Programming Logic Control

Programmable Logic Controller

A programmable logic controller is an advanced computer which is used in controlling and operations of machinery in manufacturing process. This area of manufacturing entails the following, program control instructions ,data manipulation instructions ,math instructions ,sequencer and shift register instructions and programming timers just to name a few (Stenerson,2009). Programmable logic controllers are used at least in every aspect of industries in order to expand and enhance production.

The mode of functionality of PLCs has evolved over centuries in order control systems to include capabilities which are beyond typical relay control, motion control process control and distributive control systems to name a few (Petruzella,2011). Examples of PLC in my working station include: filing machine control system, main factory feed water pump duty changeover system, lead acid battery plant ,complete manufacturing system, silo feeding control ,lift operation and industrial batch washing control system.

Advantages of PLC

  • Manufacturers are able to manage multiple machines during processing which enhances flexibility and efficiency and saving time
  • By use of PLCs ,industries have be able to achieve high level of integration and process automation of machines and therefore improving quality and cost in production
  • Support many programming languages at one point
  • Very fast in communication between controls and programming and equipment


  • They are difficult to upgrade as newer versions of windows are released to market
  • It becomes very difficult to implement some systems changes as times goes by as it is very hard to find control engineers who are familiar with this platform.
  • There must be long term product support which should be tied to old window versions.

Task 1b (i, ii??)

i)        Switches in PLC are used in operator for input in order to send instructions to the control circuit; in addition to that they are used to provide automatic feedback to the system (Morriss, 2000). They are several types of switches which include ,push button, pushbutton switch actuators, limit switches ,selector switches and indicator lamps just to name a few.

i)Five types of sensors in Engine controls ?

ii) Five devices that may be controlled in an industrial process???

Input sensors

Electronic control system is responsible for managing and monitoring engine functions which initially were performed by mechanical devices like vacuum, centrifugal advance units and carburetors (Bolton, 2006). In this type of electronic control system, some of these functions are managed in three limbs

  • Input phase of electronic control which allows for electronic control unit which monitor operating conditions in utilizing information from input sensors.
  • ????
  • Process phase of electronic control which requires ECU to use input information to make operating decisions about fuel and spark systems.
  • Output phase of electronic control which requires ECU to control output actuators, fuel injectors and ignite to achieve required results.

Input sensors used for injection and spark calculation

They include vane type air flow meters ,vane air how meter electrical circuit, Karman vortex flow meter, manifold absolute pressure sensor, engine speed crankshaft angle sensing and water temperature sensor .

Task 1c

Twisted pair cable

This is a type of wiring in which two conductors of single circuits which are twisted into single circuit for purposes of cancelling electromagnetic interference from external source (Morriss, 2000). These sources include. Electromagnetic radiation, cables and crosstalk.


  • It is less susceptible to electrical interference caused by nearby wires.
  • It is cheaper and very easier to splice.
  • It is electrically cleaner as STP wires which carry data a very fast speed.
  • Less like to cause interference among themselves


1. The STP wires are physically larger and more expensive than twisted pair.

2. STPs are more difficult to connect to terminating blocks

Coaxial cable

This is a type of a cable that has inner conductor by a tubular insulating layer which is surrounded by a tubular conducting shield. It is used to in transmission line of radio frequency and receivers (Morriss, 2000).


  • It is cheap as compared to twisted pair wires and UTP cables and easy to handle.
  • It is normally used for analogue and digital transmissions.
  • It has a better shield against electromagnet interference than twisted pair cable, also can span a longer distance of higher bits.


  • It is more expensive as compared to twisted pair cable.
  • It has slower data rates hence not suitable during data transmission.
  • It is thicker and more difficult to work with.
  • It is more expensive to install as compared to twisted cable.

Fire optic


  • Fibres do not leak light are quite difficult to tap hence data security is guaranteed.
  • Fibber is lighter than copper.
  • It is not affected by power surges, power failures or electromagnetic interferences.
  • It can handle much higher bandwidth than copper. However due to low attenuation repeaters are needed for only a distance of 30 km.


  • Fibber interfaces cost than electrical interfaces
  • Optical transmission is inherently unidirectional, therefore a two way communication is almost impossible.
  • It is unfamiliar technology which requires special skills which are not readily available.

Task 1d

1. CPU-Central processing unit is a brain of a computer where complex calculations are carried out. It is one of the computing powers of the computer system as it does complex calculations.

2.ALU-Arithemic logic unit is digital circuit that do perform anger arithmetic and logical operations .It is a fundamental building block of central processing unit of a computer and even simplest microprocessors contain at least one maintaining timers.

3. ROM-Read only memory is a class of storage medium that is used in computers and other electronic devices. When data is stored in ROM it can only be modified very slowly and normally it is used mainly to maintain distribute software.

4. RAM-Random access memory is a type of computer memory that can access randomly, and any memory can only be accessed without touching preceding bytes.

5. Register-in a computer system a register is small set of data which holds part of a processor.

6. Buses-In computer system architecture, a bias is a communication system that transfers data between components inside a computer or computers.

7. Flag-During programming, a flag is predefined bit or bits of sequence that holds a binary value.

Missing diagram

Task 2A. i)ii)iii)??

In a circuit, currently loops is a method of transmitting information and is carried in various levels of intensity which represent a continuum of values which are similar to voltage output of analogue to digital convertor and without noise and line length concerns (Stenerson,2009). In 4-20Ma currently loop, 4mA represents a zero value output of sensor and 20mA is the full scale output. This circuit allows room for wire break detection due to 4-Ma offset of zero .If the receiver reads 0mA then the circuit breaks down.

b).In electronics analogue to digital converter is a function that normally converts digital data which is usually in binary into analogue signal. It performs a reverse function where data can be manipulated and stored without degradation (Stenerson, 2009).Therefore resolution is basic variations in bit depth which primary affect noise levels from a quantization error to signal to noise ratio.

C) During automation processing, an analogue signal is required to maintain a predefined conditions .During variable conditions the maximum A/D voltage that can be obtained is 2o volts.

Task 2 b? i)ii)iii)iv)????

i) Octal numbers in a binary system which takes the form and has a base of 8. 80, 81, 82…. And Hexadecimal numbers have a base of 16

Task 2 b,?

Programmable logic controllers have used in manufacturing industries for last 20 years. It was designed as a replacement for hardwired rekey and timer logic to found in traditional control panels .PLC provides flexibility and ease of control that is based on programing and executing making logic instructions (Petruzella, 2011).

Features of PLCs

  • Standard input /output connections and signal levels
  • Ease of programming and reprogramming in plant
  • Capable of communicating with other PLCs ,intelligent devices
  • Easily understood programming language.
  • Rugged noise immune equipment.


  • PLC hardware and software are cheap to obtain
  • Programmable logic controllers digital input output are cheaper
  • Third generation DCs are cheap and easy to obtain.
  • PLCs are cost effective and ensures quality during manufacturing process
  • They increase efficiency


  • PLCs systems are expensive to obtain in current setting.
  • The required skilled labour work force is not readily available.
  • These systems are not easily upgradable and hence compatibility issues

Finally advantages of programmable control logic outweigh disadvantages us it has reduced wastage and increased quality and efficiency in our manufacturing sector.  See online tutoring.