National Instruments FP-RLY-420 User Manual

OPERATING INSTRUCTIONS

FP-RLY-420

8-Channel, SPST Relay Module

These operating instructions describe the installation, features, and
characteristics of the FP-RLY-420. For details on configuring and
accessing the FP-RL Y-420 o ver a network, refer to the user manual
for the particular FieldPoint network module you are using with
the FP-RLY-420.

Features

The FP-RLY-420 is a FieldPoint relay output module with the
following features:

• Eight Single-Pole Single-Throw (SPST) relay channels

• Switching capacity 3 A at 35 VDC or 250 VAC

• On/Off LED indicators

• Hot plug and play operation

• 3,000 V input to output isolation

• Double insulated for 250 V safe working voltage

• –40 to +70 °C operation

Power Requirement

The FP-RLY-420 is powered via the local backplane bus from the
FieldPoint network module. The FP-RLY-420 is a high-power
consumption module and requires more than the nominal power
allocated to an I/O module from the network module. In some
applications, this could limit the number of I/O modules that you
can connect to a single network module.

When defining a FieldPoint system that uses an FP-RLY-420
module, you must calculate the power consumption. First refer
to the specifications section in the user manual for your network

FieldPoint ™ is a trademark of National Instruments Corporation. Product and company names
mentioned herein are trademarks or trade names of their respective companies.

321904B-01 © Copyright 1998, 1999 National Instruments Corp. All rights reserved. June 1999

module. The maximum number of terminal bases per bank
multiplied by 1 watt is the total power the network module can
supply. For example, an FP-1000 or FP-1001 can support nine
terminal bases (9*1 W = 9 W).

Next, refer to the specifications section in the operating
instructions for the I/O modules. Use the Power from Network
Module specification. For example, a bank of modules consisting
of four FP-RL Y-420 and fi ve FP-DI-301 modules requires a total of

8.4 W from the FieldPoint network module [4*(1.7 W) + 5*(0.325
W) = 8.4 W]. This power requirement is less than the 9 W
maximum and is therefore acceptable.

Installation

The FP-RLY-420 mounts on a FieldPoint terminal base
(FP-TB-xx) unit. The hot plug and play operation of the
FP-RLY-420 allows you to install it onto a powered terminal base
without disturbing the operation of other modules or terminal
bases. The FP-RLY-420 receives operating power from the
terminal base.

T o install the FP-RLY-420, refer to Figure 1 and follow these steps:

1. Slide the terminal base key to either position X (used for any
module) or position 7 (used for the FP-RLY-420 module).

2. Align the FP-RLY-420 alignment slots with the guide rails on
the terminal base.

3. Press firmly to seat the FP-RLY-420 on the terminal base. The
terminal base latch locks the FP-RLY-420 into place when it is
firmly seated.

Key

Latch

Alignment

Slot

Guide Rails

Terminal BaseI/O Module

Figure 1.

FP-RLY-420 2 www.natinst.com

Module Installation Diagram

Field Wiring

The terminal base has connections for each of the eight relay
channels and an external supply to po wer f ield de vices. Each relay
channel of the FP-RLY-420 has two terminals: N.O. (Normally
Open) and I.C. (Isolated Common). The external supply is not
needed for the internal operation of the FP-RLY-420; however,
you may connect an external supply to power field devices by
connecting to the V and C terminals of the terminal base. If you
connect an external supply to the V and C terminals, the total
current supplied cannot exceed 6 A.

Table 1 lists the terminal assignments for the signals of each
channel.

Table 1.

Chan-

nel

0 1 2 17 18
1 3 4 19 20
2 5 6 21 22
3 7 8 23 24
4 9 10 25 26
5 11 12 27 28
6 13 14 29 30
7 15 16 31 32

N.O. I.C.

Terminal Assignments

Terminal Numbers

V

sup

COM

© National Instruments Corp. 3 FP-RLY-420

Figures 2a and 2b show examples of basic wiring connections.

+

VC

a. Total Current Less

Than 6 Amps

V

N.O.
I.C.
COM

V
N.O.
I.C.

COM

sup

sup

Load

Load

–

N.O.

Load

I.C.

N.O.

I.C.

Load

b. Total Current Greater

Than 6 Amps

+

–

+

–

Figure 2. Basic Field Connection (Two Channels Shown)

Relay Output Circuit

The outputs of the FP-RLY-420 consist of Form A
electromechanical relays. The power-up state is of f (open) to
ensure safe installation. In the ON state, the N.O. and I.C. contacts
connect together to form a short circuit. Choose the impedance of
the loads so that the current switched b y any one channel in t he ON
state is no more than 3 A.

In the ON state, there is an effectiv e resistance of 100 mΩ between
the N.O. and I.C. terminals, which causes a voltage drop. For
example, if the current is 3 A, the voltage drop across the N.O.
and I.C. terminals is 0.3 V.

FP-RLY-420 4 www.natinst.com