Conclusions on the use of digital multimeters
(1) Familiarise yourself with the significance of the symbols on the dial and the main function of each knob and selector switch.
(2) Perform mechanical zeroing.
(3) Select the stop and range of the change-over switch according to the type and size of the measurement to be made and find out the corresponding scale.
(4)Select the position of the meter pen jack.
(5) Measuring voltage: choose a good range when measuring voltage (or current), if you use a small range to measure a large voltage, there is a danger of burning the meter; if you use a large range to measure a small voltage, then the pointer deflection is too small to read. Range selection should try to make the pointer deflection to about 2/3 of the full scale. If the size of the measured voltage is not clear in advance, the highest range should be selected first, and then gradually reduced to the appropriate range.
a AC voltage measurement: a conversion switch of the multimeter is placed in the AC and DC voltage block, another conversion switch is placed in the appropriate range of AC voltage, the two pens of the multimeter and the measured circuit or load can be connected in parallel.
b DC voltage measurement: a conversion switch of the multimeter is placed in the AC and DC voltage block, and another conversion switch is placed in the suitable range of DC voltage, and "+" pen (red pen) is connected to a high potential, "-" pen (black pen) is connected to a low potential, i.e., let the current flow from the AC voltage to the DC voltage. Potential, that is, let the current from the "+" pen into, from the "-" pen out. If the pen is connected to the opposite, the pointer will be deflected in the opposite direction, easy to bend the pointer.
(6) Measurement of current: when measuring DC current, a changeover switch of the multimeter will be placed in the DC current block, and another changeover switch will be placed in the appropriate range from 50uA to 500mA, and the range selection and reading method of current is the same as that of voltage. Measurement must be disconnected from the circuit, and then in accordance with the current from "+" to "-" direction, the multimeter is connected in series to the circuit under test, that is, the current flows from the red pen, from the black pen out. If the multimeter is mistakenly connected in parallel with the load, the internal resistance of the meter head is very small, which will cause a short circuit and burn the instrument. The reading method is as follows: actual value = indication value × range / full bias
(7) Measurement of resistance: When measuring resistance with the multimeter, it should be operated according to the following methods:
a Select the appropriate magnification block. The scale of the ohmmeter block of the multimeter is uneven, so the multiplier block should be selected so that the pointer stays in the thinner part of the scale as appropriate, and the closer the pointer is to the middle of the scale, the more accurate the reading is. In general, the pointer should be made to point in the scale between 1/3 to 2/3.
b Ohm zeroing. Measurement of resistance before the two pens should be shorted, and at the same time adjust the "ohm (electrical) zero knob", so that the pointer is just pointing at the zero position on the right side of the ohm scale. If the pointer can not be adjusted to zero, it means that the battery voltage is insufficient or there are problems inside the instrument. And every time you change the multiplier block, you should carry out ohm zero adjustment again to ensure accurate measurement.
c Reading: the reading of the meter head multiplied by the multiplication rate is the resistance value of the measured resistor.
(8) Measurement of transformers: measurement of transformers and measurement of inductance with many of the same. First introduce the transformer, transformer by the primary winding, secondary winding and core. There are two kinds of step-up and step-down transformers. Primary winding is mainly connected to the power supply, if you want to measure the primary winding of the transformer of the TV on the two pens of the multimeter connected to the two ends of the plug on the line, adjusted to the ohm gear, directly connected to the socket, the resistance should be very small on the description is good. Connected to the power supply is the primary winding then the other end is the secondary winding. Measurement is also the same as the primary pen connected to the two terminals of the secondary winding can be measured, the resistance value of the secondary winding will be relatively large.
