Why is the current value 0,0 when the mAVΩ port is used?

Question

I am learning electronics as a hobby. Today, I was using the multimeter to learn current, voltage and resistance in a simple circuit.

I setup the breadboard with these parts:

• Small solderless breadboard
• 470 Ω, 1⁄4 W resistor
• Red LED, 5 mm
• 9 V battery snap connector
• 9 V battery
• Short length of jumper wire (1" or less)

I can read voltage in the circuit perfect but with current the readings on the multimeter is 0.0 when using the 10A port (LED turn ON) and with the mAVΩ port (LED doesn't light up) to replace the jumper wire. Did I burn out the fuse on the device?

Update: I checked the connections and settings on the multimeter and still 0,00.

Answer 1

If the LED lights when using the 10 A input on the meter but not when using the mA input then either the fuse for mA is blown or the shunt resistor the meter uses to measure mA is too high to allow the LED to light.

I doubt that it's the shunt, even a 100 \$\Omega\$ shunt should allow the LED to light. You can try using the 200 mA range, that might have a lower resistance than the 20 mA range. If you're not seeing the LED light up even dimly then the odds are the fuse is blown.

In that model meter the mA input is fused with a 200 mA fuse, the 10 A input is unfused, so be careful using that one, an over-current could damage the meter.

Answer 2

Assuming you wired the LED, resistor and battery in series, the LED should light up with no multimeter connected. The current, allowing for about 2.5 V across the LED, will be about (9-2.5)/470 = 14 mA. If you try to measure this with a multimeter using the 10 A range, you will likely get a reading of 0.0 A since the meter cannot read anything below 100 mA. If you use the multimeter with a ma scale, you should be able to read the 14 mA value. If not, have you set the multimeter range switch to a mA setting? It is unlikely that you blew a fuse unless you connected the battery directly to the multimeter when it was set to read current.