Unit 3: Sensor Systems & Data Acquisition - Practice Quiz

1 What is the main purpose of an Analog-to-Digital Converter (ADC) in a sensor system?

2 Which type of sensor output usually requires an ADC before it can be processed by a microcontroller?

3 How many different output levels can an 8-bit ADC represent?

4 What does a higher ADC resolution generally provide?

5 Which sensor is used to detect the concentration or presence of gases?

6 What physical quantity is measured by a temperature sensor?

7 What does a humidity sensor commonly measure?

8 Which sensor is most suitable for measuring atmospheric pressure?

9 What is the main function of a proximity sensor?

10 Why is signal conditioning sometimes used with an analog sensor?

11 Which operating mode helps a sensor node save energy when it is not collecting data?

12 What is duty cycling in a low-power sensor system?

13 Which action generally reduces the energy used for wireless sensor communication?

14 Why might a sensor take readings only at selected time intervals?

15 What does a moving average filter primarily do to sensor data?

16 What information is used by a simple moving average filter?

17 What is the moving average of the readings , , and ?

18 What is one common effect of increasing the window size of a moving average filter?

19 What is the main purpose of a Kalman filter in a sensor system?

20 Which two kinds of information does a Kalman filter commonly combine?

21 A 10-bit ADC uses a 3.3 V reference. Approximately what digital value is produced when the input voltage is 1.65 V?

22 A sensor outputs a maximum of 2.0 V, but the microcontroller ADC has a 3.3 V input range. Which design change provides better measurement resolution without exceeding the ADC limit?

23 An analog sensor has a source resistance of 100 k, while the ADC requires the source impedance to be below 10 k for accurate sampling. What is the most appropriate interface?

24 A digital temperature sensor communicates through I2C, while a photoresistor produces a continuously varying voltage. Which statement correctly compares their interfaces?

25 An ADC has a 12-bit resolution and a 4.096 V reference. What is the approximate voltage represented by a reading of 2048?

26 A thermistor is connected in a voltage divider, and its resistance decreases as temperature increases. If the thermistor is placed above the fixed resistor and the output is measured at their junction, what happens to the output voltage as temperature rises?

27 A capacitive humidity sensor produces a voltage that increases from 0.8 V at 20% relative humidity to 2.8 V at 80% relative humidity. Assuming linear behavior, what humidity corresponds approximately to 1.8 V?

28 A pressure sensor has an output range of 0.5 V to 4.5 V for pressures from 0 kPa to 100 kPa. What pressure is indicated by an output of 2.5 V?

29 Why is a load resistor commonly used with a resistive gas sensor?

30 An infrared proximity sensor gives false detections when exposed to strong sunlight. Which improvement is most directly relevant?

31 A pressure sensor output changes slowly, but the ADC readings contain high-frequency electrical noise. Which hardware addition is most suitable before the ADC input?

32 A battery-powered humidity monitor only needs one measurement every five minutes. Which strategy usually provides the greatest energy saving?

33 A gas sensor requires a heater to stabilize before measurement. Which low-power strategy best preserves measurement quality?

34 A sensor node transmits readings over a wireless link. Which change generally reduces energy use without reducing the local sensor accuracy?

35 A microcontroller has active current of 12 mA for 2 seconds and sleep current of 0.02 mA for 58 seconds in each one-minute cycle. What is its approximate average current?

36 A three-sample moving average receives the values 10, 13, and 17. What output does it produce?

37 Increasing the window size of a moving average filter generally has which effect?

38 A moving average filter is applied to a sensor signal that contains a sudden step change. What is the primary consequence near the step?

39 A Kalman filter receives a noisy measurement but has high confidence in its prediction from the system model. How will the updated estimate usually change?

40 In a one-dimensional Kalman filter, the predicted state is 20, the measurement is 24, and the Kalman gain is 0.25. What is the updated estimate?

41 A 12-bit ADC has a 20 pF sample-and-hold capacitor and a 2 s acquisition interval. Assuming a full-scale input step, what is the largest total source resistance that keeps settling error below 0.5 LSB?

42 A resistive bridge is excited from a supply that varies by . Its output is digitized by an ADC. Which design best suppresses supply variation without separately measuring the excitation voltage?

43 A multiplexed ADC alternates between a low-impedance 3.0 V channel and a high-impedance 0.2 V channel. The latter consistently reads too high. Which modification most directly addresses the error?

44 A 10-bit ADC samples a constant sensor output containing sufficient uncorrelated noise to randomize its quantization error. How many samples must be averaged to obtain approximately 12-bit effective resolution?

45 A metal-oxide gas sensor heater is PWM-driven and causes periodic offsets in the sensor's millivolt-level output. Which acquisition strategy best limits this interference?

46 An NTC thermistor forms a divider with a fixed resistor and is read by an ideal ADC. At the nominal operating temperature, which fixed resistance maximizes sensitivity to fractional thermistor-resistance changes?

47 A capacitive humidity sensor exhibits electrode polarization and long-term drift when measured using a constant DC voltage. Which interface is most appropriate?

48 A 4–20 mA pressure transmitter uses a 24 V loop, requires at least 10 V across itself, and has 200 total cable resistance. The ADC input range is 0–3.3 V. What is the largest standard sense resistance allowed by both ADC range and loop compliance at 20 mA?

49 A node repeats a 10 s cycle: sensing and processing draw 40 mA for 120 ms, transmission draws 25 mA for 20 ms, and sleep draws 20 A for the remaining time. What is its average current?

50 A radio wake-up costs 5 mJ, each transmitted sample costs 0.2 mJ, and buffering a sample costs 0.1 mJ. For 10 samples, how much energy is saved by one batched transmission rather than 10 individual transmissions?

51 An adaptive sampler reduces its rate when recent measurements vary slowly. Which addition best prevents it from indefinitely missing a short event that occurs between widely spaced samples?

52 A sensor is power-gated, but its current consumption remains unexpectedly high because an active MCU GPIO is connected to the sensor's data pin. What is the most likely cause and remedy?

53 A five-sample moving average processes data sampled at 100 Hz. Assuming ideal sampling, what happens to a sinusoidal interference component at exactly 20 Hz?

54 A centered interpretation is applied to a nine-sample causal moving average sampled at 50 Hz. By how much should each output timestamp be shifted backward to align it with the center of its data window?

55 Which update correctly implements an exact length- moving average in constant time per sample, assuming stores the current window sum?

56 A stationary noise process has variance and autocorrelation with . What is the output variance of a four-sample moving average?

57 A scalar Kalman filter has prior estimate , prior variance , measurement , and measurement-noise variance . What are the posterior estimate and variance?

58 In a scalar random-walk Kalman filter, the assumed process-noise variance is increased while measurement-noise variance remains fixed. What is the principal steady-state effect?

59 For a one-dimensional constant-velocity state driven by continuous white acceleration with spectral density , which process-noise covariance is correct for a sampling interval ?

60 A Kalman filter uses innovation gating and rejects a measurement because its normalized innovation squared exceeds the threshold. Under a standard rejection policy, what should happen during that update?