1. What is a programmable logic controller (PLC)?

- Most widely used industrial process control technology.
- Is an industrial grade computer that is capable of being programmed to perform control functions.
- Is designed for multiple input and output arrangements.
- A digital computer designed for use in machine control.

2. Identify four tasks in addition to relay switching operations that PLCs are capable of performing.
- Timing, counting
- Calculating
- Comparing
- the processing of analog signals

3. List six distinct advantages that PLCs offer over conventional relay-based control systems.
- Lower cost
- Increased reliability
- Flexibility
- Communications capability
- Faster response
- Easier to troubleshoot
- Modify

4. Explain the differences between open and proprietary PLC architecture.
- An open architecture design allows the system to be connected easily to devices and programs made by other manufacturers. A system with a closed architecture is one whose design is proprietary, making it more difficult to connect to other systems.

5. State two ways in which I/O is incorporated into the PLC.
- Fixed
- Modular

6. Explain the main function of each of the following major components of a PLC:
- Processor module (CPU): The CPU controls all PLC activity and is designed so that the user can enter the desired program in relay ladder logic.
- I/O modules: The purpose of this interface is to condition the various signals received from or sent to external field devices
- Programming device: A programming device is used to enter the desired program into the memory of the processor.
- Power supply module: The power supply supplies DC power to other modules that plug into the rack.

7. What are the two most common types of PLC programming devices?
- Hand held
- PC

8. Explain the terms program and programming language as they apply to a PLC.
- A program is a user-developed series of instructions that directs the PLC to execute actions.
- A programming language provides rules for combining the instructions so that they produce the desired actions.

9. The programmable controller operates in real time. What does this mean?
- That an event taking place in the field will result in an operation or output taking place.

10. Compare the method by which the process control operation is changed in a relay-based system to the method used for a PLC-based system.

- If a relay system were used, it would require some re-wiring of the circuit to achieve the desired change. However, if a PLC system were used, no rewiring would be necessary. The inputs and outputs are still the same. All that is required is to change the PLC ladder logic program.

11. List four criteria by which PLCs are categorized.
- functionality
- number of inputs and outputs
- cost
- physical size

12. What is the memory capacity, expressed in bits, for a PLC that uses 16-bit words and has an 8 K word capacity?
- Memory capacity is maximum value of memory on PLC for stores data instruction, and control program. 16 * 8 * 10²⁴ = 131072 bits