Devices¶
Sensors (Input)¶
Devices that - detect the state of a physical environment - quantitatively provide a corresponding output as an electrical/optical signal
Characteristics of Sensors¶
| Meaning | |||
|---|---|---|---|
| Static | After steady state condition, how the output of a sensor change in response to input change | Range | Highest and lowest value that can be sensed |
| Resolution | Smallest change in input that can be sensed | ||
| Sensitivity | Ratio of incremental change in response of system wrt incremental change in input | ||
| Error | Difference between true and measured value \(u = y_m-y\) | ||
| Accuracy | \(1-E[u]\) | ||
| Precision | \(\sigma(u)\) | ||
| Linearity | Deviation of sensor curve from particular straight line | ||
| Drift | Difference in measurements from a specific reading when kept at that value for long period of time | ||
| Repeatability | Deviation between measurements in a sequence under same conditions | ||
| Dynamic | Properties of system's transient response to input How well sensor responds to changes in input | Zero-order system | Output shows a response to input signal with no delay |
| First-order system | Output approaches final value gradually | ||
| Second-order system | Output response oscillates before steady state |
Classification¶
| Aspect | Class | Meaning | Example |
|---|---|---|---|
| Activity | Passive | Cannot independently sense input | Accelerometer Temperature Water-level Soil moisture |
| Active | Can independently sense input | Radar Sounder Laser altimeter | |
| Signal Type | Analog | ||
| Digital | |||
| Direction of Quantity | Scalar | Only magnitude | Speedometer |
| Vector | Magnitude and direction | Accelerometer Gyroscope |
Sensor Fusion¶
Combining measurements of the same quantity from multiple sensors, to obtain a combined information with lower uncertainty than any of the individual sensors. Using multiple sensors for the quantity also allows us to verify each sensor wrt others.
If we have \(s\) sensors, $$ \begin{aligned} \mu_\text{S} &= \left( \sum \limits_s^S \dfrac{\mu_s}{\sigma^2_s} \right) \sigma^2_{S} \ \sigma^2_\text{S} &= \dfrac{1}{\sum \limits_s^S \dfrac{1}{\sigma^2_s} } \end{aligned} $$ where \(S\) refers to the combination of all the sensors
Effectors (Output)¶
Devices that perform some action such as emitting light, sound, motor, etc
Sensors¶
- Motion
- Gyroscope
- Radar
- Magnetometer
- Accelerometer
- Acoustic
- Ultrasonic
- Microphones
- Geophones
- Vibrometers
- Environmental
- Temperature
- Humidity
- Pressure
- Infrared
- Touch sensors
- Capacitive
- Infrared
- Image Sensors
- Thermal
- Camera
- Biometric
- Fingerprint
- Heart rate
- Face recognition
- Force sensors
- Pressure
- Strain
- Rotation sensors
- Encoders
Actuator¶
flowchart LR
s[/Signal/] & e[/Energy/] -->
Actuator -->
mf[/"Motion/Force/Light"/]- Motor
- Valve controller
- LED light
Classification¶
| Class | Subclass | Example |
|---|---|---|
| Electric | Linear | Electric Bell |
| Rotatory | Motor | |
| Fluid Power | Linear | Cylinder, Piston |
| Rotary | Cylinder, Piston | |
| Chain | Linear | Sprockets, sections of chain |
| Manual | Linear | Gearboxes Wheels |
| Rotatory | Levers Handwheels |