Siemens SIMATIC S7-200 System Manual page 442

S7-200 Programmable Controller System Manual
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-28 shows the EM 231 Thermocouple status indicators.
Table A-28 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).
If the PLC has read the data:
All 4 channels in the EM 231 Analog Input Thermocouple 4 Inputs are updated every 405
-
milliseconds.
All channels in the EM 231 Analog Input Thermocouple 8 Inputs are updated every 810
-
milliseconds.
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.
428
SF LED 24 V LED
Channel Data
Red
Conversion data OFF
32766 OFF
--32768/32767 BLINK
--32768/32767 BLINK
0000 ON
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