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Frequency Accuracy in
Totalizer Mode
There are two steps to calculating frequency accuracy in Totalizer mode.
1. Calculate frequency accuracy.
2. Determine the application's operating conditions and add the error for
those conditions to the value obtained in step 1.
These values must be added to your frequency accuracy results in
Totalizer mode:
• Crystal error - 0.005% @ 25 °C
• Drift and crystal error - 0.01% from 0 °C to 60 °C
Calculate Frequency Accuracy
You can calculate frequency accuracy in Totalizer mode for:
•
Frequency Period
•
Speed
•
Frequency average
Frequency Period
For frequency period, you must know:
•
User-defined sample time period (T
•
Application frequency (F
•
Number of accumulated counts in sample time (Counts)
Use this equation to calculate frequency accuracy in Totalizer mode for
frequency period:
(1) x (100)
Accuracy =
(T
) x (F
s
EXAMPLE
For example, in an application with these conditions:
• 0.5 seconds time period
• 123 Hz frequency
• 25 °C operating temperature
accuracy is determined with this equation:
Rockwell Automation Publication 1756-UM010C-EN-P - June 2021
)
s
)
in
)
in
(1) x (100)
Accuracy =
+ 0.005%
(0.5) x (123)
Accuracy = 1.626 + 0.005
Accuracy = +/- 1.631%
Appendix D
Frequency Accuracy
Value is added to accuracy
to account for the crystal
error
127
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