S7-200 Specifications
A-81
S7-200 Programmable Controller System Manual
A5E00066097-02
Sense +
Sense -
Source +
Source -
RTD
RTD 4 Wire
(most accurate)
Sense +
Sense -
Source +
Source -
RTD
R
L1
R
L2
If R
L1=
R
L2
, error is minimal.
RTD 3 Wire
R
L1
+R
L2
=Error
Sense +
Sense -
Source +
Source -
RTD
R
L1
R
L2
Set switch to 4-wire mode.
RTD 2 Wire
A+*
A–
a+
a–
A+*
A–
a+
a–
A+*
A–
a+
a–
*A refers to sense; a refers to source.
*A refers to sense; a refers to source.
*A refers to sense; a refers to source.
Figure A-39 Wiring the RTD to the Sensor by 4, 3 and 2 Wire
EM 231 RTD Status Indicators
The RTD module provides the PLC with data words that indicate temperatures or
error conditions. Status bits indicate range error and user supply/module failure.
LEDs indicate the status of the module. Your program should have logic to detect
error conditions and respond appropriately for the application. Table A-34 shows
the status indicators provided by the EM 231 RTD module.
Note
The channel data format is 2’s complement, 16-bit words. Temperature is
presented in 0.1 degree units. (For example, if the measured temperature is
100.2 degrees, the reported data is 1002.) Resistance data are scaled to 27648.
For example, 75% of full scale resistance is reported as 20736 (=225Ω /300Ω *
27648).
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