Campbell Scientific CR10X TD Operating System Addendum for CR510, CR10X, and C - Page 25

THIS SECTION ENTIRELY REPLACES THE DATALOGGER MANUAL SECTION 2. SECTION 2. INTERNAL DATA STORAGE 2.1 FINAL STORAGE AND DATA TABLES Final Storage is that portion of memory where final processed data are stored. It is from Final Storage that data is transferred to your computer. With the TD datalogger, Final Storage is organized into Data Storage Tables. These data tables should not be confused with the program tables *1, *2, and *3 that contain the datalogger program. Within each data table, data is organized in records and fields. Each row in a table represents a record and each column represents a field. To understand the concept of tables it may be helpful to consider an example. A CR10X is to be used to monitor 3 thermocouples (TC). Each hour a temperature for each of the three TC is to be stored. The table has 4 fields: "DATE_TIME TEMP1 TEMP2 TEMP3." Each hour a new "record" would be added. The "hourly" table would then be organized as follows: DATE_TIME TEMP1 01/27/91 10:00:00 23.5 01/27/91 11:00:00 24.2 TEMP2 TEMP3 24.6 28.2 22.4 23.4 Only the hourly data is stored in the hourly table, Each output interval has its own table. Data tables can also be "event driven" rather than interval driven, that is a new record is stored when a specified event occurs rather than based on time. Each table is completely independent of any other tables and all records in a given table have the same number of fields. Each table is allocated (manually by the user or automatically by the datalogger) a number of records. Different tables have different numbers of records. Each data table is in a ring memory configuration such that when the allocated number of records has been stored, each subsequent new record will overwrite the oldest stored record. The *9 Mode may be used to view the size of the Data Storage Tables. (Section 1.9) The TD datalogger supports naming of tables and fields, so any data value can be referenced by the table and field names. For example, the temperature data for the first thermocouple is referenced as "HOURLY.TEMP1." As Data Tables are allocated in the datalogger program, some Final Storage Memory is reallocated for the storage of these labels and other data table overhead. NOTE: All Data Storage Tables are reallocated and erased whenever the datalogger program is recompiled (*0, *6, *B), when Input Storage Memory is reallocated (*A), or when a new datalogger program is transferred from the computer to the datalogger. ALWAYS RETRIEVE UNCOLLECTED DATA BEFORE MAKING ANY CHANGES. A time stamp and record number are automatically included with the each record in each table. These are used as part of the data collection protocol. 2.1.1 TIME AND TIMESTAMPS Each record in a table has a time stamp associated with it. With Instruction 84 set for interval output (a interval in seconds is specified as the second parameter), time is not actually stored with each record. Using the timestamp of the last record stored and the table interval, the datalogger can calculate the timestamp for any previous record. When retrieved, each record in the data file will have a timestamp. This saves 6 bytes per record by not storing time with each record. A consequence of not storing time is that if output does not occur at a scheduled time, the datalogger must keep track of the discontinuity in the timestamps so it can correctly calculate timestamps for records older than the missing record. The datalogger will keep track of the 10 most recent discontinuities in each table. If more than ten discontinuities occur, records with timestamps older than the oldest discontinuity cannot be reliably timestamped when collected. For this reason interval tables should not be used if outputs will be routinely missed. Outputs can be missed (discontinuities can occur) when: • The datalogger clock is changed such that is passes an output interval. AD-2-1