Industrial Automation Interview Questions and Answers.
Q1. What is PLC?
Ans- PLC is a microprocessor based solid state device that works on the principle of logic gates.PLC can be programmed by using programming software.
Note- Solid state device is a device in which semiconductor components Ex- Diode, transistor, Mosfet etc are used.
Q2. What are the types of PLC?
Ans. There are two types of PLC-
1- Compact PLC- In compact PLC Inputs, outputs, memory, cpu & communication port are in the same module.
2- Modular PLC- In modular PLC, we use modules, we can increase/decrease number of modules as per our requirement.
Q3. what are the types of modules of Modular PLC?
Ans- Examples of modules of are as below-
1. Power supply module
2. CPU Module
3. Interface Module
4. Signal modules( DI, DO, AI, AO )
5. Function module
Q4.What are types of PLC inputs terminals?
Ans- There are three types of input terminals based on signal type-
1. Digital Input
2. Analog Inputs
3. High speed Input
Q5. What are the types of PLC outputs terminals?
Ans- There are three types of PLC output based on signal type-
1. Digital output
2. Analog outputs
3. High speed output
Q6. What are the types of PLC Input control ( Based on wiring)?
Ans- There are three types of PLC inputs controlling-
1. Source type
2. Sink type
3. Source/sink type
Q7.What are the types of PLC output ( Based on wiring)?
Ans- There are two types of PLC output-
1. Relay type (AC/DC Type)
2. Transister type (DC type)
Further there are two types of Transister output
(1) PNP type
(2) NPN type
Q8. What is the difference between PLC & SCADA?
Ans-PLC
1. PLC stands for Programmable Logic Controller
2. It is a hardware based controlling device
3. PLC controls the outputs based on the status of input devices & programming
SCADA
1. SCADA stands for Supervisory control and data acquisition.
2. It is a software which is installed in a PC
3. Functions of SCADA are- Supervising, Controlling & Data collection of any process or devices
Q9. Difference between HMI and SCADA.
Ans- HMI
1-It is a display based operating device.
2-It is mounted in control panel or closed to a machine.
3-Generally It is used to control single machine.
4- So we can say It is used to control a machine locally.
SCADA
1- It is a software which is installed in a PC.
2- It is installed in a control room.
3- We can control more than one machine or processes using SCADA.
4- So we can say It is used to Control remotely.
Q10. What is the use of VFD?
Ans- We use VFD for-
1- To change the rpm of a 3 phase Induction Motor.
2-We can start/stop the motor locally/remotey.
3- We can change the ramp up and ramp down time of motor.
4- We can change the direction of motor.
5- We can control a motor via communication using VFD.
Q11. What is the working principle of VFD?
Ans- According to drive law
Ns=120f/p
where Ns = synchronous speed
f = frequency
p = no of pole
in this, frequency is directly proportional to speed and pole are indirectly proportional.
As we know poles are fix. so we can only vary the frequency to vary the speed. Its a energy saving method.
Q12. What are the names of some input and output devices of PLC?
Ans-Input Devices
1-Push Button (DI)
2-Toggle switch (DI)
3-Selector switch (DI)
4-Limit switch (DI)
5-Proximity sensor (DI)
6-Level switch (DI)
7-Temperature sensor (AI)
8-Pressure sensor (AI)
9-Level sensor (AI)
10-flow sensor (AI)
11- Load sensor(AI)
Output Devices
1-Lamp
2-Buzzer
3-Solenoid valve
4-Motor starter
5-Tower light
6-relay/contactor coil
7-flow regulator
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