I'm not very experiencing in breaking loops for measuring currents, but for my old Bang and Olufsen I wanted to calibrate the output quiescent currents among others.
So basically the manual says that I should put the meter in series with a given resistor, which I have done. But for some reason I do never get a reading on the meter. I have uploaded a picture of the configuration here:
**broken link removed**
The multimeter is a week old, and the resistor is connected between the two white wires. I have actually even tried connecting speakers and checking where there was sound playing in both channel after my initial try, but even then I don't get a reading on the meter? The manual says that I should expect a current of approximately 25mA, so the meter is set in the mA range, and measuring DC (also indicated on the display).
Is the meter just dead, or am I doing something basically wrong?
Also, if you want to know the current through a resistor, measure the voltage across the resistor (without disturbing the circuit) then divide by the resistor value (I = V / R).
I did that afterwards actually, it was also an excuse to try and do a current measurement since it's not something I usually need. And the current is off by 5mA or so, so I would need to fix that.
I reckon you don't loose any warranty for checking and changing fuses?
It's a 22 ohm resistor in the output stage of the power amplifying stage, in the emitter of a BJT to ground?
I have opened the multimeter now, and the fuses are ceramic, so it's not visible whether they are open circuit, but I could think so, seeing that I had a minor sparkling short accident just after I bought it... stupid, I know.
But I guess I will be ordering both a couple of F500 and F10 fuses to be sure, and covered in the future.
Edit:
I just quickly reassembled the meter without the F500, and it is indeed an open circuit. I guess the problem has been identified then.
I have opened the multimeter now, and the fuses are ceramic, so it's not visible whether they are open circuit, but I could think so, seeing that I had a minor sparkling short accident just after I bought it... stupid, I know.
Aah, I wouldn't do that. The short I made was my clumbsy fingers being in the wrong place.
That actually leads me somewhere else. I was trying to simulate me a current dummy load for exactly the purpose of measuring batteries and the like, but I am uncertain of how to simulate a source like the battery, delivering a current varying with respect to R1. Can you help me?
I'm old-school and know very little of circuit simulators. But there are plenty of helpful people here on the forum who do.
In any case, you need to replace R1 with a reference voltage source, and replace X2 with an N-channel mosfet. The op-amp will then vary the gate voltage so that the voltage across R2 matches the voltage on its non-inverting input, thus regulating the current through X2 and R2.
I don't see a "simulated battery" or other source of current in that diagram... Also, try using 12V for the op-amp power supply. It can take up to 10V or so to fully turn on a run-of-the-mill MOSFET. Plus you need headroom for the voltage developed across R2. You can also use a NPN BJT in place of the MOSFET, just include a series base resistor to limit the base current.