National Instruments CFP-RLY-421 User Manual

FieldPoint Operating Instructions

CFP-RLY-421

Eight-Channel SPST Relay Module

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:

• Eight single-pole single-throw (SPST) relay channels

• Switching capacity 1.5 A at 35 VDC or 250 VAC

• LED relay status indicators

• Hot swappable

• –40 to 60 °C operation

• 250 V

• 2,300 V

maximum isolation voltage

rms

transient overvoltage protection

rms

Power Requirement

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.

FieldPoint™, National Instruments™, NI™, and ni.com™ are trademarks of National Instruments Corporation. Product and company names mentioned herein are trademarks or trade names of their respective companies. For patents covering National Instruments products, refer to the appropriate location: Help»Patents in your software, the

patents.txt file on your CD, or ni.com/patents.

323617A-01 May 2003

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-421 mounts 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.

cFP-RLY-421 2 ni.com

2 1

1 cFP I/O Module 2 Captive Screws 3 cFP Controller Module

Figure 1. Installing the cFP-RLY-421

4 Screw Holes 5 cFP Backplane

Wiring the cFP-RLY-421

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).

or 60 VDC.

peak

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

Table 1. Terminal Assignments

Terminal Numbers

Channel

0 1 2

1 3 4

2 5 6

3 7 8

4 9 10

5 11 12

6 13 14

7 15 16

NO IC

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

17 18

19 20

21 22

23 24

25 26

27 28

29 30

31 32

COM

isolation between those modules. Cascading power from the network module defeats all isolation between modules in the FieldPoint bank.

cFP-RLY-421 4 ni.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.

V C

To next channel

cFP-RLY-421

Figure 2. Connecting a Load

SUP

COM

Sourcing

Load

–

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.

+ 9 hidden pages