Sensors and Transducers exam 1
An IMU (inertial measurement unit) contains three sensors: ______________, ______________, and ______________.
accelerometer, magnetometer, and gyroscope
To prevent an inaccurate reading, a float sensor should be placed ______________ to avoid a false measurement reading.
centrally
A sensor that measures the flow of open air is often described as an ______________.
anemometer
Semiconductor temperature sensors: When constant ______________ is flowing through the p-n junction in a ______________, the ______________ across will change by about 2mV for each change in temperature of 1 degree Celsius.
current, diode, voltage
A gas/liquid pressure sensor usually works by a sensing element that translates pressure into mechanical ______________of a flexible part. A transducer converts into an electrical effect usually either modifying ______________or creating a small ______________or ______________.
displacement, resistance, voltage, current
A proximity sensor measures the ______________between two objects.
distance
______________materials generate a voltage difference during induced vibration.
piezoelectric
A microphone is a device that converts ______________ ______________ into an alternating electrical signal.
pressure waves
The combination of pulse trains is known as ______________.
quadrature
When light falls on a photoresistor the ______________ between the electrical leads will ______________.
resistance, diminish
A gauge factor describes the relationship between the change in ______________to change in ______________.
resistance, strain
A piezoelectric force sensor converts force to a ______________and it only responds to ______________ force.
small voltage, changes in
List two applications of the accelerometer.
In the past, accelerometers were laboratory devices that calibrated the performance of cars, airplanes, and other types of vehicles. Measuring the ability of car tires to withstand cornering forces was an application where an accelerometer was used. Miniaturization of accelerometer elements, coupled with a radical reduction in their cost, has enabled them to be installed in small electronic devices ranging from smartphones to hard drives. In a phone or a camera, accelerometers can determine which way up the user is holding the device. The camera can rotate the picture appropriately, and the orientation of the picture can be saved with its image data. In an external hard drive containing rotating platters, accelerometers can protect the read- write heads by rapidly parking them during the fraction of the second that elapses between someone dropping the hard drive and its impact with the floor. Accelerometers can be installed in a 3D mouse or virtual-reality headset to determine its orientation and motion. This enables a video image to be updated appropriately. For example, the Nintendo Wii Remote has been marketed with an ADXL330 accelerometer. In an automobile, an accelerometer can trigger the deployment of an airbag when the deceleration caused by an impact exceeds a threshold level.
In liquid sensing application, perforated plates called ______________are used to prevent liquid from creating waves and ripples.
baffles
Tilt sensors use a ______________ to interrupt an internal LED shining on a ______________.
ball, phototransistor
A passive infrared motion sensor detects ______________which all objects emit as a function of their______________relative to ______________.
black-body radiation, temperature, absolute zero
A thermocouple consists of two wires made from ______________ ______________, joined at one end.
different metals
GPS depends on calculating ______________from the time it takes for ______________to travel, and accurate ______________is needed.
distance, a radio signal, timekeeping
It would be a good decision to use a GPS receiver in a deep underground cave.
false
Light falling on a ______________causes it to generate a small current.
photodiode
Explain how a reed switch works.
A reed switch is a magnetically activated mechanical switch. It consists of two metallic contacts in a small enclosure that is usually a glass capsule. The contacts are magnetic, and move in response to a magnetic field. A permanent magnet is used to activate the switch.
Why do you need two sensors to detect direction on an optical rotary encoder?
A single sensor cannot indicate the direction of rotation, but if a second emitter-sensor pair is added, 90 degrees out of phase with the first, a microcontroller can assess the phase difference between pulse streams to determine which way the wheel is turning. This principle is illustrated in Figure 7-6 where one transmitter-detector pair is located in position A and another is in position B. The resulting pulse trains, for clockwise and counterclockwise rotation of the wheel, are shown in green. The combination of pulse trains is known as quadrature, because there are four possible combinations: A and B both high, A and B both low, A high and B low, or A low and B high.
Describe how an ultrasonic proximity sensor works.
An ultrasonic proximity sensor functions by emitting a short burst of sound and then listening for echoes from objects in front of it. The sound is created by a piezoelectric transducer (see Volume 2) at a frequency between 30kHz and 50kHz, well above the range that can be detected by the human ear. The transducer may do dual duty as a microphone, sending and receiving sound on an alternating basis; or a second transducer, serving as a microphone, may be mounted beside the emitter on a small circuit board.
List an application of the magnetometer and describe the difference between the scalar magnetometer and a vector magnetometer. Explain magnetoresistance.
Applications: digital compasses, cameras, and cellular phones Scalar magnetometers measure the total strength of a magnetic field, whereas vector magnetometers measure the strength in a specified direction. Magnetoresistance is a phenomenon where the resistance of a material changes fractionally when it is exposed to a magnetic field. This is capable of yielding greater accuracy than Hall-effect sensors, but has tended to be more expensive.
A disadvantage of Hall-effect current sensing is that the sensor can be affected by stray capacitive fields.
False
A gyroscope measures linear motion.
False
A hot wire anemometer measures temperature by heating the air to create plasma.
False
A photoresistor cannot handle as much current as the phototransistor.
False
A resistive touch screen can support multiple finger pressures.
False
A tilt switch will work in space.
False
A typical maximum range of a capacitive sensor is 10cm.
False
Absence of moving mechanical parts means a touch pad is less reliable than other electromechanical switches.
False
Gray code allows only one binary digit to change per transition.
False
Gyroscope placement on a printed circuit board is not sensitive to location.
False
If two pyroelectric elements of opposite polarity are stimulated simultaneously, their voltages will add.
False
Optical grating functionally has the same operation as a magnetic linear encoder.
False
The frequency response of a microphone is flat and detects all frequencies equal.
False
The relationship between temperature and resistance of a thermistor is linear function.
False
Tilt sensors are built around electromechanical action.
False
A magnet in a float used to measure liquid level would need to be placed near a ______________sensor to generate position.
Liquid level
A temperature sensor whose resistance diminishes as its temperature increases is abbreviated as NTC. NTC stands for: ______________ ______________ ________________
Negative Temperature Coefficient
Describe why gas sensors suffer from cross-sensitivity.
One sensor may respond to more than one gas. Manufacturers control this problem to some extent by adding filtering material around the semiconductor element, or by adjusting the proportions of dopants used in the semiconductor. Datasheets should be consulted carefully to see if a sensor may give false positives as a result of other gases that are likely to be present in the area where it will be used.
An ______________, popularly known as an ______________, contains an LED opposite to a photoresistor, in a sealed package.
Optical isolator, optocoupler
A vibrating fork is used in a gyroscope design. Describe any design conditions specific to vibration frequencies.
Temperature Drift Vibrating materials at the heart of a chip-based gyroscope are likely to change their behavior with temperature. Typically the chip will contain a temperature sensor, the value of which can be used to adjust the output value of the gyroscope. Mechanical Stress Stress can be induced when a surface-mount chip is soldered to a board. The vibrating parts of a chip-based gyroscope may be adversely affected. Datasheets will supply information regarding maximum acceptable temperature during the soldering process. Vibration Because a chip-based gyroscope depends on the consistent behavior of internal vibrating parts, external vibration can degrade its accuracy. Sensor design can minimize the effects of vibration, but the datasheet should be consulted for details. Placement A gyroscope should be placed on a circuit board near a hard mounting point where deflection of the board will be minimized.
A reed switch always requires an activating magnet
True
A touch pad can form one side of the capacitor, and a human finger can form the other side. A touch sensor detects any change in low voltage AC.
True
According to Einstein's theory of equivalence, forces resulting from accelerations are indistinguishable from the force of gravity.
True
An RTD and a PTC both have positive temperature coefficients.
True
An object presence sensor verifies the presence of an object in a predetermined range without necessarily measuring how far away it is or how fast it ismoving.
True
Hall effect sensors are useful in almost any situation where a sensor must detect a mechanical operation at close range.
True
In a modern automobile as many as 20 temperature sensors are used.
True
Including impedance considerations into a microphone design is crucial.
True
Light can be parasitic to a barometric sensor and generate false readings.
True
Motion-sensitiveoutdoor lighting is almost always based around a PIR.
True
PTC sensors can have a nearly linear relationship between temperature and resistance
True
A moving-coil microphone is also called a _____________ microphone, and the overall output is an alternating ______________ signal. A ____________ microphone responds to a change in capacitance. An ____________ microphone is made from ferroelectric material.
dynamic, electrical, condenser, electret
An RTD temperature sensor exploits the ____________________________in electrical ______________ of a metal film, metal filament when the temperature rises.
fractional increase, resistance
Any mechanical system involves ______________and ______________ will degrade over time.
friction and accuracy
A ______________resists rotation around any axis at right angles to its own axis of rotation or vibration.
gyroscope
Self-______________is a problem experienced with all temperature sensors except the ______________ since it measures a relative voltage and is passive.
heating, thermocouple
List two environmental factors that can affect a capacitive sensor's measurement: ______________ and ______________.
humidity and temperature
For longer-range distance detection, one should use an ______________sensor.
infrared
The only non-contact temperature sensor listed is the ______________ temperature sensor that responds to______________ -______________ ______________ .
infrared, black-body radiation
LVDT stands for: ____________ ____________ ____________ ____________.
linear variable differential transformer
An optical encoder is well suited for use with a ____________________________.
microcontroller program
The two primary categories of object presence sensing are: ______________and ______________.
optical and magnetic
The primary risk for gas flow rate sensors is damage caused by ______________and ______________in the gas stream.
particles, contaminants
______________pressure is measured under conditions that change slowly or not at all. ______________pressure is subject to fluctuations. Pressure sensors tend to be designed for ______________condition or the other.
static, dynamic, one
______________ have the widest temperature range of any contact sensors.
thermocouples
Infrared sensors work by a process of ______________.
triangulation
Label the direction sensitive to strain.
←dat way→
Your book lists K, J, T, E, N, R, and S type thermocouples. Why are there different types of thermocouples?
The different types of thermocouples have different ranges of temperatures from which they can measure. The variation of thermocouples stems off of the different types of material each thermocouple is made with.
Describe the role of the thermopile in the heat transfer principle method to measure gas flow rate.
The gas passes over a thermopile (consisting of several thermocouples wired in series), then a heater, and then another thermopile. These components are miniaturized and can be etched into a chip measuring 2 mm square or less. The temperature difference between the two thermopiles increases as the flow of gas becomes faster and transports more heat to the second thermopile. This is known as the heat transfer principle,
What is the primary reason for using an LVDT as compared to similar sensors?
The robust, frictionless design lends itself to high reliability (Any sliding mechanism will involve friction, and will be vulnerable to wear and tear, resulting in looseness that will degrade its accuracy)
The conductivity of a plastic-film force sensor has an almost linear relationship between force and current.
True
The output signal of a photodiode is small and needs to be amplified.
True
Three accelerometers are all placed orthogonally on a chip and the chip is set level at sea level, it is guaranteed that one accelerometer will read 1g.
True
List two issues challenges to measuring liquid flow.
Turbulence (surface turbulence consisting of ripples, waves, or sloshing of liquid) and Tilting
What sensor would you use to detect abnormalities in a washing machine during the spin cycle?
Vibration sensor Smaller versions can shut down domestic appliances such as a washing machine that is seriously out of balance during a spin cycle.
What type of circuit should be used in conjunction with a strain gauge? Why?
Wheatstone Bridge circuit The very small changes in resistance in a strain gauge must be amplified to be usable.
How does the principle of the Hall-effect sensor work?
When current is flowing through the length of a conductor, and a magnetic field is applied across the width of the conductor, the field generates a force causing electrons and electron holes to accumulate asymmetrically on opposite sides. This is known as the Hall effect. The voltage difference between the electron-rich and electron-depleted zones is known as the Hall voltage. It is proportional to the magnetic field, and inversely proportional to the density of free electrons in the material.
A Hall-effect sensor responds to a magnetic field by generating a small _____________.
voltage
For sensing purposes, a potentiometer is wired as a ______________ ______________.
voltage divider
