The voltage reading measured by the analog multimeter is too high
Sometimes when we measure electronic circuits, due to the measurement mechanism of the multimeter, circuit structure, internal resistance and other accuracy-related indicators, sometimes the measurement accuracy will decrease, the working frequency of the circuit under test, the working frequency of the active device, etc. Factors such as shape may also lead to larger measurement errors.
Therefore, the measurement of some circuits is also very particular about the instrument. Generally, when measuring the voltage of the circuit, an instrument with a high internal resistance should be selected, which can reduce the shunting of the circuit by the instrument. When measuring the circuit current, try to choose an instrument with a low internal resistance. However, the internal resistance of the instrument cannot be zero. Therefore, after the ammeter is connected in series, the internal resistance of the instrument will inevitably divide the voltage of the circuit. The result is the parameter during circuit debugging and operation. Inconsistent. In order to avoid the above-mentioned errors, indirect measurement is used. When measuring voltage, measure current, and when measuring current, measure voltage. When measuring voltage, first accurately measure the resistance of the resistor, and then measure the current of the circuit, thus indirectly obtaining the measured voltage. When measuring voltage when measuring current, you also need to measure the resistance of the circuit first and then measure the voltage drop across the resistor to get a more accurate current value. Of course, these methods must be used flexibly, and circuit analysis is also very important, and it must be based on reality.
If the voltage reading measured by the analog multimeter is too high, you can try to open the back cover and find the calibration resistor on the meter head. It is usually an adjustable resistor connected in series on the meter head. At the same time, find a better digital multimeter and adjust it to see if it works. Cannot calibrate. If the deviation is not large, it can generally be calibrated.
If the deviation is large, use a digital meter to measure the voltage dividing resistors at each gear to see if any have been burned or changed in value.
If there is none, then the hairspring may be old and lose its power. The balancing force of the hairspring needs to be adjusted, which is the stress on the upstream and downstream wires when the pointer returns to zero. The greater the stress, the lower the sensitivity of the meter, but the zero return is fast and accurate. The smaller the stress, the higher the sensitivity of the meter, but the zero reset performance is not good.
In the situation you mentioned, if no signs of resistor damage are found, it should be considered a problem with the hairspring adjustment on the meter head.
The factors that affect the accuracy of voltage measurement readings are the voltage dividing circuit and the sensitivity of the meter. A high reading is a rare fault, usually a low reading. This is caused by the reduced sensitivity of the meter, attenuation of the magnet, and iron pins in the magnetic gap, which can cause low readings and stuck pointers. At this time, you can use self-adhesive glue to clean the iron pin, and the normal reading can usually be restored.
The internal resistance of multimeters is not all the same, and the allowable error is +-0.2. Each manufacturer has its own design ideas. The analog multimeter has basically withdrawn from the ranks of electrical maintenance. It is just that the analog multimeter is intuitive and convenient, but It is much inferior to the digital meter, and the accuracy is much lower, because each gear of the analog multimeter is completed by a control circuit built by resistors or capacitors, diode, and transistors, while the digital multimeter is different in that it is composed of digital It is composed of a circuit and a gate circuit, so the reading of the digital meter is more accurate. As for the high voltage displayed, it can also be measured with this method. For example, to measure 220 AC (expressed in AC), it is more accurate to use the AC 1000V level because it is more accurate. Its internal resistance is relatively high and stable, and it is safer for multimeters. It is also an MF47 multimeter but its internal resistance is different. It can be said that the design ideas of a manufacturer are the same, but they are similar. The DC range measurement follows the above method. For example, when measuring direct current (expressed as DC) above 36V, the 250V DC range is most accurate. When measuring, you must follow a rule, that is, when measuring a certain value, you must use a range that is at least twice as large as the measured value. For measurement, there are several types of MF47 multimeters produced in Nanjing. They are produced by Jinchuan, Kehua and other manufacturers. However, the circuits are similar, and each has its own design ideas. The following is the appearance of these two meters. For those who are electronic enthusiasts, Let’s give it a try, but novice electronics enthusiasts must pay attention to safety when measuring high voltage (AC 220V).
