1, and generally betterThe AC voltage stop of the multimeter uses LM358, 324 and other op-amps.
2, pointer multimeter, mainly used to measure DC current, DC voltage, AC voltage, DC resistance and so on. Dc current gear, that is, the shunt resistor and the meter head after the current measurement (with different shunt resistance, you can change the measuring range, the shunt resistance is small, the larger the range) DC voltage gear, that is, the voltage resistor and the meter head in series, in series of different values of the resistance, to obtain a different range.
3, the basic principle of the multimeter is to use a sensitive magnetoelectric DC ammeter (microammeterMake a watch head. When a small current passes through the meter head, there will be a current indication, shunt or buck some resistors in parallel and series on the meter head, so as to measure the current, voltage and resistance in the circuit. The principle of measuring DC current: shunt an appropriate resistor (called shunt resistor) in parallel on the meter head, so that the current range can be expanded.
1, offline detection of IC chip pin to ground between the positive and negative resistance value. This is compared with a good IC chip, so as to find the reasonObstacle point; On-line detection of DC resistance is the same as offline detection.
2, Read the measured value: read the resistance value displayed on the multimeter. If there is resistance between the chip pins, the multimeter will display a value. Voltage measurement: Determine the chip type: Understand the power requirements and operating voltage range of the chip. Set the measuring range: Turn the multimeter knob to the DC Voltage measuring gear and select an appropriate voltage range. Power on: If needed, connect the chip to the appropriate power supply.
3, offline detection: test the IC chip pinsPositive and negative resistance values between the ground. It is compared with a good IC chip to find the fault point. Online detection: To disconnect the power supply on the circuit board to be tested, the internal voltage of the multimeter should not be greater than 6V, and pay attention to the influence of the periphery when measuring. Such as potentiometer connected with IC chip, etc. Ac operating voltage: Use a multimeter with dB file to measure the AC voltage approximation of the IC.
4, motherboard maintenance and maintenance methods and IC good or bad judgment method Check board method: 1. Observation method: there is no burning, burning, foaming, plate surface broken line, socket rust. 2. Meter measurement method: +5V, GND resistance is too small (below 50 ohms). 3. Power inspection: For the clear broken board, the voltage can be slightly increased by 0.5-1V, and the IC on the board can be rubbed by hand after starting up to make the chip in question hot, so as to perceive it.
1. Look at the multimeter panel first. Resistance level Ω, red pen in v/Ω jack, black pen in COM jack. Measure both ends of a circuit or device. Can not be charged, otherwise burnt outUse a watch. Dc voltage file, the same resistance file measurement mode. Ac voltage file, the same resistance file measurement mode. Ac current, red pen in MA or 10A jack, black pen in COM jack. String the multimeter into the circuit for measurement.
2, the dial should be level, the reading should be correct. The pointer multimeter should be placed horizontally and read directly on the dial. The range needs to be right. The needle is too wide. Estimate the approximate range before testing, and then choose the appropriate range. If you can't estimate it, use a large scale first. Test R is not charged, test C first discharge, when the resistance must be cut off, test capacitanceAlways remember to discharge.
3, confirm the gear before measurement / : before each measurement, be sure to check the gear setting and develop good habits. Maintain stability during measurement / : The range cannot be changed at will to avoid dangerous arc damage. Dial level, accurate reading / : Ensure that the multimeter is smooth and the sight line is parallel to the watch hand.
4, the dial should be level, the reading should be correct: the use of a multimeter should be horizontal rotation, reading the line of sight should be facing the watch hand. The range should be appropriate, the needle is too much: select the range, if it is impossible to estimate the measured size in advance, you should try to choose a larger range, and then according toThe deflection Angle is gradually changed to a smaller range until the pointer is deflected to about 2/3 of the full scale.
5, multimeter use method Multimeter structure (500 type) Multimeter is composed of three main parts: meter head, measurement circuit and transfer switch. (1) meter head: It is a high-sensitivity magnetoelectric DC ammeter, the main performance indicators of the multimeter basically depend on the performance of the meter head. The sensitivity of the watch head refers to the value of the DC current flowing through the watch head when the hand is deflected to the full scale. The smaller the value, the higher the sensitivity of the watch head.
1, the digital multimeter is mainly composed of three main parts, such as the meter head, the measurement circuit and the transfer switch. The role of the watch head: It is generally composed of A A/D (analog/digital) conversion chip peripheral components liquid crystal display, for the magnetoelectric system measurement mechanism, it can only pass DC, the use of diodes to AC into DC, so as to achieve AC measurement. The measured values are displayed directly in digital form by the LCD screen.
2, the multimeter is composed of three parts: measuring mechanism, measuring line and transfer switch. The functions of each part are as follows: Measuring mechanism: The measuring mechanism of the multimeter is the meter head, whose role is to convert the measured electricity into the corresponding voltage or current signal for further processing by the measuring line.
3, the pointer is a component of the universal meter: detection unit (meter head), measurement line, transfer switch. The components of digital multimeter are: measuring line, conversion switch, analog-to-digital (A/D) conversion, computer processing and display circuit.
4, multimeter structure (500 type)The multimeter consists of three main parts: the meter head, the measuring circuit and the transfer switch. (1) meter head: It is a high-sensitivity magnetoelectric DC ammeter, the main performance indicators of the multimeter basically depend on the performance of the meter head. The sensitivity of the watch head refers to the value of the DC current flowing through the watch head when the hand is deflected to the full scale. The smaller the value, the higher the sensitivity of the watch head. The greater the internal resistance when measuring voltage, the better its performance.
5, the multimeter is composed of three main parts, such as the meter head, the measurement circuit and the conversion switch. Head The head of a multimeter is a sensitive galvanometer. The dial on the watch head is printed with a variety of symbols, engraved