USING A MULTIMETER

Analogue and digital multimeters have either a rotary selector switch or push buttons
to select the appropriate function and range. Some Digital Multimeter (DMMs) are auto
ranging; they automatically select the correct range of voltage, resistance, or current
when doing a test. However you need to select the function.
Before making any measurement you need to know what you are checking. If you are
measuring voltage, select the AC range (10v, 50v, 250v, or 1000v) or DC range
(0.5v, 2.5v, 10v, 50v, 250v, or 1000v). If you are measuring resistance, select the
Ohms range (x1, x10, x100, x1k, x10k). If you are measuring current, select the
appropriate current range DCmA 0.5mA, 50mA, 500mA. Every multimeter is different
however the photo below shows a low cost meter with the basic ranges.

The most important point to remember is this:

You must select a voltage or current range that is bigger or HIGHER than the

maximum expected value, so the needle does not swing across the scale and hit the

"end stop."

If you are using a DMM (Digital Multi Meter), the meter will indicate if the voltage or

current is higher than the selected scale, by showing "OL" - this means "Overload." If

you are measuring resistance such as 1M on the x10 range the "OL" means "Open

Loop" and you will need to change the range. Some meters show "1' on the display

when the measurement is higher than the display will indicate and some flash a set of

digits to show over-voltage or over-current. A "-1" indicates the leads should be

reversed for a "positive reading."

If it is an AUTO RANGING meter, it will automatically produce a reading, otherwise the

selector switch must be changed to another range.

 The black "test lead" plugs into the socket marked "-" "Common", or "Com," and the
red "test lead" plugs into meter socket marked "+" or "V-W-mA." The third banana
socket measures HIGH CURRENT and the positive (red lead) plugs into this. You DO
NOT move the negative "-" lead at any time.
The following two photos show the test leads fitted to a digital meter. The probes and
plugs have "guards" surrounding the probe tips and also the plugs so you can measure
high voltages without getting near the voltage-source.

MULTIMETERS

There are two types:
DIGITAL and ANALOGUE
A Digital Multimeter has a set of digits on the display and an Analogue Multimeter
has a scale with a pointer (or needle).
You really need both types to cover the number of tests needed for designing and
repair-work. We will discuss how they work, how to use them and some of the
differences between them.

                                          DIGITAL AND ANALOGUE MULTIMETERS

BUYING A MULTIMETER
There are many different types on the market.
The cost is determined by the number of ranges and also the extra features such as
diode tester, buzzer (continuity), transistor tester, high DC current and others.
Since most multimeters are reliable and accurate, buy one with the greatest number of
ranges at the lowest cost.
This article explains the difference between a cheap analogue meter, an expensive
analogue meter and a digital meter. You will then be able to work out which two
meters you should buy.
Multimeters are sometimes called a "meter", a "VOM" (Volts-Ohms-Milliamps or Volt
Ohm Meter) or "multi-tester" or even "a tester" - they are all the same.