System information

Section 3. The CR200 Datalogger
3-8
latency varies across different communication mediums but the application
should be aware of this variability and set the maximum retry interval
accordingly.
3.8 Understanding Table Definitions and Table
Signatures
Since the CR200 stores data in tables, the datalogger and the application must
understand and agree on the structure of each table in order to collect data.
Table definitions contain the parameters that describe each table, record, and
field in the datalogger. These parameters exist on the datalogger in a file with
a “.TDF” extension. Obtain table definitions from the datalogger using the File
Upload transaction requesting a file named “.TDF”.
Table definitions are used by the application to know what tables and fields
exist and what data to expect from each table when collecting values from the
CR200. In order to ensure the integrity of this table information, the
application should calculate a signature of the parameters contained in each
table within the table definitions. One signature should be calculated for each
defined table and should be stored and used by the application to verify that the
table has not changed when collecting data.
3.9 Getting Table Definitions from the CR200
Table definitions are retrieved from the CR200 with the File Upload
transaction before attempting data collection. The file name in the transaction
should be specified as “.TDF”. The datalogger recognizes this file extension
and returns the appropriate response containing the table definitions. A
hexadecimal example of the command looks like:
BD A0 01 70 04 10 01 00 04 1D 1D 00 00 43 50 55 3A 44 65 66
2E 74 64 66 00 00 00 00 00 00 00 80 27 EA BD
The response message from the datalogger contains the table definitions and
may be broken over multiple packets. A function should be created that parses
the table information from the response packet. This information should be
used by the application to calculate table signatures and to interpret data
records that are collected from the datalogger. If the table definitions are
broken over multiple packets, the last File Upload Response packet should
have a value in the FileOffset field that is smaller than the Swath field declared
in the File Upload Command packet. An example response packet looks like:
BD A0 04 00 01 10 04 00 01 9D 1D 00 00 00 00 00 01 53 74 61
74 75 73 00 00 00 00 01 0C 00 00 00 00 00 00 00 00 00 00 00
00 00 00 00 00 8B 4F 53 76 65 72 73 69 6F 6E 00 00 00 00 00
00 00 00 01 00 00 00 08 00 00 00 08 00 00 00 00 8B 4F 53 44
61 74 65 00 00 00 00 00 00 00 00 01 00 00 00 0A 00 00 00 0A
00 00 00 00 8B 50 72 6F 67 4E 61 6D 65 00 00 00 00 00 00 00
00 01 00 00 00 10 00 00 00 10 00 00 00 00 95 50 72 6F 67 53
69 67 00 00 F1 67 BD
3.9.1 How to Get and Use Table Signatures
The table definition signature is a signature for the parameters describing a
table. There must be one signature for each defined table in the File Upload