
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.
Normal 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
Содержание FLEX I/O 1794-IJ2
Страница 1: ...User Manual FLEX I O Frequency Input Module Cat No 1794 IJ2 Allen Bradley Allen Bradley Replacements ...
Страница 6: ...Publication 1794 6 5 11 November 1997 4 Using This Manual ...
Страница 19: ...Publication 1794 6 5 11 November 1997 1 10 Overview of the Frequency Input Module Allen Bradley Replacements ...
Страница 38: ...Publication 1794 6 5 11 November 1997 3 6 Programming Your Frequency Input Module ...
Страница 67: ...Publication 1794 6 5 11 November 1997 6 4 Troubleshoot the Frequency Input Module Allen Bradley Replacements ...