What is a programmable logic controller?
Programmable Logic Controllers (PLCs) are flexible automation control devices that implement a real-time control algorithm, where actuators are controlled in response to sensor inputs. Complexity varies from simple devices capable of performing elementary logic and timing functions to advanced Programmable Automation Controllers (PACs) capable of orchestrating the motions of complex moving equipment such as material handling robots. These systems are often modular and extensible, to adapt to the needs of your specific application.
Introduction to DigiKey’s Product Selection Guide
This page is one of many in DigiKey’s Product Selection Guide (PSG). This particular page is focused on controllers - programmable (PLC, PAC). It provides a description of the individual parameters used to characterize the part. This information will allow you to better understand and navigate DigiKey’s parametric search engine. Click here for a case study showing how to use the search tools.
How are PLCs and PACs categorized?
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Number of Inputs and Type: Indicates the number of signal input circuits with which a device is equipped, and whether those inputs process applied signals as continuous (analog) or discrete (digital) values.
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Number of Outputs and Type: For devices having built-in outputs, indicates the number of such outputs and the manner of their implementation.
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Expandable: Describes ability to expand device functionality through addition of modular hardware extensions.
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Voltage - Supply: Typically represented by a range, this indicates the low and high voltage limits which one can expect standard operation. Voltages outside this range may damage the device and other system components.
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Display Type: Describes the user interface for indication.
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Number of Characters Per Row: For products incorporating a segmented display, the display width in terms of number of alphanumeric characters that can be shown on each row of the display.
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Communications: Enumerates communication interface(s)/protocol(s) implemented by a controller.
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Memory Size: The amount of memory available in the device for program storage.
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Mounting Type: Indicates how the device is attached.
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Features: These are different capabilities or properties of the device such as battery backup or a cable.
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Software: Identifies the recommended software suite for programming or monitoring of a device.
Examples of DigiKey’s PLCs
- The Arduino brand Opta WiFi is a modular PLC that may be programmed from the Arduino IDE. Expansion modules are available. Datasheet
- The Schneider Electric brand Modicon TM241CE40T is medium sized PLC that may be expanded using plug-in as well as expansion modules. Refer to the Product Selector tool on the manufacturer’s webpage for configuration options. Datasheet
- The Siemens Simatic S7-1500 is high-end PLC. This PLC has zero built in I/O. Instead, it is designed to work with remote I/O. Please refer to the Siemens TIA selection tool to identify supporting I/O.
Datasheet
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If you have any general questions on the specifications for a PLC, please reply using the button below. If you have questions on a specific PLC, please post your questions in the Industrial Automation and Control category.
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