Interview Questions.

Q1. Why four-20 Ma Preferred Over zero-10 V Signal ?

The zero-10 V signal has tendency to drop due to line resistance. If the space between sensor and input card is more the sign will now not nicely represent the sector value. The 4-20 mA will tour an extended distance without losing signal price.

Q2. What Are The Specifications Of The Control Valve ?

Following specs are used for control valve:

Flow medium and running 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

Q3. What Is Encoder?

A feedback tool which converts mechanical movement into electronic signals. Usually an encoder is a rotary tool that outputs virtual pulses which correspond to incremental angular motion. The encoder includes a pitcher or metallic wheel with alternating clean and opaque stripes which are detected by means of optical sensors to produce the virtual outputs.

Q4. Explain Working Of Differential Pressure Trmitters?

Process pressure is trmitted via setting apart 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 maximum deflection of0.004 inch (0.10 mm), is proportional to the applied pressure. Capacitor plates on both aspects of the sensing diaphragm discover the placement of the diaphragm. The trmitter electronics convert the differential capacitance between the sensing diaphragm and the capacitor plates into a two- wire, 4-20 mA dc signal and a digital output signal.

Q5. What Are The Flow Measuring Instruments Used In Flow Measurement ?

Differential pressure meters

Positive displacement

Velocity meters

Q6. What Type Of Pressure Sensors Used In Pressure Measurement?

Manometers

Bourdon tubes

Bellow elements

Diaphragm elements

DP trmitters

Q7. Explain Working Of Differential Pressure Measurement ?

Suitable restriction positioned in flow circulate causes a differential pressure throughout it. As float relies upon upon differential pressure (Head) & region, so any of them or each may be various for various drift.

Q8. What Is Trmitter?

A trmitter is an electronic device that is typically established within the area in near proximity to a sensor. The sensor (also known as a trducer) measures a bodily variable together with temperature or pressure and outputs a totally low level electronic sign. The primary feature of the trmitter is to offer the appropriate electric energy to turn on (or excite) the sensor then to examine the low stage sensor sign, expand it to a better level electric signal and ship that signal a long distance to a control or examine-out device.

Since low-stage electrical alerts do not trmit lengthy distances with super accuracy, installing a trmitter commonly gives a first-rate development within the accuracy of the data brought to a bigger control device. Typically the output shape the trmitter is four-20 mA or 0-10 V

Q9. Difference Between 2 Wire, three Wire And four Wire Trmitter?

In 2 cord trmitter the electricity and signal are trmitted via same cable.

In three wire trmitter the data sign and electricity are with recognize to not unusual ground.

In four wire trmitter  wires for power supply and two for indicators. Only cutting-edge trmitters can be used as 2 wire trmitters.

Q10. What Are The Components Of Control Valve ?

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

Q11. Which Are The Leading Plc Providers ?

The main PLC carriers encompass

Rockwell Automation : Allen Bradley (Micrologix, SLC, PLC, Control Logix)

Siemens ( S7 2 hundred, S7 three hundred , S7 400)

Grouppe Schneider : Modicon ( Nano, Micro, Premium, Quantum)

GE Fanuc : Versa, Series ninety-30, ninety-70

Messung : Nextgen

Q12. What Is Actuator ?

In a closed-loop manage machine, the part of the final control element that trlates the manage signal into movement by way of the manipulate tool.

An actuator is a component of a gadget that is answerable for moving or controlling a mechanism or machine. An actuator calls for a manage signal and a source of electricity. The manipulate signal is pretty low strength and may be electric voltage or present day, pneumatic or hydraulic strain, or even human strength.

Q13. What Are The Different Components Used In Automation?

The additives of automation machine include

Sensors for sensing the input parameters (RTD, Thermocouple, Pressure, Flow, Level; and so forth)

Trmitters for trmitting the raw sign in electric shape

Control machine which incorporates PLC, DCS & PID controllers

Output gadgets / actuators like drives, control valves.

Q14. Which Are The Leading Dcs Providers ?

The leading DCS vendors consist of

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 series

Q15. What Types Of Sensors Are Used For Measuring Different Parameters?

Temperature sensors – RTD, Thermocouple, Thermister

Pressure Sensor – Borden Tube, Bellows, Strain gauge

Flow sensor – Pitot tube, Orifice, Ultrasonic+

Level, Conductivity, Density, Ph

Q16. Difference Between Plc & Relay ?

PLC can be programmed whereas a relay can not.

PLC works for analog I/Os including PID loops etc. Whereas a relay cannot

PLC is a good deal more advanced in comparison to relay.

Modifications in relay base circuit is difficult in comparison to PLCs

Q17. What Is Pc Based Control System ?

In PC primarily based control gadget, the CPU of pc acts as processor, the PCI primarily based playing cards are used for connecting Input and Output. The RAM acts as memory. Hard disk is used as storage tool. Currently this systems are very beneficial while the big facts is to be continue with very high velocity. In many cases for extra accuracy we will use the real-time running device.

Q18. What Are The Different Control Systems Used In Automation?

PID Controller based totally control system

PLC primarily based manage system

DCS based Control gadget

PC Based automation machine

Q19. What Type Of Control Valves Used In The Industry ?

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

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

NON – REVERSE FLOW :- Check valves.

Q20. Explain Working Of Rtds?

Resistance Temperature Device works at the standards that the resistance of the cloth adjustments as its temperature changes. Temperature is decided by measuring resistance after which the usage of the RTD Resistance vs Temp feature to locate temperature. 

Typical elements used for RTD are Nickel, Copper and Platinum. Platinum is extensively used in RTDs due to accuracy. PT 100 me at 0 deg temp a hundred ohms resistance. A regular RTD consists of a fine platinum cord wrapped round a mandrel and protected with a shielding coating (glass or ceramic).

Q21. Explain Working Of Thermocouple?

Thermocouple includes two strips or wires made up of various metals and joined at one cease. The temperature at that juncture induces an electromotive pressure (emf) between the opposite ends. As the temperature goes up the emf also increases. Through wellknown charts and tables the corresponding temperature can be found out.

The courting between the thermocouple output and the temperature is quite non linear. Different metallurgies produce one-of-a-kind outputs. The specific metallurgies and one of a kind lineararities result in exceptional thermocou0le designations which includes “J”, “K,”, “N”, “L”, and so forth.

Q22. What Is Field Bus ?

Fieldbus is a wellknown term for a virtual handiest, high speed communications protocol. The key characteristic to Fieldbus communications is higher pace communications with the opportunity of addressing multiple trmitters all at the equal discipline wiring. The Foundation Fieldbus is a specific virtual protocol that is frequently shortened to simply be known as Fieldbus. Other virtual best communications together with Profibus are also Fieldbus protocols

Q23. Explain Pid Based Control System?

PID (Proportional Integral Derivative) is the set of rules extensively utilized in closed loop manage. The PID controller looks after closed loop control in plant. A variety of PID controller with unmarried or a couple of loop can be taken on community.

PID Controllers are widely for independent loops. Although some good judgment may be carried out but no longer an awful lot of sequential good judgment may be implemented in PIDs.

Q24. What Are The Components Of Differential Flow Sensor ?

For developing differential pressure : Orifice plate, Venturi Tube, Flow Nozzle , pitot tube

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

Q25. What Is Control Valves ?

The manipulate valve, typically named the final manage detail of control incorporates a pneumatic tool that converts the manage signal from the controller in motion, regulating the flow.

A control valve is a valve used to govern fluid go with the flow by using varying the scale of the glide passage as directed through a sign from a controller. This allows the direct manipulate of go with the flow price and the consequential manipulate of technique portions which include stress, temperature, and liquid degree.

Q26. What Is Cold Junction Compensation?

The enterprise usual standard for the temperature at open end is zero deg C. Therefore maximum tables and chart make the assumption that the temp at open give up is 0 deg C. In enterprise the open ends are continually at actual room temperature and no longer zero deg C. The emf adjustment because of distinction between the real temp and zero deg C is referred as Cold Junction Correction (CJ Correction)

Q27. Difference Between Plc & Dcs ?

DCS: The machine makes use of more than one processors, has a significant database and the capability is sent. That is the controller sub device performs the manage features, the history node connects the facts, the IMS node offers reports, the operator station offers a terrific HMI, the engineering station permits engineering changes to be made.

PLC: The device has processor & I/O’s and a few useful gadgets like fundamental modules, communication modules and so on. Uses a SCADA for visualization. Generally the SCADA does no longer use a imperative database.

DCS is regularly used inside the massive flowers where the redundancy stage wanted is more and the analog input used are excessive.

Q28. Why four-20 Ma Preferred Over 0-20 Ma Signal ?

With 0- 20 mA you can not distinguish between minimum discipline fee and connection destroy. With 4-20 mA, inner circuit can distinguish between connection ruin of minimal fee. Normally when the cost is minimum the trmitter will give you four mA at the same time as in case of connection breakage it will provide 0 mA.

Q29. What Is Flow Coefficient ?

It is the waft of water (G=1, T= 6 to 34 deg. C) via the valve at complete lift in U.S gallon per minute with a strain drop across the valve of one psi.

Q30. Temperature Measurement Range Supported By Thermocouple ?

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

Q31. Which Are The Leading Scada Software / Mmi Providers ?

The leading SCADA software / MMI vendors include

Wonderware : InTouch

Intellution iFix (Earlier FixDMACS)

Siemens : WinCC

Allen Bradley : RS View ( Earlier Control View)

KPIT : Astra

Q32. What Is Automation?

Automation is delegation of human control functions to technical system for increasing productivity, better quality, decreased fee & multiplied in protection working conditions.

Q33. Temperature Measurement Range Supported By Rtds?

The RTD paintings on temperature variety between–250 to 850 deg C.

Q34. Can I Split My One T/c Signal To Two Separate Instruments?

No. The T/C sign is a totally low-degree millivolt signal, and have to most effective be connected to at least one tool. Splitting to 2 gadgets may also result in bad readings or lack of sign. The solution is to use a “dual” T/C probe, or convert one T/C output to a 4-20 mA signal with the aid of the use of a trmitter or signal conditioner; then the brand new signal can be sent to more than one device