Detection of resistance: Use a multimeter to detect and precautions

Resistors are the most common components in circuits. Whether you are doing questions or circuit design, you will face a problem: how to judge the quality of resistors. Let's take a look at how to detect resistance.

1. Multimeter detects resistance

There are two types of multimeters: analog and digital. Nowadays, fewer and fewer analog multimeters are used. Most of them use digital multimeters. Of course, there are also desktop multimeters that measure resistance in much the same way.

First, adjust the multimeter to the appropriate resistance range. How to choose the gear? When you test the resistor, you know the resistance value. Otherwise, how do you know that the resistor is good and the resistor you want? Therefore, the gear is selected based on the known resistance. For example, if you want to detect a resistance of 4.7K, you need to put the digital multimeter in the 1K gear, and the highest gear of the analog multimeter is the "×100" gear.

Then, place the red and black test leads of the multimeter on both ends of the resistor pins. There is no positive or negative distinction. Observe the dial or the numbers on the LCD. If the measured resistance value is the nominal resistance value, then the resistor is normal. Yes, it can be used normally. If it is 0, that is, the digital multimeter displays 0 and the pointer of the analog multimeter points to the far left, it means that the resistor has been short-circuited and cannot be used normally. If it displays infinity, that is, the digital multimeter displays 1 and the pointer multimeter points to the far right, then increase the gear and check again. If it is still the same, it means that the resistor is open circuit and cannot be used normally. Another situation is that there is a big gap between the measured resistance value and the nominal resistance value. This means that the resistor has failed and cannot be used normally.

Pointer multimeter measuring resistance

Digital multimeter measuring resistance

2. Precautions for testing

1. When using an analog multimeter, if the gear setting is too small, it will occur and the pointer will quickly move to the right. If you find this situation, disconnect the test leads quickly to avoid bending the pointer and damaging the multimeter.

2. When testing the resistance, both hands should not touch the metal parts of the test lead and the resistance pin at the same time. This will connect the human body resistance in parallel with the measurement resistance, causing the measured value to be smaller than the actual value. Introduction and functions of series, parallel and mixed circuits of resistance .

3. When a circuit fails and you want to check whether the resistor is normal, you cannot do it directly because the value detected is wrong. The value detected is the value after multiple resistors are connected in parallel, so it must be removed, or Disconnect one pin before testing. Of course, you just want to detect whether the resistor is short-circuited. There is no problem in measuring it directly. However, you still cannot be sure that the resistor is short-circuited. You still need to remove it or disconnect a pin to confirm. If the circuit can be guaranteed There is no possibility of short circuit in other circuits, and there is no problem in direct measurement.