This experiment introduces the use of digital multimeters for current measurement. Digital multimeters, or DMMs, perform a variety of functions. The DMM operates as an ammeter when measuring current in a circuit. More information relative to DMMs and their use in current measurement are provided in the links to the right.
Current is a rate at which charge passes a particular point in a circuit. DMMs generally have two terminals, or leads. When the DMM is operating as an ammeter, these leads must be placed so that the current being measured passes through the DMM—the DMM displays this current. Therefore, when measuring a current, it is generally necessary to break your circuit apart at the appropriate point and insert the DMM leads between the two ends of the break.
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Use V+ to apply 5V across the LED to light it up.
The resistor limits the current.
We want to measure the current, I, through the diode. Our sign convention is as shown; positive current is from the anode to the cathode of the diode.
Break the circuit apart between the resistor and the LED.
Connect A terminal of the DMM to the resistor terminal shown.
Connect the COM terminal of the DMM to the diode's anode as shown.
Connect V+ (red wire) to the 100Ω resistor.
Make sure the resistor and LED anode are unconnected—they should be in holes in two different rows on the breadboard.
Connect ground (, the black wire) to the cathode of the LED.
Connect the A terminal of the DMM to the resistor's cathode.
Connect the COM terminal of the DMM to the diode's anode.
Turn the function selection knob on the front of the DMM to the A position.
Open WaveForms™ to view the main window.
Click on the Voltage instrument icon to open the Power Supplies window.