Q.A.

What is Automation? 

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

What are the different components used in automation? 

Sensors for sensing the input parameters, 

Transmitters for transmitting the raw signal in electrical form, 

Control system which includes PLC, DCS & PID controllers, 

Output devices / actuators like drives, control valves.

Difference between PLC & DCS? 

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.

Which are the companies involved in automation?
There are many service provider 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 types of sensors are used for measuring different parameters?

Temperature sensors – RTD, Thermocouple, Thermistor
Pressure Sensor – Borden Tube, Bellows, Strain gauge
Flow sensor – Pitot tube
Level, Conductivity, Density, Ph

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.

What is valve?

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:-

• Hydraulic
• Pneumatic
• Manual
• Solenoid

What is transmitter?

     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.

Difference between 2 wire, 3 wire & 4 wire transmitters.

     In 2 wire transmitter the power and signal are transmitted through same cable.

     In 3 wire transmitter the data signal and power are with respect to common ground.
     In 4 wire transmitter two wires for power supply and two for signals.

Difference between Relay and Contactor.

Relay:-

• It is 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:-

• 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 motor, lighting, heating, capacitor bank.

What is PLC?
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.

What are the components in CPU? 

Central Processing Unit (CPU), Power Supply, I/O modules, Communication bus.

Explain the term Bit, Nibble, Byte, Word and Double word. 

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 contain 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 basic addressable element. 

Word

     It contains 16 bit = 2 bytes. 

Double word

     It contains 32 bit = 4 bytes = 2 word. 

     A unit of computer memory storage used in many high-level programming.

What is meaning of resolution in I/O cards in PLC?

     It is the minimum charge in I/P parameter which can sensed by 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 much bit 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. (212). For 16 bit data the counts will be from 0 to 65536 (216). More the resolution the data will be more accurate.

Give information about DH, Control net, Device net and Ethernet protocol. 

DH (Data Highway)

• 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

• A low-time, control-layer network providing high-speed transport of both time-critical IO data and messaging data, include 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

• The standard for logical communications networks developed jointly by digital equipment crop 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.

	DH+	DH485	Device Net	Control Net
Baud rate max.	230.4 Kbit/s	19.2 Kbit/s	500 Kbit/s	5 Mbit/s
No. of max. nodes	64	32	64	99
Network length	3.048	1.2 Km	0.487 Km	30 Km

Why 4 to 20 mA signal is preferred? 

     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. 

What is Encoder?

Please see the Process Instrument Section.