MECHATRONICS UPDATED CORE EXAM MANUAL
QUESTIONS AND SOLUTIONS RATED A+
✔✔For the repetition structure shown in the figure, which one of the following
statements would not create an infinite loop? - ✔✔y=y-1
✔✔An electrical resistance strain gauge, with a gauge factor of 2.5 and a resistance of
50 Ω, is getting a change in resistance of 1.25 Ω. How much is the measured strain?
Provide only the number without units. - ✔✔0.01
✔✔The dynamic characteristics of a transducer refer to values given when steady-state
conditions occur. - ✔✔False
✔✔A shaft encoder is to be used with a 40mm radius tracking wheel to monitor linear
displacement. If the encoder produces 512 pulses per revolution, what will be the
number of pulses produced by a linear displacement of 150mm? Provide only the
number without units. - ✔✔305.5 2pi*40. (150/2pi40)*512
✔✔A potentiometer consists of a resistance element with a sliding contact to: -
✔✔change the resistance of a sensor
✔✔Micro instruments make a strain gauge (MMF404146) with a resistance of 350 ohms
and a gauge factor of 2.09. If the strain gauge, when applied to a surface, reads 350
Ohms before bending and 351 Oms after bending, what is the level of strain at the
sensor? Note that the units of strain are change in length / original length and as such
are very small. - ✔✔0.00136 (rfinal-rinitial)/rinitial=2.09strain
✔✔A thermocouple is used with a compensation circuit - ✔✔Because the cold junction
is not held at 0ºC.
✔✔The range of a transducer is the: - ✔✔Limit between which the input can vary.
✔✔We need to track rapid temperature changes in a very small space. What sensor
should we use? - ✔✔thermistor
✔✔A photoresistor - ✔✔has a resistance which depends on the intensity of the light
falling on it.
✔✔n general, all other things equal, you want a sensor with: - ✔✔High sensitivity, high
linearity, and low hysteresis.
✔✔Piezoelectric sensors are mainly used for steady pressures. - ✔✔false
, ✔✔A thermocouple sensor has a time constant of 50 seconds in still air. When it is
subject to a temperature change of 100ºC, in 50 s its temperature will have changed by
about: - ✔✔63 deg
✔✔onsider the operational amplifier in the configuration below. If Vin=5V, R1=10Ω and
R2=50Ω, calculate the output voltage Vout. Provide only the number without units. -
✔✔-25
✔✔You need to filter a signal and block all frequencies from 100Hz to 200Hz. What kind
of filter will you use? - ✔✔band-stop filter
✔✔For the Wheatstone bridge circuit shown below, if R1 = 1 Ω, R2 = 2 Ω, and Rx = 3
Ω, to what value should R3 be adjusted so as to achieve a balanced condition? - ✔✔1.5
✔✔Consider the full bridge made of strain gauges attached to a metal cylinder as
shown below. When a compressive load is applied to the metal cylinder the resistance
of R1 and R3 will increase due to the stretching of the strain gauge while R2 and R4 will
decrease due to the compression of the strain gauge. Given that the voltage supplied by
the battery remains constant, what happens to the voltage potential at point A
(measured with respect to ground)? - ✔✔goes up
✔✔For the operational amplifier circuit shown in the following figure, the output is: -
✔✔Three times the difference between V1 and V2.
✔✔Which of the following statements about filtering is not true? - ✔✔Operational
amplifiers are used in filters to amplify the signal.
✔✔What pulse width modulation is used to give the following signal from a 5V DC
input? - ✔✔33.3%
✔✔From the list below, select the statements that apply to ideal operational amplifiers: -
✔✔Infinite input impedance and infinite gain
✔✔An op-amp is connected in a comparator configuration, as shown below. The
positive power supply is V+= 3.3V and the negative power supply is V-= -3.3V. If V1 =
2V and V2 = 0V, what is the output of the op-amp? - ✔✔-3.3V
✔✔A sensor gives an analog output range of 12V. How many bits are needed for an
ADC if there is to be a resolution of at least 20 mV? - ✔✔10
✔✔A sensor, for an input of 4 V, gives a digital output of a word of 8 bits. The resolution
is: - ✔✔4/2^8 V
QUESTIONS AND SOLUTIONS RATED A+
✔✔For the repetition structure shown in the figure, which one of the following
statements would not create an infinite loop? - ✔✔y=y-1
✔✔An electrical resistance strain gauge, with a gauge factor of 2.5 and a resistance of
50 Ω, is getting a change in resistance of 1.25 Ω. How much is the measured strain?
Provide only the number without units. - ✔✔0.01
✔✔The dynamic characteristics of a transducer refer to values given when steady-state
conditions occur. - ✔✔False
✔✔A shaft encoder is to be used with a 40mm radius tracking wheel to monitor linear
displacement. If the encoder produces 512 pulses per revolution, what will be the
number of pulses produced by a linear displacement of 150mm? Provide only the
number without units. - ✔✔305.5 2pi*40. (150/2pi40)*512
✔✔A potentiometer consists of a resistance element with a sliding contact to: -
✔✔change the resistance of a sensor
✔✔Micro instruments make a strain gauge (MMF404146) with a resistance of 350 ohms
and a gauge factor of 2.09. If the strain gauge, when applied to a surface, reads 350
Ohms before bending and 351 Oms after bending, what is the level of strain at the
sensor? Note that the units of strain are change in length / original length and as such
are very small. - ✔✔0.00136 (rfinal-rinitial)/rinitial=2.09strain
✔✔A thermocouple is used with a compensation circuit - ✔✔Because the cold junction
is not held at 0ºC.
✔✔The range of a transducer is the: - ✔✔Limit between which the input can vary.
✔✔We need to track rapid temperature changes in a very small space. What sensor
should we use? - ✔✔thermistor
✔✔A photoresistor - ✔✔has a resistance which depends on the intensity of the light
falling on it.
✔✔n general, all other things equal, you want a sensor with: - ✔✔High sensitivity, high
linearity, and low hysteresis.
✔✔Piezoelectric sensors are mainly used for steady pressures. - ✔✔false
, ✔✔A thermocouple sensor has a time constant of 50 seconds in still air. When it is
subject to a temperature change of 100ºC, in 50 s its temperature will have changed by
about: - ✔✔63 deg
✔✔onsider the operational amplifier in the configuration below. If Vin=5V, R1=10Ω and
R2=50Ω, calculate the output voltage Vout. Provide only the number without units. -
✔✔-25
✔✔You need to filter a signal and block all frequencies from 100Hz to 200Hz. What kind
of filter will you use? - ✔✔band-stop filter
✔✔For the Wheatstone bridge circuit shown below, if R1 = 1 Ω, R2 = 2 Ω, and Rx = 3
Ω, to what value should R3 be adjusted so as to achieve a balanced condition? - ✔✔1.5
✔✔Consider the full bridge made of strain gauges attached to a metal cylinder as
shown below. When a compressive load is applied to the metal cylinder the resistance
of R1 and R3 will increase due to the stretching of the strain gauge while R2 and R4 will
decrease due to the compression of the strain gauge. Given that the voltage supplied by
the battery remains constant, what happens to the voltage potential at point A
(measured with respect to ground)? - ✔✔goes up
✔✔For the operational amplifier circuit shown in the following figure, the output is: -
✔✔Three times the difference between V1 and V2.
✔✔Which of the following statements about filtering is not true? - ✔✔Operational
amplifiers are used in filters to amplify the signal.
✔✔What pulse width modulation is used to give the following signal from a 5V DC
input? - ✔✔33.3%
✔✔From the list below, select the statements that apply to ideal operational amplifiers: -
✔✔Infinite input impedance and infinite gain
✔✔An op-amp is connected in a comparator configuration, as shown below. The
positive power supply is V+= 3.3V and the negative power supply is V-= -3.3V. If V1 =
2V and V2 = 0V, what is the output of the op-amp? - ✔✔-3.3V
✔✔A sensor gives an analog output range of 12V. How many bits are needed for an
ADC if there is to be a resolution of at least 20 mV? - ✔✔10
✔✔A sensor, for an input of 4 V, gives a digital output of a word of 8 bits. The resolution
is: - ✔✔4/2^8 V
