Question

Indicate whether the statement is True or False.

1) Any control system goes through five stages, design, construction, installation, commissioning, &
maintenance. A PLC system brings advantages just at three stages.
2) PLC implement functions such as logic, sequencing, timing, counting, and arithmetic in order to
control machines and processes.
3) A programmable logic controller (PLC) is designed to be operated by engineers with a higher
knowledge of computers and computing languages.

4) The term logic in programmable logic controller (PLC) is used because programming is primarily
concerned with implementing logic and switching operations.
5) When compared with relay systems, PLCs are more compact than relay systems.
6) When compared with relay systems, PLCs require more maintenance than relay systems.
7) When compared with relay systems, PLCs Can be readily expanded by adding new modules to the
PLC whereas software changes are necessary with relay systems.
8) PLCs are similar to computers, but whereas computers are optimized for calculation and
display tasks, PLCs are optimized for control tasks and the industrial environment.
9) The terms sourcing and sinking are used to describe the way in which AC devices are
connected to a PLC.
10) If the current flows from the output module to an output load, the output module is referred to as
sourcing.

Answer 1

1. FALSE

Any control system goes through several stages, design, construction, installation, commissioning, &
maintenance. A PLC system also have same stages.

2. TRUE

Programmable Logic Controller (PLC) is a microprocessor based system that uses programmable memory to store instructions and implement functions such as logic, sequencing, timing, counting and arithmetic in order to control machines and processes.

3. FALSE

Programmable logic controllers. A programmable logic controller (PLC) is a special form of microprocessor-based controller that uses a programmable memory to store instructions and is designed to be operated by engineers with perhaps a limited knowledge of computers and computing languages.

4. TRUE

The term logic is used because programming is mainly concerned with implementing logic and switching operations, e.g. if A or B occurs switch on C, if A and B occurs switch on D. For example, For controlling the level of water in a tank by a sensor giving an input signal when the tank is empty and another sensor giving a signal when the tank is full. Thus when the tank-empty sensor gives an on input the controller gives an on output signal to open a valve to allow water into the tank. This output remains on until the tank-full sensor gives an input signal, the controller then switches off the output signal to the valve.

5. TRUE

• PLCs are highly reliable,
• easily programmable,
• Small and Inexpensive,
• PLCs can be designed with the communication capabilities so they can converse with the local or remote computer,
• They can sustain in robust environment less maintenance. etc…

PLC Ladder logic is microprocessor based which has faster execution times, is far more reliable and longer lasting than relay logic control systems which have a large amount of mechanical components. PLC Ladder logic control systems are far more compact than relay logic control systems.

6. TRUE

Wiring ,maintenance modification are difficult with relay but in PLC,user can easily modify the logic to add number of input and outputs. PLC is easy to maintain. There will not be much physical work. PLC has more advanced functions as compared to manual work (hardware relay-base).

7. TRUE

The PLC was developed with several advantages over earlier designs. It tolerated the industrial environment better than computers and was more reliable, compact and required less maintenance than relay systems. It was easily extensible with additional I/O modules, while relay systems required complicated hardware changes in case of reconfiguration. Control system expansion is simplified with a PLC by adding expansion modules as opposed to complex hardware and wiring modifications that would be the case with relay logic control.

8. TRUE

PLCs are similar to computers, but whereas computers are optimized for calculation and display tasks, PLCs are optimized for control tasks and the industrial environment. Thus when compared to computers, PLCs Are rugged and designed to withstand vibrations, temperature, humidity, and noise. The common personal computer is not designed for harsh environments.

9. FALSE

The terms sourcing and sinking are used to describe the way in which DC devices are connected to a PLC. With sourcing, using the conventional current flow direction as from positive to negative, an input device receives current from the input module, that is, the input module is the source of the current. With sinking, using the conventional current flow direction, an input device supplies current to the input module, that is, the input module is the sink for the current.

10. FALSE

If the current flows to the output module from an output load, the output module is referred to as sinking

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