Unit 3: Position & Light Transducers - Practice Quiz

1 What does a position transducer primarily measure?

2 Which electrical property changes when the wiper of a potentiometer moves?

3 What type of output is commonly produced by an optical encoder?

4 Why is an analog-to-digital converter used when interfacing an analog position transducer with a microcontroller?

5 What does a light transducer convert into an electrical signal?

6 What typically happens to the resistance of a photoresistor when light intensity increases?

7 What does a photodiode produce when exposed to light?

8 What is the main purpose of a photomultiplier?

9 An optical array transducer contains multiple light-sensitive elements arranged in what form?

10 A thermal detector senses radiation mainly by observing a change in which quantity?

11 Which phenomenon is used by an interferometer to make precise measurements?

12 What quantity is commonly measured by a gyroscope in a robot?

13 Which two sensors are commonly included in a basic Inertial Measurement Unit (IMU)?

14 Wheel odometry estimates robot movement primarily from which information?

15 What physical quantity does an accelerometer measure?

16 What usually activates a mechanical limit switch in a robot?

17 Which type of electromagnetic radiation is used by an infrared sensor?

18 How does an ultrasonic sensor commonly determine the distance to an object?

19 What is the main difference between incremental and absolute optical encoders?

20 Ultrasonic sensors operate using sound waves with frequencies generally above which human hearing limit?

21 A robot joint must report its shaft angle immediately after power is restored, without first moving to a reference position. Which type of position transducer is most suitable?

22 A linear potentiometer is connected across a supply. Its wiper is at of the travel measured from the grounded end. Assuming no loading, what is the wiper voltage?

23 A quadrature encoder produces pulses per revolution on each channel. A controller uses all rising and falling edges, and the shaft rotates at . What count rate does the controller receive?

24 Why is Gray code commonly used on the tracks of an absolute optical encoder?

25 A potentiometric position sensor gives incorrect readings when connected to a low-resistance ADC input. Which interface change best reduces this loading error?

26 A position sensor outputs at and at . It is connected to a 12-bit ADC with a reference. Approximately what ADC code is expected at ?

27 A point light source produces an irradiance of at a distance of . Ignoring absorption, what irradiance is expected at ?

28 An LDR forms the upper resistor of a voltage divider, with a fixed resistor connected from the output to ground. What happens to the output voltage when illumination increases?

29 A photodiode is used to detect rapid changes in light intensity. Which operating arrangement is generally preferred for faster response?

30 A photovoltaic cell has an open-circuit voltage of . Why can the terminal voltage be lower when a load is connected?

31 A photomultiplier has eight dynodes, each providing an average secondary-emission gain of . What is the approximate electron multiplication gain?

32 Two neighboring pixels in a linear optical array are at positions and , with measured intensities and , respectively. Using an intensity-weighted centroid, where is the detected light spot located?

33 A robot must detect long-wave infrared radiation without cooling, and response time is less important than broad wavelength sensitivity. Which detector principle is most suitable?

34 In a Michelson interferometer using light of wavelength , moving one mirror causes fringes to pass a reference point. What is the mirror displacement?

35 A stationary robot's gyroscope has a constant yaw-rate bias of . If the bias is not corrected, approximately how much yaw error accumulates after ?

36 A stationary IMU contains a three-axis accelerometer and a three-axis gyroscope but no magnetometer. Which orientation quantity cannot be determined as an absolute long-term reference from these sensors alone?

37 A differential-drive robot has wheel radius and wheel separation . During a motion, the left wheel turns twice and the right wheel turns three times. What is the approximate change in heading?

38 An accelerometer has a zero- output of and sensitivity of . Its output is . What acceleration does it indicate along its sensitive axis?

39 A limit switch is used to stop a robot axis at the end of travel. Which wiring choice is generally more fail-safe because a broken wire can also be detected as a stop condition?

40 A reflective infrared proximity sensor calibrated on a white wall reports a much greater distance when aimed at a black object at the same actual distance. What is the most likely cause?

41 An LVDT produces the differential signal , where the sign of is encoded by carrier phase. A synchronous demodulator multiplies this signal by and applies an ideal low-pass filter. Relative to a correctly phased demodulator, what displacement will be reported?

42 A linear potentiometer is excited by . At 50% travel, its wiper drives a load connected to ground. Assuming negligible contact resistance, what wiper voltage is measured?

43 A quadrature encoder has 2048 cycles per revolution on each channel. A decoder uses all rising and falling edges, and its maximum accepted count rate is counts/s. Ignoring electrical bandwidth limits, what is the largest shaft speed that can be measured without missing counts?

44 A 12-bit ADC has a sample capacitor and an acquisition time of . Modeling the position sensor and interface by a Thevenin resistance , what is the largest that allows a full-scale step to settle within LSB?

45 A photodetector has quantum efficiency at wavelength . Using , what is its approximate responsivity?

46 A photoresistor is connected to ground in a voltage divider with a fixed resistor connected to . The operating-point resistance is . Which choice of maximizes the magnitude of the small-signal sensitivity at ?

47 A reverse-biased photodiode supplies signal current and dark current. What is the approximate RMS shot-noise current over a noise bandwidth, assuming ?

48 A photomultiplier has quantum efficiency and ten dynodes, each with mean secondary-emission ratio . Neglecting collection losses, what is the mean anode charge produced per photon incident on the photocathode?

49 Three adjacent pixels at coordinates , , and record intensities , , and . Their ADC saturates at 150. If exposure is doubled and a center-of-mass centroid is computed from the clipped readings, what centroid is obtained?

50 A thermal infrared detector behaves as a first-order system with time constant . Radiation is chopped sinusoidally at . What fraction of the low-frequency output amplitude remains?

51 A Michelson interferometer uses a laser. Its quadrature electronics interpolate each full fringe into 1024 counts. What mirror displacement corresponds to one count?

52 A stationary robot has its gyro sensitive axis aligned vertically at latitude . Ignoring sensor bias, what Earth-rotation rate should the gyro measure about that axis? Use .

53 A stationary IMU contains only a three-axis gyroscope and a three-axis accelerometer. After roll and pitch are aligned with gravity, which state remains fundamentally unobservable without an external heading reference?

54 A differential-drive robot has wheel separation and commands both wheels to a nominal speed of . The actual left wheel radius is 1% larger than modeled, while the actual right radius is 1% smaller. What heading error accumulates after if the same nominal wheel angular speed is applied?

55 A level robot accelerates horizontally at . An estimator incorrectly assumes that the accelerometer measures gravity only and computes pitch magnitude as . Taking , what false pitch is reported?

56 A robot's end-stop switch must make a broken cable detectable as a fault rather than as a normal non-actuated condition. Which wiring and interpretation best provides this behavior?

57 A phase-based infrared range sensor modulates light at and measures a round-trip phase shift of . Ignoring fixed phase offsets, what is the nearest target distance consistent with the measurement?

58 An ultrasonic sensor converts echo time to range using , appropriate near . The actual air temperature is , where . For a true range of , what range will the sensor report?

59 A four-bit absolute encoder crosses from binary position 7 to position 8. Compare ordinary binary encoding with reflected Gray encoding. Which statement correctly describes an asynchronous read during this transition, assuming each bit is individually reliable but transition times are skewed?

60 A resolver produces and because of a 2% cosine-channel gain mismatch. The estimator uses . At a true angle of , what is the approximate angular error ?