Rockwell Automation 1756-HSC ControlLogix High Speed Counter Module - Manual (Page 31)

Rockwell Automation Publication 1756-UM007C-EN-P - November 2011
Frequency Modes 31
Sample Period for Frequency Mode
As previously mentioned, the Sample Period is a user-defined time frame to
count the number of incoming pulses for calculating frequency. This fixed,
sample period of time can be set by varying the Scaler tag, which can range
from 10…2000 in 10 ms increments. For example, a Scaler value
of 100 = 100 ms. The default value is 1 second.
In the following frequency illustration, three pulses have been accumulated
during the user-selected time period. If you had selected 100 ms as
the sample period, the frequency returned to the controller is
Frequency = Counts/Sample period = 3 counts/100 ms = 30 Hz.
Frequency Mode
IMPORTANT
A Scaler tag value of 0 equals a 1 second time period.
A Input
Encoder/Pulse Generator
1756-HSC Module
B (Not used)
Z (Not used)
Incoming Pulses on A Input
Internal Sample Period
(Scaler Value, Example: 100 ms)
No. of Pulses Occurring During
Sample Time in Present Value Tag
Totalizer Tag and
Frequency Calculated
Outputs Updated Here
(Gate/Reset)
User Selectable Sample Period,
10 ms to 2 seconds
in 10 ms increments
41690
3
...9 10 11 12 ...
Frequency in Stored Value Tag
User Selectable Sample Period
Sampled Pulses
=
3
100 ms
= 30 Hz
Total Number of Pulses in Totalizer Tag 12
1 2 3
9 Updated on Falling Edge of Scaler
* See Note Below
* Always Inactive for 10 ms Regardless of Scaler
Scaler No.
in ms