and the zero-adjustment potentiometer should be turned to zero, so that the pointer is at the ohm zero position. Moreover, after each shift, the zero adjustment potentiometer needs to be readjusted for zero adjustment. When selecting the ohm gear, try to choose the position where the measured resistance value is close to the resistance reading in the center of the dial to improve the accuracy of the test results; if the resistance is on the circuit board, one of the legs should be soldered before testing , otherwise the resistor has other shunt devices, and the reading is inaccurate! When measuring the resistance value, do not touch the test lead and the pin of the resistor with your fingers, so as to prevent the shunt of the human body resistance and increase the error~
(2) Measure the resistance value to the ground
The so-called measurement of resistance to ground is to use the red test lead of the multimeter to ground, and the black test lead to connect one of the points of the component to be measured, measure the resistance value of the point in the circuit to ground, and compare it with the normal resistance value to determine the scope of the fault. When measuring, the resistance gear is set at R*1k. When the resistance value of the measured point differs greatly from the normal one, it indicates that there is a fault in this part of the circuit, such as filter electric air leakage, resistance open circuit or integration IC damage, etc.~
(3) Measurement of transistors
Switch the range of the multimeter to the ohm file R*100 or R*1K file to measure the diode. R*10 and R*10K files cannot be used. The former is that one resistance is too small, the other resistance is too large, the current passing through the diode is too large, and the diode is easy to be damaged, while the latter is easy to break down the diode with low withstand voltage because of the high internal voltage. If the measured resistance is only a few hundred ohms to a few thousand ohms (forward resistance), you should exchange the red and black test leads and measure again. If the resistance value not measured at this time should be several hundred thousand ohms (reverse resistance), indicating that this diode can be used. When measuring the forward resistance value, the end measured by the red test pen is the negative pole of the diode, and the end measured by the black test pen is the positive pole of the diode~(the one-way conduction characteristic of the diode)~
By measuring the forward and reverse resistance values, you can check whether the diode is good or bad. Generally, the reverse resistance is required to be hundreds of 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 file and AC voltage file to measure the voltage value of the current and the AC voltage respectively, and it is time to connect the multimeter and the circuit under test in parallel. To select the gauge pointer close to the full scale deflection of 2/3 range. If the voltage on the circuit cannot be estimated, it is necessary to use a large range first, and then use a suitable range after precise measurement, which can prevent the multimeter from being damaged due to excessive voltage. When the DC voltage is not measured, touch the red meter pen of the multimeter to the positive pole of the circuit under test, and touch the black pen to the negative pole of the circuit. Hold the edge of the red and black test leads to measure, or fix a test lead at one end first, and then touch the point to be tested~
(5) Measurement of charging transformer
You can use the ohm file of the multimeter to preliminarily estimate whether the transformer is good or bad. First select the multimeter at the R*10 position, and measure the DC resistance value of the primary coil of the transformer, which is generally several hundred ohms to several thousand ohms. If the measured value is infinite, it means that the coil has been broken and cannot be used!
