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PLC: Hardware and Terminology
Transcript of PLC: Hardware and Terminology
LOGO! is a digital mini controller
which is a simplified version of a PLC
PLC Inputs and Outputs
The input module consists of the digital inputs and the analog inputs.
Recognizes either the ON or OFF condition (S/W)
Pushbuttons, toggle switches, limit switches, proximity switches
PLC analog input can accept signals that are varying (analog)
The output module consists of digital outputs and analog outputs
Solenoids, contactor coils and
lamps are usually connected to digital outputs
The analog output gives a varying signal that could drive an analog meter.
Examples of analog meter outputs are speed, weight, and temperature.
Central Control Unit
It contains the Central Processor which is the brain
of the PLC
It performs counting, timing, data
comparison and sequential operations.
A sensor is an input device that senses a physical condition and converts it to an electrical signal
Actuators convert electrical signals from PLC outputs into physical
LOGO! is a universal logic module made by Siemens
Edutrainer Compact includes the following LOGO! parts and accessories
LOGO! basic module
LOGO! expansion modules
I/O data cable
Power supply unit
The interface unit interfaces the LOGO! Controller with the EduTrainer’s sensors and one actuator.
It receives the control signals from the LOGO!
controller through the I/O Data cable
It contains an LED for every input
and output that helps visualize the signals, and makes troubleshooting
Connecting the Power Supply
PLC devices need an electrical power supply that can be either an AC, or DC supply. LOGO! 12/24 RC needs a DC supply
Connecting LOGO! Inputs
Connecting LOGO! Outputs
LOGO! …R… version is equipped with relay outputs.
The potential of the
relay contacts is isolated from the power supply and the inputs
Various loads can be connected to the relay outputs, for
example, lamps, motors, relays
Reference table for PLC and Interface Unit
Conveyor Belt Application Parts
1. Optoelectronic sensor:
Fiber optic barrier
2. Inductive Sensor
Its detection distance is up to
3. Conveyor Belt
4. Gear Box
5. DC Motor
6. Branching Module
7. Fiber optic barrier
A controller is needed for a hydraulic press.
The press uses a 24VDC double actuated solenoid valve to advance and retract the press.
This device has three wires:
one for common
one to advance and
one to retract.
A large hydraulic pump should be running as long as the press is
Three push buttons are used:
A NC stop button
A NO manual retract button
A NO start automatic cycle button.
Two limit switches at the top and bottom of the press must also be used.
Programmable Logic Controller is a device that can be programmed to perform control functions.
Since it is a digital device, it stores information in the form of ON/OFF conditions referred to as binary digits or bits.
Even though the PLC uses both digital and analog signals, the CPU can understand only digital signals.
Explain the operation of the shown PB.
All sensors can be connected as inputs to a PLC, some examples are given below:
• Inductive sensor
• Capacitive sensor
• Fiber optic sensor
• Temperature sensor
The CPU monitors the inputs and makes decisions based on instructions in its program memory.
Connecting Sensors to the LOGO!
For three wire sensor, sensor’s type must be taken into consideration while programming.
PNP sensor can be thought as normally open pushbutton and
NPN can be thought as normally close pushbutton.