Chapter 1. Modbus Communications
16
Communications Options User’s Guide
1.4.3
Notes for a Sentinel Flowmeter
The
Sentinel Flowmeter
, when equipped with the optional Modbus output card, can transmit flow data and diagnostic
information to a flow computer or SCADA, serially, using a Gould-type RTU protocol. For security and audit-trail
purposes, the unit must be programmed through the PanaView interface. This means that only the Modbus function
command
3
(read multiple registers), is valid.
Communication parameters: 9600, n, 8, 1
The format for the data exchange is as follows:
•
The
send
command (initiated by host flow computer or controller) is of the form:
<time delimiter> <Addr> <3> <First Register MSB>
<First Register LSB> <Register Count MSB>
<Register Count LSB> <CRC Low> <CRC High> <time delimiter>
•
The
response
(initiated by host flow computer or controller) is of the form:
[time delimiter] <Addr> <3> <Byte count> < Data ……… >
<CRC Low> <CRC High> <time delimiter>
Table 6 on page 14 is the data map for the
IGM878
and
Sentinel
. The refresh rate indicates how often the central
controller updates the memory map, available using the ModBus port. The most time-critical information is stored at
the top of the register. This limits how deep the user has to go into the resister stack to gather the real-time
information. All values are IEEE format MSB first (big-endian).
Note:
Regarding meter status, each bit field indicates the error number from LSB corresponding to E1, and from MSB
corresponding to E32.
Note:
Writing any non-zero value will clear the totals (unless they are locked using TOT LOCK/KEY LOCK switches on
the front panel - per MID requirements).
Note:
Writing to COMP will clear all channels.
Note:
Modbus Registers for the
Sentinel LCT
or
Sentinel LNG
Flowmeter
, Table 7 on page 17, has some fields with a grey
background. These are currently not supported and will return a value of –1.0.
