History Mechanism
General Description
Modbus history registers are only available in MasterPacT NT/NW, ComPacT NS, PowerPacT P- and R-frame, ComPacT NSX, and PowerPacT H-, J-, and L-frame circuit breakers.
Modbus history registers enable the user to track the occurrence of specific events and their corresponding dates.
Several types of history are available:
-
Alarm history
-
Trip history
-
Maintenance operation history
-
Event history
See the description of each control unit, trip unit or ULP module for details of available history registers.
History Mechanism
Each event is time-stamped.
When the history is full, the oldest event record is discarded to make room for the most recent event record, which is pushed to the top of the history.
The records are ordered in decreasing occurrence time, the most recent occurrence is in the first record.
The following tables describe the history mechanism for a 10-record history format:
Before event E
|
Record |
1 |
2 |
3 |
4 |
5 |
6 |
7 |
8 |
9 |
10 |
|
Event |
E-1 (most recent event) |
E-2 |
E-3 |
E-4 |
E-5 |
E-6 |
E-7 |
E-8 |
E-9 |
E-10 (oldest event) |
After event E
|
Record |
1 |
2 |
3 |
4 |
5 |
6 |
7 |
8 |
9 |
10 |
|
Event |
E (most recent event) |
E-1 |
E-2 |
E-3 |
E-4 |
E-5 |
E-6 |
E-7 |
E-8 |
E-9 (oldest event) |
After event E, event E-10 is lost.
History Reading
A read request is necessary to read a history record (see Modbus function read n input words, function code = 4, in Read Functions). The number of read requests varies according to the register format and required information. For example, for MicroLogic 5/6/7 trip units, a read request of 5 registers is necessary to read the most recent alarm record of the alarm history format (see Alarm History).
Furthermore, to read the last n records of a history format, a read request of (m) x (n) registers is necessary, where m is the number of registers that compose the record.
For example, for MicroLogic 5/6/7 trip units, a read request of 7 x 3 = 21 registers is necessary to read the most recent 3 trip records of the trip history format (see Trip History).
When not used, history registers return 32768 (0x8000).
See each history register description for details of how to read it.