Allen-Bradley FLEX I/O 1794-IJ2 User manual

User
Manual
FLEX I/O
Frequency
Input Module
(Cat. No. 1794-IJ2)
Allen-Bradley
Allen-Bradley Replacements

Important User Information Because of the variety of uses for the products described in this
publication, those responsible for the application and use of this control
equipment must satisfy themselves that all necessary steps have been
taken to assure that each application and use meets all performance and
safety requirements, including any applicable laws, regulations, codes and
standards.
The illustrations, charts, sample programs and layout examples shown in
this guide are intended solely for example. Since there are many variables
and requirements associated with any particular installation,
Allen-Bradley does not assume responsibility or liability (to include
intellectual property liability) for actual use based upon the examples
shown in this publication.
Allen-Bradley publication SGI-1.1, “Safety Guidelines For The
Application, Installation and Maintenance of Solid State Control”
(available from your local Allen-Bradley office) describes some important
differences between solid-state equipment and electromechanical devices
which should be taken into consideration when applying products such as
those described in this publication.
Reproduction of the contents of this copyrighted publication, in whole or
in part, without written permission of Allen-Bradley Company, Inc. is
prohibited.
Throughout this manual we make notes to alert you to possible injury to
people or damage to equipment under specific circumstances.
Attention helps you:
• identify a hazard
• avoid the hazard
• recognize the consequences
Important: Identifies information that is especially important for
successful application and understanding of the product.
Important: We recommend you frequently backup your application
programs on appropriate storage medium to avoid possible
data loss.
DeviceNet, DeviceNetManager, and RediSTATION are trademarks of Allen-Bradley Company, Inc.
PLC, PLC-2, PLC-3, and PLC-5 are registered trademarks of Allen-Bradley Company, Inc.
Windows is a trademark of Microsoft.
Microsoft is a registered trademark of Microsoft
IBM is a registered trademark of International Business Machines, Incorporated.
All other brand and product names are trademarks or registered trademarks of their respective companies.
!
ATTENTION: Identifies information about practices or
circumstances that can lead to personal injury or death,
property damage, or economic loss.

Publication 1794-6.5.11 - November 1997
Preface
Using This Manual
Purpose of this Manual This manual shows you how to use your FLEX I/O 2 input frequency
module with Allen-Bradley programmable controllers. The manual helps
you install, program and troubleshoot your module.
Audience You must be able to program and operate an Allen-Bradley programmable
controller to make efficient use of your FLEX I/O module. In particular,
you must know how to program block transfers.
We assume that you know how to do this in this manual. If you do not,
refer to the appropriate programming and operations manual before you
attempt to program your modules.
Vocabulary In this manual, we refer to:
– the frequency input module as the “input module”
– the Programmable Controller as the “controller”
Manual Organization This manual is divided into five chapters. The following chart lists each
chapter with its corresponding title and a brief overview of the topics
covered in that chapter.
Chapter Title Contents
1Overview ofFLEXI/O and Frequency
Input modules Describes FLEX I/O frequency input modules, features, and how they function
2How to Install Your Frequency Input
Module How to install and wire the module
3Module Programming Explains block transfer programming, sample programs
4Writing Configuration to and
Reading Status From with a Remote
I/O Adapter
Explains how to configure your modules and read status
information from your modules when using a remote I/O
adapter
5How Communication Takes Place
and I/O Image Table Mapping with
the DeviceNet Adapter
Explains how you communicate with your modules, and
how the I/O image is mapped when using a DeviceNet
adapter
Appendix Title Contents
ASpecifications Specifications for the frequency module
BSchematics Simplified schematics of frequency input module
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Publication 1794-6.5.11 - November 1997
-2 Using This Manual
Conventions We use these conventions in this manual:
For Additional Information For additional information on FLEX I/O systems and modules, refer to
the following documents:
In this manual, we show: Like this:
that there is more information about a topic
in another chapter in this manual
that there is more information about the
topic in another manual
Catalog
Number Voltage Description Publications
Installation
Instructions User Manual
1794 1794 FLEX I/O Product Data 1794-2.1
1794-ACN 24V dc ControlNet Adapter 1794-5.8
1794-ACNR 24V dc Redundant Media ControlNet Adapter 1794-5.18
1794-ACN15 24V dc ControlNet Adapter 1794-5.47
1794-ACNR15 24V dc Redundant Media ControlNet Adapter 1794-5.48
1794-ADN 24V dc DeviceNet Adapter 1794-5.14 1794-6.5.5
1794-ASB/C 24V dc Remote I/O Adapter 1794-5.50 1794-6.5.9
1794-ASB2/B 24V dc 2-Slot Remote I/O Adapter 1794-5.44 1794-6.5.13
1794-APB 24V dc Profibus Adapter 1794-5.40 1794-6.5.6
1794-IB8 24V dc 8 Sink Input Module 1794-5.30
1794-OB8 24V dc 8 Source Output Module 1794-5.31
1794-IB16 24V dc 16 Sink Input Module 1794-5.4
1794-OB16 24V dc 16 Source Output Module 1794-5.3
1794-IV16 24V dc 16 Source Input Module 1794-5.28
1794-OV16 24V dc 16 Sink Output Module 1794-5.29
1794-OB8EP 24V dc 8 Electronically Fused Output Module 1794-5.20
1794-IB8S 24V dc Sensor Input Module 1794-5.7
1794-IB10XOB6 24V dc 10 Input/6 Output Module 1794-5.24
1794-IE8 24V dc Selectable Analog 8 Input Module 1794-5.6 1794-6.5.21794-OE4 24V dc Selectable Analog 4 Output Module 1794-5.5
1794-IE4XOE2 24V dc 4 Input/2 Output Analog Module 1794-5.15
Table continued on next page

Publication 1794-6.5.11 - November 1997
Using This Manual -3
Summary This preface gave you information on how to use this manual efficiently.
The next chapter introduces you to the frequency module.
1794-OF4 24V dc 4 Output Isolated Analog Module 1794-5.37 1794-6.5.81794-IF4 24V dc 4 Input Isolated Analog Module 1794-5.38
1794-IF2XOF2 24V dc 2 Input/2 Output Isolated Analog Module 1794-5.39
1794-IR8 24V dc 8 RTD Input Analog Module 1794-5.22 1794-6.5.4
1794-IT8 24V dc 8 Thermocouple Input Module 1794-5.21 1794-6.5.7
1794-IRT8 24V dc 8 Thermocouple/RTD Input Module 1794-5.50 1794-6.5.12
1794-IJ2 24V dc 2 FrequencyInput Module 1794-5.49 1794-6.5.11
1794-IA8 120V ac 8 Input Module 1794-5.9
1794-OA8 120V ac Output Module 1794-5.10
1794-TB2
1794-TB3 2-wire Terminal Base 3-wire Terminal Base 1794-5.2
1794-TBN Terminal Base Unit 1794-5.16
1794-TBNF Fused Terminal Base Unit 1794-5.17
1794-TB3T Temperature Terminal Base Unit 1794-5.41
1794-TB3S Spring Clamp Terminal Base Unit 1794-5.42
1794-TB3TS Spring Clamp Temperature Base Unit 1794-5.43
1794-TB3G Terminal Base Unit 1794-5.51
1794-TB3GS Spring Clamp Terminal Base Unit 1794-5.59
1794-CE1, -CE3 Extender Cables 1794-5.12
1794-NM1 Mounting Kit 1794-2.13
1794-PS1 24V dc Power Supply 1794-5.35
Catalog
Number Voltage Description Publications
Installation
Instructions User Manual
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Publication 1794-6.5.11 - November 1997
-4 Using This Manual

Table of Contents
Publication 1794-6.5.11 - November 1997
Overview of the Frequency
Input Module Chapter 1
What This Chapter Contains . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-1
How You Use the Frequency Input Module . . . . . . . . . . . . . . . . . . . . . 1-1
What the Frequency Input Module Does. . . . . . . . . . . . . . . . . . . . . . . . 1-2
Typical Applications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-3
Input Capabilities. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-4
Selecting the Mode(s) of Operation. . . . . . . . . . . . . . . . . . . . . . . . . . 1-4
Output Capabilities . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-5
Implementing Application Features . . . . . . . . . . . . . . . . . . . . . . . . . 1-5
How Frequency is Calculated . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-5
Frequency Calculation. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-5
Termination on Number of Pulses. . . . . . . . . . . . . . . . . . . . . . . . . . . 1-6
Missing Pulse Multiplier . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .1-7
Direction Detection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-8
Chapter Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-9
How to Install Your Frequency
Input Module Chapter 2
What This Chapter Contains . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-1
Before You Install Your Input Module . . . . . . . . . . . . . . . . . . . . . . . . . 2-1
European Union Directive Compliance. . . . . . . . . . . . . . . . . . . . . . . . . 2-1
EMC Directive. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-1
Low Voltage Directive . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-2
Power Requirements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-2
Wiring the Terminal Base Units (1794-TB3G shown) . . . . . . . . . . . 2-3
Installing the Module. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-4
Mounting the Terminal Base Unit on a DIN Rail . . . . . . . . . . . . . . . 2-4
Panel/Wall Mounting. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-6
Mounting the Frequency Input Module on the Terminal Base Unit . 2-7
Connecting Wiring for Your Frequency Input Module. . . . . . . . . . . . . 2-9
Connecting Wiring using a 1794-TB3G and –TB3GS
Terminal Base Units. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-10
Wiring connections for the 1794-IJ2 Frequency Input Module . . 2-11
Examples of Wiring to a 1794-TB3G Terminal Base Unit. . . . . . . 2-12
Module Indicators . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-13
Chapter Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-13
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toc–ii Table of Contents – FLEX I/O Frequency Input Module
Publication 1794-6.5.11 - November 1997
Programming Your Frequency
Input Module Chapter 3
What This Chapter Contains . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-1
Enter Block Transfer Instructions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-1
PLC-2 Family Processor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-2
PLC-3 Family Processor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-2
PLC-5 Family Processor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-3
PLC-5/250 Processor. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-4
Chapter Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-5
Writing Configuration to and
Reading Status from Your
Module with a Remote I/O
Adapter
Chapter 4
What This Chapter Contains . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-1
Configuring Your Frequency Input Module . . . . . . . . . . . . . . . . . . . . . 4-1
Reading Data From Your Module. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-2
Mapping Data for the Module . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-2
Frequency Input Module (1794-IJ2) Image Table Mapping . . . . . 4-2
Block Transfer Read Word Assignments for the Frequency
Input Module (1794-IJ2) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-3
Bit/Word Definitions for Block Transfer Read Words for the
Frequency Input Module . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-3
Block Transfer Write Word Assignments for the Frequency
Input Module . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-5
Bit/Word Definitions for the Block Transfer Write Words for the
Frequency Input Module . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-6
Chapter Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-12
How Communication Takes
Place and I/O Image Table
Mapping with the DeviceNet
Adapter
Chapter 5
What This Chapter Contains . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-1
About DeviceNetManager Software . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-1
Polled I/O Structure. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-1
Adapter Input Status Word . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-2
System Throughout . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-3
Mapping Data into the Image Table . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-3
Frequency Input Analog Module (1794-IJ2) Image Table Mapping 5-3
Block Transfer Read Word Assignments for the Frequency
Input Module (1794-IJ2) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-4
Block Transfer Write Word Assignments for the Frequency
Input Module . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-4
Bit/Word Descriptions for the Frequency Input Module
(1794-IJ2) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-5
Defaults . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-13

Table of Contents – FLEX I/O Frequency Input Module toc–iii
Publication 1794-6.5.11 - November 1997
Troubleshoot the Frequency
Input Module Chapter 6
What This Chapter Contains . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-1
Status Indicators. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-1
Diagnostics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-3
Diagnostic Bits in Word 5 of the BTR File. . . . . . . . . . . . . . . . . . . . 6-3
What’s Next. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-3
Specifications Appendix A
What This Appendix Contains. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . A-1
Resolution and Accuracy. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . A-4
Schematics Appendix B
What This Appendix Contains. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .B-1
Input Circuits. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .B-1
Frequency Inputs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .B-1
Gate Inputs. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .B-1
Output Circuits. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .B-2
Digital Outputs. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .B-2
DC to DC Converters (24V dc power supplies) . . . . . . . . . . . . . . . .B-3
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Publication 1794-6.5.11 - November 1997
Chapter 1
Overview of the Frequency
Input Module
What This Chapter
Contains Read this chapter to familiarize yourself with the 1794-IJ2 module.
How You Use the
Frequency Input Module The 1794-IJ2 module is an intelligent I/O module designed to perform
high-speed frequency algorithms. The module provides:
• 2 Frequency Inputs,
• 2 Gate Inputs and
• 2 Outputs.
The Frequency Inputs can accept frequencies up to 32,767 Hz. The
module accepts and returns binary data.
The module measures frequency over a user-specified time interval. A
frequency calculation can start before the time interval has elapsed, if a
user-specified number of frequency input pulses have occurred.
The module’s primary use is accurate, high-speed frequency
measurement. A high-speed internal clock is synchronized with the
frequency input to count over a user-selected sampling time or a
user-defined number of frequency input pulses.
All power for input devices (4 devices, 24 Vdc @ 15 mA max) is supplied
by the I/O module.
For information on See page
How You Use the Module . . . . . . . . . . . . . . . . . . . . . . . . 1-1
What the Frequency Input Module Does . . . . . . . . . . . . . 1-2
Typical Applications . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-3
Input Capabilities . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-4
Selecting the Mode(s) of Operation. . . . . . . . . . . . . 1-4
Output Capabilities . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-5
Implementing Application Features. . . . . . . . . . . . . 1-5
How Frequency is Calculated 1-5

Publication 1794-6.5.11 - November 1997
1-2 Overview of the Frequency Input Module
What the Frequency Input
Module Does The frequency input module performs high-speed frequency and/or
scaling calculation operations for various industrial applications. The
module interfaces with a FLEX family adapter which then communicates
with a programmable controllerprocessor that has block-transfer
capability and external I/O devices.
The adapter/power supply transfers data to the module (block transfer
write) and from the module (block transfer read) using BTW and BTR
instructions in your ladder diagram program. These instructions let the
adapter read input values and status from the module, and let you write
output values and configure the module’s mode of operation. The
following illustration describes the communication process.
500/50mV
50mV
Select
24V IEC 1+ 24V IEC 1+
Magnetic
500/50mV
Magnetic
Gate Input Frequency Input
CRISP
Bus Interface Output 0 Output 1
Inter-Processor
Communication,
uP System 0/1 from
uP System 1
Data To/From Flexbus
Invert
Y/N
Invert
Y/N
Processing
Counter
Frequency / Count Data
uP System 0
Output Control
Input Control Direction Data
IEC 1+/Contact
Input
VORTEX
Vortex
3Vin 6Vin 24V Power
IEC 1+/Contact
Input 50mV
Select
GND
GND
Inputs
Module
Flexbus
24V Power
24VPower
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Publication 1794-6.5.11 - November 1997
Overview of the Frequency Input Module 1-3
Typical Applications You can use the 1794-IJ2 module in the power management, automotive,
food and beverage, and oil and gas industries for various flow and/or
turbine metering applications. Some sample applications include:
• turbine shaft speed monitoring
• automotive paint booths
• brewery flow monitoring
• petrochemical flow and custody transfer
ADAPTER
ACTIVE FAULT LOCAL
FAULT
24VDC
POWER SUPPLY
RIO ADAPTER
1794-ASB
Allen-Bradley
1
The adapter transfers your configuration data
to the module using a BTW.
Flexbus
External devices transmit
frequency signals to the module.
2
The module converts
frequency signals into integer
format and stores these values
until the adapter requests their
transfer.
3
Your ladder program instructs the
adapter to perform a BTR of the values
and stores them in a data table.
4
The adapter and module determine
that the transfer was made without error
and input values are within specified
range.
5
Your ladder program can use and/or move the data (if valid)
before it is written over by the transfer of new data in a
subsequent transfer.
6
Your ladder program performs BTWs to the module when you power
it up, and any time you wish to reconfigure the module.
7
FREQ GATE OK
0
FREQUENCY INPUT 2 CHANNEL
1
1794-IJ2
Allen-Bradley
F0F
FREQ GATE
1F1
FOUT
0OUT 1

Publication 1794-6.5.11 - November 1997
1-4 Overview of the Frequency Input Module
Input Capabilities The frequency module has 2 input channels (mode dependent). Each of
the 2 input channels may accept these input signals:
• magnetic pickup — 500mV to 28V ac peak (optional 50mV to
28V ac peak for increased signal sensitivity)
• proximity probe inputs
– compatible with Bently Nevada 3300 (5mm and 8mm) proximity
transducer systems
– provides 1 isolated 24V dc power supply (2 channels rated at
30mA each) to power external devices
– vortex flowmeter – 6V and 3V
You configure the module’s 2 input channels for your specific
application(s). Each input channel has two input selections:
Selecting the Mode(s) of Operation
You configure the 1794-IJ2 module for these modes of operation:
Channel 0
Channel 1
frequency input (F0)
gate input (G0)
frequency input (F1)
gate input (G1)
frequency input (F0-F1) - you connect
your input device to this input (ac, proximity
sensors switch, magnetic, vortex )
gate input (G0-G1) - you connect your
input device to this input (ac, proximity
sensors switch, magnetic, vortex )
used to determine direction - CW or CCW
2 input channels
FREQ GATE OK
0
FREQUENCY INPUT 2 CHANNEL
1
1794-IJ2
Allen-Bradley
F0F
FREQ GATE
1F 1F OUT
0OUT 1
Mode Use this mode to: Indicators/
Alarms Scaler values
Frequency and
% Full Scale • monitor the frequency of an input with high accuracy (e.g. shaft)
• monitor the percent of full scale frequency
• operate frequency alarm (% full scale)
• scale the frequency
• monitor the direction of shaft rotation
• wire-off alarm with dc devices
• missing pulse alarm
√
√
√
√
Frequency and
Acceleration • monitor the frequency of an input with high accuracy (e.g. shaft)
• monitor the acceleration (rate of speed change)
• operate acceleration alarm (rate of change)
• scale the frequency
• monitor the direction of shaft rotation
• wire-off alarm with dc devices
• missing pulse alarm
√
√
√
√
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Publication 1794-6.5.11 - November 1997
Overview of the Frequency Input Module 1-5
Output Capabilities The 1794-IJ2 module has 2 assignable outputs. These outputs are
designed for applications that require fast response. The outputs:
• are current sourcing at 10-31.2V dc (1A maximum per output)
• are electrically fused/current limited to 3A
• can be assigned to the associated input channel with user-selectable
frequency and acceleration values
• are isolated — this lets you use two separate external power supplies
if desired (one for output 0 and one for output 1)
Implementing Application Features
You can use the module to implement programmable application features
that are usually initiated by your PLC processor. This frees the PLC
processor to do other tasks and helps increase the overall throughput of
your PLC system.
How Frequency is
Calculated The following paragraphs detail operation of the frequency input module
algorithm and its modifying parameters.
Frequency Calculation
Frequency is determined by a general algorithm which can be modified by
user defined parameters. In its simplest form, the algorithm employs the
user defined Minimum Sampling Time to set a window in which to count
pulses to determine the frequency. At least two pulses are required within
the sample window. Frequency is determined by storing the time the first
pulse occurred and then continually storing and updating the time of
subsequent pulses, along with the number of pulses encountered. When
the window expires, the frequency is calculated and the procedure repeats.
The sequence and formula for determining frequency are shown below.
This feature Is used in these modes To Alarm is ON when
frequency alarm frequency alarm selected activate alarm when calculated or scaled frequency is higher than user-specified
frequency value. frequency >user-specified value
acceleration alarm acceleration alarm
selected activate acceleration alarm when acceleration is greater than user-specified acceleration value. acceleration> user-specified value
scaling % full scale and
acceleration multiply and/or divide frequency by scalar frequency >user-specified scaled frequency value

Publication 1794-6.5.11 - November 1997
1-6 Overview of the Frequency Input Module
If only one pulse occurs within the sampling window, when the sample
time has expired, the window is extended to 2 seconds to allow for a
second pulse to occur. As soon as a second pulse occurs, the frequency is
calculated and the procedures starts over. If no second pulse is detected,
zero frequency is reported and a Missing Pulse Alarm is generated. The
following figure depicts this situation.
Termination on Number of Pulses
The normal mode is designed to provide wide bandwidth. However, it
requires the full 2 seconds to report a missing pulse. Another user
parameter, Number of Pulses to Terminate Sampling, is provided for
those situations where many pulses are expected within the sampling
window, such that early determination of frequency is possible.
N
ormal Mode Frequency Determination, at Least Two Pulses in Sampling Time
Frequency Reported
at End Sampling Time =T2 - T1
pulses counted - 1
Minimum Sampling Time
Frequency Input
Pulses
first pulse in window,
T1 time stored
pulses counted
last pulse in window
T2, update as each
pulse occurs
Missing Pulse Alarm Would be Reported
After 2 Seconds, If No Pulse Occurs
Normal Mode, Only One Pulse in Sampling Time, Sampling Time Extended
Frequency Reported at
First Pulse in Extended Time = T2 - T1
2 - 1
Minimum Sampling Time
Frequency Input
Pulses
first pulse in window,
T1 time stored
2 = pulses counted
first pulse after window extended,
T2 time stored
Sampling Time Extended
to 2 Seconds
Missing Pulse Alarm Would be Reported After 2 Seconds, If No Pulse Occurs
Allen-Bradley Replacements

Publication 1794-6.5.11 - November 1997
Overview of the Frequency Input Module 1-7
During normal operation, there is a sufficient number of pulses to prevent
the module from entering the 2 second extension mode. Once the user
defined number of pulses is reached within the sampling window, the
frequency is immediately reported.
If the sampling window was extended to 2 seconds while waiting for a
second pulse to occur, a situation which can occur during system startup,
the module will not wait for the number of pulses to be reached. Instead,
as soon as a second pulse occurs, the frequency will be calculated based
on the time between the 2 pulses, and the procedure starts over.
Missing Pulse Multiplier
The last user parameter which is provided to modify the frequency
algorithm is the Missing Pulse Multiplier. In this case, the user can set the
number of Minimum Frequency Sampling Time windows they will allow
to extend the time to capture a second pulse, before reporting a Missing
Pulse Alarm. The intent with this parameter is to allow a tradeoff of the
bandwidth available with the response time to report a missing pulse. This
mechanism is shown in the following figure.
Termination on Number of Pulses
Frequency Reported at
Number of Pulses to Terminate Reached = T2 - T1
Pulses to Terminate - 1
Minimum Sampling Time
Frequency Input
Pulses
first pulse in window,
T1 time stored
pulses to terminate
number of pulses to
terminate reached
T2, update as each
pulse occurs
Missing Pulse Alarm Would be Reported After 2 Seconds, If No Pulse Occurs

Publication 1794-6.5.11 - November 1997
1-8 Overview of the Frequency Input Module
Direction Detection
Direction detection is accomplished by using the Frequency input, Gate
input, and two sensors. The module expects to see a Low to High
transition on the Frequency input, followed by a Low to High transition
on the Gate input. This assumes both input polarity select bits are the
same selection.
This corresponds to Clockwise rotation (see figure). If a Low to High
transition occurs on the Gate input, followed by one on the Frequency
input, the rotation is CounterClockwise.
Missing Pulse Multiplier
Frequency Reported at
First Pulse in Extended Time = T2 - T1
2 - 1
Minimum Sampling Time
Frequency Input
Pulses
first pulse in window,
T1 time stored first pulse in an extended window,
T2 time stored
extended windows added one at time, until
pulse occurs or multiplied windows exceeded
Missing Pulse Alarm Would be Reported After Last Window, If No Pulse Occurs
possible extended window
2 = pulses counted
Sensor 0
Sensor 1
Clockwise Rotation
Frequency Input
IJ2 Module
Gate Input
M
2 x M
Sensor 0 (F)
Sensor 1 (G)
Clockwise
Rotation
Counter
Clockwise
Rotation
Sensor 0 (F)
Sensor 1 (G)
Direction Detection - Principle of Operation
Allen-Bradley Replacements

Publication 1794-6.5.11 - November 1997
Overview of the Frequency Input Module 1-9
Chapter Summary In this chapter, you learned about the frequency input module, block
transfer communication, and details of how the module functions. Now
you can install the module.
Install the
IJ2 Module
2

Publication 1794-6.5.11 - November 1997
1-10 Overview of the Frequency Input Module
Allen-Bradley Replacements