Operating In High Resolution Frequency Mode - Allen-Bradley 1756-CFM User Manual

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