Choose "Resistor (2-wire terminal)" and "PTC" in STEP 7.
2. Connect the PTC using 2-wire connection technology.
If you enable the "Underflow" diagnostics in STEP 7, it will be signaled for resistance values
<18 Ω. In this case, this diagnostic signifies "Short-circuit in the wiring".
The figure below shows the address space assignment for AI 4xU/I/RTD/TC ST with PTC
resistorsIf faults occur (for example supply voltage L+ missing) that make it impossible to acquire
measured values with PTC resistors, the corresponding channels (IB x/IB x+1) report
overflow (7FFFH). If the value status (QI) is enabled, the value 0 = fault is output in the
corresponding bit.
4.2 Parameters
AI 4xU/I/RTD/TC ST parameters
When you assign the module parameters in STEP 7, you use various parameters to specify
the module properties. The following table lists the configurable parameters. The effective
range of the configurable parameters depends on the type of configuration. The following
configurations are possible:
● Central operation with a CPU
● Distributed operation on PROFINET IO in an ET 200MP system
● Distributed operation on PROFIBUS DP in an ET 200MP system
When assigning parameters in the user program, use the WRREC instruction to transfer the
parameters to the module by means of data records; refer to the section Parameter
assignment and structure of the parameter data records (Page 50).
The following parameter settings are possible:limit 1
Yes/No No Yes Channel --- 4)
• Hardware interrupt high
limit 1
Yes/No No Yes Channel --- 4)
• Hardware interrupt low
limit 2
Yes/No No Yes Channel --- 4)
• Hardware interrupt high
limit 2
Yes/No No Yes Channel --- 4)
1) If you enable diagnostics for multiple channels, you will receive an alarm surge on failure of the supply voltage because
each enabled channel will detect this fault. You can prevent this alarm surge by assigning the diagnostics function to
one channel only.
2) When "Wire break" diagnostics is disabled, the current limit of 1.185 mA is applied to the value status. For measured
values below 1.185 mA, the value status is always: 0 = fault.
3) You can set the effective range of the diagnostics for each channel in the user program with data records 0 to 3.
4) You can set the current limit for wire break diagnostics, the setting "Fixed reference temperature" as well as the limits for
hardware interrupts in the user program with data records 0 to 3.Enabling of the diagnostics, with missing or too little supply voltage L+.
Overflow

Enabling of the diagnostics if the measured value violates the high limit.
Underflow
Enabling of the diagnostics when the measured value falls below the underrange or for
voltage measurement ranges of ± 50 mV to ± 2.5 V if the inputs are not connected.
Common mode error
Enabling of diagnostics if the valid common mode voltage is exceeded.
Enable the Common mode error diagnostics when 2WMT is connected, for example, to
check for a short circuit to groundANA or a wire break. If you do not need the Common mode
error diagnostics, disable the parameter.
Reference junction
Enabling of the diagnostics reference junction when the TC channel has no reference
temperature or incorrect reference temperature.
Wire break
Enabling of the diagnostics if the module has no current flow or the current is too weak for
the measurement at the corresponding configured input or the applied voltage is too low.
Current limit for wire break diagnostics
Threshold for reporting wire breaks. The value can be set to 1.185 mA or 3.6 mA, depending
on the sensor used.
Temperature coefficient
The temperature coefficient depends on the chemical composition of the material. In Europe,
only one value is used per sensor type (default value).
The temperature coefficient (α value) indicates by how much the resistance of a specific
material changes relatively if the temperature increases by 1 °C.
The further values facilitate a sensor-specific setting of the temperature coefficient and
enhance accuracy.At analog input modules, this suppresses interference caused by the frequency of AC mains.
The frequency of AC network may corrupt measurements, particularly in the low voltage
ranges, and when thermocouples are being used. For this parameter, the user defines the
mains frequency prevailing on his system.
Smoothing
The individual measured values are smoothed using filtering. The smoothing can be set in 4
levels.
Smoothing time = number of module cycles (k) x cycle time of the module.
The following figure shows the number of module cycles after which the smoothed analog
value is almost 100%, depending on the set smoothing. It is valid for each signal change at
the analog inputhe following settings can be configured for the reference junction parameter:
Table 4- 3 Possible parameter assignments for the reference junction parameter TC
Setting Description
Fixed reference temperature The reference junction temperature is configured and stored in the module as
a fixed value.
Dynamic reference temperature The reference junction temperature is transferred in the user program from the