Explanation of common problems in the process of measuring resistance with a multimeter
Using a multimeter to measure resistance is one of the basic operations that engineers often come into contact with in their daily work. However, the seemingly simple resistance test often has some unexpected situations. Here is a summary of the three most frequently asked questions in the process of measuring resistance with a multimeter.
Question 1: Why does a negative value appear when the multimeter is measuring resistance?
In the process of measuring the resistance with the multimeter, there are two reasons for the negative value. The tested resistance is charged or the digital multimeter used by the engineer is not calibrated, which may cause this situation. If the resistance is found to be charged, it is only necessary to cut off the power supply or wait for the component to complete the discharge process independently before testing. The calibration time of the analog multimeter is limited. Once the valid calibration period has passed, the error generated by the multimeter will become larger. Engineers can correct this by themselves. Of course, it is best to take it out to a professional for calibration.
Question 2: How to reduce the error of the pointer multimeter measuring resistance?
The pointer is a multimeter, like a digital multimeter, which is a commonly used resistance detection device. For students who use the pointer to measure resistance with a multimeter, how to minimize the error is a big problem. Here I can introduce a method for you: choose a good gear, and let the pointer close to the median value will reduce the error. If the inspector does not know the approximate value of the resistance to be measured, then you can choose a gear, and then measure after the ohm is zeroed. If the deflection angle is too large, it means that the resistance is small, change to a lower gear, and measure the resistance to be measured after zeroing the ohms. Remember to reset the ohm to zero after shifting. The principle of suitable gear is that the pointer is close to the median value, because the scale near the median value is relatively uniform, and the reading error is small.
Question 3: Why is the multimeter inaccurate in measuring resistance readings for small ohms?
In the process of using a multimeter to measure resistance, inaccurate readings are often caused by these four reasons. The first case 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 lead contacts the lead will directly bring about measurement deviation. The second reason is that the contact resistance between the test lead and the lead cannot be ignored compared with the body resistance. The contact resistance between the test lead and the lead wire is connected in series with the measured resistance in the measurement circuit. The third situation that may lead to inaccurate readings is that the measurement current of the multimeter's low-resistance range is relatively large, which is likely to cause voltage changes (voltage drop in internal resistance and discharge capacity) of the built-in battery. Beyond that, the multimeter has a limited range. The lowest resistance scale of the general pointer multimeter is 0.5 ohms, and the digital meter is 0.1 ohms. The digital meter also needs to consider the problem of the lead resistance of the test leads (the resistance file of the digital meter has no zero adjustment function), and the measurement accuracy of low-value resistance is not higher than that of the pointer meter.
