Digital multimeters are particularly suitable for the diagnosis of persistent faults in electronic control systems, such as circuit short circuits, open circuits, and damage to electronic components. The digital multimeter is more accurate in measuring the static state of each sensor and actuator of the electronic control system. However, due to the slow response during dynamic measurement, it cannot change randomly with the state change, so the data display is not accurate enough.
In automotive maintenance, the use of a digital multimeter for inspection should pay attention to the following issues: 1. The digital multimeter is suitable for (23 5), humidity RH. If the liquid crystal display is blurred or the writing is incomplete, for example, 8 words are displayed as 3, it may be If the ambient temperature is too low, the multimeter will return to its normal display as soon as it is moved to a warm place. In order to improve work efficiency and avoid detours, before testing with a digital multimeter, first check the condition of the fuse, fusible link, and terminal of the circuit, whether it is open circuit or poor contact. After eliminating the faults in these areas, the digital multimeter is used for formal inspection.
When measuring, gently swing the wires in the vertical and horizontal directions to ensure good contact between the plug and the socket, the test leads, and the measured points to improve accuracy. If the line is not in good contact, an extra resistance will be generated. This part of the resistor will consume voltage, thus creating a voltage drop.
In addition, when measuring, both hands must not touch the metal end of the test lead or the object to be measured, so as to prevent the resistance of the human body from affecting the measurement result. The battery in the table is best replaced twice a year. Although the battery of the digital multimeter can be used for a long time (the service life of the alkaline battery is generally 500h), the detection accuracy decreases with the consumption of battery power. If the digital multimeter's battery indicator has been on for several weeks, it has been used and the measured data is inaccurate.
Keep test leads and wires intact and clean. Any wire insulation () part wear, test pen corrosion or bending should be replaced; the test pen from the battery connection column sticky to the dirty oxide, must be removed. The easiest way to check the integrity of the digital multimeter leads is to select the electrical barrier and then short the 2 test leads. The reading on the watch should be 0. If the reading is greater than 0, there is an extra resistance and it will be added to the The measured readings will therefore affect the accuracy of the test. In addition, if it is necessary to connect or remove the test leads during the test, turn off the ignition switch.
The range should choose the closest one. It is well known that multimeters have different ranges for voltage, current, and resistance measurements. The closer to the actual range, the more accurate the measured value. Take a 4-digit digital multimeter to measure the charging voltage of the engine (about 14V). If you select 04000V range, the reading on the meter is 0014V; if you select 0 400V range, the reading on the meter is 014 2V; If you choose the range of 0 40V, the reading on the watch is 14 25V. Obviously, the range of 0 40V should be selected because it accurately reflects the charging voltage by 0 25V.
If you do not know the range of the measured value, you cannot select the span range. There is a way to solve the problem of rotating (or pressing) the range switch until the word OL appears on the table, and then select upwards. One range.
It is forbidden to measure the resistance of the circuit under test while it is live. It is also forbidden to block the internal resistance of the measurement cell because it is equivalent to a voltage applied to the resistance measurement circuit. The measurement result completely loses meaning, and it may damage the multimeter. In the case of power-on, in order to avoid damage to the digital multimeter when dynamically measuring the line resistance, the resistance of the line can be measured indirectly by measuring the voltage drop of the line and using the formula R = V/I. After the digital multimeter is used up, the range switch should be set to the highest voltage block, and then turn off the power to prevent the next time the wrong operation and damage the multimeter.
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