Siemens Simatic S7-200 System Manual page 377

Tip
H The open wire current source could interfere with signals from some low level sources such as
thermocouple simulators.
H Input voltages exceeding approximately ±200mV will trigger open wire detection even when the
open wire current source is disabled.
Tip
H Module error could exceed specifications while the ambient temperature is changing.
H Exceeding the module ambient temperature range specification could cause the module cold
junction to be in error.
Using the Thermocouple: Status Indicators
The EM 231 Thermocouple 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-26 shows the EM 231 Thermocouple status indicators.
Table A-26 EM 231Thermocouple Status Indicators
Error Condition
No errors
24 V missing
Open wire and current source enabled
Out of range input
3
Diagnostic error
1
Range status bit is bit 3 in module error register byte (SMB9 for Module 1, SMB11 for Module 2, etc.)
2
User Power Bad status bit is bit 2 in module error register byte (SMB 9, SMB 11, etc., refer to Appendix D)
3
Diagnostic errors cause a module configuration error. The User Power Bad status bit may or may not be set before the module configuration error.
Tip
The channel data format is two'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. Voltage
data are scaled to 27648. For example, –60.0mV is reported as –20736 (=–60mV/80mV * 27648).
All four channels are updated every 405 milliseconds if the PLC has read the data. If the PLC does not
read the data within one update time, the module reports old data until the next module update after the
PLC read. To keep channel data current, it is recommended that the PLC program read data at least as
often as the module update rate.
Tip
When you are using the EM 231 Thermocouple module, you should disable analog filtering in the PLC.
Analog filtering can prevent error conditions from being detected in a timely manner.
SF LED 24 V LED
Channel Data
Red
Conversion data OFF
32766 OFF
–32768/32767 BLINK
–32768/32767 BLINK
0000 ON
Technical Specifications Appendix A
1
Range Status Bit
Green
ON 0
OFF 0
ON 1
ON 1
OFF 0
24 VDC User
2
Power Bad
0
1
0
0
3
note
A
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