These operating instructions describe how to install and use the
National Instruments cFP-RLY-421 relay module. For details on
configuring and accessing the cFP-RLY-421 over a network, refer
to the user manual for the FieldPoint network module you are
using.
Features
The cFP-RLY-421 is a Compact FieldPoint relay output module
with the following features:
The cFP-RLY-421 is powered by the FieldPoint network module
through the backplane bus. The cFP-RLY-421 is a high-power
consumption module, which may limit the number of I/O modules
that you can connect to a single network module.
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the
Before you configure a FieldPoint system that uses a cFP-RLY-421
module, calculate the total power consumption of the I/O modules
on the FieldPoint bank. You can find the power requirement
specification in the operating instructions for each I/O module.
The maximum power the network module can supply is specified
in the network module user manual. Make sure the total power
requirement for all of the I/O modules in the bank is less than the
maximum power available from the network module.
Suppose you have a bank with a cFP-2000 network module,
four cFP-RLY-421 modules, and four cFP-DI-301 modules. The
cFP-2000 can supply up to 9 W. The cFP-RLY-421 requires 1.7 W,
and cFP-DI-301 requires 0.325 W. The four cFP-RLY-421 and four
cFP-DI-301 modules require a total of 8.1 W:
4 × 1.7 W + 4 × 0.325 W = 8.1 W
This configuration meets the 9 W power requirement.
Installing the cFP-RLY-421
The cFP-RLY-421mounts on a Compact FieldPoint backplane
(cFP-BP-x), which provides operating power to the module.
Installing the cFP-RLY-421 onto a powered backplane does not
disrupt the operation of the bank.
To install the cFP-RLY-421, refer to Figure 1 and complete the
following steps:
1. Align the captive screws on the cFP-RLY-421 with the holes
on the backplane. The alignment keys on the cFP-RLY-421
prevent backward insertion.
2. Press firmly to seat the cFP-RLY-421 on the backplane.
3. Using a number 2 Phillips screwdriver with a shank of at least
64 mm (2.5 in.) length, tighten the captive screws to 1.1 N ⋅ m
(10 lb ⋅ in.) of torque. The nylon coating on the screws prevents
them from loosening.
The cFP-CB-x connector block has connections for each of the
eight cFP-RLY-421 relay channels and for an external supply to
power field devices. If you are using the cFP-RLY-421 in a
hazardous voltage application, you must use the cFP-CB-1
connector block or a suitable hazardous voltage cable. A hazardous
voltage is a voltage greater than 42.4 V
Caution Ensure that hazardous voltage wiring is
performed only by qualified personnel adhering to local
electrical standards.
Each relay channel of the cFP-RLY-421 has two terminals:
one NO (normally open) and one IC (isolated common).
Table 1 lists the terminal assignments for the signals of each
channel.
Table 1. Terminal Assignments
Terminal Numbers
Channel
012
134
256
378
4910
51112
61314
71516
NOIC
All of the COM terminals are connected internally and all of the
V
terminals are connected internally. NI does not recommend
SUP
using them with the cFP-RLY-421.
Table 2. V
Caution Cascading power between two modules defeats
and COM Terminal Assignments
SUP
V
SUP
1718
1920
2122
2324
2526
2728
2930
3132
COM
isolation between those modules. Cascading power from
the network module defeats all isolation between
modules in the FieldPoint bank.
cFP-RLY-4214ni.com
Connecting Loads to the cFP-RLY-421
Wire an external power supply to the load and IC terminal of the
individual channel as shown in Figure 2. This method of wiring
keeps the electrical connections of the cFP-RLY-421 within safe
current limits.
VC
To next channel
cFP-RLY-421
Figure 2. Connecting a Load
V
SUP
NO
IC
COM
Sourcing
Load
+
or
–
AC
The cFP-RLY-421 has eight SPST (Single-Pole-Single-Throw)
electromechanical relays. The power-up state is off (open) to
ensure safe installation. In the ON state, the NO and IC contacts
connect to form a short circuit. In the ON state, there is an effective
resistance of 100 mΩ between the NO and IC terminals, which
causes a voltage drop. For example, if the current is 1.5 A, the
voltage drop across the NO and IC terminals is 0.15 V.
The amount of current the relay can switch depends on the voltage,
the type of load, and ambient temperature. Refer to the
Specifications section for more information
.
Protecting Contacts for Inductive Loads
When inductive loads are connected to the relays, a large
counter-electromotive force may occur at relay switching time
because of the energy stored in the inductive load. These flyback
voltages can severely damage the relay contacts and greatly
shorten the life of the relay.
It is best to limit flyback voltages by installing a flyback diode
across an inductive DC load or a metal oxide varistor (MOV)
across an inductive AC load. Refer to the Guidelines for Selecting
Contact Protection Circuits section for more information.