Siemens Simatic S7-400 - Manual (Page 337)

Analog Modules
5-121
S7-400, M7-400 Programmable Controllers Module Specifications
A5E00069467-07
Wire Break Check
The wire break check is intended primarily for temperature measurements (TC,
RTD) or resistance measurements. Always parameterize the wire break check in
these cases as this ensures that in the event of a wire break the measured value
provided by the module accepts the data for overrun 7FFFH.
Special Characteristics of the Wire Break Check for the Voltage Measurement
Methods
In some transmitters, incorrect measured values may occur due to the fact that the
wire break check is enabled. If so, disable the wire break check.
The reason Some transmitters try to correct the test current and in doing so corrupt
the setpoint value they provide.
Points to Note About the Wire Break Check when Current Sensors Are
Connected
A wire break check of current sensors is not possible for the SM 431; AI 16 16
Bit except in life-zero areas. You can therefore only parameterize the wire break
check for the “Current (four-wire transmitter)” measuring method and the “4 to 20
mA” measuring range.
Checking for Reference Channel Errors when Connecting Thermocouples
If you have connected a thermocouple, you can then enable the “Reference
channel error” diagnosis if you have parameterized an “RTD on Channel 0” or
“Reference Temperature Value” reference junction.
Points to Note About Checking for “Underflow” with some Measuring Methods
and Measuring Ranges
There is now underflow in life-zero areas. A value that is too low or is negative is
interpreted as a wire break. You can therefore not parameterize the underflow
check for the SM 431; AI 16
16 Bit for the following measuring methods and
ranges:
Table 5-70 Points to Note when Checking for “Underflow”
Measuring Method Measuring Range
Voltage 1 to 5 V
Current (four-wire transmitter) 4 to 20 mA
Current (two-wire transmitter) 4 to 20 mA
Points to Note About the “Short Circuit to M” Diagnosis
You can only parameterize the check for “Short Circuit to M” for the SM 431; AI
16
16 Bit for the “Current (2-wire transmitter)” measuring method.