Functional features and tips for using multimeters
The basic principle of a multimeter is to use a sensitive magneto-electric DC ammeter (microammeter) as a meter head. When a small current passes through the head, a current is indicated. However, the head can not pass large currents, so it is necessary to connect some resistors in parallel and series on the head for shunt or voltage reduction, so as to measure the current, voltage and resistance in the Litar.
1, analog multimeter to identify the performance of the crystal transistor, generally should be used R × 100Ω or R × 1kΩ file, and should not be used R × 1Ω and R × 10kΩ file. Because R × 1Ω file is not easy to observe the leakage current of the tube; and R × 10kΩ file because of its internal high-voltage batteries (MF24, 500-type 9V; MF10, MF12 and MF30-type 15V; MF5, MF121-type 22.5V), will inevitably lead to some of the tubes of the lower withstand voltage by the high-voltage breakdown and produce erroneous test results, and even cause the measured tube damage. The tube under test will be Rosak.
Due to the high internal resistance of the digital multimeter ohm file, the test current provided is extremely weak (e.g., 20kΩ file: DT{{}}μA; DT-840D 60μA), which is not enough to overcome the dead zone voltage of the PN junction in mengenal pasti semiconductor components, and thus the measured resistance is much higher than that of an analog multimeter, and the difference between the readings of the two types of meters is much higher. And there is no linear proportionality between the readings of the two tables, so it is not a basis for judging the performance of the tube, should be changed to the diode test file on the test.
2, digital Multimeter in The OHM File, DioDE Test File and Buzzer File position, the Red Pen and the table connected to the high potential and positively charged, the black pen is connected to the table and negatively charged, which obviously with the analogue multimeter ohm file on the pen's charged polarity is completely the opposite of the detection of polar components or related circuits, be sure to pay attention to the full.
3, when using the ohm file to detect circuit components or circuit systems, must first cut off the power supply of the device or system under test, if the object under test contains a large power storage capacitor, it must also be discharged in an appropriate manner, in order to confirm that the measured part of the premise of no power supply factors before measurement, otherwise, it is sangat mudah to damage the multimeter, especially the analogu multimeter.
4, in measuring the current of low internal resistance circuit (including the network containing low internal resistance power supply and the network of low value load resistance), try to choose a larger current range; in measuring the voltage of high internal resistance circuit (or power supply), the analogue multimeter should try to choose a higher voltage range, and the digital multimeter can easily satisfy the test requirements kerana of its high internal resistance.
5. The internal resistance of various batteries should not be tested with ohm gear, and the internal resistance of the high sensitivity meter head should not be measured directly. The former is very easy to damage the multimeter, the latter often cause the measured head to break the needle, and may even burn out the moving coil.
6, for digital multimeter, when the measured current is large (such as more than 200mA), should be changed to use the panel of the meter on the large current special jack (such as 10A or 20A, etc.) plug the pen, but the vast majority of the meter's large-current range has not been set up to overcurrent protection measures, we must beware of the phenomenon of overload. In addition, the meter should not be strung into the load line for a long time as a large range of ammeter use, the measurement time is generally not more than 15 seconds.
7, ordinary multimeter AC measurement file is only suitable for measuring sine wave voltage or current RMS value, it can not directly measure the sawtooth wave, triangle wave, square wave and other non-sinusoidal power. Even if it is sinusoidal power, its frequency parameter and waveform distortion must also comply with the technical conditions of the multimeter, the measurement error will increase significantly. RMS value of non-sinusoidal voltage or current can generally be measured by electric, electromagnetic instruments or RMS digital multimeter (such as DT-980).
8, in the process of measuring voltage and current, it is best not to change the selector switch gear, especially at higher voltages and larger currents, the selector switch in the switching process is easy to produce arc and burn the switch contacts, and damage to the internal components and lines.
9, meet the table fuse fuse, according to the instructions specified in the specifications for replacement, do not arbitrarily expand or reduce.
10, for analog multimeter, in order to reduce the parallax of reading data, the eye line of sight must be right on the needle. For the dial equipped with reflector, should adjust the line of sight to the table needle and the mirror in the shadow of the needle overlap shall prevail, at this time the parallax is minimum. The multimeter must also be placed horizontally with a maximum inclination daripada not more than 10 darjah.
