Why the multimeter does not light up the LED light
Multimeter to detect LED can use diode file
LED is also a diode, which also has the characteristic of unidirectional conduction, and only allows current to flow from the positive pole of the LED to the negative pole, so we can use the diode gear of the multimeter to measure the quality of the LED. The red and black test leads have directions. First The first step is to exchange the test leads and measure it to avoid misjudgment. However, LEDs are different from ordinary diodes, and their forward voltage drop is relatively high. If the voltage is lower than the forward conduction voltage drop of the LED, the LED can only light up slightly or even not light up.
Multimeter diode gear measurement principle
The diode file will provide a constant current, generally 1mA (some multimeters are 2mA), when the diode is connected, the voltage drop of the PN junction of the diode can be measured, so as to judge whether the diode is good or bad. Since the current provided by the diode gear is very small, when measuring the LED, if the LED requires a large current, the brightness will be relatively low.
Is there a difference in accuracy between a clamp meter and a multimeter?
The ammeter must disconnect the line when measuring, and then connect the ammeter in series in the circuit, which is very troublesome. In addition, the range of the ammeter is limited, and it cannot measure large currents. The general range is 5A.
In actual work, current transformers are generally used to expand the range of the ammeter. The clamp meter is actually a combination of a feed-through current transformer and an ammeter, so it can not only measure AC current without power supply, but also easily measure large currents.
The current clamp meter is no longer the clamp meter of decades ago. It adopts the principle of Hall induction, which can not only measure AC circuit and DC current; , frequency and other parameters. As for the accuracy, it is the same as the digital multimeter, there is no difference.
they differ
If you have to say which one is easier to use, the clamp meter or the multimeter, there are still some differences in their experience during use.
1. The clamp meter can continuously measure the current, which the multimeter cannot do. If you need to measure AC and DC current frequently, it is recommended to buy a clamp meter; if you don’t need to measure current frequently, buy a multimeter.
2. In order to continuously measure the current, the clamp meter must have a jaw, so its body is relatively slender. Because there is no bracket on the back of the clamp meter, I personally feel that the clamp meter is more inclined to be measured in the hand; the multimeter has a bracket on the back, and it is more inclined to measure on the table. So if you often sit at the table for maintenance, it is more convenient to buy a multimeter, otherwise it is very uncomfortable to stretch your neck to look at the screen of the clamp meter.
3. In terms of price, the clamp meter not only has most of the functions of a multimeter, but also has more current transformers, so the price is relatively more expensive.
