Chapter 2
Installation
National Instruments UMI-7774/7772 User Manual
2-4
ni.com
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.
•
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.
Operate this device only at or below the
installation category
1
marked on
the hardware label. Measurement circuits are subjected to
working
voltages
2
and transient stresses, such as overvoltage, from the circuit they
are connected to during the 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:
•
Installation 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.
1
Installation categories, also referred to as measurement 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.
