Sensor - Intro, working mechanism, latest Flashcards
Sensors Definition
A sensor transforms a stimulus into a measurable signal, which can subsequently be converted into an observable output for further processing.
Sensors System Design
Sensor Classifications, 4 types? and examples of each
- Mechanical: strain gage, displacement, accelerometer, force, pressure, etc
- Thermal: thermal couple
- Optical: camera, infrared sensor
- Chemical: moisture sensor, pH sensor
Resistor sensor equation
Capacitance sensor equation
Inductance sensor equation
Classification based on sensor placement 2 types?
- Contact sensors.
- Non-contact sensors
Passive sensor definition
Passive sensor: response to its environment so does not require a power source
Active sensor definition
Active sensor: requires a power source to emit a signal that is scatter back to the sensor
What are the Sensor Specifications, 10 types?
- Sensitivity
- Linearity
- Hysteresis
- Environmental Effects
- Drift
- Accuracy
- Precision (Repeatability)
- Threshold
- Range
- Resolution
Calibration
The calibration procedure involves the comparison of the output from the sensor with a known measurement system.
Sensitivity
- Sensitivity is a measure of the change in output of a sensor for a unit change in input.
- Sensitivity can be obtained from the gradient of a graph of output as a function of input
Linearity
A sensor is linear if the output is linearly proportional to the input i.e. corresponding values of input and output lie on a straight line and sensitivity is constant across the input range
* This is considered desirable!
* The sensitivity of a non-linear sensor varies across part or all of the input range
Hysteresis
For a given input, the output from the sensor varies depending on whether the input stimulus is increasing or decreasing at the time
* Hysteresis is normally expressed as a percentage of the full scale output reading
Environmental Effects? 3 things
Sensitivity drift defines the amount by which the sensitivity of a sensor varies with environmental conditions.
In general, the output of a sensor depends not only on the input but on environmental conditions, such as
* Ambient temperature
* Atmospheric pressure
* Relative humidity etc.
Accuracy
Precision (Repeatability)
Accuracy is a measure of how close the measured value (the output from the system) is to the ‘true’ value (the input)
Repeatability is a measure of the similarity of output values when the same input is applied repetitively (it is NOT an indication of accuracy!)
What are the two types of Measurement errors?
System errors: imperfect design of the measurement setup and the approximation.
Random errors: variations due to uncontrolled variables. Can be reduced by averaging.
Threshold
Range or span
Resolution
- Threshold is the smallest input that will produce a detectable change in the output of a sensor
- The range of a sensor defines the minimum and maximum values of a quantity that the sensor is designed to measure
- Resolution is the smallest change in input that will produce a detectable change in the output of a sensor at a particular point in its active range
Temperature Sensors - three mechanisms to gain or lose heat
- Conduction - The transfer of heat within a substance, or between substances through molecular interaction
- Convection - Heat transfer within a fluid by the movement of heated molecules from one place to another
- Radiation – heat transfer in the form of electromagnetic waves, generally in the infra-red region of the electromagnetic spectrum
3 types of Contact Temperature Sensors?
Thermocouples - It utilise the thermoelectric effect where a small voltage is generated at the join between two metals. It have quick response times, and they can operate over the widest temperature range.
Thermistor - It contain a material in which a large changes in electrical resistance is produced by a small changes in temperature (High accuracy).
Resistance thermometer - RTDs materials have a positive temperature coefficient (the resistance of a metal increases with temperature). RTDs typically have higher thermal mass, and therefore they usually respond slower to temperature changes than thermocouple temperature sensors
Non-Contact Temperature Sensors
Thermographic camera - It contains a sensor capable of non- contact detecting infrared radiation emitted from a surface.
Contact Vs non-contact Temperature Sensor
What is a force sensor?
A Force sensor is defined as a transducer that converts an input mechanical load, weight, tension, compression or pressure into an electrical output signal.
Examples
* Piezoelectric force sensor
* Strain Gauge
* Resistive force sensor
Piezoelectric force sensor?
Strain Gauge?
- Piezoelectric materials generate an electrical potential (output voltage) when subjected to a force.
- The electrical resistance of a length of wire varies in direct proportion to the change in any strain applied to it.
Sources of error in strain gauge measurements, 5 things?
- Bonding faults – a good bond is vital to ensure strain in the specimen is fully transmitted to the gauge element
- Hysteresis – resistance values are slightly higher when unloading than loading
- Cross-sensitivity – strain gauge response to strain at right angles to the main measurement axis
- Moisture – strain gauges are susceptible to moisture and need to be encased in a damp-proof coating
- Temperature – temperature influences strain gauge resistance, and can cause expansion of the gauge and the specimen which
will all affect the output
SPORTTECH
These high-functional and smart textiles are increasingly adding value to the sports and leisure industry by combining utilitarian functions with wearing comfort that leads to achieving high level of performance.
What is a Smart Textile?
Smart Textile or Electronic Textile (E-textiles) can be defined as the materials and structures which can sense the environmental/human body changes. These stimuli could be thermal, chemical, mechanical, electric, magnetic or from other source.
Smart Clothes can monitor body functions eg:
* Heart Rate
* Breathing Rate
* Muscle Fatigue
* Movement
* Sweat
Nanotechnology
Nanotechnology is the understanding and control of matter at dimensions of roughly 1 to 100 nanometres, where unique phenomena enable novel applications.
Gore-Tex?
Gore-Tex is a waterproof/breathable fabric that is manufactured from PTFE into a laminated membrane
* Properties: breathable, lightweight, waterproof. When worn Gore-Tex releases water vapour(sweat) from the body but stops raindrops entering
Nano/Micro-encapsulated fibre/fabrics
Microencapsulated textiles describes fabric which has microcapsules embedding in the fibres, which can be controlled to bleed due to a environmental change e.g friction, pressure or gradually by diffusion or during the process of biodegradation.
Advantages of nanomaterial in sports equipment, 7 things?
Examples where Nanotechnology is in sports?
Tennis and Golf: Nanomaterials in racket frames and clubheads improve strength and reduce weight, leading to better control and distance in shots.
* Cycling: Nanomaterials in bike frames enhance strength and aerodynamics, making bikes more efficient.
* Hockey: Sticks with nanomaterials offer improved power and precision, while protective gear enhances safety.
* Swimming: Competitive swimwear uses nanomaterials to reduce water drag, leading to faster times.
* Skiing and Snowboarding: Nanomaterial coatings on equipment improve performance and durability.
* Athletic Footwear: Nanomaterials enhance cushioning, flexibility, and durability for better comfort and support.
* Sports Balls: Nanomaterial coatings optimize aerodynamics, durability, and performance.
* Safety Equipment: Helmets and protective gear incorporate nanomaterials for better impact resistance and safety.
* Wearable sensors: flexible, breathable, lightweight and unobtrusive monitoring.
Sustainability issues with nanotechnology
Challenges with nanotechnology? 3 things
- Rigid connections
- Poor stability
- Weak mechanical performance
