Siemens SIMATIC S5-115U, User Manual

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Analog Value Processing S5-115U Manual
10.10 Example of Analog Value Processing
Problem Definition:
A closed container contains a liquid. It should be possible to read the current liquid level on an
indicating instrument whenever required. A flag is to be set when the liquid level reaches a
specified limiting value.
• A 0 - 20 mA transducer transmits the liquid level signal (between 0 and 10 m) to a 6ES5
460-7LA12 (460 AI) analog input module.
• The analog input module converts the analog current values into digital units (0 - 2048 units),
which can be postprocessed by the S5-115U's application program.
• The application program compares the values with a limiting value (max. permissible liquid
level), sets a flag if necessary, and sends these values to a 6ES5 470-7LB12 (AO 470) analog
output module.
• The analog output module reconverts the values into voltages (0 - 10 V). In response to these
voltages, the needle on the analog display swings proportionally to the liquid level.
Figure 10-31 shows the system configuration.
Figure 10-31. Example of Analog Value Processing
Liquid
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a a a a a a a a a a a a a a a a a a a a
Inlet
Discharge
460 analog input
module
Applica-
tion
program
470 analog output
module
Analog
display
CPU
a a a a
a a a a
a a a a
a a a a
Differential
pressure
transducer
p
1
p
2
p
1
: Pressure of the filled container
p
2
: Pressure generated by the current liquid level
10-64
EWA 4NEB 811 6130-02b