Introduction to multimeter selection principles
1. The reading accuracy of the pointer meter is poor, but the process of the pointer swinging is relatively intuitive, and its swing speed can sometimes reflect the measured size more objectively (such as measuring the slight deviation of the TV data bus (SDL) when transmitting data). Jitter); the digital meter reading is intuitive, but the process of digital changes looks messy and not easy to watch.
2. There are generally two batteries in an analog watch, one with a low voltage of 1.5V, and one with a high voltage of 9V or 15V. The black test lead is the positive terminal relative to the red test lead. Digital meters commonly use a 6V or 9V battery. In the resistance mode, the output current of the test pen of the pointer meter is much larger than that of the digital meter. Using the R×1Ω gear can make the speaker make a loud "click" sound, and using the R×10kΩ gear can even light up the light-emitting diode (LED).
3. In the voltage range, the internal resistance of the pointer meter is smaller than that of the digital meter, and the measurement accuracy is relatively poor. In some high-voltage and micro-current situations, it is even impossible to measure accurately because the internal resistance will affect the circuit under test (for example, when measuring the acceleration stage voltage of a TV picture tube, the measured value will be much lower than the actual value). The internal resistance of the voltage range of the digital meter is very large, at least in the megohm level, and has little impact on the circuit under test. However, the extremely high output impedance makes it susceptible to the influence of induced voltage, and the measured data may be false in some situations with strong electromagnetic interference.
4. In short, pointer meters are suitable for measuring analog circuits with relatively large currents and high voltages, such as televisions and audio amplifiers. Digital meters are suitable for measuring digital circuits with low voltage and small current, such as BP machines, mobile phones, etc. It is not fixed, and a pointer table and a digital table can be selected according to the situation.
operating procedures
1. Before use, you should be familiar with the various functions of the multimeter, and correctly select the gear, range and test lead socket according to the object being measured.
2. When the size of the measured data is unknown, you should first set the range switch to the maximum value, and then switch from the large range to the small range, so that the meter pointer indicates more than 1/2 of the full scale.
3. When measuring resistance, after selecting the appropriate magnification level, touch the two test leads to make the pointer point at the zero position. If the pointer deviates from the zero position, adjust the "zero adjustment" knob to return the pointer to zero to ensure accurate measurement results. . If it cannot be zeroed or the digital display issues a low-voltage alarm, it should be checked in time.
4. When measuring the resistance of a certain circuit, the power supply of the circuit under test must be cut off, and the measurement must not be carried out while it is powered on.
5. When using a multimeter for measurement, pay attention to the safety of the person and the instrument equipment. During the test, you are not allowed to touch the metal part of the test pen with your hands, and it is not allowed to switch the gear switch while the power is on to ensure accurate measurement and avoid accidents such as electric shock and burning of the meter. .
