NI PCIe-8244 Getting Started Guide
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© National Instruments
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Operate the device only at or below Pollution Degree 2. Pollution consists of any foreign
matter—solid, liquid, or gas—that may reduce dielectric strength or surface resistivity. The
following is a description of Pollution Degrees.
•
Pollution Degree 1—No pollution or only dry, nonconductive pollution occurs. The
pollution has no effect. Typical level for sealed components or coated PCBs.
•
Pollution Degree 2—Only nonconductive pollution occurs in most cases. Occasionally,
however, a temporary conductivity caused by condensation must be expected. Typical level
for most products.
•
Pollution Degree 3—Conductive pollution or dry, nonconductive pollution occurs.
Nonconductive pollution becomes conductive because of condensation.
Operate the hardware at or below the measurement category
1
in the hardware 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 Category
establishes standardized impulse withstand voltage levels that commonly occur in electrical
distribution systems. The following is a description of measurement categories:
•
Measurement Categories CAT I and CAT O (Other) are equivalent and are for
measurements performed on circuits not directly connected to the electrical distribution
system referred to as MAINS
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voltage. This category is for measurements of voltages from
specially protected secondary circuits. Such voltage measurements include signal levels,
special hardware, limited-energy parts of hardware, circuits powered by regulated
low-voltage sources, and electronics.
•
Measurement Category II is for measurements performed on circuits directly connected to
MAINS. This category refers to local-level electrical distribution, such as that provided by
a standard wall outlet (for example, 115 AC voltage for U.S. or 230 AC voltage for Europe).
Examples of Measurement Category II are measurements performed on household
appliances, portable tools, and similar hardware.
•
Measurement Category III is for measurements performed in the building installation at the
distribution level. This category refers to measurements on hard-wired hardware such as
hardware 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 typically outside buildings. Examples include electricity meters and
measurements on primary overcurrent protection devices and on ripple control units.
1
Measurement categories, also referred to as overvoltage or installation categories, are defined in electrical
safety standards IEC 61010-1 and IEC 60664-1.
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 hardware. Suitably rated
measuring circuits may be connected to the MAINS for measuring purposes.
