Reference Manual
00809-0100-4738, Rev DA
May 2006
Rosemount 3095FB
C-2
NOTE
Function code 04 (read input registers) is the most common command to read
the DP, SP, and T process variables measured by the 3095FB.
PROCESS VARIABLE
REGISTERS
Floating Point Numbers
The 3 process variables (DP, SP, and T) are saved as 32-bit floating point
numbers in three different address locations. In two of the locations, the
32-bit floating point number is saved in two 16-bit registers. In the third
location, the number is saved in one 32-bit register.
NOTE
Depending on whether the Modbus host is referenced to a 1 or 0, you may
need to add or subtract a 1 from the registers listed below (ex. 0400 instead of
0401) for successful data acquisition between the host and transmitter.
Scaled Variables
The 3 process variables can also be read as scaled 16-bit registers in 5
different locations. For example, 0 – 100 in.H20 could correspond to 0 –
65534 (65534 is the maximum value for a 16-bit number).
OTHER
CONSIDERATIONS
For the successful integration of 3095FB transmitters with various
installations, it may also be necessary to consider some of the following:
•
Make sure the RS-485 network is terminated only twice on the entire
bus (once on each end). Termination at multiple points on the bus will
hamper communication.
•
It may be necessary to alter the way the 3095FB transmits floating
point numbers so that Modbus host interprets the data correctly (see
page 23 of the
Modbus Protocol Guide
in chapter 3 of this manual).
•
If there is noise on the RS-485 bus, try turning on the pull-up and
pull-down jumpers (see page 2-12) on only one transmitter.
Process Variable
Register Locations
16-bit
32-bit
Differential Pressure
0401, 0402
20401, 20402
7401
Static Pressure
0403, 0404
20403, 20404
7402
Temperature
0404, 0405
20404, 20405
7403
Process Variable
16-bit Register Locations
Differential Pressure
0116
3116
30116
40116
50116
Static Pressure
0117
3117
30117
40117
50117
Temperature
0118
3118
30118
40118
50118
