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pH ARC Sensors Modbus RTU Programmer’s Manual (EPHUM011)
624300/01 page 11 / 67
2.4.5 Configuration of the 4-20 mA Interface
Note:
The configuration of AO1 / AO2 is only effective if register 4360 / 4488 (active analog interface mode) is
set to the value 0x01, 0x02 or 0x04.
2.4.5.1 Reading the Available Primary Measurement Channels to be Mapped to the Analog
Output
Start
register
Number of
registers
Reg1 / Reg2 Modbus
function code
Read
access
Write
access
4362 2 Available Primary Measurement Channels
for AO1
3, 4 U/A/S none
4490 2 Available Primary Measurement Channels
for AO2
3, 4 U/A/S none
Figure 2.4.5.1.1: Definition of register 4362 / 4490.
For the definition of the Primary Measurement Channels (PMC), see chapter 2.5.
Code
(Hex)
Primary Measurement Channel (PMC)
0x01 PMC1 (pH)
not available
0x20 PMC6 (temperature)
Figure 2.4.5.1.2: Code for selection of the primary measurement channel.
Command: Available PMC AO1
Modbus address: 4362 Length: 2 Type: 3
Read
Parameter: Available PMC 20 mA
Format: hex
Value:
0x21
Figure 2.4.5.1.3: Example to read the available Primary Measurement Channels (PMC) for AO1. The
hexadecimal value of “0x21”defines that PMC1 (pH) or PMC6 (temperature) can be mapped to
AO1. Register 4490 contains the same value “0x21”. Accordingly, PMC1 or PMC6 can be
mapped to AO2 as well.
2.4.5.2 Selecting the Primary Measurement Channel to be Mapped to the Analog Interface
Start
register
Number of
registers
Reg1 / Reg2 Modbus
function code
Read
access
Write
access
4364 2 Selected PMC for AO1 3, 4, 16 U/A/S S
4492 2 Selected PMC for AO2 3, 4, 16 U/A/S S
Figure 2.4.5.2.1: Definition of register 4364 / 4492. Only one bit can be set.
Command: Active PMC AO1
Modbus address: 4364 Length: 2 Type: 3
Read
Parameter: Current PMC 20mA
Format: hex
Value:
0x01
Figure 2.4.5.2.2: Example to read the current primary measurement channel mapped to AO1, defined
in register 4364. The value “0x01”is returned, saying that PMC1 is mapped to AO1 (factory
setting).
The factory setting for register 4492 is “0x20”, mapping PMC6 to AO2.