User manual

IEC61131 User and Reference Manual
April 22, 2008
267
flow
Flow Accumulator
Description
The flow function accumulates flow from pulse type devices such as turbine flow meters.
When the accumulate input is ON the function accumulates volume and calculates the flow
rate.
When the Log Data input goes from OFF to ON, the accumulated volume is saved in the
history registers. Older history is pushed down and the oldest record is discarded. The Log
Data input must be triggered at least once every 119 hours (at the maximum pulse rate of
10kHz). Otherwise the volume accumulator will overflow, and the accumulated volume will
not be accurate.
Note: The accuracy of the FLOW block improves with longer periods between logging
data. For greatest accuracy avoid logging small periods of time.
When the accumulator enabled input is ON, accumulation and rate calculations are enabled.
When the input is OFF, all accumulators, stored data and the outputs are set to zero.
The function reads and accumulates the number of pulses, and divides by the K factor to
calculate the total volume. This is done on each scan of the controller logic. The function
calculates the flow rate in engineering units based on the K-factor provided. The rate
updates once per second if there is sufficient flow. If the flow is insufficient, the update slows
to as little as once every ten seconds to maintain resolution of the calculated rate.
Stored data is retained when the program is stopped, and when the controller is powered off
or reset.
enable
log
accumulate
K
input
type
flow
rate
status
vol1
time1
end1
volP
timeP
endP
period
units
ID
Arguments
Inputs
Type
Description
enable
Boolean
ON = enable accumulation
OFF = clear outputs
log
Boolean
Log Data
OFF to ON = log data
Accumulate
Boolean
Accumulate Flow
ON = accumulate flow
K
Real
K factor
K must be a positive value.