plc中文翻译plc中文翻译.docx

Programmable Logic Controllers (PLCs)1 .About Programmable Logic Controllers (PLCs)PLCs (/Industrial-Directory/programmableprogrammable logic /Industrial-Directory/controllerscontrollers) are the control hubs for a wide variety of /Industrial-Directory/automated_systemsautomated systems and processes. They contain multiple inputs and outputs that use transistors and other circuitry to simulate switches and relays to control equipment. They are /Industrial-Directory/programmableprogrammable via software interfaced via standard computer interfaces and proprietary languages and network options. /Industrial-Directory/programmableProgrammable logic /Industrial-Directory/controllerscontrollers I/O channel specifications include total number of points, number of inputs and outputs, ability to expand, and maximum number of channels.? Number of points is the sum of the inputs and the outputs. PLCs may be specified by any possible combination of these values.? Expandable units may be stacked or linked together to increase total control capacity.? Maximum number of channels refers to the maximum total number of input and output channels in an expanded system.? PLC system specifications to consider include scan time, number of instructions, data memory, and program memory.? Scan time is the time required by the PLC to check the states of its inputs and outputs.? Instructions are standard operations (such as math functions) available to PLC software.? Data memory is the capacity for data storage.? Program memory is the capacity for control software. Available inputs for /Industrial-Directory/programmableprogrammable logic /Industrial-Directory/controllerscontrollers include DC, AC, analog, thermocouple, RTD, frequency or pulse, transistor, and interrupt inputs.? Outputs for PLCs include DC, AC, relay, analog, frequency or pulse, transistor, and triac.? Programming options for PLCs include front panel, hand held, and computer. /Industrial-Directory/programmableProgrammable logic