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or an external MVT, the user selects the downstream tap location during MVT
configuration, the MVT firmware changes the sign of the differential pressure to provide a
positive DP value.
1.5.3 Archives
The ControlWave EFM stores two distinct types of archive data. The first type is Audit
Trail data, which is a recording of the various events and alarms that have an impact on
the calculated and reported rates and volumes. The second type is historical data, which
includes records of rates and volumes and other signals over time. When an archive log
becomes full, new entries replace the oldest entries in the log.
Where feasible, both forms of archive data conform to the requirements of the API Chapter
21 (the Committee on Gas Measurement's EFM document). Specifically, the averages of the
process variables stored in the data archive are for flowing periods, appropriate to their
usage in the equations, and any gas-related parameter designated an event that is changed
by an operator either remotely or locally causes an entry in the audit log.
The ControlWave EFM supports the "breaking" of a log period when an operator-entered
parameter is changed. When this occurs, the log period in process is closed out, a log is
made, and a new log is begun. This feature is disabled by default and may be enabled by
the operator. Note: To prevent several very short logs from being created due to a series of
successive configuration changes, the ControlWave EFM will not create a log which
contains less than 60 seconds (flowing or otherwise) of data. Therefore if a user enters 15
configuration changes over a 2minute period, the log will only be broken twice.
1.5.3.1 Hourly Historical Data Log
The Hourly Data Log holds one record for every contract hour. Hourly logs hold 840 entries
or 35 days; this ensures that the previous period of hourly data is always resident in
ControlWave EFM FLASH memory.
The following items are stored in the Hourly Data Log:
• Corrected Volume
• Uncorrected Volume
• Accumulated Energy
• Average Static Pressure
• Average Temperature
• Average Differential Pressure
• Average Specific Gravity
• Average Heating Value
• Flow Time
• Uncorrected Count
Each log entry also contains the date and time. The ControlWave EFM has a Hourly
Historical Log for each of four runs.
1.5.3.2 Daily Historical Data Log
The Daily Data Log holds one record for every contract day. The contract hour may be
changed by the user. The daily log holds 62 entries; this ensures that the previous calendar
month of daily data is always resident in ControlWave EFM FLASH memory.
1-24 / Introduction
CI-ControlWave EFM
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