Data Tables

Data storage follows a fixed structure in the datalogger in order to optimize the time and space required. Data are stored in tables such as:

The user's program determines the values that are output and their sequence. The datalogger automatically assigns names to each field in the data table. In the above table, TIMESTAMP, RECORD, RefTemp_Avg, and TC_Avg(1) are fieldnames. The fieldnames are a combination of the variable name (or alias if one exists) and a three letter mnemonic for the processing instruction that outputs the data. Alternatively, the FieldNames instruction can be used to override the default names.

The data table header may also have a row that lists units for the output values. The units must be declared for the datalogger to fill this row out (e.g., Units RefTemp = degC). The units are strictly for the user's documentation; the datalogger makes no checks on their accuracy.

The above table is the result of the data table description in the example program:

All data table descriptions begin with DataTable and end with EndTable. Within the description are instructions that tell what to output and the conditions under which output occurs.

DataInterval(TintoInt, Interval, Units, Lapses) DataInterval(0,10,msec,10)

The DataTable instruction has three parameters: a user specified name for the table, a trigger condition, and the size to make the table in RAM. The trigger condition may be a variable, expression, or constant. The trigger is true if it is not equal to 0. Data are output if the trigger is true and there are no other conditions to be met. No output occurs if the trigger is false (=0). The size is the number of records to store in the table. You can specify a fixed number, or enter –1 to have the datalogger auto allocate the number of records. The example creates a table name Temp, outputs any time other conditions are met, and retains 2000 records in RAM.

DataInterval is an instruction that modifies the conditions under which data are stored. The four parameters are the time into the interval, the interval on which data are stored, the units for time, and the number of lapses or gaps in the interval to track. The example outputs at 0 time into (on) the interval relative to real time, the interval is 10 milliseconds, and the table will keep track of 10 lapses. The DataInterval instruction reduces the memory required for the data table because the time of each record can be calculated from the interval and the time of the most recent record stored. The DataInterval instruction for the CR200 does not have lapses.

NOTE: Event driven tables should have a fixed size rather than allowing them to be allocated automatically. Event driven tables that are automatically allocated are assumed to have one record stored per second in calculating the length. Since the datalogger tries to make the tables fill up at the same time, these event driven tables will take up most of the memory leaving very little for the other, longer interval, automatically allocated data tables.

The output processing instructions included in a data table declaration determine the values output in the table. The table must be called by the program using the CallTable (Tablename) instruction in order for the output processing to take. That is, each time a new measurement is made, the data table is called. When the table is called, the output processing instructions within the table process the current inputs. If the trigger conditions for the data table are true, the processed values are output to the data table. In the example below, several averages are output.

Average is an output processing instruction that will output the average of a variable over the output interval. The parameters are repetitions (the number of elements in an array to calculate averages for), the Source variable or array to average, the data format to store the result in (see following table), and a disable variable that allows excluding readings from the average if conditions are not met. A reading will not be included in the average if the disable variable is not equal to 0; the example has 0 entered for the disable variable so all readings are included in the average.

Formats for Output Data
Code	Data Format	Size	Range	Resolution
FP2	Campbell Scientific floating point	2 bytes	±7999	13 bits (about 4 digits)
IEEE4	IEEE four byte floating point	4 bytes	1.8 E –38 to 1.7 E 38	24 bits (about 7 digits)
LONG	4 byte Signed Integer	4 bytes	–2,147,483,648 to +2,147,483,647	1 bit (1)