Task 1 - Characteristics of a PLC system
A steel company is planning to automate various parts of its factory. One application is a simple automation of specific machines such as bar cutting with up to 10 I/Os, while the other application relates to a material sorting and handling conveyor syste, that can support 4 cutting disk stations (1 station is shown below).
Considering unitary, and modular PLCs, you have been asked to select a real commercial PLC of each type that would be suitable each application and describe the following:
i. The construction and application for unitary and modular type of PLC selected for the steel company above (2 PLCs)
ii. With the aid of block diagram layouts, provide details of their specific requirements for each application (2 PLC diagrams including any additional modules). Support with a table of their field devices including types (e.g proximity sensor, motor), analogue/digital voltage/current required.
iii. An appropriate real network configuration diagram that connects the 4 cutting disk PLCs together to the conveyor. Also draw the field devices for at least 1 cutting disk PLC and the conveyor PLC and describe the communication links used.
Guidance: The exact machines are not specified, so you are free to pick a relevant machine e.g. a sheet metal bender, a steel pipe cutter, spot welder, etc The conveyor or material handler could be feeding the machine or taking steel parts away hence the idea of networked PLCs and automation. 1a(i) 2 PLC types and construction must be different (i.e. unitary and modular) 1a(ii) ‘block’ diagram should show the physical layout and not the software. 1a(iii) should include an appropriate commercial network example suitable for the selected PLCs.
Checklist of evidence required:
T1a – 1000 word written report with appropriate diagrams, commercial examples and references.
Task 2 - PLC information, programming and communication techniques
2a (i) Design and write a program to implement the process illustrated in Figure 2a(i). An up-counter must be programmed as part of a batch-counting operation to sort parts automatically for quality control. The counter is installed to divert 1 part out of every 8 for quality control or inspection purposes.
The circuit operates as follows:
• When the Start ‘push to make’ (not toggle) switch (I1) is pressed/released, and gets latched on (B1: RS latch), the main conveyor line (Q1) will be energised, and parts will start to pass the proximity switch (B2) every 2 s
• The pulses generated by the proximity switch (B2: pulse generator) should be used to increment the quality check counter (B3). When the B3 = 4, the conveyor gate solenoid (Q2) will then activate for 1.5 s and the quality line conveyor (Q3) will run for 4 s to take a sample object
• The gate Q2 returns to its normal position when the 1.5 s time period ends, and the counter also resets back from 4 to 0. The main line Q1 does not stop (unless the stop is pressed)
• The process is repeated with a sample taken at every 4 object counts
• A reset ‘push to make’ (not toggle) switch (I2) is provided to reset the counter manually but not to stop the process.
• A stop ‘push to make’ (not toggle) switch (I3) is provided to stop the process at any time.
• The process should automatically reset and repeat until the stop switch is pressed
The design should include a flowchart of the process, and program written in LOGO using LLD or FBD
2a (ii) With the aid of diagrams and examples, such as a conveyor system, explain the communication connections for Device-net and Profibus. Also explain how a distributive control differs from the supervisory control of a SCADA system?
Checklist summary of evidence required:
• a commentary/label list of inputs, functions and outputs
• flow chart against the task’s circuit operation above and
• print-screens/image snips of key stages, showing the program operating correctly in the PLC simulator
• a separate copy of the LOGO program (do not embed)
T2a(ii) - 600 word written report with appropriate diagrams and examples