Rockwell Automation 1756-CFM ControlLogix Configurable Flowmeter Module - Manual (Page 39)

39 Rockwell Automation Publication 1756-UM010B-EN-P - December 2011
Configurable Flowmeter Module Features and Operational Modes 39
Acceleration Calculation
Acceleration Calculation is derived by using the rate of change of frequency
over a specified number of samples (1 to 255). This moving average produces
quick responses when the number of samples = 1 and stable, but slower,
responses when the number of samples =255.
The default number of samples used = 255, but a typical application uses 50
samples. There are significant differences between response times. For
example, the quick response offer acceleration calculations more often but is
more likely to set off the Acceleration Alarm for calculation spikes at low
frequencies. The stable responses are slower but ignore acceleration spikes in
favor of definitive operational trends.
Meter Factor
Meter Factor is used to calibrate the frequency (Hz) to a user-defined standard.
For example, the CFM module may read 59.9Hz while the standard is set for
59.7Hz. In this case, the meter factor (default = 1.0) should be changed to
0.99666 to correct the reading.
Trigger On
Use Trigger On to determine what state triggers an output to energize in high
resolution frequency mode (i.e. an output can be configured to turn ON if the
Frequency Average reaches a particular frequency.
 Frequency - Input exceeds MaxAllowedFreq.
 Acceleration - Input speed accelerates beyond AccelAlarmValue.
Tie to Counter
Choose which output is connected to which flowmeter input.
IMPORTANT
Acceleration Calculation values can be entered on the bit
level or byte level. If you are entering values at the byte
level, you must use -1 to represent 255. If you are entering
values on the bit level, you can use the actual number value.
IMPORTANT
For the Trigger On feature, Frequency and Acceleration are
tied to the Overspeed Alarm and Acceleration Alarm
respectively. The alarms remain latched ON once set and
can only be reset if you toggle the Alarm Enable bits.