Panametrics Sentinel, Руководство пользователя, Страница: 118 / 166

Chapter 7. Specifications
118 Sentinel™ User’s Manual
7.2 Electronics Specifications (cont.)
Modbus Map
The IGM878 Flow Transmitter, 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>
The format for the returned data types is as follows:
Table 13 on page 109 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).
Integer Integer (I) 1 Register
Floating Point Single Precision (FP) 2 Registers
Double Precision Double Precision (DP) 4 Registers