Chapter 1. Modbus Communications
8
Communications Options User’s Guide
1.4.1
Notes for a Gas Flowmeter:
1.
Clear Totalizers:
Write 1 to Reg 1 to clear Channel 1 totalizers.
Write 1 to Reg 2 to clear Channel 2 totalizers.
2.
Values in these registers are floating point numbers and require no scaling. The number of decimal digits is set in
meter programming.
3.
Require scaling by value in register 13.
4.
Require scaling by value in register 20.
5.
AVG Error Code:
0=Both Ch1 and Ch2 are in error.
1=Ch1 only is in error
2=Ch2 only is in error
3=Both channels are error free
6.
MODBUS baud rate:
5 = 2400, 6 = 4800, 7 = 9600
7.
MODBUS parity:
0 = none, 1 = odd, 2 = even
8.
MODBUS stop bits:
1 = 1 stop bit, 2 = 2 stop bits
9.
Error Code:
Highest single number, or combination of error numbers, listed without an “E”. Error codes should be explained in
the user’s manual or guide.
IMPORTANT:
If the unit is reading over range, an error condition will occur and output
20mA
(for a 0-20mA range) or
21.10mA (for a 4-20mA range).
112, 113*
CH2 SNR Up
--
4 (IEEE 32 bit Float)
114, 115*
CH2 SNR Down
--
4 (IEEE 32 bit Float)
508
6
MODBUS baud rate
0
2
509
7
MODBUS parity
0
2
510
8
MODBUS stop bits
0
2
511
MODBUS meter addr
0
2
512
RESERVED
---
---
*
The complete floating point value is constructed by combining readings from the first register with
a second register. An eight Hex digits number will represent the IEEE-754 hexadecimal floating point
value. 32-bit Hexadecimal Representation To Decimal Floating-Point conversion can be performed
if needed.
Example: Reg 14 reading is 44d7, Reg 15 reading is 4000, Mass Flow is 44d74000, which corresponds
to 1722.
**The complete Long integer value is constructed by combining readings from the first register with
the second register. Eight Hex digits will represent the Long integer value.
Example: Reg 24 is 0019, Reg 25 is ED30, Hexadecimal Sound Speed is 0019ED30, which is converted
to 1699120 decimal. Taking into account that Sound Speed has 3 decimal places (from the map), it
corresponds to a value of 1699.120.
Table 3: MODBUS Registers for a 2-Channel Gas Flowmeter
MODBUS Reg #
Description
Scaling
(decimal places)
Size in Bytes
