What Is the Measurement Accuracy of a Multimeter?
The voltage values of the chopped mains power measured between Fluke 15B and 187 are different, one is an entry-level multimeter and the other is a high-end multimeter, with significant differences. Then I compared different multimeters and found that each one is different, but when measuring sine waves, they accurately display 220V. The forum expert told me that it was due to differences in algorithms, which broadened my horizons.
A few days ago, I saw someone on the forum talking about the reliability of a multimeter. Coincidentally, I have also encountered this phenomenon in practical operation. Let me give you another reference. An ideal multimeter has no impact on our products, but there will inevitably be interference in practice. In actual measurement, we need to make corresponding estimates to select the appropriate gear and try to avoid errors as much as possible. And our instruments must also undergo corresponding calibration during use. Many power supply devices have significant drift in accuracy, so it is necessary to first calibrate them with measuring devices such as multimeters.
Because it is not a programmable power supply, the price is cheap and the error is relatively large. When only one 3030 1W patch LED is lit, the power supply displays 1.9V 0.1A, while the multimeter displays 2.023V, so the multimeter should be used as the standard.
But when the current range of the multimeter is connected in series, there will be a significant difference in the current value. However, what's even more strange is that the results measured in mA and A ranges have almost doubled the difference. Which one is true?
After replacing the resistor, the difference is not so significant. It is estimated that the resistance of the LED is around 20R at 2V/100mA; Using a 10R ceramic disc resistor as a load will result in a difference of about 30mA between the mA and A positions, but not as significant as the difference in LED.
Why is there such a big difference in LED? Is the multimeter malfunctioning? That's definitely impossible, because the newly inspected multimeter has a very low probability of errors. In fact, this is just an extremely simple measurement of DC voltage and current, and each measurement result is correct, but which result is more reliable? Of course, measuring resistance in gear A is the most reliable!
Why is it said that the measurement results are correct but unreliable? It is because the introduction of a multimeter caused errors. The following diagram is a circuit diagram of a multimeter, which seems to be 15B. The principles of various multimeters are similar. From the figure, we can see that the resistance connected in series between different current levels is different. In fact, the principle of an ammeter is to pass the current of the circuit through a constant resistor and measure the voltage across the resistor. Therefore, the larger the current level, the smaller the resistance connected in series, and the less impact it has on the circuit. From the figure, it can be seen that the 10A gear is connected to 0.01R, and mA/uA will be connected to 9.99R/990R and other resistors respectively. So the test results above show that measuring resistance in gear A is the most reliable.
