Emerson Process Management 3420 ユーザーズマニュアル
Reference, Installation, and Operations Manual
Section 6: Meter operation
3-9000-743 Rev S
June 2013
Data polling
229
6.5.4
Data polling
The meter periodically polls the GC looking for data updates. If the meter is communicating
normally with the GC, then it polls the GC every one minute looking for an update (i.e., a change
in the GC analysis time). Otherwise, the meter polls the GC every 15 seconds.
normally with the GC, then it polls the GC every one minute looking for an update (i.e., a change
in the GC analysis time). Otherwise, the meter polls the GC every 15 seconds.
When the meter determines that a GC update is available for the specified stream number, it
then reads the GC data using multiple reads one second apart until all the data is read. The GC
analysis time is read again at the end of the data collection to determine if another update
occurred during the data collection (i.e., the data is not all from the same update). If so, the
meter discards the gas property data just read and begins looking immediately for the next
update.
then reads the GC data using multiple reads one second apart until all the data is read. The GC
analysis time is read again at the end of the data collection to determine if another update
occurred during the data collection (i.e., the data is not all from the same update). If so, the
meter discards the gas property data just read and begins looking immediately for the next
update.
If the meter cannot successfully communicate with the GC after four consecutive polls
(15 seconds apart), then the meter indicates the communication alarm via the
(15 seconds apart), then the meter indicates the communication alarm via the
IsGCComErr
data point with the
GCCommStatus data point indicating an error code (listed in
below).
Table 6-16 GC Communication status list
GCComm status value
Error description
0
No error.
1
Desired stream not found.
2
GC controller is busy (error defined by Modbus protocol).
3
GC detected an illegal Modbus function code from the meter.
4
GC detected an illegal Modbus data address from the meter.
5
GC detected an illegal data value from the meter.
6
Failure in associated device (Modbus defined error).
7
GC has accepted the meter’s request but is still processing.
8
A firmware logic error was detected.
9
Modbus address mismatch.
10
Modbus function code mismatch.
11
GC reports an exception code that is unrecognized.
12
The meter’s Modus request message is too long (exceeds the maximum allowable
length).
length).
13
The GC’s Modbus response message is too long (exceeds the maximum allowable
length).
length).
14
GC response message has incorrect number of registers.
15
GC does not support the requested message data type.
16
GC does not support the requested data protocol.
17
GC response not received within the communication timeout.
18
GC response message (ASCII protocol) incomplete.