Unit 2: Force & Velocity Transducers - Practice Quiz

1 What physical quantity is measured by a force transducer?

2 What is the SI unit of force?

3 What property of a strain gauge changes when it is stretched?

4 A strain gauge is commonly bonded to which part of a force sensor?

5 Which circuit is commonly used with strain gauges to measure small resistance changes?

6 Which transducer produces an electrical charge when subjected to force?

7 Which type of transducer changes capacitance when its mechanical dimensions change?

8 What is the main purpose of a load cell?

9 Which sensing element is frequently used inside a strain-gauge load cell?

10 What happens to the output of an ideal load cell when the applied force increases within its rated range?

11 Why is an instrumentation amplifier often used with a strain-gauge load cell?

12 Which device converts an analog force-transducer signal into digital data?

13 Velocity describes how quickly an object's position changes with respect to what quantity?

14 Which unit is commonly used for linear velocity?

15 What quantity does a tacho-generator primarily measure?

16 For a typical DC tacho-generator, the generated output voltage is approximately proportional to what quantity?

17 What does an optical incremental encoder commonly produce as a rotating disk moves?

18 What can the phase difference between channels A and B of a quadrature encoder indicate?

19 Which method can be used to estimate speed from an incremental encoder?

20 What is a basic purpose of a Kalman filter in a sensor system?

21 A force transducer has a range of to and an accuracy of of full scale. What is the maximum possible measurement error?

22 A robotic gripper must detect whether an object is being squeezed without significantly changing the gripper's mechanical stiffness. Which sensor characteristic is most important?

23 A strain gauge has a gauge factor of and experiences a strain of . What is the approximate fractional change in resistance?

24 Why is a Wheatstone bridge commonly used with strain gauges in force measurement?

25 Two identical strain gauges are bonded to opposite sides of a bending beam. One is in tension and the other is in compression. Which bridge arrangement best improves sensitivity?

26 A piezoelectric force transducer is most suitable for measuring which type of force?

27 An inductive force transducer produces a change in inductance as its core moves. Which circuit property is most directly affected by this change at a fixed excitation frequency?

28 A load cell has a rated capacity of and an output sensitivity of . With a excitation and a load, what output voltage is expected, assuming linearity?

29 A load cell output changes slightly when its temperature changes even though the applied force is constant. Which specification describes this behavior?

30 A robotic arm uses a six-axis force-torque sensor. A force applied along the tool's -axis also produces a small reported torque about the -axis. What is the most likely cause?

31 A strain-gauge bridge produces a differential output of only a few millivolts in a noisy robotic system. Which interface is most appropriate before analog-to-digital conversion?

32 A force sensor is sampled at , but significant noise is present above . Which interface change best reduces aliasing?

33 A mobile robot travels in , then stops for . What is its average velocity over the entire interval?

34 A wheel encoder measures angular position at discrete sampling instants. Which method estimates angular velocity most directly from these measurements?

35 A tacho-generator has a sensitivity of . What voltage should it produce at an angular speed of , ignoring loading effects?

36 A tacho-generator output contains noticeable ripple at low speed. Which change is most likely to improve the measured velocity signal?

37 An incremental encoder has pulses per revolution and is decoded in quadrature using four edges per pulse. What is its angular resolution per count?

38 In a two-channel quadrature encoder, channel A leads channel B during forward rotation. What information is obtained from this phase relationship?

39 An encoder generates pulses per revolution at . What pulse frequency must the interface count?

40 An encoder interface misses counts when the motor speed increases. Which change directly addresses the most likely timing limitation?

41 A force transducer has sensitivity and is excited by a supply. Its output is measured with an amplifier whose input-referred offset is . For a measured output of , what is the most accurate estimate of the applied force after offset correction?

42 A force sensor is specified as linear within of full scale, with a full-scale range of . If the measured force is , what is the worst-case force uncertainty due only to the stated linearity specification?

43 A quarter-bridge strain-gauge circuit uses a gauge factor of , excitation , and measured small-signal output . Assuming the gauge is the only active arm and the output magnitude is , what strain is indicated?

44 A full Wheatstone bridge has four identical strain gauges. Two gauges in opposite arms experience , while the other two experience . Which behavior is expected for the bridge output and temperature sensitivity?

45 A bonded strain gauge has nominal resistance and temperature coefficient of resistance . Its apparent strain coefficient is . If the gauge factor is , what mechanical strain must be applied to produce zero net resistance change during a temperature rise?

46 A capacitive force transducer has differential capacitance for displacement toward one electrode. At , which statement best describes its local sensitivity compared with the sensitivity at ?

47 A piezoelectric force sensor is connected to an amplifier with input resistance and total input capacitance . For a force step that should be observed without significant droop, which approximate lower frequency limit is imposed by the sensor-amplifier high-pass behavior?

48 An inductive displacement transducer is used to infer force through a compliant element. The compliance has stiffness , and the inductive sensor has sensitivity after demodulation. What demodulated voltage corresponds to a force of , assuming linear behavior?

49 A load cell has rated output , excitation , and capacity . The instrumentation amplifier gain is . What output voltage should be expected at a load of , neglecting offsets?

50 A load cell has a rated-capacity overload limit, a rated capacity of , and a measured load consisting of a static force plus a sinusoidal component of amplitude . What is the maximum instantaneous load, and does it exceed the overload limit?

51 A differential load-cell output has common-mode voltage and differential signal . An instrumentation amplifier has gain , CMRR , and ideal supply headroom. What is the approximate output error caused by common-mode rejection imperfection?

52 A bridge sensor has source resistance and produces open-circuit at full load. If it is connected directly to an ADC input with resistance , what voltage reaches the ADC before amplification?

53 A robot joint velocity is estimated by finite differences from position samples at . Quantization noise in each position sample has standard deviation and is independent between samples. What is the standard deviation of the velocity noise using a first difference?

54 A motor accelerates uniformly from to in . A velocity estimator uses a moving average over . Assuming the average represents the velocity at the center of the window, what velocity should be reported at after acceleration begins?

55 A tachogenerator produces at with negligible offset. Its armature resistance causes a drop at the measured operating current, and the output polarity is positive for the chosen rotation direction. What generated emf corresponds to the measured speed if the terminal voltage is ?

56 A tacho-generator has sensitivity and output ripple of peak-to-peak at a particular speed. If the ripple is not filtered, what peak-to-peak speed error does it introduce?

57 A quadrature encoder has pulses per revolution on channel A. Decoding all four quadrature edges, followed by a mechanical reduction from motor to joint, is used to estimate joint position. How many counts correspond to one joint revolution?

58 An incremental encoder provides cycles per revolution on each quadrature channel. The controller counts four edges per cycle. At a shaft speed of , what minimum counter sampling rate is required to observe every edge without aliasing under an ideal timing assumption?

59 A velocity signal is sampled at and contains useful content up to plus interference at . What alias frequency will the interference appear at after sampling?

60 An encoder-based velocity interface measures counts during a gate time of . The encoder resolution is counts per revolution. What shaft speed is estimated?