PROGRAMMABLE_DEVICES_LECT

PROGRAMMABLE_DEVICES_LECT - DMR/COX CH04 2p 10/18/0 4:13 PM...

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61 Objectives After completing this chapter, you should have the knowledge to: • Describe the function of a programming device. • Describe the three types of programming devices. • List advantages and disadvantages of the three types of programmers. • Explain the term on-line and off-line programming . PROGRAMMING DEVICES A programming device is needed to enter, modify, and troubleshoot the PLC program, or to check the condition of the processor. Once the program has been entered and the PLC is running, the programming device may be disconnected. It is not necessary for the programming device to be connected for the PLC to operate, but it can be used to monitor the PLC program while the pro- gram is running. Programming devices, or programmers as they are most often called, come in three types: hand- held, dedicated desktop, and computer (Figures 4–1, 4–2a, and 4–2b). 00 0 01 1 02 0 03 0 04 1 05 0 06 0 07 0 10 0 11 0 12 0 13 0 14 0 15 0 16 0 17 0 00 0 01 0 02 0 03 0 04 0 05 0 06 0 07 0 10 0 11 0 12 0 13 0 14 0 15 0 16 0 17 1 00 0 01 1 02 0 03 0 04 1 05 0 06 0 07 0 10 0 11 0 12 0 13 0 14 0 15 0 16 0 17 0 Programming Devices (Programmers) CHAPTER 4 Figure 4–1 Hand-Held Programmer (Courtesy of Modicon Inc.) DMR/COX CH04 2p 10/18/0 4:13 PM Page 61
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62 Technician’s Guide to Programmable Controllers Each type of programmer has advantages and disadvantages. After all three types have been de- scribed, the merits of each will be discussed. Dedicated Desktop Programmers Dedicated desktop programmers like the one pictured in Figure 4–2a are primarily designed for programming and monitoring the PLC. They are not capable of performing other computer func- tions like running software programs for word processing and spreadsheets, but are, however, de- signed to be portable and withstand the mechanical shock associated with moving the programmer from job site to job site. They are also designed to function in the industrial environment where there is electromagnetic noise, high temperatures, and humidity. A typical dedicated programmer consists of a keyboard, VDT (video display terminal), and the necessary electronic circuitry and operating memory for developing, modifying, and loading a program into the processor memory. Keyboard The keyboard of the dedicated programmer may have raised keys, like a standard computer terminal, or have a flush, sealed touchpad-type keyboard (Figure 4–3). The flush, sealed touchpad keyboard is ideally suited for environments that are dusty or have metallic particulates in the air. Figure 4–2a Dedicated Desktop Programmer (Courtesy of Allen-Bradley) Figure 4–2b IBM ® Laptop Computer DMR/COX CH04 2p 10/18/0 4:13 PM Page 62
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Programming Devices (Programmers) 63 Keyboards on dedicated programmers vary quite a bit, depending on the manufacturer. Most dedi- cated programmer keyboards have electrical symbol keys for normally open contacts, normally closed contacts, timer contacts, and the like. The various symbols are also referred to as instruc- tions . The normally open contact symbol key, when pressed, is an instruction to the processor that
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PROGRAMMABLE_DEVICES_LECT - DMR/COX CH04 2p 10/18/0 4:13 PM...

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