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The construction and application for unitary and modular type of PLC selected for the steel company above (2 PLCs)

Part 1a) - 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 system, 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 aeach 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 4 cutting disk station PLCs together to an overall 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 conveyor or material handler PLC will be feeding the machine by sensing a stock of bars, drop them onto the bar cutter, and after cutting, weigh and move full boxes away and replace with empty boxes. The bar cutter starts when it senses a new bar on it bed, then will push and clamp the bar at a pre-set length, cut and push the bar into the box, and repeat a pre-set number of times. 1a(i) 2 PLC types and construction must be different (i.e. unitary – for cutting operations and modular- for moving handling pipes and communication with the 4 unitary PLCs) 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. 1000-word written report with appropriate diagrams, commercial examples and cited references.

See https://new.siemens.com/global/en/products/automation/systems/industrial/plc/logo.html

Part 1b

I. List the 4 different programming languages identified in IEC 61131-3 and write a short description of the advantages and disadvantages of each. Your answer should include a sample image example of each to highlight how they are presented to the user/programmer.

II. Function Block or Ladder Logic Diagrams were used in Task 2a below. Justify your choice of programming method for this application and use LOGO to display an image of the program in both formats, to aid your discussion.

III. Analyse the internal architecture of a commercial modular PLC (e.g. Siemens S7-1200), to determine its suitability for operational applications such as your example in task T1a(ii). Include analysis on PSU, memory, CPU, bus system, processing instructions, and I/O module types.

 

Guidance 1200 words written report with appropriate diagrams, commercial examples and cited references.

Part 2a - PLC programming and communication techniques

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 

Fig 2a(i) 

Guidance 2a(i):

• 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)

ii. With the aid of diagrams and examples, such as a conveyor system explain:

• the communication connections for Device-net and Profibus.
• how a distributive control differs from the supervisory control of a SCADA system?

Guidance 2a(ii): 600 word written report with appropriate diagrams, examples and cited references

Part 2b

i. Examine the methods, and programmed design elements, that have to be considered in the debugging and testing prior to hardware use. 

ii. Discuss the general steps should be followed when commissioning a PLC system.

Guidance T2b(i-ii) – 600 word written report with appropriate cited references, diagrams and examples

iii. Consider a chemical mixing application in a paint factory. Use LOGO to design and build the above system, using function block or ladder logic, which will control the operation as follows:

• When the ‘push to make’ Start (not toggle) switch (I1) is pressed/released, and gets latched on (B1: RS latch), the start ‘fill’ solenoid A (Q1) will be energised and the tank will start to fill.
• A flow meter 1 (B2: 1s pulse generator) can be used to increment the counter (B3: Up/down).
• Tank level full sensor switch indicator (Q2) can be activated when the counter function on = 8 (e.g. use on/off flag: M1) causing the fill solenoid A (Q1) to be shut-off
• When the tank is full, start the mixer motor (Q3) and run for 12 seconds (B4: off-delay timer).
• When the 12 seconds has expired, stop the mixer (Q3) and energise ‘empty’ solenoid B (Q4) until the tank is empty
• To monitor the tank emptying, pulses generated by a flow meter 2 (B5: 1s pulse generator) should be used to decrement the counter (B3: Up/down). 
• Tank empty can be detected using the empty sensor switch indicator (Q4) when the tank low level counter B3 function off = 1. (e.g. use on/off flag: M1)
• When the ‘push to make’ Stop button (I2) is operated, the process must stop immediately (Q5), but can continue from where it left off, when restarted (I1).
• The process should automatically reset and repeat until the stop switch is pressed

Test your LOGO build and comment on your testing using LOGO simulation mode. This requires at least 3 print-screens of testing the system using the LOGO simulator below at the filling, mixing and emptying stages.

Guidance T2b(iii) -print-screens/image snips of 3 key stages, showing with comments, the program operating correctly in the PLC simulator. A copy of the LOGO program