Explanation of common problems in measuring resistance with a multimeter

Using a multimeter to measure resistance is one of the most basic operations that engineers often encounter in their daily work. However, the seemingly simple resistance test often encounters some unexpected situations. Here are three most common problems that occur during the multimeter resistance measurement process.

Question 1: Why does a negative value appear when measuring resistance with a multimeter?

There are two reasons why negative values ​​appear when measuring resistance with a multimeter. The resistor being tested is charged or the digital multimeter used by the engineer is not calibrated. If the resistor is found to be charged, just cut off the power supply or wait for the component to complete the discharge process before testing. The calibration time of the pointer multimeter is limited. Once the effective calibration period has passed, the error of the multimeter will become larger. Engineers can calibrate it themselves, but it is better to take it out for calibration by professionals.

Question 2: How to reduce the error when measuring resistance with a pointer multimeter?

Pointer multimeters, like digital multimeters, are currently more commonly used resistance detection devices. For students who use pointer multimeters to measure resistance, how to control the error to the minimum is a big problem. Here I can introduce a method for everyone: choose a good gear and let the pointer close to the median value to reduce the error. If the tester does not know the approximate value of the resistance to be measured, then you can choose a gear and measure it after adjusting the ohm to zero. If the deflection angle is too large, it means that the resistance is small. Change to a small gear, measure the resistance to be measured after adjusting the ohm to zero. If the deflection angle is too small, it means that the resistance is large, and you need to change to a large gear. After adjusting the ohm to zero, measure the resistance to be measured. Remember to adjust the ohm to zero again after changing gears. The principle of the appropriate gear is that the pointer is close to the median value, because the scale near the median value is more uniform, and the reading error is smaller.

Question 3: Why are the readings of small ohm resistances inaccurate when measured by a multimeter?

In the process of using a multimeter to measure resistance, inaccurate readings are often caused by the following four reasons. The first situation is that the lead resistance of a small resistance resistor cannot be ignored compared to the body resistance. In this way, the position where the test pen touches the lead will directly lead to measurement deviation. The second reason is that the contact resistance between the test pen and the lead cannot be ignored compared to the body resistance. The contact resistance between the test pen and the lead is in series with the measured resistance in the measurement circuit. The third situation that may cause inaccurate readings is that the measurement current of the low resistance range of the multimeter is large, which is easy to cause the voltage change of the built-in battery (internal resistance voltage drop and discharge capacity voltage drop). In addition, the range of the multimeter is limited. The minimum resistance scale of a general pointer multimeter is 0.5 ohms, and that of a digital meter is 0.1 ohms. The digital meter also needs to consider the problem of the lead resistance of the test pen (the resistance range of the digital meter does not have a zero adjustment function), and the accuracy of measuring low-value resistance is not higher than that of the pointer meter.