PLC Programming Languages

Types of PLC Programming Language

• Structured Text (ST) programming: a high-level language similar to Pascal, with statements used to assign values to variables.
• Logic Diagram (LD) programming: a graphical language, widely used, with Boolean mnemonics to represent the process before converting into a logic diagram.
• Functional Block Diagram (FBD) programming: a graphical language used in applications involving signal flow between control blocks.
• Instruction List (IL) programming: a low-level programming language, similar to assembly language programming.
• Sequential Function Chart (SFC) programming: a graphical programming method useful for describing sequential type processes.

Instruction Lists (IL)

• A programming method that can be considered as entering a ladder program using text.
• Programs consist of a series of instructions, each on a new line, with an operator followed by one or more operands.
• Mnemonic codes are used, each corresponding to an operator/ladder element, and differ from manufacturer to manufacturer.

Ladder Programs and Instruction Lists

• Whenever a rung is started, it must use a 'start a rung code' (e.g., LD, A, or L).
• The rung must end with an output or store result code (e.g., OUT, =, or ST).
• Examples of codes used in ladder programs and instruction lists, including those from Mitsubishi and Siemens.

Sequential Function Charts (SFC)

• A pictorial representation of a system's operation, showing the sequence of events involved in its operation.
• SFC charts have elements such as steps, transitions, and actions.
• Part of an SFC and its equivalent ladder program.

Structured Text

• A programming language that strongly resembles Pascal.
• Programs are written as a series of statements separated by semicolons (;).
• Assignment statements are used to indicate how the value of a variable is to be changed.
• Conditional statements (IF...THEN...ELSE) are used to execute selected statements when certain conditions occur.

Electromagnetic Control Relays

• The PLC's original purpose was to replace electromagnetic relays with a solid-state switching system that could be programmed.
• Electromagnetic relays make logic decisions but are not designed to handle heavy current or high voltage.

Contactors

• A special type of relay designed to handle heavy power loads that are beyond the capability of control relays.
• Unlike relays, contactors are designed to make and break higher-powered circuits without being damaged.

Motor Starters

• A motor starter is designed to provide power to motors.
• Motor starters are made up of a contactor with an overload relay attached physically and electrically to it.
• Overload relays are designed to meet the special protective needs of motor control circuits.

Manually Operated Switches

• Manually operated switches are controlled by hand, including toggle switches, pushbutton switches, knife switches, and selector switches.
• Pushbutton switches are the most common form of manual control.

Mechanically Operated Switches

• Mechanically operated switches are controlled automatically by factors such as pressure, position, or temperature.
• Examples include mechanically operated limit switches, temperature switches, and pressure switches.

Sensors

• Sensors are used for detecting and often measuring the magnitude of something, converting mechanical, magnetic, thermal, optical, and chemical variations into electric voltages and currents.
• Examples of sensors include proximity sensors, capacitive proximity sensors, light sensors, and ultrasonic sensors.

Output Device Control

• Solenoid valves are output devices controlled by PLCs.
• Solenoid valves are used to control the flow of fluids, air, or other media.
• Solenoids can be normally open (NO) or normally closed (NC).

This quiz covers the different types of programming languages used for PLCs, including structured text, logic diagram, and functional block diagram programming.