אוטומציה ובקרה – PLCs Topic – Part 2
This articular is the third part of our review about PLCs. After PLCs Functionality&Features and PLCs Topic – part 1 that covers the subjects of Scan Time, System Scale, User interface & Communications, this part is about PLCs Programming, Digital and Analog Signals & PLC Advantages.
PLC– Programming
PLC programs are typically written in a special application on a PC, then downloaded by a direct-connection cable or over a network to the PLC. The program is stored in the PLC either in battery-backed-up RAM or some other non-volatile flash memory.
IEC 61131-3 defines several programming languages for programmable control systems, which emphasize logical organization of operations.
While the fundamental concepts of PLC programming are common to all manufacturers, differences in I/O addressing, memory organization and instruction sets mean that PLC programs are never perfectly interchangeable between different makers. Even within the same product line of a single manufacturer, different models may not be directly compatible.
PLC – Digital and Analog Signals
Digital or discrete signals behave as binary switches, yielding simply an On or Off signal (1 or 0, True or False, respectively). Push buttons, limit switches, and photoelectric sensors are examples of devices providing a discrete signal. Discrete signals are sent using either voltage or current, where a specific range is designated as On and another as Off. For example, a PLC might use 24 V DC I/O, with values above 22 V DC representing On, values below 2VDC representing Off, and intermediate values undefined. Analog signals are like volume controls, with a range of values between zero and full-scale. These are typically interpreted as integer values (counts) by the PLC, with various ranges of accuracy depending on the device and the number of bits available to store the data. Pressure, temperature, flow, and weight are often represented by analog signals. Analog signals can use voltage or with a magnitude proportional to the value of the process signal. Current inputs are less sensitive to electrical noise (i.e. from welders or electric motor starts) than voltage inputs.
PLC Advantages Relative to Other Control Systems
PLCs are well adapted to a range of automation tasks. These are typically industrial processes in manufacturing where the cost of developing and maintaining the automation system is high relative to the total cost of the automation, and where changes to the system would be expected during its operational life. PLCs contain input and output devices compatible with industrial pilot devices and controls; little electrical design is required, and the design problem centers on expressing the desired sequence of operations. PLC applications are typically highly customized systems, so the cost of a packaged PLC is low compared to the cost of a specific custom-built controller design.
Here are some examples of the PLCs used by smartlogic: 6XV1830-0EH10, 6ES7131-4BF00-0AA0,6ES7193-4CA40-0AA0,6ES7134-4GD00-0AB0,6ES7193-4CA40-0AA0, 6ES7138-4CA01-0AA0,6ES7193-4CC20-0AA0, 6ES7590-1AB60-0AA0, 6ES7511-1AK00-0AB0, 6ES7954-8LP01-0AA0,6ES7155-6AU00-0BN0
