pH ARC SensorsModbus RTU Programmer’s Manual (EPHUM011)
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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 softwareis needed. The Modbus RTU is an open standard and a number of free and
commercial applicationtoolkits are available.
This manual contains examplesand illustrations from WinTECH Modbus Master ActiveX Control tool:
WinTECH (www.win-tech.com)“ModbusMaster 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 presentmanual the addressing of the Modbus registers starts at 1. But the Modbus master
protocol operateswith register addressesstarting at 0. Usually, the Modbus master software translates
the addressing.Thus, the register address of 2090 will be translated by the Modbus master softwareto
2089 whichis sent to the sensor (Modbus slave).
Attention:
When configuringand calibrating the sensor, please limit write operations to a reasonablenum ber.
More than 100’000write operations will physically damagethe memory of the sensor.
Furthermore,f orthe Free User Memory Space (see chapter 2.9.3), the write operations arel imited to
10’000.

2.2 Operator levels and Passwords

2.2.1 Reading / Setting Operator Level

A pH ARC Sensorcan be operated in three different operator levels. Each operator level allowsa
defined accessto a specific set of commands.
Abbreviation Description Code (hex) Password(decimal)
U User(l owestlevel) 0x03 0
A Administrator 0x0C 18111978
S Specialist 0x30 16021966
Figure 2.2.1.1: Definitionof operator level and default passwords
At each powerup or processor reset, the operator level falls back to the default level U.
The active operatorlevel 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 OperatorLevel Password 3, 4, 16 U/A/S U/A/S
Figure 2.2.1.2: Definition of register 4288.
Command: Active operatorl evel Modbusaddress: 4288 Length: 4Type: 3Read
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 address4288,
number of registers4): The active operator level is 0x03 (User). The sensor does not report the
password.The v alue 0 is returned instead.