Question - Answer

Automation is delegation of human control functions to technical equipment for increasing productivity, better quality, and reduced cost & increased safety working conditions.

DCS: The system uses multiple processors, has a central database and the functionality is distributed. That is the controller sub system performs the control functions, the history node connects the data, the IMS node gives reports, the operator station gives a good HMI, the engineering station allows engineering changes to be made.
PLC: The system has processor & I/O’s and some functional units like basic modules, communication modules and so on. Uses a SCADA for visualization. Generally the SCADA does not use a central database.

There are many service providers who work in industrial automation. Some of them include Siemens (Germany), Rockwell Automation Allen Bradley (USA), Schneider (France), Yokogawa (Japan), Emerson Process Management, Honeywell (USA).

➤ What is PID?

Proportional Integral Derivative is an algorithm widely used in automation for closed loop control.
PID produces a control signal consisting of three terms-one proportional to error signal, another one proportional to integral of error signal and third one proportional to derivative of error signal.

A valve is a device that regulates, directs or controls the flow of a fluid (gases, liquids, fluidized solids) by opening, closing, or partially obstructing various passageways.
Types:-

A transmitter is an electronic device that is generally mounted in the field in close proximity to a sensor. The sensor (also known as a transducer) measures a physical variable such as temperature or pressure and outputs a very low level electronic signal.
The basic function of the transmitter is to provide the correct electrical power to turn on (or excite) the sensor then to read the low level sensor signal, amplify it to a higher level electrical signal and send that signal a long distance to a control or read-out device.
Since low-level electrical signals do not transmit long distances with great accuracy, installing a transmitter generally gives a tremendous improvement in the accuracy of the information delivered to a larger control system.

In 2 wires transmitters the power and signal are transmitted through the same cable.
In 3 wires transmitters the data signal and power are with respect to common ground.
In 4 wires transmitter two wires for power supply and two for signals.

Relay:-
1. - It is an electrically operated switch.
  - Relays are used where it is necessary to control a circuit by a low-power signal (with complete electrical isolation between control and controlled circuits), or where several circuits must be controlled by one signal.
  - Simple electromagnetic relay consists of a coil wrapped around a soft iron core.

Contactor:-
1. - It is an electrically controlled switch used for switching a power circuit. Similar to relay expect with higher current rating.
  - It is used to control electric motors, lighting, heating, capacitor bank.

PLC means Programmable Logic Controller. The PLC is programmed interface between the field I/P element like limit switches, sensors, push button and the final control elements like actuator, solenoid/control valves, drives, hooters etc.

Bit
- - It is a variable or computed quantity that can have only two possible values 0 or 1.

Nibble
- - It is a four bit aggregation or half an octal. It contains 4 bit, there are sixteen (24) possible values, so a nibble corresponds to a single hexadecimal digit.
Byte
- - It is a unit of digital information in computing and telecommunication that must commonly consist of eight bit.
  - Range 0 to 255 (28)
  - It is a basic addressable element.
Word
- - It contains 16 bit = 2 bytes.
Double word
- - It contains 32 bit = 4 bytes = 2 words.
  - A unit of computer memory storage used in many high-level programming.

It is the minimum charge in the I/P parameter which can be sensed by the I/P card. As far as digital I/O is connected it takes only one bit for operation.
In case of analog I/P the resolution determines how many bits are used for I/P or O/P.
For example a 12 bit resolution card means I/P will come as 0 to 4095 count. (2^12). For 16 bit data the counts will be from 0 to 65536 (2^16). The resolution of the data will be more accurate.

DH (Data Highway)
1. - The proprietary data network used by Allen Bradley PLCs to communicate information to and from other PLCs on the network or to and from host computers attached to the network.

Control net
1. - A low-time, control-layer network providing high-speed transport of both time-critical IO data and messaging data, including upload/download of programming and configuration data and peer-to-peer messaging, on a single physical media link.
Device net

A low cost communication link that connects industrial devices to a network. It is based on broadcast oriented communication protocol-the controller area network.

Ethernet
1. - The standard for logical communications networks developed jointly by digital equipment corp Xerox and intel.
  - Ethernet baseband coaxial cable transmits data at speed up to 10 megabits per second. Ethernet is used as the underlying vehicle by several upper-level protocols, including TCP/IP.

4 to 20 mA signal is standard now a days because it is perfect to sense by any sensor condition for 0 (OFF) & 1 (ON). If we select 0 to 20 mA signal then it is very difficult to identify between sensors OFF condition or signal lost condition.
This (4 to 20 mA) range is also very good for noise reduction. That is why we can get exact result & output.