Q.1 Which type of sensor is most commonly used to measure dissolved oxygen (DO) in a bioreactor?
Thermocouple
Clark-type electrochemical sensor
Capacitive humidity sensor
Hall-effect sensor
Explanation - Clark-type electrochemical sensors generate a current proportional to the amount of oxygen that diffuses through a membrane, making them standard for DO measurement in bioprocesses.
Correct answer is: Clark-type electrochemical sensor
Q.2 What is the primary purpose of a signal conditioner in a bioreactor sensor system?
To amplify and filter the raw sensor signal
To store large data sets
To regulate temperature
To sterilize the bioreactor medium
Explanation - Signal conditioners adjust the amplitude, offset, and filter noise from the sensor output to make it suitable for data acquisition and control.
Correct answer is: To amplify and filter the raw sensor signal
Q.3 Which parameter is most directly measured by a pH electrode based on the Nernst equation?
Electrical conductivity
Hydrogen ion concentration
Oxygen saturation
Carbon dioxide pressure
Explanation - The Nernst equation relates the electrode potential to the logarithm of the hydrogen ion activity, which is what pH electrodes measure.
Correct answer is: Hydrogen ion concentration
Q.4 In a typical bioreactor, which sensor type requires periodic calibration using standard buffer solutions?
Temperature sensor
pH sensor
Optical turbidity sensor
Pressure transducer
Explanation - pH sensors drift over time and need calibration with known pH buffer solutions to maintain accuracy.
Correct answer is: pH sensor
Q.5 What advantage does a non‑contact infrared temperature sensor provide in a bioreactor environment?
Higher accuracy at low temperatures
Elimination of sensor fouling
Direct measurement of internal pH
Measurement of dissolved gases
Explanation - Since infrared sensors measure surface temperature without touching the medium, they are not affected by fouling or contamination.
Correct answer is: Elimination of sensor fouling
Q.6 Which data acquisition (DAQ) sampling rate is typically sufficient for monitoring temperature changes in a bioreactor?
1 kHz
100 Hz
1 Hz
0.01 Hz
Explanation - Temperature in bioreactors changes relatively slowly; a 1 Hz sampling rate captures changes adequately without excessive data volume.
Correct answer is: 1 Hz
Q.7 A conductivity probe in a bioreactor is most useful for estimating which of the following?
Cell density
Nutrient concentration
Osmolarity of the medium
pH level
Explanation - Conductivity correlates with the ionic strength and thus the osmolarity of the solution, providing indirect information on solute concentration.
Correct answer is: Osmolarity of the medium
Q.8 Which control strategy uses real‑time sensor data to maintain a setpoint by adjusting actuator output?
Open‑loop control
Feed‑forward control
Closed‑loop (feedback) control
Manual control
Explanation - Closed‑loop control continuously compares sensor measurements to a setpoint and corrects deviations via actuators.
Correct answer is: Closed‑loop (feedback) control
Q.9 In a bioreactor, an optical sensor that measures scattered light intensity is primarily used to monitor:
Dissolved oxygen
Cell growth (biomass concentration)
pH
Temperature
Explanation - Turbidity or optical density measured by scattered light correlates with cell concentration in suspension cultures.
Correct answer is: Cell growth (biomass concentration)
Q.10 What is the main source of drift in amperometric DO sensors over long operation periods?
Electrode fouling
Temperature fluctuations
Magnetic interference
Changes in ambient light
Explanation - Biomass and media components can coat the sensor membrane, reducing oxygen diffusion and causing drift.
Correct answer is: Electrode fouling
Q.11 Which communication protocol is commonly used for real‑time sensor data transmission in industrial bioprocess control systems?
USB 2.0
Ethernet/IP
Bluetooth Low Energy
Wi‑Fi Direct
Explanation - Ethernet/IP provides deterministic, high‑speed communication suitable for industrial automation and process control.
Correct answer is: Ethernet/IP
Q.12 A bioreactor’s pressure transducer is calibrated to output 4–20 mA for a pressure range of 0–200 kPa. What current corresponds to 100 kPa?
12 mA
10 mA
14 mA
16 mA
Explanation - The range is 16 mA over 200 kPa → 0.08 mA/kPa. 100 kPa × 0.08 mA/kPa = 8 mA + 4 mA (offset) = 12 mA.
Correct answer is: 12 mA
Q.13 Which sensor technology is best suited for real‑time measurement of carbon dioxide (CO₂) in a sterile bioreactor environment?
Infrared (NDIR) gas sensor
Electrochemical CO₂ sensor
Metal‑oxide semiconductor sensor
Thermal conductivity sensor
Explanation - NDIR sensors detect CO₂ by measuring absorption of infrared light at specific wavelengths and are reliable in sterile, humid conditions.
Correct answer is: Infrared (NDIR) gas sensor
Q.14 In a PID controller, increasing the proportional gain (Kp) will:
Reduce steady‑state error but may cause overshoot
Eliminate overshoot completely
Increase integral wind‑up
Have no effect on response speed
Explanation - Higher Kp speeds up response and reduces error, but excessive Kp can cause the system to overshoot the setpoint.
Correct answer is: Reduce steady‑state error but may cause overshoot
Q.15 Which method is commonly employed to prevent biofouling on in‑situ optical sensors?
Increasing sensor temperature
Applying anti‑fouling coatings
Using higher voltage excitation
Mounting sensors outside the bioreactor
Explanation - Special coatings (e.g., silicone, fluoropolymers) reduce adhesion of cells and proteins on sensor surfaces, extending sensor life.
Correct answer is: Applying anti‑fouling coatings
Q.16 What is the typical unit for expressing the signal from a pH sensor after conditioning?
Volts
Millivolts
Degrees Celsius
Pascal
Explanation - pH electrodes generate a voltage of about -59 mV per pH unit, so the conditioned signal is usually in millivolts.
Correct answer is: Millivolts
Q.17 During online monitoring, why is it important to implement a low‑pass filter on the sensor signal?
To increase the signal amplitude
To remove high‑frequency noise
To convert analog to digital
To calibrate the sensor automatically
Explanation - Low‑pass filters attenuate high‑frequency components, which are often noise, improving measurement reliability.
Correct answer is: To remove high‑frequency noise
Q.18 Which parameter is directly measured by a capacitance‑based sensor in a cell culture bioreactor?
Cell viability
Cell concentration
Oxygen uptake rate
Glucose concentration
Explanation - Capacitive sensors detect changes in dielectric properties caused by the presence of cells, providing a measure of cell density.
Correct answer is: Cell concentration
Q.19 A bioreactor uses a flow‑through sensor for measuring glucose concentration. What is the main advantage of this configuration?
No need for sensor calibration
Continuous sampling without sensor exposure to fouling
Higher temperature tolerance
Direct measurement of dissolved oxygen
Explanation - Flow‑through designs allow fresh sample to pass the sensor, reducing fouling and enabling real‑time monitoring.
Correct answer is: Continuous sampling without sensor exposure to fouling
Q.20 Which of the following is a common cause of baseline drift in optical density (OD) sensors?
Changes in ambient light intensity
Variations in sensor temperature
Electrical interference from nearby motors
Magnetic field fluctuations
Explanation - Optical sensors are sensitive to external light; variations can shift the baseline reading unless properly shielded.
Correct answer is: Changes in ambient light intensity
Q.21 In a supervisory control and data acquisition (SCADA) system, what role does the historian database serve?
Real‑time control of actuators
Long‑term storage of process data for trend analysis
Generating alarm sounds
Providing power to sensors
Explanation - The historian archives time‑stamped data, enabling operators to review historical trends and perform post‑run analysis.
Correct answer is: Long‑term storage of process data for trend analysis
Q.22 Which sensor type is most appropriate for monitoring the agitation speed (rpm) of a bioreactor impeller?
Hall‑effect tachometer
Thermocouple
pH electrode
Capacitive humidity sensor
Explanation - Hall‑effect sensors detect magnetic field changes from a rotating magnet on the shaft, providing accurate rpm measurements.
Correct answer is: Hall‑effect tachometer
Q.23 When converting a 12‑bit ADC reading to a physical voltage range of 0–5 V, what is the voltage resolution per count?
0.00122 V
0.00488 V
0.00098 V
0.00500 V
Explanation - Resolution = 5 V / (2¹²‑1) ≈ 5 / 4095 = 0.00122 V per count.
Correct answer is: 0.00122 V
Q.24 Which of the following sensor outputs is most immune to electromagnetic interference (EMI) in a noisy bioprocess environment?
Analog voltage (0‑10 V)
Current loop (4‑20 mA)
Digital I²C
Frequency output (Hz)
Explanation - Current loops are less affected by EMI because the signal is defined by current, not voltage, and can travel long distances.
Correct answer is: Current loop (4‑20 mA)
Q.25 Why is it important to perform a temperature compensation for pH measurements?
pH electrodes change resistance with temperature
The Nernst slope varies with temperature
Temperature affects the color of the indicator solution
Temperature does not influence pH
Explanation - The Nernst equation shows the electrode potential per pH unit depends on temperature; compensation ensures accurate pH readings.
Correct answer is: The Nernst slope varies with temperature
Q.26 In a bioreactor, which sensor would you select to monitor foam formation?
Capacitive level sensor
Optical infrared (IR) foam detector
Pressure transducer
pH electrode
Explanation - IR foam detectors sense the scattering/absorption of infrared light caused by foam, providing early detection.
Correct answer is: Optical infrared (IR) foam detector
Q.27 A sensor's response time is defined as the time required to reach 63.2% of a step change. If a temperature sensor has a time constant of 5 s, what is its response time?
5 s
3.2 s
6.3 s
7.5 s
Explanation - For first‑order systems, the time constant τ equals the time to reach 63.2% of the final value.
Correct answer is: 5 s
Q.28 Which calibration method uses a series of known standards to generate a regression curve for sensor output?
One‑point calibration
Two‑point calibration
Multi‑point calibration
Zero‑offset calibration
Explanation - Multi‑point calibration fits a curve (linear or higher order) to several standards, improving accuracy over a wide range.
Correct answer is: Multi‑point calibration
Q.29 In an online monitoring system, what is the main purpose of a watchdog timer?
To increase sensor sampling rate
To reset the controller if the software hangs
To amplify the sensor signal
To calibrate the sensor automatically
Explanation - A watchdog timer ensures reliability by restarting the system if it becomes unresponsive.
Correct answer is: To reset the controller if the software hangs
Q.30 Which type of sensor would be most suitable for measuring the level of liquid in a stirred‑tank bioreactor without direct contact?
Ultrasonic level sensor
Capacitive level sensor
Differential pressure sensor
Float‑type level sensor
Explanation - Ultrasonic sensors emit sound waves that reflect off the liquid surface, allowing non‑contact level measurement.
Correct answer is: Ultrasonic level sensor
Q.31 A bioreactor uses a 0‑10 V analog output for the DO sensor. If the measured voltage is 7 V, what is the approximate dissolved oxygen percentage assuming a 0‑100 % range?
70 %
50 %
85 %
30 %
Explanation - Voltage is linearly mapped: (7 V / 10 V) × 100 % = 70 %.
Correct answer is: 70 %
Q.32 Which phenomenon can cause a shift in the baseline of a pH sensor due to temperature changes in the medium?
Joule heating
Thermal drift
Electrolyte depletion
Magnetic hysteresis
Explanation - Temperature variations affect the electrode potential, causing baseline drift if not compensated.
Correct answer is: Thermal drift
Q.33 For a bioreactor equipped with a PLC, which programming language is most commonly used for sensor interfacing?
Python
Ladder Logic
JavaScript
C++
Explanation - Ladder Logic is the traditional IEC 61131‑3 language used in PLCs for industrial automation.
Correct answer is: Ladder Logic
Q.34 In sensor data analysis, what does the term “filtering outliers” refer to?
Increasing the sampling frequency
Removing data points that deviate significantly from the norm
Amplifying low‑amplitude signals
Converting analog signals to digital
Explanation - Outlier filtering discards anomalous readings that may be caused by noise or sensor errors, improving data quality.
Correct answer is: Removing data points that deviate significantly from the norm
Q.35 Which sensor principle relies on measuring the change in light absorption at a specific wavelength to determine glucose concentration?
Electrochemical amperometry
Spectrophotometry
Capacitance measurement
Magnetoresistance
Explanation - Glucose reacts with reagents to produce a colored product; spectrophotometric sensors measure absorbance proportional to concentration.
Correct answer is: Spectrophotometry
Q.36 A bioreactor’s online monitoring system records a sudden spike in temperature that later returns to normal. What is the most probable cause?
Sensor failure
Transient exothermic reaction
Power outage
Calibration error
Explanation - A brief metabolic burst can generate heat, causing a temporary temperature rise before the control system stabilizes it.
Correct answer is: Transient exothermic reaction
Q.37 Which factor primarily determines the selection of a sensor’s material for use inside a sterile bioreactor?
Electrical conductivity
Biocompatibility and sterilizability
Magnetic permeability
Cost
Explanation - Materials must withstand sterilization (e.g., autoclaving) and not leach contaminants into the culture.
Correct answer is: Biocompatibility and sterilizability
Q.38 In an online monitoring setup, what is the purpose of a “dead band” in control logic?
To increase sensor resolution
To prevent frequent actuator toggling for minor variations
To amplify sensor signals
To store historical data
Explanation - A dead band defines a range around the setpoint where no control action is taken, reducing wear and oscillations.
Correct answer is: To prevent frequent actuator toggling for minor variations
Q.39 Which type of sensor is typically used to monitor the pO₂ (partial pressure of oxygen) in a bioreactor gas phase?
Piezoelectric sensor
Clark‑type sensor
Capacitive humidity sensor
Thermistor
Explanation - Clark sensors can be configured for both dissolved and gaseous oxygen, providing pO₂ measurements.
Correct answer is: Clark‑type sensor
Q.40 When implementing a redundancy scheme for critical sensors, which architecture provides the highest reliability?
1‑out‑of‑2 (parallel)
1‑out‑of‑3 (majority voting)
Series connection
Single sensor with backup
Explanation - With three sensors, the system can tolerate one failure and still determine the correct value via majority voting.
Correct answer is: 1‑out‑of‑3 (majority voting)
Q.41 A sensor's datasheet lists a “linearity error” of ±0.5 % of full scale. What does this specification indicate?
The sensor output deviates up to 0.5 % from a straight line over its range
The sensor will drift 0.5 % per hour
The sensor requires 0.5 % power overhead
The sensor can only be used for 0.5 % of the full range
Explanation - Linearity error quantifies how far the actual response departs from an ideal linear relationship.
Correct answer is: The sensor output deviates up to 0.5 % from a straight line over its range
Q.42 In a digital communication link for sensor data, which error‑checking method adds a short checksum to each data packet?
Pulse‑width modulation
Cyclic redundancy check (CRC)
Analog modulation
Frequency division multiplexing
Explanation - CRC generates a checksum based on polynomial division, allowing detection of transmission errors.
Correct answer is: Cyclic redundancy check (CRC)
Q.43 A bioreactor’s DO sensor output drifts upward by 5 % over 24 hours without any change in actual DO. Which corrective action is most appropriate?
Increase the sampling rate
Perform a mid‑run calibration
Replace the temperature sensor
Ignore the drift
Explanation - Periodic in‑process calibration compensates for sensor drift and restores accuracy.
Correct answer is: Perform a mid‑run calibration
Q.44 Which sensor characteristic defines the smallest change in the measured quantity that can be reliably detected?
Range
Resolution
Accuracy
Linearity
Explanation - Resolution is the minimum increment that produces a distinguishable change in the sensor output.
Correct answer is: Resolution
Q.45 In a bioreactor, the term “specific growth rate (µ) monitoring” most often relies on which online measurement?
pH
Dissolved oxygen
Optical density (OD)
Temperature
Explanation - OD correlates with cell concentration; tracking its change over time yields the specific growth rate.
Correct answer is: Optical density (OD)
Q.46 Which type of sensor output is inherently digital and does not require an external ADC?
Analog voltage (0‑10 V)
4‑20 mA current loop
Pulse‑width modulation (PWM)
I²C temperature sensor
Explanation - I²C devices provide digital data over a serial bus, eliminating the need for separate analog‑to‑digital conversion.
Correct answer is: I²C temperature sensor
Q.47 When a bioreactor’s pH sensor is placed in a highly viscous medium, which issue is most likely to arise?
Increased electrical noise
Slow response time due to diffusion lag
Higher temperature drift
Signal saturation
Explanation - Viscous media impede the movement of hydrogen ions to the sensor surface, slowing the pH response.
Correct answer is: Slow response time due to diffusion lag
Q.48 Which method can be used to detect sensor fouling without halting the bioprocess?
Comparing sensor output to a model‑predicted value
Increasing the sensor’s power supply
Physically removing the sensor
Changing the sensor’s communication protocol
Explanation - Model‑based residual analysis can flag deviations indicative of fouling while the process continues.
Correct answer is: Comparing sensor output to a model‑predicted value
Q.49 A 16‑bit ADC is used to digitize a temperature sensor with a range of –20 °C to 80 °C. What is the temperature resolution per bit?
0.0015 °C
0.015 °C
0.15 °C
1.5 °C
Explanation - Total range = 100 °C. Resolution = 100 °C / (2¹⁶‑1) ≈ 100 / 65535 ≈ 0.0015 °C per count.
Correct answer is: 0.0015 °C
Q.50 In a bioprocess, why is it advantageous to use a reference electrode placed outside the sterile zone for pH measurement?
It improves measurement speed
It reduces the risk of contamination of the reference solution
It eliminates the need for temperature compensation
It allows for higher voltage outputs
Explanation - Keeping the reference electrode external prevents sterile media from contacting the reference electrolyte, maintaining sterility.
Correct answer is: It reduces the risk of contamination of the reference solution
Q.51 Which of the following best describes the term “sensor latency”?
The time taken for a sensor to warm up after power‑on
The delay between the actual change in the measured variable and the sensor’s output response
The maximum sampling frequency of the sensor
The total lifespan of the sensor
Explanation - Latency is the time lag from a physical change to the corresponding change in sensor output.
Correct answer is: The delay between the actual change in the measured variable and the sensor’s output response
Q.52 For continuous monitoring of biomass in a mammalian cell culture, which sensor technology is most often employed?
Impedance (bio‑impedance) sensor
Thermistor
Optical fluorescence sensor
Magnetometer
Explanation - Bio‑impedance measures changes in electrical properties of the suspension caused by cells, giving a real‑time biomass estimate.
Correct answer is: Impedance (bio‑impedance) sensor
Q.53 What is the primary advantage of using a digital twin of the bioreactor for sensor data interpretation?
It eliminates the need for physical sensors
It provides a virtual model to predict sensor behavior and detect anomalies
It reduces power consumption of the control system
It speeds up the fermentation process
Explanation - A digital twin simulates the process, allowing comparison of real sensor data with predicted values to spot faults.
Correct answer is: It provides a virtual model to predict sensor behavior and detect anomalies
Q.54 A bioreactor uses a pressure sensor to infer gas flow rate via the equation Q = k√P. If the pressure reading doubles, how does the inferred flow rate change?
It doubles
It increases by √2
It quadruples
It stays the same
Explanation - Q ∝ √P, so Q_new/Q_old = √(2P)/√P = √2.
Correct answer is: It increases by √2
Q.55 Which sensor characteristic is most affected by electromagnetic shielding and grounding practices?
Range
Sensitivity
Noise immunity
Response time
Explanation - Proper shielding and grounding reduce external electromagnetic interference, improving noise immunity.
Correct answer is: Noise immunity
Q.56 In an online monitoring system, a “trend plot” typically displays:
Sensor hardware schematics
Historical sensor data over time
Manufacturing tolerances
Future predicted values only
Explanation - Trend plots visualize how a measured parameter evolves during the run, aiding in process assessment.
Correct answer is: Historical sensor data over time
Q.57 Which of the following sensor types would be least suitable for measuring high‑temperature sterilization (121 °C) inside a bioreactor?
Thermocouple
RTD (Resistance Temperature Detector)
Silicon‑based thermistor
Fiber‑optic temperature sensor
Explanation - Silicon thermistors degrade at temperatures above ~125 °C, making them less reliable for sterilization monitoring.
Correct answer is: Silicon‑based thermistor
Q.58 When using a 4‑20 mA loop for a pH sensor, what is the advantage of the loop over a voltage output in terms of signal integrity?
Current loops are less affected by voltage drops over long cable runs
Current loops provide higher resolution
Current loops eliminate the need for grounding
Current loops increase the sensor’s lifespan
Explanation - Since the signal is current, resistive losses along the cable do not change the measured value.
Correct answer is: Current loops are less affected by voltage drops over long cable runs
Q.59 Which calibration technique involves adjusting sensor output to match a known reference at the start and end of the measurement range?
One‑point calibration
Two‑point calibration
Zero‑span calibration
Dynamic calibration
Explanation - Two‑point calibration sets gain and offset by aligning sensor readings with reference values at two extremes.
Correct answer is: Two‑point calibration
Q.60 A bioreactor’s online monitoring software flags an alarm when the DO signal deviates more than 10 % from the model prediction for 30 seconds. This is an example of:
Set‑point control
Model‑based fault detection
Open‑loop monitoring
Manual inspection
Explanation - The alarm is triggered by a discrepancy between measured data and a predictive model, indicating a potential sensor or process fault.
Correct answer is: Model‑based fault detection
Q.61 In the context of sensor integration, what does the term “hot‑swap” refer to?
Replacing a sensor while the system remains powered and operational
Calibrating a sensor at high temperatures
Using sensors that operate only at elevated temperatures
Swapping the sensor data with a backup file
Explanation - Hot‑swap capability allows maintenance without shutting down the bioreactor, minimizing downtime.
Correct answer is: Replacing a sensor while the system remains powered and operational
Q.62 Which of the following best describes a “soft sensor” in bioprocess monitoring?
A physical sensor made from flexible material
A mathematical model that estimates a variable from other measured data
A low‑cost disposable sensor
A sensor that operates at low voltage
Explanation - Soft sensors combine data and models to infer unmeasured variables, reducing the need for expensive hardware sensors.
Correct answer is: A mathematical model that estimates a variable from other measured data
Q.63 During a batch fermentation, the online pH sensor shows a gradual upward drift despite no addition of base. Which corrective action is most appropriate?
Increase aeration rate
Perform an in‑process pH calibration
Replace the temperature sensor
Decrease agitation speed
Explanation - Drift suggests sensor aging; recalibration restores accuracy without stopping the run.
Correct answer is: Perform an in‑process pH calibration
Q.64 What is the main benefit of using a fiber‑optic based sensor for measuring dissolved gases in a bioreactor?
Higher electrical conductivity
Immunity to electromagnetic interference
Lower cost than electrochemical sensors
Ability to measure temperature directly
Explanation - Fiber‑optic sensors transmit light, not electrical signals, making them resistant to EMI in electrically noisy environments.
Correct answer is: Immunity to electromagnetic interference
Q.65 A sensor specification lists a “repeatability” of ±0.2 % of reading. What does this indicate?
The sensor’s reading changes by 0.2 % each hour
When measuring the same value repeatedly, the readings vary within ±0.2 %
The sensor can only be used for 0.2 % of its full range
The sensor loses 0.2 % accuracy after each calibration
Explanation - Repeatability reflects the sensor’s consistency under unchanged conditions.
Correct answer is: When measuring the same value repeatedly, the readings vary within ±0.2 %
Q.66 Which sensor principle is utilized by a quartz crystal microbalance (QCM) when used for bio‑film detection in a bioreactor?
Piezoelectric frequency shift
Optical absorption
Thermal conductivity
Magnetic resonance
Explanation - Mass loading on the crystal changes its resonant frequency, enabling detection of thin films or fouling.
Correct answer is: Piezoelectric frequency shift
Q.67 In the context of data acquisition, what does “sampling aliasing” refer to?
Loss of data due to insufficient storage
Distortion caused by sampling below the Nyquist frequency
Improvement of signal quality by averaging samples
A method of encrypting sensor data
Explanation - Aliasing occurs when high‑frequency components masquerade as lower frequencies due to inadequate sampling rates.
Correct answer is: Distortion caused by sampling below the Nyquist frequency
Q.68 Which of the following sensor technologies can simultaneously measure both pH and temperature on the same probe?
Electrochemical pH sensor with integrated thermistor
Optical turbidity sensor
Hall‑effect magnetic sensor
Capacitive humidity sensor
Explanation - Combining a glass pH electrode with an embedded temperature sensor provides both measurements on a single probe.
Correct answer is: Electrochemical pH sensor with integrated thermistor
Q.69 During an online monitoring session, a sudden loss of signal from the DO sensor is observed. Which of the following is the most likely immediate cause?
Battery depletion
Cable disconnection or break
Sensor fouling
Calibration drift
Explanation - A complete loss of signal typically results from a physical interruption in the wiring rather than gradual drift or fouling.
Correct answer is: Cable disconnection or break
Q.70 A bioreactor’s control system uses a cascade control loop where the inner loop regulates agitation speed based on the outer loop’s dissolved oxygen setpoint. This architecture is known as:
Feed‑forward control
Cascade control
Dead‑time compensation
Ratio control
Explanation - Cascade control uses a secondary (inner) loop to meet the primary (outer) loop’s objective, improving dynamic response.
Correct answer is: Cascade control
Q.71 Which sensor attribute is most critical when selecting a probe for high‑shear, high‑speed mixing environments?
Low cost
Mechanical robustness
High resolution
Fast response time
Explanation - Sensors must withstand physical forces without damage in turbulent mixing conditions.
Correct answer is: Mechanical robustness
Q.72 For a bioreactor operating at 5 bar pressure, which type of pressure sensor is best suited to maintain accuracy?
Piezoresistive sensor
Capacitive pressure sensor
Strain‑gauge sensor
Mercury manometer
Explanation - Piezoresistive sensors provide good accuracy over a wide pressure range, including several bars, and are compatible with electronic systems.
Correct answer is: Piezoresistive sensor
Q.73 When implementing a redundancy scheme with two identical DO sensors, which logic ensures the system only triggers an alarm if both sensors disagree beyond a tolerance?
AND logic
OR logic
XOR logic
NOT logic
Explanation - Using AND logic, an alarm is generated only when both sensors indicate a fault, reducing false positives.
Correct answer is: AND logic
Q.74 A sensor’s “temperature coefficient” of 0.01 %/°C indicates that:
The sensor’s output changes by 0.01 % of full scale for each degree Celsius change in temperature
The sensor can only operate within 0.01 °C temperature range
The sensor consumes 0.01 % more power per °C
The sensor’s accuracy improves by 0.01 % per °C
Explanation - Temperature coefficient quantifies output variation with temperature.
Correct answer is: The sensor’s output changes by 0.01 % of full scale for each degree Celsius change in temperature
Q.75 Which method can be used to extend the life of a pH electrode in a bioreactor?
Operating it at high temperatures
Storing it dry when not in use
Regularly cleaning with distilled water and storing in a suitable buffer solution
Applying high voltage continuously
Explanation - Proper cleaning and storage in a buffer prevent drying and contamination, preserving electrode performance.
Correct answer is: Regularly cleaning with distilled water and storing in a suitable buffer solution
Q.76 In a real‑time monitoring system, which statistical tool is commonly used to detect gradual sensor drift over time?
Fourier Transform
Moving average filter
Control chart (e.g., Shewhart chart)
Histogram analysis
Explanation - Control charts track process parameters and highlight trends or shifts indicating drift.
Correct answer is: Control chart (e.g., Shewhart chart)
Q.77 When a sensor is specified with a “full‑scale output” of 20 mA, what does this term describe?
The maximum current the sensor can draw from the power supply
The current representing the highest measurable value of the measured parameter
The sensor’s internal resistance
The amount of power consumed during calibration
Explanation - Full‑scale output corresponds to the maximum signal the sensor produces for its measurement range.
Correct answer is: The current representing the highest measurable value of the measured parameter
Q.78 A bioreactor’s online system uses a 1 kHz sampling rate for temperature but a 0.1 Hz rate for biomass (optical density). This choice is justified because:
Temperature changes rapidly, while biomass changes slowly
Temperature sensors are cheaper
Biomass measurements require more power
Regulatory standards limit biomass sampling
Explanation - Fast‑changing variables need higher sampling rates; slow‑varying parameters can be sampled less frequently.
Correct answer is: Temperature changes rapidly, while biomass changes slowly
Q.79 Which of the following best describes the term “electrode polarization” in amperometric DO sensors?
A change in the magnetic field around the electrode
Accumulation of gas bubbles on the electrode surface affecting current
A shift in the sensor’s temperature coefficient
A modification of the electrode’s mechanical strength
Explanation - Polarization refers to gas bubble formation that blocks diffusion, altering the measured current.
Correct answer is: Accumulation of gas bubbles on the electrode surface affecting current
Q.80 In an online monitoring context, the term “latency” and “response time” are often used interchangeably. Which statement correctly differentiates them?
Latency is the total delay from measurement to display; response time is the sensor’s internal delay.
Latency is the sensor’s internal delay; response time includes data processing and communication.
Both terms mean exactly the same thing.
Latency refers to network delay, while response time refers to actuator movement.
Explanation - Latency describes the sensor’s physical delay; response time accounts for the entire chain up to the user interface.
Correct answer is: Latency is the sensor’s internal delay; response time includes data processing and communication.
Q.81 Which sensor technology can provide real‑time monitoring of the redox potential (Eh) in a bioreactor?
Silver/silver chloride reference electrode paired with a platinum working electrode
Thermocouple
Capacitive humidity sensor
Ultrasonic level sensor
Explanation - Redox potential is measured with a potentiometric cell consisting of a reference and a working electrode.
Correct answer is: Silver/silver chloride reference electrode paired with a platinum working electrode
Q.82 A bioreactor uses a non‑contact laser displacement sensor to measure the height of a liquid column. Which parameter does this sensor directly provide?
Liquid density
Liquid level (height)
Liquid conductivity
Dissolved oxygen concentration
Explanation - Laser displacement sensors measure distance to the liquid surface, giving the level directly.
Correct answer is: Liquid level (height)
Q.83 When integrating multiple sensors into a PLC, why is it advisable to use isolated input modules?
To reduce cost
To protect the PLC from ground loops and voltage spikes
To increase sampling speed
To simplify wiring
Explanation - Isolation prevents unwanted currents and voltage differences from damaging the controller.
Correct answer is: To protect the PLC from ground loops and voltage spikes
Q.84 Which of the following is a primary advantage of using a soft‑sensor (model‑based estimator) for measuring substrate concentration in a bioreactor?
Eliminates the need for any physical sensor
Provides instantaneous measurements without lag
Reduces cost and maintenance associated with chemical analyzers
Increases the bioreactor’s maximum volume
Explanation - Soft sensors estimate concentrations from existing data, avoiding expensive and fouling‑prone analyzers.
Correct answer is: Reduces cost and maintenance associated with chemical analyzers
Q.85 A data logger records temperature with a resolution of 0.01 °C but a repeatability of ±0.1 °C. What is the practical significance of this specification?
The logger can detect changes as small as 0.01 °C, but repeated measurements may vary by up to 0.1 °C.
The logger cannot measure below 0.1 °C.
The logger will drift by 0.01 °C each hour.
The logger’s battery lasts for 0.1 °C of operation.
Explanation - Resolution is the smallest step; repeatability indicates measurement variability under unchanged conditions.
Correct answer is: The logger can detect changes as small as 0.01 °C, but repeated measurements may vary by up to 0.1 °C.
Q.86 In an online monitoring system, what is the function of a “watchdog timer”?
To periodically calibrate sensors
To reset the control system if it becomes unresponsive
To increase data acquisition speed
To store historical sensor data
Explanation - A watchdog timer monitors software health and forces a restart if the system hangs, enhancing reliability.
Correct answer is: To reset the control system if it becomes unresponsive
Q.87 Which sensor type can be used to measure the concentration of carbon dioxide (CO₂) dissolved in the liquid phase of a bioreactor?
Amperometric CO₂ sensor
Capacitive humidity sensor
Thermocouple
Hall‑effect sensor
Explanation - Amperometric sensors generate a current proportional to the CO₂ concentration in solution.
Correct answer is: Amperometric CO₂ sensor
Q.88 A bioreactor uses a 24‑bit ADC for sensor acquisition. What is the theoretical voltage resolution if the input range is ±10 V?
0.000001 V
0.000003 V
0.00001 V
0.0003 V
Explanation - Resolution = 20 V / (2²⁴‑1) ≈ 20 / 16,777,215 ≈ 1.19 µV ≈ 0.000001 V.
Correct answer is: 0.000001 V
Q.89 Which of the following best describes the purpose of a “calibration curve” for a sensor?
A plot showing sensor output versus known reference values to correct measurements
A diagram of the sensor’s internal wiring
A schedule for sensor replacement
A list of sensor manufacturers
Explanation - Calibration curves map raw sensor signals to actual values, enabling accurate interpretation.
Correct answer is: A plot showing sensor output versus known reference values to correct measurements
Q.90 In a high‑precision bioreactor, why might a user select a platinum‑based DO sensor over a Clark‑type sensor?
Platinum sensors have lower cost
Platinum sensors are less affected by temperature variations
Platinum sensors can operate without a membrane, reducing fouling
Platinum sensors provide faster response times
Explanation - Membrane‑less platinum electrodes avoid membrane fouling, extending sensor life in demanding processes.
Correct answer is: Platinum sensors can operate without a membrane, reducing fouling
Q.91 When a sensor’s datasheet lists a “settling time” of 2 seconds, what does this indicate?
The time required for the sensor to reach a stable output after a step change in the measured variable
The time needed to calibrate the sensor
The time the sensor can operate before overheating
The time between data transmissions
Explanation - Settling time quantifies how quickly a sensor stabilizes after a rapid change.
Correct answer is: The time required for the sensor to reach a stable output after a step change in the measured variable
Q.92 Which communication protocol is specifically designed for deterministic real‑time data exchange in industrial automation and is often used for sensor networks?
Modbus TCP
PROFINET IRT
Bluetooth Classic
ZigBee
Explanation - PROFINET IRT (Isochronous Real Time) provides deterministic timing suitable for high‑speed control loops.
Correct answer is: PROFINET IRT
Q.93 A bioreactor’s temperature sensor is located 5 cm away from the heating element. The measured temperature lags the actual medium temperature by about 10 seconds. This lag is primarily caused by:
Sensor electrical noise
Thermal conduction delay
Signal processing algorithm
Cable length
Explanation - Heat must travel from the heating element to the sensor location, introducing a physical lag.
Correct answer is: Thermal conduction delay
Q.94 Which of the following sensor failure modes is most likely to produce a constant high reading irrespective of actual process conditions?
Open‑circuit failure
Short‑circuit failure
Calibration drift
Noise interference
Explanation - A short circuit forces the output to a fixed high value (e.g., max current), independent of the measured variable.
Correct answer is: Short‑circuit failure
Q.95 In a bioreactor, an optical sensor measures absorbance at 600 nm to estimate cell density. If the path length of the cuvette is 1 cm, which law relates absorbance to concentration?
Charles's law
Boyle's law
Beer‑Lambert law
Raoult's law
Explanation - Beer‑Lambert law states A = ε · c · l, linking absorbance (A) to concentration (c) with path length (l) and molar absorptivity (ε).
Correct answer is: Beer‑Lambert law
Q.96 Why is it important to maintain a reference temperature when calibrating a pH sensor?
Because the electrode’s response is temperature dependent
Because pH changes with pressure
Because temperature affects sensor wiring resistance
Because pH sensors generate heat
Explanation - The Nernst slope varies with temperature; calibrating at a known temperature ensures accurate pH readings.
Correct answer is: Because the electrode’s response is temperature dependent
Q.97 A sensor’s “signal‑to‑noise ratio” (SNR) of 60 dB indicates:
The signal is 60 times larger than the noise
The noise level is 60 dB above the signal
The signal power is 1 000 times greater than the noise power
The sensor can operate for 60 hours without noise
Explanation - SNR (dB) = 10 · log₁₀(P_signal / P_noise); 60 dB corresponds to a power ratio of 10⁶⁄¹⁰ = 1 000.
Correct answer is: The signal power is 1 000 times greater than the noise power
Q.98 Which of the following is a typical advantage of using a fiber‑optic DO sensor over an electrochemical DO sensor in a bioreactor?
Lower initial cost
Higher resistance to fouling and longer lifespan
Simpler calibration procedure
Direct measurement of pH
Explanation - Fiber‑optic sensors are not in direct contact with the medium, reducing fouling and extending service life.
Correct answer is: Higher resistance to fouling and longer lifespan
Q.99 A 4‑20 mA loop is used to transmit temperature data over 500 m of cable. If the loop resistance is 250 Ω, what is the maximum voltage drop across the cable when the loop is at 20 mA?
2 V
5 V
10 V
0.5 V
Explanation - Voltage drop = I · R = 0.02 A × 250 Ω = 5 V.
Correct answer is: 5 V
Q.100 Which sensor type is typically employed to monitor the level of foam on the surface of a bioreactor?
Capacitive level sensor
Ultrasonic sensor
Optical IR foam detector
Thermocouple
Explanation - IR detectors sense changes in light scattering caused by foam, providing early detection.
Correct answer is: Optical IR foam detector
Q.101 When implementing a PID controller for pH control, which term primarily eliminates steady‑state error?
Proportional (P)
Integral (I)
Derivative (D)
Feed‑forward
Explanation - The integral term accumulates error over time, driving the steady‑state error toward zero.
Correct answer is: Integral (I)
Q.102 In sensor data acquisition, which technique reduces the effect of quantization noise?
Oversampling and averaging
Increasing the sensor’s temperature coefficient
Using a lower resolution ADC
Shortening the cable length
Explanation - Oversampling at a higher rate and averaging the results lowers quantization noise and improves effective resolution.
Correct answer is: Oversampling and averaging
Q.103 Which factor is most critical when selecting a pressure sensor for use inside a sterile bioreactor vessel?
Low cost
Ability to be sterilized (e.g., autoclave compatible)
High power consumption
Large physical size
Explanation - Sensors inside the vessel must withstand sterilization processes without degradation.
Correct answer is: Ability to be sterilized (e.g., autoclave compatible)
Q.104 A sensor's output is digitized using a 12‑bit ADC with a ±10 V range. What is the smallest voltage change the ADC can resolve?
0.0049 V
0.0012 V
0.0024 V
0.0098 V
Explanation - Total range = 20 V. Resolution = 20 V / (2¹²‑1) ≈ 20 / 4095 ≈ 0.0049 V per count.
Correct answer is: 0.0049 V
Q.105 Which of the following sensor technologies can be used for non‑invasive measurement of dissolved CO₂ in a bioreactor?
Near‑infrared (NIR) spectroscopy
Thermistor
Capacitive humidity sensor
Hall‑effect sensor
Explanation - NIR spectroscopy can penetrate the vessel wall and detect CO₂ absorption bands, enabling non‑invasive measurement.
Correct answer is: Near‑infrared (NIR) spectroscopy
Q.106 In a multi‑sensor array for online monitoring, which technique helps to detect and reject outlier sensor readings?
Median filtering across sensor outputs
Increasing sensor gain
Reducing sampling frequency
Using a single sensor only
Explanation - Median filtering compares multiple sensor readings, discarding values that deviate markedly from the median.
Correct answer is: Median filtering across sensor outputs
Q.107 Why is it advantageous to place temperature sensors as close as possible to the culture medium rather than near the reactor walls?
To reduce sensor cost
To obtain a more accurate representation of the medium temperature
To simplify wiring
To increase sensor lifespan
Explanation - Temperature gradients can exist; placing the sensor in the medium captures the actual culture temperature.
Correct answer is: To obtain a more accurate representation of the medium temperature
Q.108 A bioreactor’s online monitoring system uses a 0‑10 V analog output for pH. If the pH range is 0–14, what pH corresponds to an output of 5 V?
7.0
5.0
10.0
12.0
Explanation - Voltage maps linearly: (5 V / 10 V) × 14 pH = 7 pH.
Correct answer is: 7.0
Q.109 Which sensor technology is most suitable for measuring the viscosity of a culture broth in real time?
Rotational viscometer with magnetic coupling
Capacitive humidity sensor
Thermocouple
Ultrasonic level sensor
Explanation - Magnetically coupled rotational viscometers can be mounted through a sealed wall, providing real‑time viscosity data.
Correct answer is: Rotational viscometer with magnetic coupling
Q.110 When a sensor’s output is digitized using an ADC with a sampling rate of 500 Hz, what is the highest frequency component that can be accurately captured according to the Nyquist theorem?
250 Hz
500 Hz
1000 Hz
125 Hz
Explanation - Nyquist frequency = half the sampling rate; thus, 500 Hz / 2 = 250 Hz.
Correct answer is: 250 Hz
Q.111 Which of the following best describes the purpose of a “dead‑time compensator” in a control loop for a bioreactor?
To speed up sensor response
To mitigate the effect of delay between measurement and control action
To increase the gain of the controller
To reduce power consumption
Explanation - Dead‑time compensators predict future process behavior to offset the inherent delay, improving stability.
Correct answer is: To mitigate the effect of delay between measurement and control action
Q.112 A sensor manufacturer states the device has a “linearity error” of 0.2 % FS. For a sensor with a 0‑10 V output, what is the maximum deviation from a perfect linear response?
0.02 V
0.2 V
2 V
0.002 V
Explanation - 0.2 % of full scale (10 V) = 0.002 × 10 V = 0.02 V.
Correct answer is: 0.02 V
Q.113 Which sensor principle relies on measuring the change in electrical resistance of a material as a function of temperature?
Thermocouple
Resistance Temperature Detector (RTD)
Hall‑effect sensor
Capacitive sensor
Explanation - RTDs exploit the predictable increase in resistance of metals (e.g., Pt100) with temperature.
Correct answer is: Resistance Temperature Detector (RTD)
Q.114 What is the main advantage of using a digital sensor with built‑in calibration over an analog sensor requiring external calibration?
Lower power consumption
Reduced wiring complexity and automatic compensation
Higher temperature range
Ability to operate underwater
Explanation - Digital sensors often include on‑board calibration and output directly in digital format, simplifying integration.
Correct answer is: Reduced wiring complexity and automatic compensation
Q.115 Which of the following sensors can directly measure the redox potential (Eh) in a bioreactor?
Silver/silver chloride reference electrode
Platinum working electrode paired with a reference electrode
Thermocouple
Capacitive humidity sensor
Explanation - A potentiometric cell consisting of a platinum working electrode and a reference electrode measures Eh.
Correct answer is: Platinum working electrode paired with a reference electrode
Q.116 A bioreactor’s online monitoring software displays a sudden spike in the temperature reading that returns to normal within 2 seconds. The most probable cause is:
Sensor failure
Electrical interference (spike)
Process overheating
Calibration error
Explanation - Transient electrical noise can cause brief spikes that disappear quickly, unlike sensor failure which persists.
Correct answer is: Electrical interference (spike)
Q.117 Which sensor type is most suitable for measuring the concentration of dissolved nitrogen (N₂) in a bioreactor gas phase?
Mass flow sensor
Thermal conductivity sensor
Infrared (IR) gas sensor
Electrochemical nitrogen sensor
Explanation - Thermal conductivity sensors differentiate gases based on their thermal properties, useful for N₂ detection.
Correct answer is: Thermal conductivity sensor
Q.118 A sensor’s “repeatability” spec is ±0.05 % FS, while its “accuracy” is ±0.5 % FS. What does this tell you?
The sensor is highly consistent but may be offset from the true value.
The sensor’s measurements vary widely each time.
The sensor cannot be calibrated.
The sensor has poor resolution.
Explanation - Repeatability reflects consistency; accuracy reflects closeness to the true value, indicating possible systematic error.
Correct answer is: The sensor is highly consistent but may be offset from the true value.
Q.119 In a bioreactor, which sensor would you use to directly detect the presence of microbial contamination via metabolic heat generation?
Thermocouple
pH electrode
Dissolved oxygen sensor
Infrared gas sensor
Explanation - Microbial activity releases heat; a thermocouple can detect subtle temperature increases indicative of contamination.
Correct answer is: Thermocouple
Q.120 Which method is commonly employed to mitigate sensor fouling in continuous glucose monitoring within a bioreactor?
Increasing sensor temperature
Implementing a flow‑through cell with a membrane filter
Using a higher voltage excitation
Mounting the sensor outside the reactor
Explanation - Flow‑through cells allow fresh sample to contact the sensor while a filter reduces fouling agents.
Correct answer is: Implementing a flow‑through cell with a membrane filter
Q.121 A 16‑bit ADC with a ±5 V input range is used to digitize a sensor output. What is the quantization step size?
0.000153 V
0.00153 V
0.0153 V
0.153 V
Explanation - Total range = 10 V. Step size = 10 V / (2¹⁶) ≈ 10 / 65536 ≈ 0.000153 V.
Correct answer is: 0.000153 V
Q.122 When using a 4‑20 mA current loop, why is it advantageous to include a shunt resistor at the receiving end?
To convert the current signal into a voltage readable by an ADC
To increase the current range
To provide power to the sensor
To filter high‑frequency noise
Explanation - A shunt resistor creates a voltage drop proportional to the current, which can be measured by an ADC.
Correct answer is: To convert the current signal into a voltage readable by an ADC
Q.123 Which sensor technology can be used for real‑time monitoring of ethanol concentration in a fermentation broth?
Near‑infrared (NIR) spectroscopy
Thermocouple
Hall‑effect sensor
Capacitive humidity sensor
Explanation - NIR spectroscopy detects specific absorption bands of ethanol, enabling inline concentration measurement.
Correct answer is: Near‑infrared (NIR) spectroscopy