PLC QUESTIONS

Que:- Describe Different types of PLC inputs and outputs. 

Ans :- There are two types of PLC inputs and outputs.

           1) Analog

           2) Digital

Que:- Give example of Digital Inputs and outputs of PLC.

Ans :- Digital Inputs are as described below.

                 1) Push button,

              2) Selector Switch,

              3) Limit Switch,

              4) Reed Switch,

              5) Proximity Sensor, etc.

           Digital Outputs are as described below.

              1) Indication (Lamp),

              2) Motor ,

              3) Solenoid Coil (Direction control valve),

              4) Hooter, etc.

Que:- Give example of Analog Inputs and outputs of PLC. 

Ans:- Analog inputs are as described below. (0 - 10v or 4 - 20ma)

          

         1)  RTD (Temperature sensor)

         2)  Pressure Sensor,

         3)  Flow sensor,

         Analog Outputs are as described below. (0 - 10v or 4 - 20ma)

        1) Analog Speed control.

        2) Flow-meter control.

Que:- What is PLC scan Cycle and Scan Time?

Ans:-  PLC Scan Cycle:-

          "A PLC program is generally executed repeatedly as long as the controlled   system is running.

• The status of physical input points is copied to an "I/O Image Table". (This memory area accessible to Processor so it can read Input status of the Inputs)

• The program is then run from its first instruction rung down to the last rung.

• It takes some time for the processor of the PLC to evaluate all the rungs and update the I/O image table with the status of outputs."

         PLC Scan Time:-

"This scan time may be a few milliseconds for a small program or on a fast processor, but older PLCs running very large programs could take much longer (say, up to 100 ms) to execute the program."

Example:- 

Scan Cycle in details.

 Que:- Draw the block diagram of the PLC?

Ans:-

Que:- What is Sink & Source? 

Ans:-

•  Voltage "Sinks" current to the ground.
  
  

•  Voltage "Sources" current from a voltage "source".

 Wiring Circuit for Sink and Source :-

Sink/Source Wiring

 and also,

For More detail Please go through Followings:-  
http://support.motioneng.com/hardware/io/slice-io/topic_sink_source.htm

Que:- What is Communication Protocols? and Describe Different types of protocols.

 Ans:- Communication Protocol:- "It is a set of rules for data transmission when PLC is  connected to Network.Cable is used to connect different external device?

Types of the different communication Protocols are as under
 1) RS 232 (Serial Communication)
 2) RS 422 (Serial Communication)
 3) RH 485 (Serial Communication)
 4) CAN BUS
 5) MOD BUS
 6) DEVICE NET
 7) PROFIBUS-PA
 8) PROFIBUS-DP
 9) ETHERNET
10) ETHERCAT
11) INTER BUS-S
12) SERIPLEX 
Out of this 0 to 10 are most commonly used protocols.every protocol has a different "Baud rate"
Baud Rate:- "Rate of data transmission on network."

Unit:- Bits/Second.
Range:- 120 bits/sec  To  100 Mbps.
  
Que:- What is Pneumatics & hydraulics? what is FCV & DCV? Type of DCV?
Ans:-  

• Pneumatic:- "Study of compressed Air."
• Hydraulics:- "Study of compressed liquid like oil."  
• FCV:- "Flow control valve", Remember through flow control valve we are controlling exhaust air of the cylinder not incoming air.
• DCV:- "Direction control valve",Air exhaust is decide by direction control valve.

 Types of Direction control valve:-

1.  2/2 valve.
2.  3/2 valve.
3.  4/2 valve.
4.  5/2 valve.
5.  5/3 valve (Center Pressure).
6.  5/3 valve (Center Exhaust).
7.  5/3 valve (Center Closed).

Important:- Every DCV contains Solenoid Coil to energies it and we can check solenoid coil by giving simply +24V.
 
Types of Cylinder:- 

1. Single Acting.
2. Double Acting. 

Leading Company in Pneumatics:- SMC, Festo, TPC.

References:-  SMC Pneumatic Cylinders, Pressure Switch, FRL Unit.


Que:- Howmany Timers and Counters are in PLC?
Ans:-  Timers:-

1.  TON (ON Delay Timer),
2.  TOFF (Off Delay Timer),
3.  RTO (Retentive Timer),
4.  TPULSE (Pulse Timer),         

           Counters:-

1. CTU (Up Counter),
2. CTD (Down Counter),
3. CTUD (Up-Down Counter),
4. High Speed Counter.
5. Retentive Counter.