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pH ARC Sensors Modbus RTU Programmer’s Manual (EPHUM011)
624300/01 page 20 / 67
2.5.2 Primary Measurement Channel 1 (pH)
2.5.2.1 Description of PMC1
In register 2080, a plain text ASCII description of PMC1 is given.
Start
register
Number of
registers
Reg1 … Reg8
16 ASCII characters
Modbus
function code
Read
access
Write
access
2080 8 Description of PMC1 3, 4 U/A/S none
Figure 2.5.2.1.1: Definition of register 2080.
Command: PMC 1 text
Modbus address: 2080 Length: 8 Type: 3
Read
Parameter: Text
Format: Character
Value:
pH
Figure 2.5.2.1.2: Example to read the description. It is “pH”.
2.5.2.2 Selecting the Physical Unit for PMC1
In register 2088, the available physical units for this channel are defined.
Start
register
Number of
registers
Reg1 / Reg2
(bitwise defined)
Modbus
function code
Read
access
Write
access
2088 2 Available physical units of PMC1 3, 4 U/A/S none
Figure 2.5.2.2.1: Definition of register 2088.
Command: PMC1 available units
Modbus address: 2088 Length: 2 Type: 3
Read
Parameter: Units
Format: Hex
Value:
0x201000
Figure 2.5.2.2.2: Example to read the available physical units of PMC1: pH (0x001000) + mV
(0x200000), total 0x201000.
In register 2090, the active physical unit for this channel can be selected, by choosing one of the
physical units that are defined in register 2088.
Start
register
Number of
registers
Reg1 / Reg2
(bitwise defined)
Modbus
function code
Read
access
Write
access
2090 2 Selected active physical unit for the
PMC1
16 none S
Figure 2.5.2.2.3: Definition of register 2090. Only one bit can be set.
Command: PMC1 set unit
Modbus address: 2090 Length: 2 Type: 16
Write
Parameter: Unit
Format: Hex
Value:
0x1000
Figure 2.5.2.2.4: Example to set the physical unit of PMC1 to pH (0x1000).
Attention:
Changing the physical unit has also an influence on the output of AO1 / AO2, as the same physical unit
is active for the analog outputs. All limits of the 4-20 mA analog output have to be redefined after
changing the physical unit!