GETTING STARTED GUIDE
NI 9421
8-Channel Sinking Digital Input Module
This document explains how to connect to the NI 9421. In this
document, the NI 9421 with screw terminal, NI 9421 with spring
terminal, and NI 9421 with DSUB are referred to inclusively as
the NI 9421.
Note Before you begin, complete the software and
hardware installation procedures in your chassis
documentation.
Note The guidelines in this document are specific to
the NI 9421. The other components in the system might
not meet the same safety ratings. Refer to the
documentation for each component in the system to
determine the safety and EMC ratings for the entire
system.
Safety Guidelines
Operate the NI 9421 only as described in this document.
Caution Do not operate the NI 9421 in a manner not
specified in this document. Product misuse can result in
a hazard. You can compromise the safety protection
built into the product if the product is damaged in any
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way. If the product is damaged, return it to NI for
repair.
Safety Guidelines for Hazardous Voltages
If hazardous voltages are connected to the device, take the
following precautions. A hazardous voltage is a voltage greater
than 42.4 Vpk voltage or 60 VDC to earth ground.
You can connect hazardous voltages only to the NI 9421 with
screw terminal and the NI 9421 with spring terminal. Do not
connect hazardous voltages to the NI 9421 with DSUB.
Caution Ensure that hazardous voltage wiring is
performed only by qualified personnel adhering to local
electrical standards.
Caution Do not mix hazardous voltage circuits and
human-accessible circuits on the same module.
Caution Ensure that devices and circuits connected to
the module are properly insulated from human contact.
Caution When module terminals are hazardous
voltage LIVE (>42.4 Vpk/60 VDC), you must ensure
that devices and circuits connected to the module are
NI 9421 Getting Started Guide | © National Instruments | 3
properly insulated from human contact. You must use
the NI 9932 connector backshell kit to ensure that the
terminals are not accessible.
NI 9421 with Screw/Spring Terminal Safety
Voltages
Connect only voltages that are within the following limits:
...........................................................Channel-to-COM 30 V max
Isolation
...................................................Channel-to-channel None
Channel-to-earth ground
...........................................Continuous 250 Vrms,
Measurement Category II
...........................................Withstand 2,300 Vrms, verified by a
5 s dielectric withstand test
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.
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Caution Do not connect the NI 9421 with screw
terminal or NI 9421 with spring terminal to signals or
use for measurements within Measurement
Categories III or IV.
NI 9421 with DSUB Safety Voltages
Connect only voltages that are within the following limits:
...........................................................Channel-to-COM 30 V max
Isolation
...................................................Channel-to-channel None
Channel-to-earth ground
...........................................Continuous 60 VDC,
Measurement Category I
...........................................Withstand 1,000 Vrms, verified by a
5 s dielectric withstand test
Measurement Category I is for measurements performed on
circuits not directly connected to the electrical distribution system
referred to as MAINS voltage. MAINS is a hazardous live
electrical supply system that powers equipment. This category is
for measurements of voltages from specially protected secondary
circuits. Such voltage measurements include signal levels, special
NI 9421 Getting Started Guide | © National Instruments | 5
equipment, limited-energy parts of equipment, circuits powered
by regulated low-voltage sources, and electronics.
Caution Do not connect the NI 9421 with DSUB to
signals or use for measurements within Measurement
Categories II, III, or IV.
Note Measurement Categories CAT I and CAT O are
equivalent. These test and measurement circuits are not
intended for direct connection to the MAINS building
installations of Measurement Categories CAT II,
CAT III, or CAT IV.
Safety Guidelines for Hazardous Locations
The NI 9421 is suitable for use in Class I, Division 2, Groups A,
B, C, D, T4 hazardous locations; Class I, Zone 2, AEx nA IIC T4
and Ex nA IIC T4 hazardous locations; and nonhazardous
locations only. Follow these guidelines if you are installing the
NI 9421 in a potentially explosive environment. Not following
these guidelines may result in serious injury or death.
Caution Do not disconnect I/O-side wires or
connectors unless power has been switched off or the
area is known to be nonhazardous.
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