Hi all - I hope someone can help me.
I've recently started electronics and have a simple circuit showing how a transistor switches a LED.
When powered up at 5V, the power supply shows the current at 0.01A.
If I put my multimeter in series with the circuit it reads 0.013A on the 10A range. However, if I put the meter on to the mA range and repeat, the fuse blows. The fuse is rated at 500mA and has now been replaced twice in case the original was faulty. This meter is a Uni-T UT71D and does alert me if the test leads are not connected correctly for the range selected.
I retried with another (cheap) meter and it read 133mA no problem.
Any thoughts? It sort of defeats the object of having a multimeter if it's "not multi"
Thanks- Jonathan
Er... no, the meter alerts you if the test leads are not connected _to the meter_ correctly for the range selected. As you have now discovered, fortunately in a low-power circuit, the meter doesn't know or care if you have it connected improperly _to the circuit_ under test -- and can't inform you except by blowing fuses.
This is why, when asking questions about probing a circuit, you should always include in your schematic exactly _where_ you are probing the circuit with your meter or scope. Simply posting the schematic is nice and necessary, but we also need to know where/how the meter is connected; after all it's part of the circuit too. Anyhow, it's good that you've got the problem sorted now.
Blowing the low-range current fuse, and not realizing it, is the root cause of many many "meter current range not working" complaints and questions I've seen on this forum. There are a couple threads active right now that probably have this as the root cause or at least a major contributor of difficulty in understanding what's going on. It gives us used-to-be-newbies something we can help with, at least!