Agilent Technologies U1270 Series Spezifikationen PDF herunterladen (Seite 10)

Think Safety When Selecting a Handheld DMM

Energy capacity

In addition to the transient voltage ratings of circuits, you need to consider the

energy capacity of the circuit. To protect yourself, you should know the energy

capacity of the circuit before you start taking measurements. Circuits with

higher energy capacity can deliver more current and energy into faults than low-

energy circuits. Therefore, measurements performed on higher-energy circuits

are much more hazardous than measurements performed on lower-energy

circuits. The energy capacity of the circuit is generally defined by three charac-

teristics: the operating voltage, the circuit impedance, and the characteristics of

the circuit fuse or circuit breaker.

The International Electrotechnical Commission (IEC) has defined three

“Measurement Categories” for mains circuits (Table 1) the higher the category

number, the greater the danger posed by transient voltages on the mains circuit.

All manufacturers of handheld DMMs are required to mark their products with

the rated measurement category (CAT II, CAT III, or CAT IV). This marking is a

convenient way for users to identify the maximum transient voltage that the

meter can safely withstand. Most handheld DMMs display this rating near the

handheld DMM’s voltage/current input terminals.

Table 1. IEC measurement categories defined by IEC

Category Description

CAT II This category is applied to all equipment connected from the

wall socket up to the equipment’s first level of power conversion.

Measurements at the wall socket itself might not be limited to

CAT II levels. Handheld DMM should always be capable of CAT III

measurements.

CAT III This category is applied to building circuit installations that are

completely within the building, including parts of the service panel

and the branch circuits. It also applies to many of the building’s fixed

equipment, which is connected directly to the building mains instead of

being connected through cords and plugs.

CAT IV This category is applied to the source of the building’s electrical

installation: the entrance service panel, the primary mains meter, or

perhaps the secondary side of the building distribution transformer, if

the transformer is located within the building.

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Agilent Technologies U1270 Series Spezifikationen Seite 10