©
National Instruments Corporation
7
NI 6509 User Guide and Specifications
Operate the DIO device at or below the
measurement category
1
marked
on the hardware label. Measurement circuits are subjected to
working
voltages
2
and transient stresses (overvoltage) from the circuit to which they
are connected during measurement or test. Installation categories establish
standard impulse withstand voltage levels that commonly occur in
electrical distribution systems. The following is a description of installation
categories:
•
Measurement Category I is for measurements performed on circuits
not directly connected to the electrical distribution system referred to
as MAINS
3
voltage. This category is for measurements of voltages
from specially protected secondary circuits. Such voltage
measurements include signal levels, special equipment, limited-energy
parts of equipment, circuits powered by regulated low-voltage sources,
and electronics.
•
Measurement Category II is for measurements performed on circuits
directly connected to the electrical distribution system. This category
refers to local-level electrical distribution, such as that provided by a
standard wall outlet (for example, 115 V for U.S. or 230 V for Europe).
Examples of Measurement Category II are measurements performed
on household appliances, portable tools, and similar DIO devices.
•
Measurement Category III is for measurements performed in the
building installation at the distribution level. This category refers to
measurements on hard-wired equipment such as equipment in fixed
installations, distribution boards, and circuit breakers. Other examples
are wiring, including cables, bus-bars, junction boxes, switches,
socket-outlets in the fixed installation, and stationary motors with
permanent connections to fixed installations.
•
Measurement Category IV is for measurements performed at the
primary electrical supply installation (<1,000 V). Examples include
electricity meters and measurements on primary overcurrent
protection devices and on ripple control units.
1
Measurement categories, also referred to as
installation categories
, are defined in electrical safety standard IEC 61010-1.
2
Working voltage is the highest rms value of an AC or DC voltage that can occur across any particular insulation.
3
MAINS is defined as a hazardous live electrical supply system that powers equipment. Suitably rated measuring circuits may
be connected to the MAINS for measuring purposes.
