National Instruments PCI-8254R Getting Started page 4

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.
• Pollution Degree 2—Normally only nonconductive pollution occurs. Occasionally, nonconductive
pollution becomes conductive because of condensation.
• Pollution Degree 3—Conductive pollution or dry, nonconductive pollution occurs. Nonconductive
pollution becomes conductive because of condensation.
Clean the device and accessories by brushing off light dust with a soft, nonmetallic brush. Remove
other contaminants with a stiff, nonmetallic brush. The unit must be completely dry and free from
contaminants before returning it to service.
You must insulate signal connections for the maximum voltage for which the device is rated. Do not
exceed the maximum ratings for the device. Remove power from signal lines before connection to or
disconnection from the device.
Caution
National Instruments measurement products may be classified as either Measurement
Category I or II. Operate products at or below the Measurement Category level specified in the
hardware specifications.
Measurement Category
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 (Installation
Categories:
• Measurement Category I is for measurements performed on circuits not directly connected to the
electrical distribution system referred to as MAINS
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 (e.g., 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 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
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Measurement Categories as defined in electrical safety standard IEC 61010-1.
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Working voltage is the highest rms value of an AC or DC voltage that can occur across any particular insulation.
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Measurement Category is also referred to as Installation Category.
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MAINS is defined as the (hazardous live) electrical supply system to which equipment is designed to be connected for
the purpose of powering the equipment. Suitably rated measuring circuits may be connected to the MAINS for measuring
purposes.
© National Instruments Corporation
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: Measurement circuits are subjected to working voltages
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voltage. This category is for measurements of
Getting Started with the NI PCI-8254R
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and transient
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)