GE 750, Instruction Manual

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750/760 Feeder Management Relay GE Power Management
16.3 MODBUS PROTOCOL 16 COMMUNICATIONS
16
16.3.13 READING TRACE MEMORY
All Trace Memory waveform data can be read from Modbus registers found in the address range 2100h to
215Fh. In order to understand the following description, familiarity with the settings for Trace Memory is
required; refer to Section 8.6: TRACE MEMORY on page 8–6.
The ‘Number of Trace Memory Triggers Since Last Clear’ register is incremented by one every time a new
Trace Memory is triggered. This register is cleared to zero when Trace Memory is cleared. When a new trigger
occurs, the associated waveform data is assigned a ‘Trace Memory Number’ which is equal to the incremented
value of this register; the newest data will have a number equal to the Number of Trace Memory Triggers. This
register can be used to determine if any new data has been captured by periodically reading it to see if the
value has changed; if the Number of Trace Memory Triggers has increased then there is new data available.
The Trace Memory
BUFFER ORGANIZATION
setpoint determines the number of samples that are captured per
channel for each separate trigger. This setpoint also determines how many data triggers are stored in memory.
For example if the setting is
4x1024 then there are 1024 samples per channel per trigger and the last three
data triggers can be read from memory. Note that only 64 samples of one data channel for a single waveform
can be read from the Modbus memory map in a single data packet. The ‘Trace Memory Selectors’ registers
determine which waveform data can be read from the memory map.
The ‘Trace Memory Number Selector’ determines which Trace Memory can be read. For example, to read the
data for Trace Memory number 3, the value 3 must first be written to this register. Data for Trace Memory num-
ber 3 can now be read from the ‘Trace Memory Information’ registers at addresses 2111h to 2119h. These reg-
isters include a trigger cause (see Section 16.3.12: READING THE EVENT RECORDER on page 16–13 for a
description of the data format), a trigger time and date stamp, and the sampling frequency. There is also the
‘Start Index’ and ‘Trigger Index’ which determine how to ‘unravel’ the data samples; see the description of the
circular data structure below.
The ‘Trace Memory Channel Selector’ determines which data channel samples can be read from the ‘Trace
Memory Samples’ registers at addresses 2120h to 215Fh; refer to format F26 for a complete listing of the
available data channels. For example, to read Vc voltage samples a value of 6 is written to this register. Note
that this register also determines the data format of the samples.
The ‘Trace Memory Sample Selector’ (TMSS) determines which block of 64 samples can be read from the
‘Trace Memory Samples’ registers. The total number of samples stored for one channel is variable and
depends on the ‘Buffer Organization’ setpoint. The ‘Number of Trace Memory Samples Stored’ register indi-
cates the number of samples that have already been accumulated for the selected Trace Memory Number; this
register may have a value less than the total number of samples that can be stored if a trigger just occurred
and there are an appreciable number of post-trigger samples to capture.
Table 16–12: EVENT CAUSE INTERPRETATION
EVENT CAUSE REGISTER
VALUE EVENT CAUSE INTERPRETATION
1003h Breaker Opened
3501h A-C Phase Time Overcurrent 1 Trip
8501h A-C Phase Time Overcurrent 1 Dropout
4212h B Overvoltage 1 Alarm
6514h User Input A Asserted via Contact Input
7009h Clock Not Set