multimeter
I am new to electronics, but I don't know what the readings mean. I took measurements with a digital multimeter, the power source is a 9V battery and I have a load a LED.
Setting Reading
20 0.05
200m 00.5
20m 0.6
2m .600
Which setting on the A range indicates the milliamps?
I did the measurement correctly in series, on DC. The manual doesn't say, it was made in China
Here is the image of the multimeter:
The Fluke meters I am familiar with are specified as +/-(given percent of measurement + given number of least significant digits). For the given info, using the 400 ohm range, this yields +/-(0.004 * 0.22 + 2 * 0.1) = +/-0.20088 or approximately +/-0.2 ohms, if the meter is accurately calibrated.
When measuring low resistance values, especially at the sub 1 ohm level, you will need to consider the impedance of your probes and the connections to the meter and the resistor. If you make a resistance measurement with your probes shorted together, you can get an idea of the resistance of you probe connections.
To more accurately measure sub 1 ohm resistors without using a Wheatstone bridge or other indirect measurement methods, I would recommend using a bench DVM with a 4-wire (Kelvin) resistance measurement capability. This will remove the resistance of your probes from the measurement.
Note added by barlop- It was the third one that was it. I tested it by sticking wires into the breadboard and touching the top of the wires with the probes. And then the bulb lit.
hypothesis: 1/3
You blew the fuse on the mA current measurement channel. The mA current channel is fused for 200 mA. A light bulb can sink that much (especially during inrush current), and a 9V alkaline battery can easily source that much.
It's possible that you have exceeded the current rating of the current measurement channel and blew the fuse inside of the multimeter. Make sure that you read the manual and know the rating. Make sure that you estimate the expected value for current before you probe it.
You can open the multimeter and examine the fuse.
You could try the other channel (the one that's marked 10A).
hypotheses: 2/3
It's possible that the positive (red) probe goes to the socket for voltage measurements. It should go to the socket for current measurement. I think in your multimeter the current measurement socket is on the left hand side (the one that says 10A).
hypothesis: 3/3
Yet another possible reason is that the probes are too thick and they don't reach the conductors in the breadboard. You can check this by setting the meter to continuity (plug probes in sockets that do continuity, of course) and probing two points on the same row of the breadboard.
Best Answer
All of the settings with "m" in them represent milliamps. The "setting" is what we call the range, or the "full scale value". It indicates the highest value that can be read without being "out of range". The reason the readings look different is that the precision changes. Specifically, .600ma is the same as 0.6ma. It's also the same as the 0.5 reading (shown as "00.5") but you'll notice it is "off by one count". This is what happens when you measure something that is a tiny fraction of the full-scale value. The accuracy of the measurement suffers. And that's why you should choose a range that is comparable to what you're measuring.
The remaining measurement was done on the "20" scale, which is 20 Amps. You got a reading of 0.05 A there, which would be 50mA, but that's just too far "down in the noise" to be useful.