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Chapter 1 Introduction
NI 783xR User Manual 1-10 ni.com
to the system. Remove power from signal lines before connecting them to
or disconnecting them from the NI 783xR.
Operate the NI 783xR at or below the measurement category
1
listed in the
Maximum working voltage section of Appendix A, Specifications.
Measurement circuits are subjected to working voltages
2
and transient
stresses (overvoltage) from the circuit to which they are connected during
measurement or test. Measurement categories establish standard impulse
withstand voltage levels that commonly occur in electrical distribution
systems. The following list describes installation categories:
• Measurement Category I—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—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 products.
• Measurement Category III—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—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 can
be connected to the MAINS for measuring purposes.