We have prepared an article for questions and answers for interviews with industrial automation engineers.
Interview questions for industrial automation engineers
1. What is automation?
AutomationIt is the delegation of human control functions to technical teams to increase productivity, improve quality, reduce costs and increase safety conditions at work.
2. What are the different components used in automation?
Automation system components include
- Sensors to detect input parameters (RTD, thermocouple, pressure, flow, level, etc.)
- Transmitters to transmit the raw signal in electrical form
- control system includingANONYMOUS SOCIETY,DCS&PID controllers
- Output devices/actuators such as actuators, control valves.
3. What are the different control systems used in Automation?
- PID controller based control system
- PLC based control system
- DCS based control system
- PC based automation system
4. Explain the PID based control system.
PID (Proportional Integral Derivative) is the widely used algorithm in closed-loop control.
The PID controller is responsible for the closed loop control in the plant. Multiple single loop or multiloop PID controllers can be used on the network.
PID controllers are largely for independent loops. While some logic can be implemented, little sequential logic can be implemented in PIDs.
5. Difference between PLC and relay?
- The PLC can be programmed while a relay cannot.
- PLC works for analog I/O like PID loops etc whereas a relay cannot.
- PLC is much more advanced compared to relay.
- Relay base circuit modifications are difficult compared to PLCs.
6. Difference between PLC and DCS?
The system uses multiple processors, has a central database, and the functionality is distributed. That is, the controller subsystem performs control functions, the history node connects data, the IMS node provides reports, the operator station provides a good HMI, the engineering station allows for engineering changes.
The system has processor and I/O and some functional units like basic modules, communication modules, etc. It uses a SCADA for visualization. usually theSCADAit does not use a central database.
DCS is often used in large plants where the required level of redundancy is higher and the analog input used is high.
7. What is a PC-based control system?
In PC-based control system, the computer's CPU acts as the processor, PCI-based boards are used to connect input and output. RAM works like memory. The hard disk is used as a storage device.
Currently, these systems are very useful when large amounts of data must be processed at very high speed. In many cases, for greater accuracy, we can use the operating system in real time.
8. What is the encoder?
A feedback device that converts mechanical motion into electronic signals. Typically, an encoder is a rotating device that emits digital pulses that correspond to incremental angular motion.
oencoderIt consists of a glass or metal wheel with alternating light and opaque stripes that are detected by optical sensors to produce digital outputs.
9. What are the main PLC suppliers?
The leaderPLC suppliersinclude
- Rockwell Automation: Allen Bradley (Micrologix, SLC, PLC, Control Logix)
- Siemens (S7 200, S7 300, S7 400)
- Schneider Group: Modicon (Nano, Micro, Premium, Quantum)
- GE Fanuc: Versa, Series 90-30, 90-70
- Measure: Nextgen
10. Who are the main DCS vendors?
Major DCS providers include
- Yokogawa: Centum VP, CS 3000, CS 5000 (formerly Centum Excel, Micro Excel)
- Honeywell: TDC 3000
- Fisher-Rosemant-Delta V
- ABB – Independent 2000
- Moore – APACS
- Foxboro – Série I/A
11. What are the main SCADA software vendors?
The leadersoftware SCADA/ MMI providers include
- Wonderware: in touch
- Intellution iFix (anterior FixDMACS)
- Siemens: WinCC
- Allen Bradley: RS View (formerly Control View)
- KPIT: Astra
12. What types of sensors are used to measure different parameters?
- temperature sensors– RTD, thermocouple, thermistor
- pressure sensor– Borden Tube, Fole, Strain Gauge
- flow sensor– Pitot Tube, Orifice, Ultrasonic+
- Level, Conductivity, Density, Ph
13. What is the transmitter?
A transmitter is an electronic device typically mounted in the field near 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 oftransmitteris to provide the correct electrical power to turn on (or trigger) the sensor, then read the low-level sensor signal, amplify it to a higher-level electrical signal, and send that signal over a long distance to a device. control or reading.
Since low-level electrical signals are not transmitted over long distances with great accuracy, installing a transmitter often provides a great improvement in the accuracy of the information provided to a larger control system. Normally, the transmitter output is 4 to 20 mA or 0 to 10 V.
14. Why is a 4-20 mA signal preferred over a 0-10 V signal?
The 0-10V signal tends to drop due to line resistance. If the distance between the sensor and the input card is greater, the signal will not correctly represent the field value.
o4-20mAit will travel a long distance without losing signal value.
15. Why is a 4-20 mA signal preferred over a 0-20 mA signal?
With 0-20 mA it is not possible to distinguish between the minimum value of the field and the interruption of the connection. With 4-20mA, the internal circuit can distinguish between minimum value connection breakage.
Normally, when the value is minimum, the transmitter will supply 4 mA, while in case of connection break, it will supply 0 mA.
16. Difference between 2-wire, 3-wire and 4-wire transmitter.
No2 wire transmitterpower and signal are transmitted through the same cable.
No3 wire transmitterData signal and power are relative to the common ground.
No4 wire transmittertwo wires for power and two for signals. Only current transmitters can be used as 2-wire transmitters.
17. What is a “smart” transmitter?
A "smart" transmitter is a transmitter that uses a microprocessor as the heart of the electronics.
Furthermore"Smart" Transmitterit will generate some sort of remote digital communication that will allow you to read and configure the device from a remote location.
18. What is fieldbus?
Fieldbus is a general term for a digital-only high-speed communication protocol. The key attribute of Fieldbus communications is higher speed communications with the ability to address multiple transmitters on the same field wiring.
Foundation Fieldbus is a specific digital protocol that is often abbreviated to simplyfieldbus. Other digital-only communications such as Profibus are also Fieldbus protocols
19. What is the actuator?
In a closed-loop control system, thelast control elementwhich translates the control signal into action by the control device.
EsolenoidIt is a component of a machine responsible for moving or controlling a mechanism or system.
Esolenoidrequires a control signal and a power source. The control signal is of relatively low energy and can be electrical voltage or current, pneumatic or hydraulic pressure, or even human power.
20. Explain the operation of RTDs
The resistance temperature device works on the principle that the resistance of the material changes as its temperature changes.
Temperature is determined by measuring resistance and then using the RTD Resistance vs Temp feature to detect temperature.
Typical elements used for RTDs are nickel, copper and platinum. Platinum is widely used in RTDs because of its precision.
PT 100 means at 0 degrees temperature 100 ohms resistance. A typical RTD consists of a thin platinum wire wound on a mandrel and covered with a protective coating (glass or ceramic).
21. Temperature measurement range allowed by RTD?
The RTD works in a temperature range between -250 and 850 degrees C.
22. Explain the thermocouple operation
The thermocouple consists of two strips or wires made of dissimilar metals and joined at one end. The temperature at that point induces an electromotive force (emf) between the other extremes.
As the temperature increases, the emf also increases. Using standard charts and tables, you can find out the corresponding temperature.
The relationship between thethermoelectric coupleoutput and temperature are quite non-linear.
Different metallurgy produce different results. Different metallurgy and different linearities result in different thermocouple designations, such as "J", "K", "N", "L", etc.
23. What is Cold Junction compensation?
The industry accepted standard for open end temperature is 0°C.
Therefore, most tables and graphs assume that the temperature at the open end is 0 °C. In industry, open ends are always at actual ambient temperature, not 0°C.
The adjustment of emf due to the difference between the actual temperature and 0 degrees C is known as the cold junction correction (CJ correction).
24. Temperature measurement range supported by thermocouple?
The thermocouple works in a wide temperature range, i.e. from –270 to 2300.
25. Can we split a T/C signal into two separate instruments?
Do not. The T/C signal is a very low level millivolt signal and should only be connected to one device.
Splitting two devices can result in poor readings or signal loss.
The solution is to use a “dual” T/C probe or convert a T/C output to a 4-20 mA signal using a transmitter or signal conditioner; then the new signal can be sent to more than one instrument
26. What are the flow measuring instruments used in flow measurement?
- Differential Manometers
- of positive displacement
- speed meters
27. Explain how differential pressure measurement works?
Proper restriction placed on the flowing stream causes adifferential pressurethrough him.
As the flow depends on the differential pressure (head) and the area, one or both can be varied to vary the flow.
28. What are the components of the differential flow sensor?
To create differential pressure:Orifice Plate, Venturi Tube, Flow Nozzle, Pitot Tube
To measure the pressure:U-tube gauges, balance ring gauge, D.P. Cell
29. What type of pressure sensor is used in pressure measurement?
- pressure gauges
- bourdon tubes
- bellows elements
- diaphragm elements
- PD transmitters
30. Explain the operation of differential pressure transmitters.
Process pressure is transmitted through isolating diaphragms and oil fill fluid to a sensing diaphragm. The sensing diaphragm is a stretched spring element that deflects in response to the differential pressure across it.
The displacement of the sensing diaphragm, a maximum deviation of 0.004 inches (0.10 mm), is proportional to the applied pressure.
capacitor plateson both sides of the diaphragm sensors detect the position of the diaphragm.
The transmitter electronics convert the differential capacitance between the sensing diaphragm and capacitor plates into a 2-wire 4-20 mA DC signal and a digital output signal.
31. What are control valves?
The control valve, commonly referred to as the final control element of the control, contains a pneumatic device that converts the control signal from the controller into action, regulating flow.
ONEcontrol valveIt is a valve used to control fluid flow by varying the size of the flow passage as directed by a signal from a controller.
This allows direct control of flow rate and subsequent control of process quantities such as pressure, temperature and liquid level.
32. What type of control valves are used in the industry?
- ON - OFF SERVICES: -Trigger, ball, diaphragm, male, butterfly valves.
- ACCELERATION SERVICES:-Globe, butterfly, diaphragm, sleeve valves.
- NON-REVERSE FLOW:-Check valves.
33. What are the control valve specifications?
The following specifications are used for the control valve
- Flow medium and operating temperature
- Flow rate kg/h or Nm3/h Max./Min./Normal
- Inlet and outlet pressure: kg/cm2 Max/Min/Normal
- maximum permissible pressure difference: kg/cm2
- Average density: kg/m3
- Cv: Valve flow coefficient
34. What are the components of the control valve?
- Actuator, Body, Gasket, Diaphragm, Diaphragm Plate, Actuator Rod
- Actuator spring, seat, travel indicator, valve stem, gaskets, yoke, handwheel
35. What is the flow coefficient?
It is the water flow (G = 1, T = 6 at 34 degrees C) through the valve at full opening in US gallons per minute with a pressure drop across the valve of 1 psi.
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