ExxonMobil Control & Instrumentation Engineer Interview Questions and Answers

Q1. Why 4-20 mA Preferred over 0-20 mA signal ?
Ans. 
4-20 mA signal is preferred over 0-20 mA signal due to its ability to detect faults and provide a clear zero point.
• 4-20 mA signal has a clear zero point, making it easier to detect faults in the system.

• It allows for a wider range of measurement values, as the 0-4 mA range can be used to indicate faults or out-of-range conditions.

• 4-20 mA signal is less susceptible to noise and interference compared to 0-20 mA signal.

• It ...read more
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Q2. What is the Purpose of an orifice Tab?
Ans. 
An orifice tab is used to accurately measure the flow rate of a fluid through a pipeline.
• It creates a differential pressure across the orifice plate, which is proportional to the flow rate.

• The tab is placed upstream of the orifice plate to ensure accurate measurement.

• The tab can be designed in different shapes and sizes depending on the application.

• It is commonly used in industries such as oil and gas, chemical, and wa...read more
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Q3. How do you identify an orifice in the pipeline ?
Ans. 
An orifice in a pipeline can be identified by measuring the pressure drop across it.
• Measure the pressure drop across the pipeline using a differential pressure transmitter

• Compare the pressure drop with the expected value for the given orifice size

• Use a flow meter to confirm the flow rate through the orifice

• Inspect the pipeline for any markings or labels indicating the presence of an orifice
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Q4. Why is the orifice tap provided ?
Ans. 
Orifice tap is provided to measure the pressure drop across the orifice plate.
• Measures pressure drop

• Helps calculate flow rate

• Used in flow measurement systems
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Q5. Why is the Orifice tab provided ?
Ans. 
Orifice tab is provided to indicate the size of the orifice and its flow rate.
• Orifice tab helps in identifying the size of the orifice and its flow rate.

• It is used in flow measurement devices like orifice plates, venturi meters, etc.

• The tab is usually made of stainless steel and is welded to the orifice plate.

• The tab is marked with a number or letter to indicate the size of the orifice.

• The flow rate can be calculated u...read more
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Q6. What is the main difference between RTD and Thermistor?
Ans. 
RTD measures temperature using resistance while thermistor uses resistance-temperature relationship.
• RTD has a linear resistance-temperature relationship while thermistor has a non-linear one.

• RTD has a higher accuracy and stability compared to thermistor.

• RTD is more expensive than thermistor.

• RTD is commonly used in industrial applications while thermistor is used in consumer electronics.

• Examples of RTD include platinum,...read more
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Q1. What is a Transmitter, types/functions and general configuration/calibrations
Ans. 
A transmitter is a device that converts a signal from a sensor into a standardized output signal for measurement or control purposes.
• Types of transmitters include pressure transmitters, temperature transmitters, level transmitters, and flow transmitters.

• Functions of transmitters include sensing a physical parameter, converting it into an electrical signal, and transmitting the signal to a control system.

• General configu...read more
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Q1. Instrument Technician
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Q2. Personal Details
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Q1. All the related questions in instrumentation
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Q2. Calibration mathead
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Q3. The calibration mathead is following formula AI AO and. DI Do
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Q1. How much you earn
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Q1. Any instrumentation equipment explain
Ans. 
Instrumentation equipment refers to devices used to measure, control, and monitor various parameters in industrial processes.
• Instruments like pressure gauges, flow meters, and temperature sensors are commonly used in instrumentation.

• Control valves and actuators are used to regulate the flow of fluids or gases.

• Programmable Logic Controllers (PLCs) are used for automation and control of processes.

• Analytical instruments l...read more
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Q2. PLC and scada and DCS
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Q3. PLC panel wiring diagram
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A PLC panel wiring diagram is a visual representation of the electrical connections and components in a programmable logic controller panel.
• A PLC panel wiring diagram shows the layout and connections of various components such as power supplies, input/output modules, relays, and sensors.

• It helps technicians understand how the electrical signals flow within the panel and how different devices are interconnected.

• The diag...read more
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Q4. What is the control valve
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A control valve is a device used to regulate the flow of fluid or gas in a process system.
• Control valves are commonly used in industries such as oil and gas, chemical, and power plants.

• They can be operated manually or automatically through an electrical or pneumatic signal.

• Control valves consist of a valve body, actuator, and positioner.

• They can control variables such as flow rate, pressure, temperature, and level.

• Exam...read more
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Q5. What is the transmitter
Ans. 
A transmitter is a device used in instrumentation to convert a physical measurement into an electrical signal.
• Transmitters are commonly used in industries such as oil and gas, chemical, and power plants.

• They are used to measure variables such as pressure, temperature, flow rate, level, and pH.

• Transmitters typically consist of a sensing element, signal conditioning circuitry, and an output signal.

• The sensing element det...read more
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Q6. What is the flow meters
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Flow meters are devices used to measure the flow rate of a fluid or gas.
• Flow meters are commonly used in industries such as oil and gas, water treatment, and manufacturing.

• They can measure flow rates in various units such as liters per minute, cubic meters per hour, or gallons per minute.

• Different types of flow meters include electromagnetic, ultrasonic, turbine, and differential pressure flow meters.

• Flow meters can be...read more
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Q1. How many years experience?
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Q2. What is tha qualification?
Ans. 
The qualification for an Instrumentation Technician typically includes a degree or diploma in instrumentation technology or a related field.
• A degree or diploma in instrumentation technology or a related field is usually required.

• Knowledge of electrical and electronic systems is important.

• Experience with calibration and troubleshooting of instruments is often necessary.

• Familiarity with industry standards and regulations...read more
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Q3. Is currently working?
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Q4. Before working company
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Q1. What is Thermocouple range?
Ans. 
Thermocouple range refers to the temperature range within which a thermocouple can accurately measure temperature.
• Thermocouple range varies depending on the type of thermocouple used.

• Common thermocouple types include J, K, T, E, and N.

• For example, a type K thermocouple has a range of -200 to 1350 degrees Celsius.

• It is important to select the appropriate thermocouple type for the temperature range being measured.
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Q2. What is anti surge valve?
Ans. 
An anti-surge valve is a control valve used in a compressor system to prevent surge and maintain stable operation.
• An anti-surge valve is typically installed in the discharge line of a compressor.

• It is designed to protect the compressor from surge, which is a phenomenon of unstable flow and pressure that can cause damage to the compressor.

• The valve opens or closes based on the compressor's operating conditions to mainta...read more
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Q3. Are you working gas turbine?
Ans. 
Yes, I have experience working with gas turbines.
• I have worked with gas turbines in my previous job as an instrumentation technician.

• I am familiar with the maintenance and troubleshooting of gas turbines.

• I have experience in calibrating and testing gas turbine sensors and instruments.

• I have knowledge of the safety protocols and regulations related to gas turbines.
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Q4. How many types vibration is there in field?
Ans. 
There are three types of vibration in the field: axial, radial, and tangential.
• Axial vibration occurs parallel to the axis of rotation.

• Radial vibration occurs perpendicular to the axis of rotation.

• Tangential vibration occurs at a right angle to both axial and radial vibration.

• Vibration analysis is used to detect and diagnose problems in rotating machinery.

• Excessive vibration can lead to premature failure of bearings, g
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Q5. Are you know that preventive maintenance jobs?
Ans. 
Yes, I am familiar with preventive maintenance jobs.
• Preventive maintenance involves regularly scheduled inspections, cleaning, and repairs to prevent equipment breakdowns.

• I have experience performing preventive maintenance on various types of instrumentation equipment, such as calibrators, transmitters, and controllers.

• Examples of preventive maintenance tasks I have performed include checking for leaks, replacing worn ...read more
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Q1. Are you instrument technician?
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Q2. What kind of precautions need in Plant running time?
Ans. 
Precautions are necessary to ensure safe and efficient plant operation.
• Regular maintenance of equipment and machinery

• Proper training and certification of personnel

• Strict adherence to safety protocols and procedures

• Regular inspections and audits to identify potential hazards

• Effective communication and coordination among team members

• Use of personal protective equipment (PPE) as required

• Emergency response planning and dri...read more
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I am interested to work in maintenance field and troubleshooting

Q1. Types of Instruments
Ans. 
Instruments used in control and instrumentation include sensors, transmitters, controllers, and actuators.
• Sensors: devices that detect changes in physical properties and convert them into electrical signals (e.g. temperature sensors, pressure sensors)

• Transmitters: devices that send signals from sensors to controllers (e.g. signal transmitters)

• Controllers: devices that receive signals from sensors and transmitters to re...read more
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Q2. PID loop working in Complete
Ans. 
PID loop is a control system feedback mechanism used in industrial processes to maintain desired setpoints.
• PID stands for Proportional, Integral, Derivative

• Proportional term responds to the current error

• Integral term corrects past errors

• Derivative term predicts future errors

• PID controller continuously calculates an error value as the difference between a desired setpoint and a measured process variable

• Example: PID loop...read more
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