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21
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The Sentrius sensor incorporates a flash memory chip that is used to store records of sensor data. Separate areas, with a
capacity of 4096 records, are maintained for normal sensor data, and for data that has triggered alarm limits. Each backlog log
or alarm includes the time that reading was taken. During data retrieval, the alarm section is prioritized over the non-alarm
data.
The backlog data can be retrieved via the LoRa interface or the Bluetooth interface. Note that in some situations, such as the
lowest data rate in the US or AS regions, it may not be practical to retrieve backlog data over LoRa due to bandwidth
limitations.
There are separate commands for retrieving the backlogs in FIFO or LIFO mode. With FIFO, the oldest log is retrieved first.
With LIFO the latest log is retrieved first. Both commands are identical as described in the sections below.
Once retrieval of logs commences in a certain mode, ALL logs must be retrieved using that mode or a reformat performed
(erase all of the logs) of the flash memory once all logs required have been retrieved. Using the LIFO option means there can
be gaps of already retrieved logs in flash. The LIFO option can handle this; FIFO cannot.
Note
:
The backlog feature only functions if the sensor has received a timestamp from the server.
In situations where
the timestamp is not available, any logs that are not successfully received by the server are lost.
Note
:
For the Laird Packet Format, the Logging Mode is fixed to ‘
On Fail’
.
For the Laird 2 Packet Format, logging can be configured to work in one of two ways, as follows.
In the ‘
On Fail
’ mode of operation, Confirmed Packets, that are not acknowledged by the Network Server are stored to the
flash memory. For successful operation of this mode, Confirmed Packets must be enabled.
In the ‘
Continuous
’ mode of operation, all sensor data is stored to the flash memory. Limitations on storage space result in
increasing Read Periods of the sensor consuming available space more rapidly. The Logging Duration parameter is used to
determine how many days (between 1 and 7) of data should be stored before wrapping around and overwriting the oldest
data.
The relationship between Sensor Read Period and the number of days of data that can be stored is shown in
Table 12
– Number of days of data available depending upon Sensor Read Period
Maximum Read Period (s)
Maximum Number of Days
Total Records at Maximum Update Rate
< 43
1
2057
< 64
2
2743
< 85
3
3085
< 106
4
3291
< 126
5
3456
< 148
6
3550
-
7
(Read Period dependent)
Note
: When the Logging Mode is changed, existing backlog data is lost due to the flash memory needing to be
resynchronised.
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