Basic use of a pointer multimeter:
(1) Before the test, firstly place the multimeter in a horizontal state, and see whether its needle is at the zero point (the zero point of the current and voltage scale), if not, adjust the "mechanical zero adjustment" under the meter head to make the needle point to the zero point.
(2) According to the measured items, correctly select the measurement items and range switch on the multimeter. If the order of magnitude of the measured value is known, then select the corresponding order of magnitude range. If you do not know the order of magnitude of the measured value, you should choose the maximum range to start measuring, when the angle of deflection of the pointer is too small to read accurately, and then reduce the range. Generally, the deflection angle of the pointer is not less than 30% of the maximum scale as a reasonable range.
(3) Use the multimeter as an ammeter
When connecting the multimeter in series in the circuit under test, pay attention to the direction of the current. That is, the red pen is connected to the end of the current inflow, and the black pen is connected to the end of the current outflow. If you do not know the direction of the measured current, you can connect a pen at one end of the circuit, another pen at the other end of the circuit gently touch, if the pointer swings to the right, indicating that the wiring is correct; if the pointer swings to the left (lower than zero), indicating that the wiring is incorrect, the multimeter should be switched to the position of the two pens.
② in the pointer deflection angle greater than or equal to 30% of the maximum scale, try to use a large range gear. Because the larger the range, the smaller the shunt resistance, the smaller the equivalent internal resistance of the ammeter, the smaller the error introduced by the measured circuit.
③ In the measurement of large current (such as 500mA), do not toggle the range selection switch during the measurement process, so as not to produce an arc, burn the contacts of the conversion switch.
(4) Use the multimeter as a voltmeter
① Connect the multimeter in parallel on the circuit to be measured. When measuring DC voltage, pay attention to the polarity of the measured voltage, i.e. connect the red pen to the high voltage end and the black pen to the low voltage end. If you do not know the polarity of the measured voltage, you can try the test method as described above when measuring current, such as the pointer deflected to the right, you can measure; such as the pointer deflected to the left, the red and black pens are switched to the position, can be measured.
② and the above ammeter, in order to reduce the internal resistance of the voltmeter introduced error, in the pointer deflection angle greater than or equal to 30% of the maximum scale, the measurement try to choose a large range gear. Because the larger the range, the larger the voltage divider resistance, the larger the equivalent internal resistance of the voltmeter, which introduces less error to the measured circuit. If the internal resistance of the circuit under test is very large, the internal resistance of the voltmeter is required to be larger, in order to make the measurement accuracy is high. At this time, the need to replace the voltage sensitivity (greater internal resistance) of the multimeter to carry out measurements. Such as MFl0 type multimeter maximum DC voltage sensitivity (100 kΩ / V) than the ME30 type multimeter maximum DC voltage sensitivity (20 kΩ / V) high.
③ In the measurement of AC voltage, do not have to consider the polarity of the problem, as long as the multimeter can be connected in parallel to the measured ends. In addition, generally do not have to choose a large range of files or select a high voltage sensitivity of the multimeter. Because in general, the internal resistance of the AC power supply are smaller than the gum. It is worth noting that the measured AC voltage can only be sinusoidal, and its frequency should be less than or equal to the permissible operating frequency of the multimeter, otherwise it will produce a large error.
④ Do not toggle the range selector switch when measuring higher voltages (e.g. 220v) to avoid generating arcs and burning the contacts of the changeover switch off.
⑤ When measuring high voltage greater than or equal to 100v, you must pay attention to safety. It is better to fix the meter pen on the common ground of the circuit under test, and then touch the other end of the test point with the other meter pen.
