electrical and electronic engineering digital multimeter user...
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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.