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EM3555
Data Logging
ZL0093-0A
11/2011
DATA LOGGING
The EM3555 includes a data logging feature that records 10 meter parameters,
each in its own buffer.
Configuration
Use register 150 to set the data logging time subinterval. Writing to the storage
buffer is triggered by the subinterval timer. The default subinterval is 15 minutes
(at a 15 minute interval setting, the buffers hold 60 days of data). An external
timer can be used over Modbus by setting this register to 0.
Use register 159 to turn on data logging and select either Single Shot or
Continuous mode. The default settings are data logging on and set to
Continuous mode. In Single Shot mode, the meter records data until the buffer
is full. When the buffer is full, the meter stops recording new readings. Data
for this time period is kept, but newer energy information is lost. In Continuous
mode, the meter continues to record energy data as long as the meter is
operating. The buffer can only hold 5760 entries at one time, however, so when
the number of records exceeds 5760, the oldest entry is deleted to make room
for the newest.
Registers 169-178 contain the pointers to 10 data storage buffers. Each buffer
is user-congurable with the Modbus address of the 16-bit data output to be
stored. Measurement variables with 32-bit data, such as oating point data or
32-bit integer energy accumulators, require two buffers. However, the lower 16
bits of an integer energy accumulator can be stored in a single buffer (optional).
When the EM3555 is rst installed, the buffers contain QNAN data, with a value
of 0x8000. This data is considered invalid. If the buffer is reset at any point, all
entries in the buffers are overwritten with this 0x8000 value, indicating that it is
invalid. All invalid data is overwritten as the meter lls the buffer with new data
entries.
Reading Data
Use register 158 to choose which buffer to read. When this register value is set
to 0, the meter is in data logging mode. Changing this value from 0 (to 1 through
10) switches the meter to reading mode and selects a buffer to read. Data from
the selected buffer appears in registers 8000 to 13760.
Read/Write Collision
If the demand sub-interval timeout occurs while the user is reading a page
(register 158 ≠ 0), the log data will be held in RAM until the next demand
subinterval. At that time, both the saved data from the previous cycle and
the new data will be written to the log, whether the page register has been
set back to 0 or not. Error bits in the Log Status Register (160) track these
conditions. Subsequent log writes will proceed normally. Provided the log read
is concluded in less time than the demand sub-interval, this mechanism handles
the occasional collision and prevents the user from reading data as the buffer is
being updated.
The Log Status Register has additional error ag bits that indicate whether
logging has been reset or interrupted (power cycle, etc.) during the previous
demand sub-interval, and whether the Real Time Clock has been changed
(re-initialized to default date/time due to a power-cycle or modied via Modbus
commands).