Programmable Logic Controllers with ControlLogix
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PROGRAMMING CONTROLLOGIX PROGRAMMABLE AUTOMATION CONTROLLERS strength is its breadth and depth of coverage, taking the reader from an overview of the Programmable Logic Controllers through ladder logic, structured text, sequential function chart, and function block programming. Students learn more and more easily because of the practical coverage, numerous examples and extensive exercises.
MORE ON THE USE OF TASKS Remember that a CLX project can have multiple tasks and that tasks can be scheduled. The default RSLogix 5000 project provides a single task for all your logic. Although this is sufficient for many applications, some situations may require more than one task. 40 PROGRAMMING CONTROLLOGIX® PROGRAMMABLE AUTOMATION CONTROLLERS A Logix5000 controller supports multiple tasks that can be used to schedule and prioritize the execution of programs. This can help balance the
execute at one time. What are the three execution types for tasks? What is a watchdog timer? How can the watchdog time be changed? This page intentionally left blank CHA P T ER 3 Ladder Logic Programming OBJECTIVES On completion of this chapter, the reader will be able to: ■ ■ ■ ■ Define terminology such as rung, contact, coil, scan, examine if open, examine if closed, normally open, and normally closed. Explain the difference in operation between normally open and normally closed
instruction is executed. Source B is subtracted from Source A; the result (798) is stored in the Dest tag named Number_Left. Source A in this example is a constant (1250). Source B is a tag named Qty_Parts. Qty_Parts has a value of 452. Note that a constant (1250) was used for Source A. A tag could have been used. Figure 7-2 Use of a SUB instruction. CHAPTER 7—MATH INSTRUCTIONS 153 Divide (DIV) Instruction The DIV instruction can be used to divide two numbers. The source of the two numbers
of 45 degrees is 0.707. Figure 7-30 Use of a SIN instruction. We could utilize math instructions to do the degrees-to-radians conversion. Figure 7-31 shows a CPT instruction that is used to convert degrees to radians. The result of the CPT instruction is then put into the Dest tag (Rads). The value of Rads was then used as the Source value in the SIN instruction. Note that there are CLX instructions available to do these conversions. Figure 7-31 Use of a CPT and a SIN instruction. The CPT is
the PID system functions. The setpoint is set by the operator and is an input to a summing junction. The output from the level sensor becomes the feedback to the summing junction. The summing junction sums the setpoint and the feedback and generates an error. The PLC then uses the error as an input to the PID equation. There are three gains in the PID equation. The P gain is the proportional function. It is the largest gain, and it generates an output that is proportional to the error signal. If