Siemens SIMATIC S7-200 - Wiring Scheme; Wiring the EM 231 RTD Module

S7-200 Specifications
A-79
S7-200 Programmable Controller System Manual
A5E00066097-02
Selecting sensor burnout direction Use DIP switch 6 to set the sensor burnout
direction as shown in Table A-31.
Table A-31 Selecting Sensor Burnout Direction
Burnout Direction
SW6
Upscale (+3276.7 degrees) 0
Downscale (-3276.8 degrees) 1
Selecting the temperature scale The RTD module can report temperatures in
Celsius or Fahrenheit. The Celsius to Fahrenheit conversion is performed inside
the module. Use switch 7 to select the temperature scale as shown in Table A-32.
Table A-32 Selecting Temperature Scale
Scale
SW7
Celsius (

C) 0
Fahrenheit (

F) 1
Selecting the wiring scheme Use switch 8 to select the wiring scheme as shown
in Table A-33.
Table A-33 Wiring Scheme
Wiring Scheme
SW8
3 wire 0
2 wire or 4 wire 1
Wiring the EM 231 RTD Module
You can wire the EM 231 RTD module directly to the S7-200 module, or you can
use extension wires. Use shielded wires for best noise immunity. If you use
shielded wires, connect the shield to the grounds on pins 1 to 4 of the signal
connector. This ground is the same ground as is present on the power connector
pins 3 to 7. If you do not use an RTD input channel, you should wire a resistor to
the unused channel inputs to prevent errors from floating inputs from blocking error
indications from valid channels.
Connect user power to the power connector pins 1 and 2. You must connect pin 3
to a nearby chassis ground (Figure A-38).
You can wire the RTD module to the sensor in three ways (shown in Figure A-39).
The most accurate is 4 wire (see Figure A-39). The least accurate is 2 wire, which
is only recommended if errors due to wiring can be ignored in your application.