Emerson Daniel 3415 Operation Manual page 58

Configurations
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, TrigDeltaPosVolBase, 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:
•
•
Read delta volume registers (either the FLOAT registers or the LONG register pairs) in a
single Modbus read. If the delta volume registers are read as LONG register pairs, calculate
each delta volume as follows:
Equation 5-5:
where
Equation 5-5
46
INITIAL 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.
Periodic 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.
Triggered delta volume
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3410 Series Gas Ultrasonic Flow meters