Chapter 1 HW

12. The programmable controller operates in real time. What does this mean?

A programmable logic controller operates in real time in that an event taking place in the field will result in an operation or output taking place

20. What is the memory capacity, expressed in bits, for a PLC that uses 16-bit words and has an 8 K word capacity?

16x8x1024= 131,072

3. List six distinct advantages that PLCs offer over conventional relay-based control systems.

Increased Reliability More Flexibility Lower Cost Communications Capability Faster Response Time Easier to Troubleshoot Easier to Test Field Devices

10. What is the standard programming language used with PLCs?

Relay ladder logic (RLL)

7. Explain the main function of each of the following major components of a PLC: a. Processor module (CPU) b. I/O modules c. Programming device d. Power supply module

a) the "brain" of the PLC. usually consists of a microprocessor for implementing the logic and controlling the communications among the modules b) forms the interface by which field devices are connected to the controller c)is used to enter the desired program into the memory of the processor d) supplies DC power to other modules that plug into the rack

2. Identify four tasks in addition to relay switching operations that PLCs are capable of performing.

timing, counting, calculating, comparing, and the processing of analog signals.

6. Describe how the I/O modules connect to the processor in a modular-type PLC configuration.

The modules plug into a rack. When a module is slid into the rack, it makes an electrical connection with a series of contacts called the backplane, The PLC processor is also connected to the backplane and can communicate with all the modules in the rack.

13. Answer the following with reference to the process control PLC ladder logic diagram of Figure 1-20 of this chapter: a. What do the individual symbols represent? b. What do the numbers represent? c. What field device is the number I/2 identified with? d. What field device is the number O/1 identified with? e. What two conditions will provide a continuous path from left to right across the rung? f. Describe the sequence of operation of the controller for one scan of the program.

a)instructions b)instruction location addresses c) Temperature switch d)Motor starter coil e)the coil O/1 is energized when contacts I/1 and I/2 are closed or when contact I/3 is closed f) Read inputs, Execute program, Update outputs

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

fixed and modular