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Inputs and Outputs
What are
Inputs and Outputs?
In the following activity, you will activate and use a PLC to control a number of devices. These devices can be divided into two main categories: input and output devices.
In the following activity, you will activate and use a PLC to control a number of devices. These devices can be divided into two main categories: input and output devices.
- Input
devices transmit data to the PLC. The status of the input devices reflects the
status of the controlled system or an operating requirement. The PLC constantly
monitors the status of these devices and checks it with a pre-defined set of
instructions.
- Output
devices receive activation instructions from the PLC. The status of the
output devices is determined by the status of the input devices and the control
instructions.
Input and Output
Devices
As you have already learned, programmable logic controllers control real world inputs and outputs in order to automate a process. Move your mouse over the image to see some input and output devices. Input and output devices include:
As you have already learned, programmable logic controllers control real world inputs and outputs in order to automate a process. Move your mouse over the image to see some input and output devices. Input and output devices include:
- Input Devices:
- Proximity Switches
- Flow Meters
- Limit Switches
- Output Devices:
- Solenoid
Valve
- Electromagnetic
Relay
- Motor
Starter
- Pressure
Gauges
- Horn
fitted in a car
Real-World
Example
Observe the example of a PLC-controlled level control system. A float is fitted on a tank at the level marked as 2. The float is an input device that is used as a level sensor. By controlling an on/off valve that serves as an output device, the user can control the water level.
The control instructions are stored in the PLC's memory. The PLC constantly receives an input signal (in this case, the water level). The PLC controls the output device (valve) according to the input (water level) and the instructions programmed in its memory.
Observe the example of a PLC-controlled level control system. A float is fitted on a tank at the level marked as 2. The float is an input device that is used as a level sensor. By controlling an on/off valve that serves as an output device, the user can control the water level.
The control instructions are stored in the PLC's memory. The PLC constantly receives an input signal (in this case, the water level). The PLC controls the output device (valve) according to the input (water level) and the instructions programmed in its memory.
Discrete and
Analog
I/O devices refer to the data read and written by the programmable controller.
There are two types of input and output:
Discrete
I/O consists of data represented by 1s and 0s. Discrete I/O systems are
used to control systems that can be in only one of two states, such as an ON or OFF state for a motor or a lamp.
Analog
I/O uses a number of bits to represent an integer value. For example, the pressure in a pneumatic system could be any
value between 0 and the highest integer value available on a particular
pressure gauge's scale.
Discrete input signals are usually used to determine if a certain event has happened (for example, the piston is fully extended or the pressure is above 3 bars). Discrete output devices are used to control elements that can be only in one out of two possible states.
You will learn more about this concept in the next module.
I/O devices refer to the data read and written by the programmable controller.
There are two types of input and output:
Discrete
I/O consists of data represented by 1s and 0s. Discrete I/O systems are
used to control systems that can be in only one of two states, such as an ON or OFF state for a motor or a lamp.Analog
I/O uses a number of bits to represent an integer value. For example, the pressure in a pneumatic system could be any
value between 0 and the highest integer value available on a particular
pressure gauge's scale. Discrete input signals are usually used to determine if a certain event has happened (for example, the piston is fully extended or the pressure is above 3 bars). Discrete output devices are used to control elements that can be only in one out of two possible states.
You will learn more about this concept in the next module.
Introduction
to Ladder Logic
In this module, you will use a virtual PLC and input devices to control output devices. You will program a virtual PLC using ladder logic programming language, a programming language typically used in PLC programming.
Throughout this module, you will learn basic commands in the ladder logic programming language. You will then program ladder diagrams using those commands to control various industrial-type control systems. This graphical language closely resembles electrical relay logic diagrams.
In this module, you will use a virtual PLC and input devices to control output devices. You will program a virtual PLC using ladder logic programming language, a programming language typically used in PLC programming.
Throughout this module, you will learn basic commands in the ladder logic programming language. You will then program ladder diagrams using those commands to control various industrial-type control systems. This graphical language closely resembles electrical relay logic diagrams.
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