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pH ARC Sensors Modbus RTU Programmer’s Manual (EPHUM011)
624300/01 page 5 / 67
2 pH ARC Sensor Commands in Modbus RTU
2.1 General
In order to communicate with a pH ARC Sensor over Modbus RTU protocol a Modbus master terminal
application software is needed. The Modbus RTU is an open standard and a number of free and
commercial application toolkits are available.
This manual contains examples and illustrations from WinTECH Modbus Master ActiveX Control tool:
WinTECH (www.win-tech.com) “Modbus Master OCX for Visual Basic”. The Modbus Organisation
(www.modbus.org/tech.php) provides other links to a wide variety of Modbus terminal softwares.
In the present manual the addressing of the Modbus registers starts at 1. But the Modbus master
protocol operates with register addresses starting at 0. Usually, the Modbus master software translates
the addressing. Thus, the register address of 2090 will be translated by the Modbus master software to
2089 which is sent to the sensor (Modbus slave).
Attention:
When configuring and calibrating the sensor, please limit write operations to a reasonable number.
More than 100’000 write operations will physically damage the memory of the sensor.
Furthermore, for the Free User Memory Space (see chapter 2.9.3), the write operations are limited to
10’000.
2.2 Operator levels and Passwords
2.2.1 Reading / Setting Operator Level
A pH ARC Sensor can be operated in three different operator levels. Each operator level allows a
defined access to a specific set of commands.
Abbreviation Description Code (hex) Password (decimal)
U User (lowest level) 0x03 0
A Administrator 0x0C 18111978
S Specialist 0x30 16021966
Figure 2.2.1.1: Definition of operator level and default passwords
At each power up or processor reset, the operator level falls back to the default level U.
The active operator level can be read and written in register 4288.
Start
register
Number of
registers
Reg1 / Reg2 Reg3 / Reg4 Modbus
function code
Read
access
Write
access
4288 4 Operator Level Password 3, 4, 16 U/A/S U/A/S
Figure 2.2.1.2: Definition of register 4288.
Command: Active operator level
Modbus address: 4288 Length: 4 Type: 3
Read
Parameter: Operator level Password
Format: hex decimal
Value:
0x03 0
Figure 2.2.1.3: Example to read the active operator level (function code 3, start register address 4288,
number of registers 4): The active operator level is 0x03 (User). The sensor does not report the
password. The value 0 is returned instead.