Technical data

Appendix
27.6 Sample Programs
Programming with STEP 7
Manual, 05/2010, A5E02789666-01 637
Describing the Parts of a Process
Part 1 of the manual included a description of how you divide up the sample process into functional
areas and individual tasks. The individual areas are described below.
The area for ingredients A and B:
• The pipes for each of the ingredients are equipped with an inlet and a feed valve and feed
pump.
• The inlet pipes also have flow sensors.
• Turning on the feed pumps must be interlocked when the tank level sensor indicates that the
tank is full.
• The activation of the feed pumps must be interlocked when the drain valve is open.
• The inlet and feed valves must be opened at the earliest 1 second after starting the feed pump.
• The valves must be closed immediately after the feed pumps stop (signal from the flow sensor)
to prevent ingredients leaking from the pump.
• The activation of the feed pumps is combined with a time monitoring function, in other words,
within 7 seconds after the pumps start, the flow sensor must report a flow.
• The feed pumps must be turned off as quickly as possible if the flow sensor no longer signals a
flow while the feed pumps are running.
• The number of times that the feed pumps are started must be counted (maintenance interval).
Mixing tank area
:
• The activation of the agitator motor must be interlocked when the tank level sensor indicates
"level below minimum" or the drain valve is open.
• The agitator motor sends a response signal after reaching the rated speed. If this signal is not
received within 10 seconds after the motor is activated, the motor must be turned off.
• The number of times that the agitator motor starts must be counted (maintenance interval).
• Three sensors must be installed in the mixing tank:
- Tank full: a normally closed contact. When the maximum tank level is reached, the contact
is opened.
- Level in tank above minimum: a normally open contact. If the minimum level is reached,
the contact is closed.
- Tank not empty: a normally open contact. If the tank is not empty, the contact is closed.
Drain area:
• Drainage of the tank is controlled by a solenoid valve.
• The solenoid valve is controlled by the operator, but must be closed again at the latest when
the "tank empty" signal is generated.
• Opening the drain valve is interlocked when
- the agitator motor is running
- the tank is empty