ML-x17 DATA LOGGER MANUAL
Manufacturers of low power instruments
page 110
4.44 Compacted Data Format
The compacted data format is meant for use in case of message size constrained or payload expensive
communication, like satellite communication.
Compacting is required to get sufficient measurements in a size constrained message or to reduce
expensive payload costs.
A common method to compact data is by using algorithms like “zip” and “rar”, but those algorithms are not
suitable to compress size constrained messages and would make the payload rather bigger than smaller.
A first stage in compacting, is eliminating data that is not strictly necessary and to include the real
interesting data only. The compacted data contains timestamped measurement values only, it does not
contain diagnostic data or supportive info like system identifications, parameter codes, names or units.
The compacted format is limited to contain up to 15 logger parameters/channels. As textual parameter
codes would use to much data, the identification of the individual channels is based on a number between
1 and 15. Assigning the numbers to individual parameters is a matter of configuration by starting their
code names with a capital P followed by a number between 1 and 15. The P will be stripped of, as well as
any trailing characters, so you could specify meaning full codes like: P1TMP or P02HUM or P15LEV.
Make sure that the number parts are unique.
The compacted data is a binary and unreadable format as representing times and values in ASCII format
would take too much space. Storing values as IEEE floats is out of the question either, because every
value would take at least 4 bytes, while less bytes would be sufficient in most cases.
The compacted data exists out of time and value records. Each record specifies the delta to the previous
corresponding record. So, in case of big numbers (like with time or totalizers) only the first occurrence will
take the max required bytes, while consecutive occurrence might need just one byte.
When a time record is specifying a delta of 5 minutes, all value records following will be 5 minutes
younger than the ones before. When a value record is specifying a delta of 0 it means that the measured
parameter value did not change since the previous measurement.
The starting reference time for each message is 1-jan-2017 00:00:00. The first record in the message will
be a time record specifying the difference in time since 1-jan-2017 00:00:00 for the first value records.
The starting reference value is 0.0 for each individual parameter.
Note
: The “Source” of the “Compacted Data” can be identified by the info contained in the encapsulating
“Delivery Message” (e.g. the IMEI number of an Iridium Satellite Transceiver). The format and transfer
method of the “Delivery Message” is dependent of the used “communication provider” (e.g. an Iridium
TCP-direct message).
