PLC Data Communication System Data communications refers to the different ways that PLC microprocessor-based systems talk to each other and to other devices. The two general types of communications links that can be established between the PLC and other devices are point-to-point links and network links. Figure 1 illustrates a point-to-point serial communications link. Serial communications …
Process Control Systems Types of Processes: Process control is the automated control of a process. Such systems typically deal with analog signals from sensors. The ability of a PLC to perform math functions and utilize analog signals makes it ideally suited for this type of control. Manufacturing is based on a series of processes being …
Troubleshooting of PLC In the event of a PLC fault, you should employ a careful and systematic approach to troubleshoot the system to resolve the problem. PLCs are relatively easy to troubleshoot because the control program can be displayed on a monitor and watched in real time as it executes. If a control system has …
Installation and Commissioning of PLC A PLC system, if installed properly, should give years of trouble-free service. The design of PLCs includes a number of rugged features that allow them to be installed in almost any industrial environment. However, problems can occur if the system is not installed properly. Programmable logic controllers (PLCs) require protection …
This article explains how the PLC shift register functions operate and how it can be applied to control problems. Shift registers are often used to track parts on automated manufacturing lines by shifting either status or values through data files. PLC Shift Register Instructions & Programs The PLC not only uses a fixed pattern of …
PLC Sequencer Instructions This article explains how the PLC sequencer functions operate and how they can be applied to control problems. The sequencer instruction evolved from the mechanical drum switch, and it can handle complex sequencing control problems more easily than does the drum switch. Mechanical Sequencers Sequencer instructions are designed to operate much like …
Most PLCs have arithmetic function capabilities. Basic PLC math instructions include add, subtract, multiply and divide to calculate the sum, difference, product, and quotient of the content of word registers. The PLC is capable of doing many arithmetic operations per scan period for fast updating of data. This article covers the basic mathematical instructions performed …
PLC Data Manipulation Programs Data manipulation instructions give new dimension and flexibility to the programming of control circuits. For example, consider the hardwired relay-operated, time-delay circuit in Figure 1 . This circuit uses three electro-mechanical time-delay relays to control four solenoid valves. The operation of the hardwired circuit can be summarized as follows: The hardwired time-delay …
Data manipulation involves transferring data and operating on data with math functions, data conversions, data comparison, and logical operations. This article covers both data manipulation instructions that operate on word data and those that operate on file data, which involve multiple words. Data manipulations are performed internally in a manner similar to that used in …
The program control instructions covered in this article are used to alter the program scan from its normal sequence. The use of program control instructions can shorten the time required to complete a program scan. Portions of the program not being utilized at any particular time can be jumped over, and outputs in specific zones …
