How to use a multimeter to detect automotive circuits?

How to use a multimeter to detect automotive circuits?

Observe and understand the structure of the multimeter.

There are many types of multimeters and different shapes, but the basic structure and use method are the same.
The king on the universal surface board should have a meter head and a selector switch. There are also ohm gear zero adjustment knob and test lead jack.
The role of each part is described below:

(1) Table header

The head of the multimeter is a sensitive ammeter. The dial on the head is printed with various symbols, tick marks and values. The symbol A-V-Ω indicates that this meter is a multimeter that can measure current, voltage and resistance.
There are multiple scale marks printed on the dial. Among them, the “Ω” mark on the right end is the resistance scale line. The right end is zero and the left end is ∞. The scale value distribution is uneven. The symbol “-” or “DC” indicates direct current, “~” or “AC” indicates alternating current, and “~” indicates the scale line shared by AC and DC. The lines of numbers below the scale line are the scale values corresponding to the different gears of the selector switch. A
The head of the meter is also provided with a mechanical zero adjustment knob, which is used to correct the pointer to indicate the zero position on the left end.

(2) Selection switch

The selector switch of the multimeter is a multi-position rotary switch. Used to select measurement items and ranges. General multimeter measurement items include: “mA”; DC current, “V”: DC voltage, “V”: AC voltage, “Ω”: resistance. Each measurement item is divided into several different ranges for selection. A

(3) Test lead and test lead jack

The test leads are divided into red and black. During use, the red test lead should be inserted into the jack marked with “+”, and the black test lead should be inserted into the jack marked with “-“.

How to use the multimeter

(1) Before using the multimeter, it should do:

  1. The multimeter is placed horizontally. A
  2. It should be checked whether the hands stop at the zero position on the left end of the dial. If there is a deviation, use a small screwdriver to gently turn the mechanical zero adjustment knob on the meter head to make the hands of the meter zero. A
  3. Insert the test lead into the test lead jack as required above. A
  4. Turn the selector switch to the corresponding item and range. It can be used.

(2)After the multimeter is used, it should do:

  1. Pull out the test leads.
  2. Turn the selector switch to the “OFF” gear. If there is no such gear, it should be turned to the maximum range of the AC voltage, such as “again 1000V” gear.
  3. If it is not used for a long time, the battery in the watch should be taken out to prevent the battery electrolyte from leaking and corroding the internal circuit.

The steps to measure DC voltage are:

Select the range.

The DC voltage range of the multimeter is marked with “V” and has five ranges of 2.5V, 10V, 50V, 250V and 500V. Select the range according to the power supply voltage in the circuit. Since the power supply voltage in the circuit is only 3 volts, 10 volts is selected. If you don’t know the voltage level, you should first measure with the highest voltage level and gradually switch to the lower voltage level.

Measurement methods.

The multimeter should be connected in parallel with the circuit under test. The red pen should be connected to the junction of the circuit under test and the positive pole of the power supply, and the black pen should be connected to the junction of the circuit under test and the negative pole of the power supply.

Correct reading.

Observe the dial carefully. The DC voltage scale is the second scale. When using the 10V scale, you can directly read the measured voltage value using the third line of numbers under the scale. Pay attention to the reading, the line of sight should face the pointer

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