Interview Questions

Ratio Control System MCQs in Industrial Instrumentation

February 7, 2025

Welcome to the “Ratio Control System in Process Instrumentation” quiz! Designed for process industry professionals and enthusiasts, this quiz tests your advanced understanding of ratio control systems, a critical component in optimizing industrial processes. You will encounter 25 multiple-choice questions, each with detailed answers and explanations to deepen your knowledge. Topics range from the principles of ratio control to its applications in maintaining process stability and efficiency. Whether you are an experienced engineer or a learner exploring process instrumentation, this quiz offers an excellent opportunity to assess and enhance your expertise. Let us get started and master ratio control systems!

Dive into the world of ratio control systems in process instrumentation! This advanced quiz features 25 MCQs, complete with answers and explanations, to test your knowledge of maintaining precise process ratios in industries. From basic concepts to practical applications, challenge your skills and gain valuable insights into this essential industrial control mechanism. Begin your learning journey today!

1 / 27

In a chemical reaction, reactants X and Y must be mixed in a 2:5 ratio to optimize the reaction’s yield. Due to a sensor failure, the flow rate of X cannot be measured accurately. What steps should you take to ensure the ratio is maintained?

Stop the process and fix the sensor before continuing.

Use historical data to estimate X's flow rate and adjust Y accordingly.

Switch the control system to manual mode and rely on operator judgment.

Reduce the flow of Y until X's flow rate can be measured accurately.

Since accurate measurement is critical for ratio control, the process should be stopped until the sensor issue is resolved. Continuing without accurate data risks compromising the product quality and process stability.

2 / 27

A paper mill uses ratio control to maintain a 4:1 ratio of water to pulp for the papermaking process. During a batch run, the pulp flow rate fluctuates due to a blockage in the feed line. What action should the ratio control system take?

Pause the process to clear the blockage.

Increase the water flow rate to maintain the 4:1 ratio.

Reduce the water flow rate proportionally to the pulp flow reduction.

Ignore the fluctuation and continue with the current settings.

The ratio control system should reduce the water flow rate proportionally to the reduced pulp flow rate to maintain the 4:1 ratio. This ensures that the paper’s quality remains unaffected while the blockage issue is resolved.

3 / 27

In a fuel-air mixture system for a boiler, the air supply fan speed increases due to a power surge, causing the air-to-fuel ratio to deviate from the optimal value. How should the ratio controller respond?

Shut down the boiler immediately to prevent damage.

Increase the fuel flow rate to match the increased air supply.

Reduce the air supply back to its original value.

Maintain the current ratio and monitor the system for further disturbances.

The ratio controller should increase the fuel flow rate to maintain the desired air-to-fuel ratio. This ensures efficient combustion and prevents potential issues like incomplete combustion or excessive emissions.

4 / 27

you are operating a blending system where two chemicals, A and B, must be mixed in a 1:3 ratio (A:B) to produce a product with the desired quality. During operation, the flow rate of chemical A suddenly drops due to a pump issue. What should the ratio control system do?

Stop the process until the pump is fixed.

Increase the flow rate of chemical B to match chemical A's reduced flow rate.

Reduce the flow rate of chemical B to maintain the 1:3 ratio with chemical A.

Continue running with the current flow rates until the issue resolves.

The ratio control system should reduce the flow rate of chemical B proportionally to the reduced flow rate of chemical A to maintain the 1:3 ratio. This ensures the product quality remains consistent despite the disturbance.

5 / 27

What type of controller is most commonly used in ratio control systems?

P-only controller

PID controller

On-off controller

Fuzzy logic controller

PID controllers provide precise adjustments needed for ratio control.

6 / 27

Ratio control is unsuitable when:

Variables are unrelated

High precision is required

Disturbances are minimal

Setpoint changes are frequent

Ratio control relies on the relationship between variables; it is unsuitable if they are unrelated.

7 / 27

The term “secondary flow” in ratio control refers to:

The primary variable

A controlled dependent variable

An unrelated process flow

Auxiliary measurements

Secondary flow is adjusted to maintain the desired ratio with the primary flow.

8 / 27

An incorrect ratio in a chemical reaction could result in:

Improved yield

Process instability

Higher energy efficiency

Increased safety

An incorrect ratio can disrupt reactions, causing instability and affecting product quality.

9 / 27

What determines the primary variable in ratio control?

Operator input

Process design

External disturbances

It is independent of the ratio controller

Process design dictates which variable is considered primary in ratio control.

10 / 27

A ratio control system’s response to disturbances is faster when paired with:

Feedback control

Feedforward control

Proportional-only control

Integral-only control

Feedforward control anticipates changes and adjusts variables to maintain the ratio.

11 / 27

Which process industry heavily relies on ratio control systems?

Pharmaceutical

Food and beverage

Chemical

All of the above

Ratio control is critical across industries for precise and consistent process outcomes.

12 / 27

The main advantage of ratio control is:

Reduced operating costs

Improved product quality

Increased production rate

Simplified process design

Ratio control ensures precise relationships, leading to consistent and high-quality output.

13 / 27

How is the secondary variable in ratio control determined?

It is fixed

By the ratio setpoint

Randomly selected

By operator input

The secondary variable is adjusted based on the ratio setpoint and primary variable.

14 / 27

Ratio control can be considered a subset of:

Batch control

Regulatory control

Sequential control

Predictive control

Ratio control focuses on maintaining specific relationships within regulatory control frameworks.

15 / 27

Which sensor is crucial in a ratio control loop?

Flow sensor

Level sensor

Temperature sensor

Pressure sensor

Flow sensors measure the process streams to maintain the desired ratio.

16 / 27

The ratio controller output adjusts:

The independent variable

The dependent variable

Both variables

Neither variable

The dependent variable is manipulated to match the desired ratio.

17 / 27

Ratio control is particularly useful in blending systems because:

It ensures product uniformity

It increases process speed

It eliminates manual intervention

It reduces energy consumption

By maintaining precise proportions, ratio control ensures uniform blending.

18 / 27

A deviation in the controlled ratio typically indicates:

Process efficiency improvement

Measurement error or process disturbance

System shutdown

Reduced operator workload

Deviations often result from disturbances or errors, requiring corrective action.

19 / 27

Which parameter is typically measured to control the air-fuel ratio in combustion systems?

Temperature

Pressure

Flow rate

pH level

Flow rate measurements of air and fuel are crucial for maintaining the desired combustion ratio.

20 / 27

The setpoint in a ratio control system is expressed as:

Absolute values

A fixed ratio

Percentage deviation

None of the above

The setpoint is defined as the desired ratio between two process variables.

21 / 27

Ratio control systems are often paired with:

Feedforward control

Feedback control

Cascade control

All of the above

Feedforward control works well with ratio control to anticipate changes and maintain desired proportions.

22 / 27

What happens if the ratio setpoint in a system is incorrect?

System becomes more efficient

Quality and stability decrease

Process variables remain unaffected

No impact on the system

An incorrect setpoint disrupts the desired relationship, affecting product quality and system stability.

23 / 27

In a fuel-air mixture control system, the ratio controller ensures:

Equal amounts of fuel and air

Optimal combustion efficiency

Minimum fuel consumption

Maximum air flow

The ratio controller adjusts the fuel and air inputs to maintain optimal combustion efficiency.

24 / 27

Ratio control is most commonly used in:

Batch processes

Continuous processes

Discrete processes

Manual operations

Ratio control is essential in continuous processes to ensure consistency and quality.

25 / 27

Which of the following components is essential in a ratio control loop?

Flow transmitter

Ratio setpoint generator

Control valve

All of the above

All these components work together to measure, compare, and adjust the process variables.

26 / 27

What is the primary purpose of a ratio control system in process industries?

Maintain constant pressure

Maintain a specific ratio between two process variables

Control temperature fluctuations

Optimize production efficiency

Ratio control systems are designed to maintain a fixed ratio between two interdependent variables, ensuring process stability.

27 / 27

In a ratio control system, the manipulated variable is typically:

Independent

Dependent

Fixed

Unrelated

The manipulated variable depends on the set ratio and is adjusted accordingly to maintain the desired relationship.

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Sundareswaran Iyalunaidu

With over 24 years of dedicated experience, I am a seasoned professional specializing in the commissioning, maintenance, and installation of Electrical, Instrumentation and Control systems. My expertise extends across a spectrum of industries, including Power stations, Oil and Gas, Aluminium, Utilities, Steel and Continuous process industries. Tweet me @sundareshinfohe

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