Flow Rate Calculations; Zero Flow Calculation - Honeywell Mini-AT User Manual

Flow Rate Calculations

The Mini-AT calculates corrected and uncorrected gas flow rates. There are two types of calculations
made for corrected and one type for uncorrected volume. The calculations are:
Average Flow Rate (Item 208) - the average amount of corrected volume flow per Log
Interval (Item 202), expressed in Cor Vol Units (Item 090) per hour.
Instantaneous Flow Rate (Item 209) - the instantaneous amout of corrected volume flow,
expressed in Cor Vol Units (Item 090) per hour.
Instantaneous Dial Rate (Item 218) - the instantaneous amount of uncorrected volume flow,
expressed in cubic foot per hour.
Note: Instantaneous Rates are based on the duration of time between the last two
input pulses.
The Instantaneous Flow and Dial Rate calculations require two conditions to be satisfied before calculations
can be made. The first is, at least two correction cycles have occurred, and the second is that one minute
must have elapsed. If both conditions are not satisfied, then the Instantaneous Flow and Dial Rates will
remain constant until the next point at which the conditions are satisfied.

Zero Flow Calculation

Based on the method described above, the flow rate will not be able to indicate a flow rate zero. A Zero-
Flow Detection algorithm has been developed (Mini-AT firmware 6.60 and higher) to check for a zero flow
condition. This algorithm calculates the expected time for the next meter input from the average time
between the five previous meter inputs, added to the time period of the most recent consecutive switch
input. The Mini-AT will 'wake up' once a minute to check and see if the expectation time has been ex-
ceeded. If the expectation time is exceeded and there has not been a switch input, the instantaneous dial
and flow rates are set to zero.
The expectaion time can be scaled by changing a multiplier stored at item 460. The default value of item
460 is 2. Thus the expectation time would be scaled by a factor of 2. If Item 460 is set to zero, the Zero-
Flow Detection calculation is disabled.
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Mini-AT User Guide