Technical data

Working Out the Automation Concept
3.3 Describing the Individual Functional Areas
Programming with STEP 7
62 Manual, 05/2010, A5E02789666-01
3.3 Describing the Individual Functional Areas
As you describe each area and task within your process, you define not only the operation of each
area, but also the various elements that control the area. These include:
• Electrical, mechanical, and logical inputs and outputs for each task
• Interlocks and dependencies between the individual tasks
The sample industrial blending process uses pumps, motors, and valves. These must be described
precisely to identify the operating characteristics and type of interlocks required during operation.
The following tables provide examples of the description of the equipment used in an industrial
blending process. When you have completed description, you could also use it to order the
required equipment.
Ingredients A/B: Feed Pump Motors
The feed pump motors convey ingredients A and B to the mixing tank.
• Flow rate: 400 l (100 gallons) per minute
• Rating: 100 kW (134 hp) at 1200 rpm
The pumps are controlled (start/stop) from an operator station located near the mixing tank. The number of
starts is counted for maintenance purposes. Both the counters and the display can be reset with one button.
The following conditions must be satisfied for the pumps to operate:
• The mixing tank is not full.
• The drain valve of the mixing tank is closed.
• The emergency off is not activated.
The pumps are switched off if the following condition is satisfied:
• The flow sensor signals no flow 7 seconds after the pump motor is started.
• The flow sensor signals that the flow has ceased.
Ingredients A/B: Inlet and Feed Valves
The inlet and feed valves for ingredients A and B allow or prevent the flow of the ingredients into the mixing
tank. The valves have a solenoid with a spring return.
• When the solenoid is activated, the valve is opened.
• When the solenoid is deactivated, the valve is closed.
The inlet and feed valves are controlled by the user program.
For the valves to be activated, the following condition must be satisfied:
• The feed pump motor has been running for at least 1 second.
The pumps are switched off if the following condition is satisfied:
• The flow sensor signals no flow.