Schneider Electric EM3555 manual Data Logging, Configuration, Reading Data, Read/Write Collision

EM3555	ZL0093-0A
Data Logging	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-configurable with the Modbus address of the 16-bit data output to be stored. Measurement variables with 32-bit data, such as floating 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 first 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 fills 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 flag 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 modified via Modbus commands).

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