Electrical and Electronic Engineering

Digital Multimeter User Guide

October 2014

What is a ‘multimeter’?

A ‘multimeter’ is a device that is able to measure different electrical parameters, such as

voltage, current and resistance. Multimeters can be switched different modes in order to

measure these parameters. It can be switched into a voltmeter to measure voltage, an

ammeter to measure current and an ohmmeter to measure resistance. Multimeters can

have analogue or digital displays. The lab is furnished with a digital multimeter (DMM) on

each bench.

The Lab’s DMM

The lab’s DMM is made my Agilent (now known as Keysight). The model is the U3401A, and

is a highly advanced, and is purposely designed to facilitate educating students in electronic

measurements. It can perform up to 11 basic measurements, with 6 in-built mathematical

functions.

This guide will help you to perform basic electrical measurements using the DMM.

Switching on the DMM

To switch on and off the DMM, press the ‘Power’ button located on the lower right hand

side. When the DMM is first switched on, it is set up to measure DC Volts by default.

Measuring DC Voltage

When first switched on, the DMM by default boots up in DC voltmeter mode, and hence is

ready to measure a DC voltage. Leads then need to plugged into the red ‘V’ socket in the top

left corner, and one of the black ‘LO’ sockets underneath it, as indicated above. If you have

been using the DMM in a different mode, you will have to switch it manually to measure a

DC voltage by pressing the ‘DCV’ button, located in the top left position underneath the

digital display. Note that voltmeters are connected in parallel with the component whose

voltage you are measuring across.

Measuring DC Current up to 500mA

To measure DC currents up to 500mA, first set the DMM to the correct mode

by pressing the ‘DCI’ button, and then connect leads to the red ‘mA’ socket,

and one of the black ‘LO’ sockets.

Using lower half of the breadboard

Four series connected resistors

connected to the power supply

Note how the internally connected

rows and columns are used to

connect the components and wires

Parallel connection

There is no connection between the

top half outer column lines and

those in the lower half.

‘Jumper’ wires are needed to

connect the power supply lines from

the top part to the lower segment.

Note how the resistor straddles

both left and right halves of the

board. The central groove separates

the left and right sides, and there is

no internal connection across it.

Incorrect connection

Three resistors connected in parallel

with the power supply.

Close up of short circuit

Both legs of the resistor are

connected in the same row. The

piece of metal underneath the row

‘shorts out’ the resistor and also the

terminals of the power supply.

Current will simply bypass the

resistor, and flow through the

metallic contact underneath. The

power supply will detect the short

circuit, and will switch off. Short

circuits cause very high currents due

to being of 0Ω resistance. The

power supplies are ‘current limited’

to 500mA, so when anything over

500mA (such as in a short circuit) is

detected, it will switch off.

Measuring current

Never connect the legs of a

component in the same row!

Measuring voltage

Cables from power supply Cables to multimeter, set to ammeter mode

The cables from the ammeter are

placed in series with the resistor.

Cables from power supply Cables to multimeter, set to voltmeter mode

The cables from the voltmeter are

placed in parallel with the resistor.