1. What is Measurement?
This is a function that compares the unknown quantity to the standard, resulting in the knowledge of the unknown quantity’s quantity based on the standard used for comparison.
2. What is a Thermocouple?
It is a junction of two materials used to convert heat into electrical energy. When a pair of wires made up of two completely different metals are joined together and kept both the joints in two different temperatures, as a result, a voltage difference is produced proportional to the heat.
3. Types of Thermocouples
Type B
Type C
Type D
Type E
Type G
Type J
Type K
Type N
Type R
Type S
Type T
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4. Working Principle of Thermocouple?
The principle of thermocouple depends on the three effects;
See beck, Peltier, and Thompson.
See beck-effect
This type of reaction occurs when two metals with different properties are mixed. When heat is applied to any of the metal wires, electrons flow from the hot metal wire to the cold metal wire. As a result, direct current energizes the circuit.
Peltier-effect
Peltier’s effect is the total opposite of See beck’s. This effect states that by applying a potential difference between two dissimilar conductors, a temperature difference can be formed.
Thompson-effect
The voltage induces the total conductor’s length due to the temperature gradient as two disparate metals fix together and form two joints, according to this effect. This is a physical term that describes the rate and direction of temperature change at a specific location.
5. Advantages of thermocouple
• High-temperature range (-180 to 2320 °C)
• Inexpensive
• Large variety
• Large temperature range
• Rugged
• Self-powered
6. Disadvantages of thermocouple
• Non-linear
• Low voltage
• Require reference
• Less stable
7. What is RTD?
RTD stands for Resistance Temperature Detector. RTDs are sensors used to measure temperature
8. Types of RTD?
• Wire-Wound RTD
• Thin Film RTD
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9. Working principle of RTD?
The relationship between the resistance and temperature of the metal is the working principle of RTD, which means that the resistance of a metal varies with temperature. The amount of change in the material’s resistance value caused by a per degree increase in temperature is measured, and the sensor is calibrated accordingly.
10. Difference between 2 wire, 3 wire, and 4 wire transmitters.
A 2-wire transmitter transmits both power and signal over a single cable. Power and data signal is always directly proportional to the common ground in a 3-wire transmitter but in a 4-wire transmitter, there is a dedicated 2- wire each for both the power supply and data signals
11. Difference between Thermocouple & RTD?
12. Advantages of RTD
• More accurate
• Linear output
• High sensitivity
13. Disadvantages of RTD
• Expensive
• Require external current source
• Small
• Small base resistance
14. What is Thermistor?
The term thermistor is derived from “thermal” and “resistor”. It is a kind of resistor whose resistance is proportional to the temperature. They’re made of metallic oxide that’s been molded into a bead, disc, or cylindrical shape, then covered in epoxy or glass.
15. Types of thermistors
• Positive Temperature Coefficient (PTC) Thermistor
• Negative Temperature Coefficient (NTC) Thermistor.
16. What is a Positive Temperature Coefficient Thermistor?
In a PTC thermistor, the resistance is directly proportional to the temperature that means the value of resistance increases when the value of temperature increases. These types of sensors are used in fuses for the protection of circuits
17. What is a Negative Temperature Coefficient Thermistor?
In an NTC thermistor, the resistance is indirectly proportional to the temperature that means the value of resistance decreases when the value of temperature increases and its conductivity increases. When temperature increases the electrons are formed and increase the conductivity of an object.
NTCs are used in temperature measuring devices.
18. Advantages of thermistor
• High sensitivity to the temperature
• Low cost
• Small in size
• Easy to dismantle
19. Disadvantages of thermistor
• Limited range in measurement
• Non-linear characteristics for NTC
20. What is Process control?
It is the ability of a device to monitor and analyze the process to get the desired outcome. It helps to keep the quality and performance in the industry.
21. What is thermowells?
Thermowells are used to protect thermocouple elements installed in industrial processes. It is cylindrical in shape.
22. Why thermowells are used?
In most cases, it is not practical to place a temperature sensor on material directly. In these cases, we use thermowells to protect the sensor from damage, corrosion, erosion, high pressure, etc. It also protects the sensor element from physical damages too.
23. What materials are used in thermowells?
Stainless steel, Inconel, Monel, Alloy Steel, and Hastelloy
24. Different type of Level measuring instruments?
• Mechanical or Direct Method
• Inferential or Indirect Methods
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25. What is Zero suppression and Zero elevation?
Zero elevation
The amount of the measured variable zero is above the lower range value for an elevated zero range. It can be expressed in percent of span or in units of measured variables.
Zero suppression
The amount of the measured variable zero is below the lower range value for a suppressed zero range. It can be expressed in percent of span or in units of the measured variable.
26. What is flow?
Flow is the volume per unit of time at a given temperature and pressure. Positive displacement or rate meters are commonly used to measure flow.
Units of flow are: kg / hr, litre / min, gallon / min, m3 / hr, Nm3 / hr.
27. What is temperature?
Temperature is the measure of hotness or coldness of an object expressed in terms of Fahrenheit or Celsius or Kelvin.
28. What is pressure?
Force acting per unit area.
Units: bar, Pascal, kg /cm2
29. What is the formula for calculating pressure?
P= F/A
P = Pressure
F = Force
A = Area
30. What is a differential pressure transmitter?
A differential pressure transmitter is a device that can create a pressure drop in a pipe consistently and accurately, then measure the pressure on both sides to determine the flow rate inside the pipe.
31. What are the types of pressure?
• Absolute
• Gauge
• Differential
32. What is absolute pressure?
The combined pressure of the atmosphere and the measured point is known as absolute pressure.
33. What is gauge pressure?
The difference between a measured point and the atmosphere
34. What are differential pressure switches?
Differential pressure switches are mechanical devices that detect the difference between two measured points.
35. Working principle of differential pressure switches
There are two ports in differential pressure switches. The differential pressure switch will analyze the pressure of the object when we placed it on the pressure source and it will either make or break the circuit after the pressure reaches a preset level. This will let the alarm ring and alert the user that the pressure has a variation or change.
36. Uses of differential pressure switches
Differential pressure switches are mainly used in the energy-saving method to regulate a device that is not working as it should. This can be used while in maintenance and other safety-required applications
37. Applications of differential pressure switches
• Air conditioners
• Determining the respiratory flow in medical devices
• Air proving
• Exhaust ducts
38. What is a float switch?
Float level switches are sensors that are used to detect the liquid level inside a tank
39. Types of float level switch
Horizontal float switch
Vertical float switch
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40. What is the difference between accuracy & precision?
Accuracy: It refers to how close an instrumentation reading comes to matching the true value of the quantity of the medium to be measured.
Precision: It is a measure of reproducibility
41. Explain Bernoulli’s theorem.
Bernoulli’s theorem states that the total energy of a liquid flowing from one point to another remains constant.
42. Applications of Bernoulli’s theorem
Applications
• Lift of an aircraft wing
• Blowing of roofs
• Bunsen burner
43. What are the primary elements used for flow measurement?
• Orifice Plate
• Venturi tube
• Pitot tube
• Flow Nozzle
• Weir
• Flumes
44. Electromagnetic flow meters are not suitable for which kind of fluids?
Non - conductive fluids.
45. Name different parts of a pressure gauge
• ‘C’ type bourdon tube.
• Connecting link
• Sector gear
• Pinion Gear
• Hair spring
• Pointer
• Dial
46. How D.P. transmitter can be applied to the close tank?
In a closed tank, the bottom of the tank is connected to the high-pressure side of the transmitter. The top of the tank is connected to the lower pressure side of the transmitter. Vessel pressure can be measured in this way.
47. How D.P. transmitter can be applied to an open tank?
The side with lower pressure is opened to the atmosphere in an open tank. so, the entire pressure is applied to the side with high pressure and measure the pressure through the high-pressure side.
48. Explain the working of the Rotameter.
Variable area meter is also a type of head meter. To hold the differential pressure constant there is a flow restrictor in variable area meters. The vertical tapered tube is present in the rotameter to make the fluid flow in the upward direction.
49. What is the working principle of the magnetic meter?
While a conductor moves through a magnetic field, there will be an electrical potential developed. The wire is used as a conductor in almost every piece of electrical machinery. This principle is also applicable for electrically moving conductive liquid.
The main device of a commercial magnetometer consists of an insulated straight cylindrical tube with a pair of electrodes that are approximately horizontal to the wall of the tube and located at the opposite end of the diameter tube. This device can be used only in electrically conducting liquid. The magnetic meter is mainly used in slurries and dirty liquids.
50. What is direct and indirect level measurement?
Direct means that the fluid level being measured is in direct contact with the sensor.
Ex:
• Sight glass type
• Float type
• Magnetic level gauge
Indirect The level of a liquid is calculated by a variable that changes according to the level in the indirect method of level measurement.
Ex:
• Pressure gauge type
• Differential pressure type
• Ultrasonic type
• Radar type
51. What is point and continuous level measurement?
A point-level sensor detects liquid levels at specific points in a tank. This is mostly used when a high or low level needs to be controlled.
A continuous level sensor is used to detect liquid levels continuously at every point in a chamber or tank. This is mainly used in processes where it is always very important to know the level and for applications where precision increased is necessary.
52. What is a flowmeter?
Flow meters are a device used to measure the rate of fluid flow rate. It can be used to detect the linear, non-linear, mass, or volumetric flow rate of both gas and liquid.
53. Types of flow meters
• Orifice Flow Meters
• Glass Tube Flow Meter
• Electromagnetic Flow Meter
• Coriolis Flow Meter
54. What are the different types of Orifice plates?
• Concentric
• Segmental
• Eccentric
55. State use of different orifice plates
• Concentric: This plate is ideal for liquid, gas, and steam service. As the name implies these plates have concentric holes
• Segmental: This plate has holes in the form of circular segments. This tray is used to measure the flow of colloids and sherry.
• Eccentric: This plate has unusual holes, and this plate is used to measure viscose and sherry flow.
56. Why is the orifice tab provided?
• A line indicating the orifice plate
• It has a mark on it that indicates the diameter of the orifice.
• The orifice plate’s material.
• The orifice plate’s tag number.
• To indicate the orifice’s inlet.
57. What is the disadvantage of orifice meters?
A permanent pressure loss.
58. Why orifice meters are preferred in industries?
Due to the low cost
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59. What is P&ID?
P&ID stands for Process and Instrumentation Diagram. It shows the process equipment’s interconnection that is used to control a process
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60. What are the documents and drawings used in Instrumentation?
• Process Flow Diagram
• Piping & Instrumentation Diagram (P&ID)
• Loop Diagram
• Functional Diagram
• Hoop-up drawing
• Instrumentation index
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61. How is flow measured in the square root?
The flow rate is directly related to the square root of the pressure. So, F = K is the square root of the applied pressure. Flow rate changes for the square root of the pressure drop.
62. What is impulse tubing?
Normally impulse tube is a small diameter tube or pipe made of stainless steel material used to transmit the pressure signal from the process tapping to the transmitter.
63. What are the different types of cabinets involved in control system design?
• System Cabinet
• Marshalling cabinet
• Intermediate cabinet
• Network cabinet
• Power Distribution cabinet
• Remote IO cabinet
• Remote RTU cabinets
• Fibre optic patch panel wall mount console cabinet
64. What is a Safety barrier?
A safety barrier is required to ensure if any failure in the safe/non-hazardous zone (control room) will not be able to produce enough energy to ignite the gaseous atmosphere in the hazardous zone. This Safety barrier becomes a crucial element in an Intrinsically safe circuit design.
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65. What is a Junction box?
A junction box is an electrical box that is used as an intermediate junction between field devices and marshaling panels. The basic elements of a junction box are terminal blocks.
66. What are the different types of signal connections?
• RF (Radio Frequency) Modulated Television
• Composite Video
• S-Video
• Component Video
• RGB and its variants: RGSB, RGBS, RGBHV:
• SDI
67. What is conventional type signal connection?
In a conventional type connection, the signal from the field transmitter will be sent in the form of electromagnetic waves through copper wires to the field signal processor (like Field Terminal assembly) for further signal processing and connection to the control system. Normally the transmitted signal will be in the range of 4-20 mA.
68. What is the Foundation field bus connection?
Foundation Fieldbus (FF) is one of the new network communication protocols, which is used to connect field devices with the control system. This system uses a digital, multi-drop, serial two-way communication to connect field devices. This digital protocol enables two-way communication between field devices and the control system. Apart from the field signal we can calibrate, configure and pull various diagnostics information from the FF-based smart field transmitters and final control elements.
69. What is Trunk cable?’
The main H1 or HSE link single pair cable used to connect the control system with the Foundation Fieldbus junction box in the field is termed as Trunk Cable.
70. What is Spur cable?
The H1 or HSE link cable used to connect the field instruments such as transmitters, switches, valves, solenoid valve, etc., with Foundation Fieldbus junction box is termed as a Spur Cable.
71. What is Profibus connection?
Profibus, also known as Process Field Bus, is a field bus communication standard used in the automation field. A network designed for industrial computers that can handle a lot of noise. Different network topologies, such as the star, tree, and line, or a mix, are feasible with the two-wire Profibus cable.
72. What are the different types of communication protocols used in a control system environment?
• ControlNet
• DeviceNet
• DirectNet
• Ethernet Global Data (EGD)
• EtherNet/IP
• Ethernet Powerlink
• FOUNDATION Fieldbus – H1 & HSE
• HART Protocol
• Modbus Plus
• Profibus
• PROFINET
• AS-i – Actuator-sensor interface
• BSAP – Bristol Standard Asynchronous Protocol
• CC-Link Industrial Networks
• CIP (Common Industrial Protocol)
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73. What is the difference between a Transducer and a Transmitter?
A transducer is a device that converts any form of field signal into an equivalent electrical signal.
A transmitter is a device that converts reading from a sensor or a transducer into a standard electrical signal and transmits that signal to a controller (DCS/PLC Controller).
74. Why is a 4-20mA analog signal preferable to a 0-20mA analog signal?
The following are the main reasons for using 4-20mA instead of 0-20mA:
• The value of 4mA is considered engineering zero. Due to this, 0.0mA is referred to as an invalid input or dead zero. As a result, 0mA to the analog input indicates that the circuit is open and no current is flowing.
• Wire breaks are easy to find with 4-20mA.
75. Why 20mA is used in 4-20mA signal connection?
As per Ohms law V= IR
Where V = Voltage, I = Current and R = Resistance
Above shown is the illustration of the conventional 4-20mA signal connection diagram. Due to line voltage drop issues, the voltage signal from the transducer is converted to a current signal inside the transmitter and transmitted through pair of copper wires to the controller input card, where a resistance of 250 ohms is connected across the wire to convert the signal back to a voltage signal of 1 – 5V DC level so that controller input card can read the value.
The signal conversion table is shown below
This is the reason why 20mA is used on the higher side of the current signal.
76. Why voltage signals are not used?
The voltage signal is more non-linear than that of the current signal, so the current signal is preferred over the voltage signal.
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77. Why earthing is required in the control system?
During operation, all equipment in the control system, whether low-power or high-power, produces some electrical leakage and noise. As a result, when we connect these devices to the earth, they will stay grounded.
• Preventing electric shocks keep people safe.
• It protects electrical appliances and devices from harm.
• It reduces the risk of fire produced by current leakage, which could otherwise result in a fire.
78. What is Safety earth?
Safety earth is a connection of an installation’s exposed conductive portions to the installation’s primary earthing connection. The safety earth’s function is to ensure a safe low resistance path for any leakage current in the body of an installation, equipment, or device to flow to the earth so that personnel can work in the installation, equipment, or device safely.
79. What is Instrument/Signal earth?
The instrument earth/signal earth’s function is to provide a low impedance path to the noise currents introduced by unwanted RFI/EMI interference, which may result in the induction of faulty unwanted noise signals into the 4-20mA analog signals. Shields of multi-pair analog instrument signal cables are connected to this earth in the marshaling cabinets.
80. Why shield cables are used in multi-core cables?
It is utilized to minimize and prevent the effects of EMI and other risks prevalent in busy, industrial environments.
81. What should be the resistance value of safety earth?
Less than 5 Ohms
82. What should be the resistance value of Instrument/signal earth?
Less than 1 Ohm
83. What is Megger?
The Megger is the instrument used for measuring the resistance of the insulation.
84. Why test the insulation of a cable?
When cable insulation is pulled through raceways, it can be nicked or scraped from individual conductors. Moisture, high heat, and certain chemicals can all cause damage to insulation. An insulation resistance test must be performed after installation to ensure that the insulation has not been damaged during the installation procedure.
85. What is HART?
HART (Highway Addressable Remote Transducer) Protocol is an open standard used globally to send and receive digital information using analog wiring between smart devices and control systems.
86. What is Sourcing and sinking?
Sinking and sourcing are two important concepts to understand when connecting a PLC to the outside world. These two concepts only have an impact on DC modules.
The sinking circuit connects the load to the ground (-DC ).
The sourcing circuit provides a +24-volt source to the load (+DC).
87. Define controller.
A controller is an instrument used to control a process variable for measurement. Its job is to monitor the error signal continuously and give a corrective output to the final control element
88. What are the types of controllers?
• Proportional controllers.
• Integral controllers.
• Derivative controllers
We can make the combination of the above controllers and make the following controllers
• Proportional and integral controllers (PI Controller)
• Proportional and derivative controllers (PD Controller)
• Proportional integral derivative control (PID Controller)
89. What is a proportional controller?
Every controller is designed to meet some specific use. The proportional controllers are designed for the following reasons.
• We can use proportional controllers only if the deviation is not large.
• Can use only if the deviation is sudden
90. Advantages of proportional controllers
• It makes the system more stable by reducing steady-state error
• We can make an overdamped system much faster
91. Disadvantages of proportional controllers
• We will have some offsets due to the use of this controller
• It increases the maximum overshoot of the system
92. What is an integral controller?
As the name implies, in integral controllers the actuating signal (also called the output) is directly proportional to the integral of an error signal.
93. Advantages of integral controllers
Following a disturbance, integral controllers can return the controlled variable to its exact set point
94. Disadvantages of integral controllers
Due to the slow response to the produced error, it makes the unstable system.
95. What is a derivative controller?
We can’t use the derivative controllers alone due to the disadvantages. Check next Q&A for knowing the disadvantages
96. Disadvantages of a derivative controller?
• It never reduces steady-state error.
• It generates saturation effects and amplifies the system’s noise signals.
97. Why we cannot use a derivative controller alone?
• It never reduces steady-state error.
• It generates saturation effects and amplifies the system’s noise signals.
98. Advantages of Derivative Controller
It helps to improve the system’s transient response
99. What are the span and zero of a transmitter?
Span: The difference between the lowest point and the highest point in a configured measurement range
Zero: It is the lowest pressure at which the transmitter was calibrated
100. What is a range of a transmitter?
The range of a transmitter is defined as setting the scale for the 4mA and 20mA points. “Calibrated range” or “calibration range” are two other names given to the scale. This defines the reading at which transmitter output is at 4mA known as the Lower Range Value (LRV) or as “zero” meaning 0% and the reading at which the input is 20mA known as Upper Range Value (URV), also known as “full scale”, meaning 100%.
101. What is a cable schedule?
A cable schedule is a document that lists all of the instrument cables available. Each instrument or connection requires a cable and a gland as shown in this paper.
The cable schedule contains the following information:
• Number of Cables
• Type / Specification of Cable
• Size of the Cable
• Length of the Cable
• Termination descriptions at the source and destination
• For each incoming cable, determine the kind and size of the cable gland.
102. What is JB Schedule?
JB Schedule is a file that contains a JB list. Each instrument or connection requires a different cable and gland as shown in this document/file.
The JB schedule contains the following information:
• JB Type / Specification
• JB Number
• JB Location/Area
• Termination point
103. What is Instrument Index?
It is a list of documents that contains all the instruments in a plant or industry
104. What are the different modes of a PID?
• Manual
• Auto
• Cascade
105. Various types of PIDs?
• Proportional Control
• Standard Type PID Controller
• Real-Time PID Controllers
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106. What is Feedback control?
A feedback control system is one in which the output is regulated by a feedback signal generated by the system’s measurement. This feedback signal is compared to a reference signal to produce an error signal, which is then filtered by a controller to produce the control input for the system.
107. What is Feed-Forward Control?
Feedforward control is designed to anticipate the impact of a measured disturbance on the process variable and deploys control action to counteract the impending disruption in a timely manner. This will significantly improve disturbance rejection performance, but only specific to the particular disturbance variable which is being measured.
108. What Ratio control?
Ratio control is used when we need to mix two fluids in a specific ratio
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109. What is three-element Control?
A three-element controller is used in the level control system that usually measures the flow rate of steam from the boiler, water level, and flow rate of water to the boiler to control the water flow into the boiler.
110. What is loop check?
The loop check is the last stage of commissioning a project. We could say that loop checking is a process to check individual analog and digital loops connection is proper as per the engineering documents and also to check that each loop is working or not properly.
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111. What is Manifold?
Instrumentation manifolds are a kind of process connection system that provides various types of pressure management applications such as isolation, ventilation, and equalization. Manifolds are usually used in other measuring instruments like pressure transmitters, gauges, and other pressure sensing devices.
112. What is the equalization valve in the DP transmitter?
It is used to make ensure that the same pressure will be applied to both sides of the transmitter i.e., zero differential pressure.
113. What is an Analyser?
An analyzer is a tool that is used to evaluate process data of various process variables.
114. Different types of analyzers?
• Combustion Analyser
• Gas Analyser
• Liquid Analysis
• pH Analyser
115. Brief about vibration measurement?
The vibration measurement system is a device that measures vibration levels. Optional features include frequency measurement, a frequency-weighting network, and a display such as a meter, printer, or recorder.
116. What is a density meter?
A density meter is a device that is designed to calculate the density of the liquid. Density meters are mainly used to measure the density of slurries, sludges, and other liquids that flow through pipelines.
Density is usually represented as either rho or D.
117. Types of density meters
• Red Meter
• Coriolis
• Nuclear
• Microwave
• Ultrasonic
118. Major control system manufacturers
• ABB.
• Emerson Electric.
• Honeywell International.
• Siemens.
• Yokogawa Electric.
• General Electric.
• Metso
• Mitsubishi Heavy Industries.
119. Various units of Pressure measurement?
The SI unit for pressure is pascals ¶. Other units of pressure include torr, barr, atm, at, ba, psi, and manometric units like mm Hg and fsw.
120. Various units of Temperature measurement?
• Celsius
• Fahrenheit (°F)
• Celsius (°C)
• Kelvin (K)
121. Various units of flow measurement?
• Cubic feet per second (CFS)
• Cubic meters per second (cms)
• Gallons per minute (GPM)
122. What is a weighing scale?
The weight scale is a device used to measure the weight or mass of an object. These are also known as mass scales, mass balances, and weight balances.
123. What is the working principle of the weighing scale?
The weighing scale’s working principle is based upon the Electro-Magnetic Force Restoration(EMFR). The fundamental idea is similar to that of a simple beam balance. As a result, the coil is attached to the other side and seeks to travel away from the object’s magnetic field.
124. What are various PLC programming languages?
• Function Block Diagram (FBD)
• Instruction List (IL)
• Ladder Diagram (LD)
• Sequential Function Chart (SFC)
• Structured Text (ST)
125. What is IP rating?
The IP rating or IP code classifies the degree of protection given by an enclosure.
The international standard EN 60529 defines IP ratings.