Rockwell Automation Publication 1756-UM010C-EN-P - June 2021
31
Chapter 3 Configurable Flowmeter Module Features and Operational Modes
Operating in High Resolution
Frequency Mode
In High Resolution Frequency mode, the module calculates frequency over a
user-defined time period up to 2 seconds. Frequency sampling begins on the
leading edge of the first pulse and ends on the next pulse to occur after the
sampling period expires.
This figure shows a 1756-CFM module in a turbine shaft speed-monitoring
application in High Resolution Frequency mode.
You must calculate a resolution for this mode. Use this equation to calculate
resolution.
This table lists sample F
in
and T
sample
values and the corresponding resolution.
The values listed in
are listed for example purposes. Specific values will
change according to your application.
42731
CV
Pulse output
Fuel
Monitors fuel flow and
total gallons
Generator
Electricity
Shaft
encoder
Turbine
Shaft speed
1756-CFM
Logix controller:
• monitors shaft speed
• performs PID calculations
• adjusts valve by a 1756-OF8I analog
output module.
1756-OF8I
Table 4 - Sample Resolutions
F
in
T
sample
Resolution
60Hz
0.033 seconds
0.00045Hz
5000Hz
0.020 seconds
0.0625Hz
50,000Hz
0.050 seconds
0.25Hz
F
in
(250 x 10
-9
)
T
sample
Resolution =
Where:
• F
in
is the input frequency
• T
sample
is the sample time period
