Emerson Micro Motion 3711, Руководство по конфигурации и использованию, Страница: 134 / 234

126 Micro Motion
®
Model 3711 Gas Flow Computers
Function Sequence Tables
11.8.6 Database commands
Database commands provide access to the configuration and historical databases. Operations include
reading and writing configuration parameters, reading, writing, and storing values from historical
databases, and timestamping values to a history point.
Historical database commands
The RDB, WDB, and WTM commands are historical database commands. These commands allow
you to establish a non-periodic history database (one that has no specific time interval), a periodic
history database (one that has a specific time interval), or a storage array for data (similar to a soft
point).
Before you use a historical database command, you must define the history point that the command
will reference. The Archive Type of the point must be set to FST Time – Minute, FST Time – Second,
or FST Data. See Section 8.3 for information on defining history points. For each history point, space
is reserved in memory to allow 840 log entries. A history index is used to define the next log entry to
be read or written. Typically, an FST register or a soft point is used to store the history index.
Each historical database command requires two arguments:
• ARGUMENT1 is the number that identifies the history point in standard history (1 through
35). It can be a constant or a reference to any database point in the Model 3711’s memory.
• ARGUMENT2 can be a constant or a reference to a database point that contains the history
index.
Automatic rollover handling
If the historical database write commands are used with ARGUMENT2 as a reference to a history
index, and the history index is stored as a floating-point value (always true for FST registers or soft
points), the historical database commands check for rollover in the history database as follows:
1. Following the write or read, the value in the history index is incremented by 1 and then
checked against the maximum number of log entries (840).
2. When the history index value reaches the maximum number, it is reset to 0.
Note: If any data type other than floating-point is used to store the history index, rollover is not
handled automatically.
Table 11-12 Database commands
Name Description Arguments Results
VAL Sets RR(out) to the argument value,
converted to floating-point notation. RR(out) = ARG1
SAV Sets ARGUMENT1 to the current value
of RR(in). • ARG1 = Database Value ARG1 = RR(in)