How to measure the internal resistance of the multimeter when it is in the current range?
question:
Using a light bulb and a battery to form a discharge circuit, I want to connect the multimeter to the circuit to measure the current, but it is found that the brightness of the light bulb is obviously dimmed after the multimeter is connected to the circuit, which means that the internal resistance of the multimeter has produced a voltage drop. How to know the current range of the multimeter Can the internal resistance be tested with another multimeter? But if the internal resistance of the multimeter is less than 0.1 ohm, my two multimeters seem to be powerless, because the minimum accuracy is only 0.1 ohm. Is there any other good way?
answer:
The internal resistance of your test lead should be very large. If you want to measure it, you can only test the lead wire from the place where the test lead is inserted and then connect it to the circuit for testing. This can improve the accuracy. Then use another meter to measure the voltage drop of the meter connected to the circuit. You can ask for it!
Do you have a multimeter with an accurate point of 200mV? Find a constant current source, or use LM317 or something to make your own, first use an ammeter to adjust the exact constant current of 1A or how many mA - if the ammeter is not accurate, then there is no way - and then use a 200mV multimeter to measure this Short-circuit the voltage at both ends of the ammeter on the constant current source, know the current and the known voltage, and calculate the resistance value.
I put my two digital meters into the circuit, and measured the internal resistance of the next two multimeters respectively, and the result was between 0.3-0.5 ohms. Basically it is the resistance value of the respective meter lines of the two watches. It means that the internal resistance of the multimeter itself is extremely small, and it may not be less than 0.1 ohm at all, because the minimum accuracy of the resistance of the two meters is 0.1 ohm.
