Agilent Technologies U1270 Series Spezifikationen PDF herunterladen (Seite 5)

Multimeter Basic Features

A basic DMM measures AC voltage, DC voltage, AC current, DC current, resis-

tance, continuity, and diodes. More expensive DMMs also measure capacitance,

frequency, temperature, and pressure. Before purchasing a handheld DMM, you

should first identify the type of testing you will need to perform, establish which

features are important, and determine the anticipated tolerance range for those

tests.

AC/DC voltage measurement

There are many main voltage ratings for the operation of household and indus-

trial electrical appliances. It is important to know the voltage range that is going

to be present on the circuit you are going to measure, and choose a DMM with

a voltage rating that is higher than that range. All European and most South

American, African, and Asian countries use a supply that is within 10% of 230 V,

whereas Japan, North America, and some parts of northern South America use

voltages between 100 and 127 V.

AC/DC current measurement

The same applies for measuring current with a DMM. Users have to know the

maximum current of the circuit that will be measured. For example, using a

100 ampere-rated DMM to measure a 1,000 ampere circuit leaves technicians

exposed to a high risk of electrical hazards.

Resistance measurement/

continuity check

Another important DMM feature is the ability to measure resistance. To mea-

sure resistance, the component must be removed from the circuit altogether.

Resistance measurement works by passing a current through the component

being tested. Resistance measurement is also commonly used to test for con-

tinuity. An open circuit will have infinite resistance. A closed circuit will have a

small resistance measurement. Most of the DMMs currently on the market are

designed with a continuity beeper to indicate continuity, rather than relying on

the resistance display. Some DMMs come with both an audible and visual alert

for continuity, which can be beneficial in noisy environments where the audible

alert may be difficult to hear.

Diode check

Today’s DMMs are equipped with a diode check function that displays the actual

forward voltage drop of the diode. The meters inject a small current through

the diode and measure the voltage dropped between the two test leads. The

forward bias voltage reading of a silicon type diode will be will be about 0.7 volts

and 0.3 volts for Germanium-type diodes.

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Agilent Technologies U1270 Series Spezifikationen Seite 5