Interview Questions.

Question 1. What Is Automation?

Answer :

Automation is delegation of human control capabilities to technical equipment for increasing productiveness, better great, reduced price & expanded in protection running conditions.

Question 2. What Are The Different Components Used In Automation?

Answer :

The components of automation device consist of

Sensors for sensing the input parameters (RTD, Thermocouple, Pressure, Flow, Level; and many others)
Transmitters for transmitting the raw sign in electrical form
Control gadget which incorporates PLC, DCS & PID controllers
Output gadgets / actuators like drives, manage valves.
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Question 3. What Are The Different Control Systems Used In Automation?

Answer :

PID Controller based control gadget
PLC based manage system
DCS based totally Control gadget
PC Based automation system
Question four. Explain Pid Based Control System?

Answer :

PID (Proportional Integral Derivative) is the algorithm widely utilized in closed loop control. The PID controller takes care of closed loop manipulate in plant. A number of PID controller with single or a couple of loop can be taken on network.

PID Controllers are broadly for independent loops. Although some good judgment may be applied however now not a whole lot of sequential common sense may be carried out in PIDs.

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Question 5. Difference Between Plc & Relay ?

Answer :

PLC can be programmed whereas a relay can't.
PLC works for analog I/Os such as PID loops etc. Whereas a relay can't
PLC is much greater advanced in comparison to relay.
Modifications in relay base circuit is difficult in comparison to PLCs
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Question 6. Difference Between Plc & Dcs ?

Answer :

DCS: The gadget makes use of more than one processors, has a principal database and the functionality is distributed. That is the controller sub gadget plays the control features, the history node connects the statistics, the IMS node offers reports, the operator station offers a good HMI, the engineering station allows engineering adjustments to be made.

PLC: The machine has processor & I/O’s and some purposeful devices like fundamental modules, verbal exchange modules and so forth. Uses a SCADA for visualization. Generally the SCADA does no longer use a central database.

DCS is often used inside the massive flowers where the redundancy stage needed is more and the analog enter used are excessive.

Question 7. What Is Pc Based Control System ?

Answer :

In PC primarily based manipulate device, the CPU of computer acts as processor, the PCI based totally playing cards are used for connecting Input and Output. The RAM acts as memory. Hard disk is used as garage device. Currently this systems are very useful while the large facts is to be proceed with very high velocity. In many cases for greater accuracy we will use the real-time working device.

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Question eight. What Is Encoder?

Answer :

A feedback tool which converts mechanical motion into digital signals. Usually an encoder is a rotary tool that outputs virtual pulses which correspond to incremental angular movement. The encoder includes a glass or metallic wheel with alternating clear and opaque stripes which can be detected through optical sensors to provide the digital outputs.

Question nine. Which Are The Leading Plc Providers ?

Answer :

The leading PLC companies include

Rockwell Automation : Allen Bradley (Micrologix, SLC, PLC, Control Logix)
Siemens ( S7 2 hundred, S7 300 , S7 four hundred)
Grouppe Schneider : Modicon ( Nano, Micro, Premium, Quantum)
GE Fanuc : Versa, Series 90-30, 90-70
Messung : Nextgen
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Question 10. Which Are The Leading Dcs Providers ?

Answer :

The leading DCS companies include

Yokogawa : Centum VP, CS 3000 , CS 5000 (Earlier Centum Excel, Micro Excel)
Honeywell : TDC 3000
Fisher – Rosemant – Delta V
ABB – Freelance 2000
Moore – APACS
Fox boro – I/A collection
Question eleven. Which Are The Leading Scada Software / Mmi Providers ?

Answer :

The main SCADA software / MMI companies include

Wonderware : InTouch
Intellution iFix (Earlier FixDMACS)
Siemens : WinCC
Allen Bradley : RS View ( Earlier Control View)
KPIT : Astra
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Question 12. What Types Of Sensors Are Used For Measuring Different Parameters?

Answer :

Temperature sensors – RTD, Thermocouple, Thermister
Pressure Sensor – Borden Tube, Bellows, Strain gauge
Flow sensor – Pitot tube, Orifice, Ultrasonic+
Level, Conductivity, Density, Ph
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Question thirteen. What Is Transmitter?

Answer :

A transmitter is an digital device that is usually mounted inside the field in near proximity to a sensor. The sensor (also called a transducer) measures a bodily variable which includes temperature or pressure and outputs a very low stage digital signal. The simple feature of the transmitter is to offer the right electrical energy to show on (or excite) the sensor then to examine the low degree sensor sign, extend it to a better stage electric sign and send that sign an extended distance to a control or examine-out device.

Since low-level electric indicators do not transmit long distances with first-rate accuracy, putting in a transmitter commonly offers a extraordinary improvement in the accuracy of the facts added to a larger manipulate machine. Typically the output shape the transmitter is four-20 mA or 0-10 V

Question 14. Why 4-20 Ma Preferred Over 0-10 V Signal ?

Answer :

The 0-10 V signal has tendency to drop due to line resistance. If the space among sensor and input card is extra the signal will no longer nicely constitute the field price. The 4-20 mA will journey an extended distance without dropping sign price.

Question 15. Why 4-20 Ma Preferred Over 0-20 Ma Signal ?

Answer :

With 0- 20 mA you can not distinguish among minimum subject cost and connection smash. With four-20 mA, internal circuit can distinguish among connection destroy of minimum fee. Normally whilst the price is minimal the transmitter will give you four mA while in case of connection breakage it'll supply 0 mA.

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Question 16. Difference Between 2 Wire, three Wire And four Wire Transmitter?

Answer :

In 2 cord transmitter the strength and sign are transmitted thru equal cable.
In three twine transmitter the facts signal and electricity are with recognize to commonplace floor.
In 4 cord transmitter two wires for electricity supply and two for indicators. Only contemporary transmitters can be used as 2 wire transmitters.
Question 17. What Is A “clever” Transmitter ?

Answer :

A “Smart” transmitter is a transmitter that makes use of a microprocessor because the coronary heart of the electronics. In addition, a “Smart” transmitter will output a few sort of faraway digital communications permitting you to study and set-up the device from a far flung position. 

Industrial Instrumentation Interview Questions
Question 18. What Is Field Bus ?

Answer :

Fieldbus is a fashionable term for a digital only, excessive pace communications protocol. The key characteristic to Fieldbus communications is higher speed communications with the opportunity of addressing a couple of transmitters all at the same subject wiring. The Foundation Fieldbus is a specific virtual protocol that is regularly shortened to just be referred to as Fieldbus. Other digital only communications which includes Profibus also are Fieldbus protocols

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Question 19. What Is Actuator ?

Answer :

In a closed-loop manage machine, the a part of the very last manipulate element that translates the manage sign into movement with the aid of the manipulate device.

An actuator is part of a machine this is answerable for moving or controlling a mechanism or device. An actuator requires a control signal and a source of power. The control signal is highly low energy and can be electric powered voltage or current, pneumatic or hydraulic strain, or maybe human energy.

Question 20. Explain Working Of Rtds?

Answer :

Resistance Temperature Device works at the ideas that the resistance of the material modifications as its temperature adjustments. Temperature is determined by using measuring resistance after which the use of the RTD Resistance vs Temp function to detect temperature. 

Typical factors used for RTD are Nickel, Copper and Platinum. Platinum is widely utilized in RTDs because of accuracy. PT one hundred way at 0 deg temp a hundred ohms resistance. A typical RTD includes a pleasant platinum twine wrapped around a mandrel and covered with a defensive coating (glass or ceramic).

Question 21. Temperature Measurement Range Supported By Rtds?

Answer :

The RTD paintings on temperature range among–250 to 850 deg C.

Question 22. Explain Working Of Thermocouple?

Answer :

Thermocouple includes  strips or wires made up of various metals and joined at one give up. The temperature at that juncture induces an electromotive force (emf) between the other ends. As the temperature is going up the emf also will increase. Through popular charts and tables the corresponding temperature may be found out.

The relationship among the thermocouple output and the temperature is quite non linear. Different metallurgies produce one of a kind outputs. The distinct metallurgies and exceptional lineararities bring about exceptional thermocou0le designations which includes “J”, “K,”, “N”, “L”, and many others.

Question 23. What Is Cold Junction Compensation?

Answer :

The enterprise normal general for the temperature at open end is 0 deg C. Therefore maximum tables and chart make the assumption that the temp at open end is zero deg C. In enterprise the open ends are always at actual room temperature and now not 0 deg C. The emf adjustment due to distinction between the actual temp and zero deg C is referred as Cold Junction Correction (CJ Correction)

Question 24. Temperature Measurement Range Supported By Thermocouple ?

Answer :

The thermocouple work on huge temperature variety ie –270 to 2300.

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Question 25. Can I Split My One T/c Signal To Two Separate Instruments?

Answer :

No. The T/C sign is a very low-stage millivolt sign, and need to most effective be linked to one device. Splitting to two gadgets may bring about bad readings or loss of signal. The answer is to use a “dual” T/C probe, or convert one T/C output to a four-20 mA sign by means of the use of a transmitter or signal conditioner; then the new signal may be sent to a couple of device

Question 26. What Are The Flow Measuring Instruments Used In Flow Measurement ?

Answer :

Differential pressure meters
Positive displacement
Velocity meters
Question 27. Explain Working Of Differential Pressure Measurement ?

Answer :

Suitable restriction placed in waft circulate reasons a differential stress across it. As waft relies upon upon differential stress (Head) & region, so any of them or each can be numerous for varying glide.

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Question 28. What Are The Components Of Differential Flow Sensor ?

Answer :

For growing differential stress : Orifice plate, Venturi Tube, Flow Nozzle , pitot tube

For measuring pressure : U-Tube Manometers, Ring–Balance Manometer, D.P. Cell

Question 29. What Type Of Pressure Sensors Used In Pressure Measurement?

Answer :

Manometers
Bourdon tubes
Bellow elements
Diaphragm elements
DP transmitters
Question 30. Explain Working Of Differential Pressure Transmitters?

Answer :

Process pressure is transmitted via isolating diaphragms and oil fill fluid to a sensing diaphragm. The sensing diaphragm is a stretched spring element that deflects in response to differential strain throughout it. The displacement of the sensing diaphragm, a most deflection of0.004 inch (zero.10 mm), is proportional to the implemented stress. Capacitor plates on each facets of the sensing diaphragm hit upon the placement of the diaphragm. The transmitter electronics convert the differential capacitance among the sensing diaphragm and the capacitor plates into a two- twine, four-20 mA dc signal and a virtual output signal.

Question 31. What Is Control Valves ?

Answer :

The control valve, generally named the final manipulate element of manage carries a pneumatic tool that converts the manipulate sign from the controller in motion, regulating the float.

A manage valve is a valve used to control fluid drift by means of varying the scale of the drift passage as directed by means of a signal from a controller. This enables the direct manage of go with the flow price and the consequential control of technique quantities which include strain, temperature, and liquid degree.

Question 32. What Type Of Control Valves Used In The Industry ?

Answer :

ON – OFF SERVICES :- Gate, Ball, Diaphragm, Plug, Butterfly valves.

THROTTLING SERVICES :- Globe, Butterfly, Diaphragm, Pinch valves.

NON – REVERSE FLOW :- Check valves.

Question 33. What Are The Specifications Of The Control Valve ?

Answer :

Following specifications are used for control valve:

Flow medium and operating temperature
Flow price kg/hr or Nm3/hr Max/Min/Normal
Inlet and Outlet stress : kg/cm2 Max/Min/Normal
Max. Allowable diff. Pressure : kg/cm2
Density of medium : kg/m3
Viscosity
Cv : Valve Flow Coefficient
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Question 34. What Are The Components Of Control Valve ?

Answer :

Actuator, Body, Trim, Diaphragm, Diaphragm plate, Actuator stem, Actuator spring, Seat, Travel Indicator, Valve stem, Gaskets, Yoke, Hand wheel

Question 35. What Is Flow Coefficient ?

Answer :

It is the waft of water (G=1, T= 6 to 34 deg. C) through the valve at complete raise in U.S gallon according to minute with a stress drop throughout the valve of 1 psi.