What are Programmable Logic Controllers?
October 7, 2011 by Motion Control Tips Editor
Filed under Controllers, Motion Control Handbook, PLC - PACs
Programmable logic controllers,or PLCs, are highly specialized, programmable microprocessor-based controllers used to control a specific application on a machine or a process. They are used in automation and manufacturing to control assembly lines and machinery on factory floors as well as many other types of mechanical, electrical, and electronic equipment in a plant. They can be used in applications ranging from vending machine controls and packaging machinery to roller coasters and complex camera positioning systems.
The earliest PLCs came along to replace large cabinets of electromechanical relays which were used to control machine processes. Cabinet-based control systems were big and bulky and required an enormous amount of wiring. And when a change in the control system was desired, the only way to do so was to go into the cabinet and rewire connections, which was costly and took up a lot of time.
The introduction of PLCs meant that the same control functions could be accomplished in a fraction of the space of a traditional control cabinet with far less wiring and complexity. Also, if a change in control was desired, the change could be handled via simple ladder-logic programming, eliminating the need to rewire large portions of a control cabinet.
The basic parts of any PLC system include the processor, I/O modules to handle inputs to the controller and outputs to the controlled devices, and some type of user interface which could be as simple as a keypad or a touchscreen interface or a programming link via a PC. The PLC’s processor is programmed via the user interface. The I/O modules are used to bring input signals into the PLC’s CPU and output control signals to controlled devices such as motors, valves, sensors and actuators, among others.
Individual PLC manufacturers may have different programming languages, but most are still based on the fundamental ladder logic programming structure. Although now, they can be programmed in higher-level languages such as C and BASIC. Communication options may include simple RS-232 serial communications to more advanced Ethernet protocols.
One of the most important considerations for any PLC is the scan time. Basically, this is the time in which the PLC runs through the program taking in data and updating outputs. This is typically a few milliseconds but can be much longer depending on the program length and the speed of the processor. Higher scan times can accommodate processes with more real-time demands than traditional slower applications where scan speed is not as critical.
Other points to consider include the I/O count and the ability to expand I/O if needed. This can range from a handful of I/O for simple applications to hundreds in more complex machinery. The type of I/O, whether analog or digital, is also important. It’s common for manufacturers to supply modules designed for unique input types, such as counting encoder inputs.
Another point to consider is the level of customization needed. For instance, PLCs can be set up with individual web pages where operators can go to view system parameters and machine conditions. They can also be programmed to send alerts and condition status updates to mobile devices such as cell phones to keep operators and engineers abreast of machinery and processes.
More recently, some manufacturers have introduced so-called PACs (programmable automation controllers). A PAC is similar to a PLC but denotes a controller that accommodates better real-time control needed in some automation applications. Also, special PLCs can include dedicated safety PLCs which monitor machine inputs such as photoelectric sensors, light curtains, magnetically operated sensors, emergency stop buttons, and safety mats.
Tyco Electronics introduces Mini I/O Connector ideal for industrial controllers
June 3, 2010 by Motion Control Tips Editor
Filed under Controllers, PLC - PACs
Tyco Electronics Corp. (www.tycoelectronics.com) is proud to announce the release of the new Industrial Mini I/O connector system. This compact connector features two points of contact to increase reliability and maintain performance in high vibration environments. The mini I/O connector system, which is approximately four times smaller than the size of a traditional RJ-45 plug, has a latching system made to protect the plug from pull-out during collision or high vibration.
The new compact connector from Tyco Electronics also features two points of contact interface, polarized, small, compact size and latching feature. It is best suited for programmable logic controllers (“PLCs”), industrial controls, motion controls and robotics.
“Our new product meets the stringent demands of industrial devices. The rigid latching system and multiple contact points significantly reduce the risk of information loss in a high vibration environment,” said James Gula, product manager of Tyco Electronics. “The connector system is an excellent replacement for existing RJ-45 technology. It occupies significantly less space while offering increased functionality.”
The polarized, wire-to-board interface feature in the new compact connector has two keying options to prevent mismating and it is consist of individual circuits to accommodate I/O signals. Its electrical specifications include a current rating of 0.5Amps and a 30V rating on 0.635-millimeter centerline spacing. The connector’s operating temperature is ranging from -40° to +70° Celsius with a durability of 1500 cycles.
The product is ideal for robotics, motion control, PLCs and industrial controllers in the industrial automation market. It meets the Cat5e requirements when utilized in Ethernet applications.
Controller Makes Networking Easy for Small Applications
April 21, 2009 by Miles Budimir
Filed under Controllers, Stand-Alone Controllers
Middletown, PA – The ILC 170 ETH 2TX controller from Phoenix Contact features two Ethernet ports, allowing easier networking for small applications. The ILC 170 is the latest addition to the company’s ILC 1xx series of small, programmable controllers.
The ILC 170’s two Ethernet ports come with a built-in Ethernet switch, eliminating the need for a separate Ethernet switch in certain applications, and making it easier to daisy-chain multiple controllers. The ILC’s optional SD card memory provides easy program transfer between ILC 170 controllers. It also has a large on-board data and program memory (512 KB) and retentive memory (48 KB).
The ILC 170 has eight digital inputs and four digital outputs (500 mA) integrated on-board. I/O can be expanded directly by adding Inline I/O modules. Additional features include an integrated real-time clock, PLC switch and support of up to three local remote bus branch modules.
The ILC 1xx series controllers are programmed with PC WorX Express, part of the IEC 6113-based AUTOMATIONWORX Software Suite 2008. PC WorX Express is a free programming tool that supports up to 4,096 I/O points. The ILC 170 controller also supports Modbus TCP for data exchange to any Modbus TCP-capable device.
For more information on the ILC 170 controller or any Phoenix Contact product, call the Phoenix Contact Technical Service Department at 1-800-322-3225, or e-mail info@phoenixcon.com.
AllMotion Questions and Answers
February 20, 2009 by Motion Control Tips Editor
Filed under Controllers, Drives, Servo Drives, Stepper Drives
Q. Can I daisy chain the intelligent motor control systems and run three stepper motors using one serial connection?
A. Yes, you can daisy chain up to 16 devices on the same serial bus. Each has an address switch to easily set the address of the unit. You can also use firmware settable address for up to 64 devices on the same bus.
Q. Do I need the starter kit or can I wire a serial cable directly to the intelligent motion unit?
A. The devices communicate via RS-485. Our starter kit includes the necessary USB to 485 converter and will
allow you to get up and running quickly. The starter kit is free for first time buyers.
