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202 Triggered Delta Volumes
Section 6: Meter operation Reference, Installation, and Operations Manual
June 2013 3-9000-743 Rev S
6.1.11 Triggered Delta Volumes
The “triggered delta volume” feature provides the ability to measure total gas flow volume
(flow- and base-condition) between two successive external event triggers.
To trigger an event, set the DoUpdtTrigDeltaVols data point to TRUE. This causes the meter to
save the current accumulated flow- and base-condition volume values (forward and reverse).
The meter then calculates the difference between these values and the corresponding values
saved from the previous event trigger. Finally the meter writes the delta volume values to the
appropriate data points (TrigDeltaPosVolFlow, TrigDeltaNegVolFlow, TrigDeltaPosVol-
Base, and TrigDeltaNegVolBase) and sets the DoUpdtTrigDeltaVols data point to FALSE to
clear the trigger and indicate the calculation completion.
The triggered delta volume functionality is retained across power cycles as the accumulated
volumes values at the last event trigger are saved in non-volatile memory.
The delta volume data points are stored internally in non-volatile memory as double-precision
floating point numbers. The delta volume data points can be read via Modbus as either 32-bit
floating point values or as integer values (using the [overflow,lower] LONG register pair in a
manner similar to reading the accumulated volumes).
Suggested user access logic
The following pseudo-code demonstrates the logic to access the triggered delta volume
functionality:
I
NITIAL SET-UP:
Ensure Modbus units are set-up as desired: set Modbus register 10026 (UnitsSystem) to 0 for
U.S. Customary units or to 1 for metric units.
P
ERIODIC LOOP:
Wait for external event for synchronizing the start of the meter delta volumes.
Send trigger Modbus message: set Modbus register 12199 (DoUpdtTrigDeltaVols) to 1 (TRUE).
Read trigger Modbus register 12199 (DoUpdtTrigDeltaVols) in a loop until it is read as 0
(FALSE) indicating that the delta volumes have been updated.