Hach 911, User Manual

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SCADA-Modbus® System Guidelines
The memory data is stored in 16-bit words. Within the predefined function codes of the
Modbus ASCII protocol, the data fields are subject to interpretation by the device
manufacturer. For example, the 940 Flow Meter places temperature information in
registers 40001-40002.
D.9 Modbus ASCII Function Codes Supported
Currently, the 940 Flow Meter is capable of a read-only function to retrieve channel and
total flow information. All data addresses in the Modbus ASCII message are referenced to
zero. Therefore, a reference to holding register 40001 is addressed as register 0000. The
function code field specifies the type of register accessed; therefore, the 4XXXX is implicit.
Function 03: Read Holding Registers
Reads the register (4X reference) contents of the 940 Flow Meter as defined in the tables
that follow.
Table 13 Modbus ASCII Memory Input/Output Referencing System
Reference Indicator Reference Type Meaning
0xxxx Discrete Output or Coil Binary
1xxxx Discrete Input Binary
3xxxx Input Register Real
4xxxx Output Holding Register Real
6xxxx Extended Memory Register Real
Table 14 Channels’ Read Holding Register Addresses
Name Type Size (bits) # of Registers
Start Address
Hi
Start Address
Lo
Registers
Temperature Float 32 2 00 00 40001-40002
Rainfall Float 32 2 00 02 40003-40004
pH (or ORP) Float 32 2 00 04 40005-40006
Level 1 Float 32 2 00 06 40007-40008
Velocity 1 Float 32 2 00 08 40009-40010
Channel 1 Float 32 2 00 0A 40011-40012
Channel 2 Float 32 2 00 0C 40013-40014
Channel 3 Float 32 2 00 0E 40015-40016
Channel 4 (D.O.) Float 32 2 00 10 40017-40018
Channel 5 (D.O. Temp.) Float 32 2 00 12 40019-40020
Channel 6 (Conductivity) Float 32 2 00 14 40021-40022
Channel 7 (Cond. Temp.) Float 32 2 00 16 40023-40024
Level 2 Float 32 2 00 18 40025-40026
Velocity 2 Float 32 2 00 1A 40027-40028
Flow 1 Float 32 2 00 20 40033-40034
Power Float 32 2 00 26 40039-40040