Siemens CP 1243-1 Operating Instructions Manual page 108

Configuration
4.10 Data points
Set limit value 'low' / Set limit value 'high'
Requirements for the function
● Configuration of the threshold trigger for this data point
● PLC tag in the bit memory operand area or data area
The analog value data point must be linked to a PLC tag in the bit memory or data area
(data block). For PLC tags of hardware modules (input operand area) limit value
configuration is not possible.
The configuration of limit values is pointless for measured values that have already been
preprocessed on the CPU.
Function
In these two input boxes, you can set a limit value in the direction of the start of the
measuring range or in the direction of the end of the measuring range. You can also
evaluate the limit values, for example as the start or end of the measuring range.
Status identifier "OVER_RANGE" / "overflow"
With protocols that support status identifiers, if the limit value is overshot or undershot, the
status identifier of the data point is set for measured range violation known below as the
identifier "OV". This status identifiers are described in the section Status IDs of the data
points (Page 95).
The "OV" bit of the status identifier of the data point is set as follows when the relevant
analog value is transferred:
● Limit value 'high':
– If the limit value is exceeded: OV = 1
– If the value then falls below the limit value: OV = 0
● Limit value 'low':
– If the value falls below the limit value: OV = 1
– If the value then exceeds the limit value: OV = 0
Configuration of the limit value
The limit value is configured as a whole decimal number. The range of values is based on
the range of values of the raw value of analog input modules.
Entry as a decimal number according to the range of values of the assigned PLC tag from
the bit memory or data area.
The entry of the value 0 (zero) is interpreted as a deactivated limit value.
108
Operating Instructions, 04/2017, C79000-G8976-C365-03
CP 1243-1