Reading a multimeter
metron9
Posts: 1,100
I am trying to read current with my radioshack digital multimeter and here is what I have done.
Flashlight Battery measures 0.8 ohms
2 1.5 volt batteries in series measures 3.06 volts
Measuring across the bulb I get 2.2 volts
So doing the math 2.2 volts / 0.8 ohms = 2.75A
I set the meter to 20A and read the current through the bulb and I get .14A
The problem is on the 20A scale the reading of .14 is = 140 milliamps
Also when I switch to the 200mA scale it says overload.
When I use a 1/4 watt resistor that measures 49.6 ohms I read 2.9 volts across the RESISTOR
I read 57.3mA for current on the meter
and that checks out as 2.9V / 49.6ohms = .058 or 58mA
What am I missing here?
Flashlight Battery measures 0.8 ohms
2 1.5 volt batteries in series measures 3.06 volts
Measuring across the bulb I get 2.2 volts
So doing the math 2.2 volts / 0.8 ohms = 2.75A
I set the meter to 20A and read the current through the bulb and I get .14A
The problem is on the 20A scale the reading of .14 is = 140 milliamps
Also when I switch to the 200mA scale it says overload.
When I use a 1/4 watt resistor that measures 49.6 ohms I read 2.9 volts across the RESISTOR
I read 57.3mA for current on the meter
and that checks out as 2.9V / 49.6ohms = .058 or 58mA
What am I missing here?
Comments
Is there an intermediate amp scale on your meter? 20 amp to 200ma seems like a large jump for a meter. Depending on the meter, it could be adding different amounts of meter resistance on different scales, thereby affecting your readings.
hope this helps, Kevin
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There are 10 kinds of people in the world.... those that know binary, and those that don't.
Cold resistance is not the same as hot resistance in light bulbs with a tungsten or other similar filiment.
Don't fall into that trap.
How to prove it? Place a small resitance in series with the bulb and measure the voltage drop across the resistor with a scope.