Reading high voltages using multimeters
Sometimes we measure electronic circuits, due to the multimeter measurement mechanism, circuit structure, internal resistance and other types of precision-related indicators and other reasons, sometimes leading to a decline in measurement accuracy, the measured circuit operating frequency, the active components of the work of the state and other factors, can also lead to larger measurement errors.
Therefore, the measurement of some circuits on the instrumentation is also more concerned about the general situation of measuring the circuit voltage when choosing a higher internal resistance of the instrument, which can reduce the instrument to the circuit shunt. When measuring the circuit current, try to choose a lower internal resistance instrument, but the internal resistance of the instrument can not be zero, so the internal resistance of the instrument after the series into the ammeter will inevitably be divided into the circuit voltage, so the result is that the circuit debugging with the work of the parameters are not consistent. In order to avoid the above errors using indirect measurement, measuring current when measuring voltage, measuring voltage when measuring current. When measuring voltage, first accurately measure the resistance of the resistor, and then measure the current of the circuit so that indirectly get the measured voltage. Measure the voltage when measuring the current, also measured the resistance of the circuit and then measured the voltage drop on the resistor can also get a more accurate value of the current. Of course, these methods should also be flexible to master the use of analysing the circuit is also very important, more from the practical point of view.
Pointer multimeter to measure the voltage reading is high, you can try to open the back cover, find the head of the calibration resistor, generally an adjustable resistor in series on the head of the table, while looking for a good piece of digital multimeter, adjust it to see if it can be calibrated. If the deviation is not too large, it can usually be calibrated over.
If the deviation is large, use a digital meter to measure the voltage divider resistors in each gear to see if any are burned out and change value.
If none of them are, then the hairspring may be aging and running out of steam. Need to adjust the balance of the hairspring force, that is, the pointer to zero when the upper and lower hairspring against the stress. The greater the stress, the lower the sensitivity of the head, but fast and accurate zeroing, the lower the stress, the higher the sensitivity of the head, but the zero reset performance is not good.
In the case you mentioned, if no signs of resistor damage are found, it should be considered as a problem with the adjustment of the meter head hairspring.
The factors that affect the accuracy of voltage measurement readings are the voltage divider circuit and the sensitivity of the meter head. Large readings are not common faults, usually small readings, that is due to the reduced sensitivity of the meter head, the magnet steel attenuation, magnetic gap within the iron pin will cause low readings, pointer stagnation phenomenon. At this time, you can use self-adhesive to clean up the iron pin, generally can restore the normal reading.
The internal resistance of the multimeter is not the same as the big, allowable error in the +-0.2, each manufacturer has each manufacturer's design ideas, pointer multimeter has basically withdrawn from the ranks of electrical maintenance, only the pointer multimeter is intuitive and convenient, but compared to the digital table to be a lot worse, the accuracy of a lot lower, because the pointer multimeter is built by the resistance or capacitance of each grade, diode, triode Control circuit is completed, the digital multimeter is different he is composed of digital circuits and gate circuits, so the digital meter readings are more accurate, as for the display of high voltage can also be measured in this way, such as the measurement of 220 alternating current (expressed in AC) to be measured with AC 1000V gear is more accurate, because of its relatively high internal resistance is also more stable, on the multimeter is also safer, the same MF47 type multimeter. The same is MF47 multimeter but its internal resistance are not the same, it can be said that a manufacturer's design ideas, but similar, DC file measurement in accordance with the above method, such as the measurement of DC (expressed in DC) 36V above the need for 250V DC file measurement is the most accurate, in the measurement of the measurement must follow the rule that is the measurement of a certain value than the measurement of the value of the file at least twice as big! to measure, now produced in Nanjing, MF47 multimeter there are several kinds of manufacturers such as Jinchuan, Kewa production but the circuit is similar, each with its own design ideas, the following is the appearance of the two tables, look for electronic enthusiasts friends to measure try, but note that novice electronics enthusiasts in the measurement of high-voltage (AC 220V) must pay attention to safety.
