Allen-Bradley FLEX I/O 1794-IJ2, User Manual, Page: 10 / 80

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