Table of Contents
Advertisement
Commissioning
7.5.9
Output 0 ... 20 mA - scalable data format
– Value range 0 ... 20 mA
– Data format scalable from -32768 ... 0 ... 32767
– Scaling above the lower and upper critical limit
– Use of the critical limits for diagnostics
– Current value output in case of overflow (> 22 mA): 22 mA
– Current value output in case of underflow (< 0 mA): 0 mA
– Conversion of the digital output value to the analogue setpoint value (current value output)
Current value = 20 x (digital output value - lower critical limit) / (upper critical limit - lower critical
limit)
Digital output value
> 32767
-32768 ... 0 ... 32767
< -32768
Tab. 42: Range of values for scalable data format (output 0 ... 20 mA)
7.6
Scaling the range of values
For the scalable data format, the range of values can be scaled by setting the critical limits. To process
the diagnostics correctly, the distance between both critical limits should amount to at least 100
1. Set the "linear scaling" data format è Tab. 18 Description of the "Data format, monitoring
according to NAMUR NE43" module parameter.
2. Set the critical limits for each channel è Tab. 20 Description of "Lower critical limit of channel 0 ...
3", è Tab. 21 Description of "Upper critical limit of channel 0 ... 3".
The critical limits represent the scaling end values:
– When the upper critical limit is positive, set the upper critical limit before setting the lower
critical limit.
– If the upper critical limit is negative, set the lower critical limit before setting the upper critical
limit.
Example: scaling appropriate for a pressure sensor
The sensor linearly converts the measuring range 0 ... 6 bar to analogue current values 0 ... 20 mA um.
Actual value (examples)
0 mA
10 mA
20 mA
22 mA
Tab. 43: Example of scaling and limit monitoring for a pressure sensor
44
Current value output
22 mA
0 ... 20 mA
0 mA
Digital input value
0
3000
6000
6600
Meaning
Overflow
Nominal range, freely scalable
Underflow
Meaning
Lower critical limit
Value in nominal range
Upper critical limit
Critical limit exceeded
Festo — CPX-4AE-4AA-H — 2021-06b
.
dec
Advertisement
Table of Contents
