Display Of Analog Values - Siemens Simatic SM331 Getting Started

7.3

Display of analog values

The CPU can only process analog values in binary format. Analog input
modules convert the analog process signal into a digital format (16 bit
word).
Five ranges have to be taken into account when converting from digital to
analog values:
Table 7-3
Hex value Current range
7FFF 22,96 mA
7F00
7EFF 22,81 mA
6C01
6C00 20 mA
5100 15 mA
1 4 mA + 578,7 nA
0 4 mA
FFFF
ED00 1,1185 mA
ECFF
8000
It is necessary to convert the binary format of the values in order to display
analog process values. In our example mA are displayed. This is done by
converting the display of analog values in mA in a programmed function
(FC1).
In our example we look at the values from the output of the transducer.
With the aid of a current meter you can now compare the values on the me-
ter with the values of the analog values display. The values will be identical.
Display of analog value in the current range 4 to 20 mA
Comment
Overflow
Oversteering
range
Nominal range
Understeering
range
Underflow
45 Getting Started SM331 AI 8x12bit Part1: 4-20mA
Meaning
From hex value 16#F700 on, the sensor
value is above the configured measure-
ment value range and is no more valid.
This range corresponds to a tolerance
band before the overflow range is reached.
Within this range the resolution is not opti-
mal though.
The nominal range is the normal range for
recording measurement values. This range
guarantees optimal resolution.
Range according to the oversteering range
but for low values.
From hex value 16#ECFF on, the sensor
signal is below the configured measure-
ment value range and is no more valid.
A5E00253410