How to measure the internal resistance of a multimeter during its current range?
Question:
Using a flashlight light bulb and a battery to form a discharge circuit, I wanted to connect a multimeter to the circuit to measure the current level. However, I found that after being connected to the circuit, the brightness of the bulb significantly dimmed, indicating that the internal resistance of the multimeter has caused a voltage drop. How can I know the internal resistance of the multimeter at the current level? Can I use another multimeter to test it? But if the internal resistance of the multimeter is less than 0.1 ohms, my two multimeters seem powerless because the minimum accuracy is only 0.1 ohms. Is there any other good way?
Answer:
The internal resistance of your probe should be very large. If you want to measure it, you have to lead a line from the place where the probe is inserted and then connect it to the In-circuit testing for testing. This can improve the accuracy. Then use another meter to measure the voltage drop of the meter connected to the circuit!
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 a Ammeter to adjust the accurate constant current of 1A or how many mA - it's no use if the Ammeter is not accurate - then use a 200mV multimeter to measure the voltage at both ends of the Ammeter shorted to the constant current source, know the current, know the voltage, and calculate the resistance.
Resolve and string my two digital meters into the circuit, measure the internal resistance of each multimeter, and the result is between 0.3-0.5 ohms. Basically, it is the resistance value of each meter line of two meters. The internal resistance of the multimeter itself is extremely small, and may not be less than 0.1 ohms at all, because the minimum resistance accuracy of both meters is 0.1 ohms.
