Rockwell-automation 1794-IJ2XT FLEX I/O Frequency Input Modules User M Instrukcja Użytkownika Pobierz pdf (Strona 18)

Publication 1794-6.5.11 - September 2011

8 Overview of the Frequency Input Module

processor to do other tasks and helps increase the overall throughput of your

controller system.

How Frequency Is

Calculated

The following paragraphs explain the 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.

Application Features

Feature Mode Purpose 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

1 2 ... 13 14 15 16 17 18 19 20 21 22 23 ... 86 87

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Rockwell-automation 1794-IJ2XT FLEX I/O Frequency Input Modules User M Instrukcja Użytkownika Strona 18