In this article, we adopt a rigorous categorization of sensors based on their primary underlying physical principles. This approach is chosen because the performance of a sensor is predominantly determined by the physics governing its principle of operation. For instance, a position sensor can be realized using various methods such as resistive, capacitive, inductive, acoustic, or optical techniques. The characteristics of these sensors are closely tied to the specific physical transduction processes they employ.
While a magnetic sensor of a certain type could be employed as a displacement sensor, velocity sensor, or tactile sensor, its performance remains governed by the fundamental physics of that magnetic sensor. Position and movement are notably among the most crucial measurement quantities, and various terms in everyday language are used to describe these parameters. Many transducers are actually named after these descriptive terms.
Sensor Types Based on Measurement Parameters
Here is a brief overview of various transducers based on their measurement parameters:
- Distance Sensor: Measures the straight-line distance between two defined points.
- Position Sensor: Determines the coordinates of a specific point on an object in a designated reference system.
- Displacement Sensor: Measures the change in position relative to a reference point.
- Range Sensor: Calculates the shortest distance from an observer to various points on object boundaries in a 3D space, providing information about their position and orientation.
- Proximity Sensor:
- (a) Determines the sign of the linear distance between an object point and a fixed reference point, often used as a switch.
- (b) A contact-free sensor that measures short distances, even down to zero.
- Level Sensor: Measures the distance from the top level of a liquid or granular substance in a container with respect to a specified horizontal reference plane.
- Angular Sensor: Measures the angle of rotation relative to a reference position.
- Encoder: A displacement sensor (linear or angular) with a binary-coded ruler or disk.
- Tilt Sensor: Measures the angle relative to the earth’s normal.
- Tachometer: Measures rotational speed.
- Vibration Sensor: Measures the motion of a vibrating object in terms of displacement, velocity, or acceleration.
- Accelerometer: Measures acceleration.
Each of these transducers serves specific measurement purposes and is categorized based on the type of quantity they detect or measure.
Sensor Types Based on Measurement of Force
Here is a summary of transducers used for the measurement of force and related quantities:
- Pressure Sensor: Measures pressure relative to vacuum, a reference pressure, or ambient pressure.
- Force Sensor: Measures the force (normal and/or shear) applied to the transducer’s active point.
- Torque Sensor: Measures torque or moment.
- Force-Torque Sensor: Measures both forces and torques, including up to six components.
- Load Cell: Measures weight and force, often used in weighing applications.
- Strain Gauge: Measures the linear relative elongation of an object caused by compressive or tensile stress.
- Touch Sensor: Detects the presence or position of an object through mechanical contact.
- Tactile Sensor: Measures the 3D shape of an object using touch, either sequentially through an exploring touch sensor or instantly via a matrix of force sensors.
These transducers are designed to measure various force-related quantities and contribute to a wide range of applications in different fields.
Sensor Types Based on Operating Principles
Certainly, here are some examples of transducers named according to their operating principles, construction, or specific properties:
- Hall Sensor: Measures magnetic fields based on the Hall effect, named after the American physicist Edwin Hall (1855-1938).
- Coriolis Mass Flow Sensor: Measures mass flow of fluids using the Coriolis force on a rotating or vibrating channel, named after Gustave-Gaspard de Coriolis, a French scientist (1792-1843).
- Gyroscope (Gyrometer): Measures angles or angular velocities by utilizing the gyroscopic effect in rotating or vibrating structures.
- Eddy Current Sensor: Measures short-range distances between the sensor and a conductive object using currents induced by an AC magnetic field, also used for defect detection.
- LVDT (Linear Variable Displacement Transformer): A voltage transformer with a linearly movable core used for measuring linear displacement.
- NTC (Negative Temperature Coefficient): Refers to temperature sensors, especially thermistors, that exhibit a decrease in resistance with increasing temperature.
These names reflect the specific principles, effects, or properties that these transducers utilize for measurement.
Certain sensors involve a combination of transduction steps to achieve their measurement objectives. For instance, a displacement sensor when combined with a spring can function as a force sensor. When paired with a calibrated mass, a displacement sensor can serve as an accelerometer. The performance of such sensors is influenced not only by the primary sensor but also by the added components, such as the compliance of the spring or the mass of the accelerometer.
Calculations can also provide information about a specific quantity by utilizing relationships between quantities. The accuracy of these results depends on the precision of both the directly measured quantities and the parameters within the mathematical model that describes the relationships between these quantities. For instance, in acoustic distance measurements, the distance is calculated based on the time-of-flight (ToF) and the sound velocity. To achieve accurate results, knowledge of the acoustic velocity under the current temperature conditions is crucial.
Electronic signal processing can derive certain variables from others. For example, speed and acceleration can be determined from a displacement sensor by performing first and second differentiations, respectively. Conversely, integrating the output signal of an accelerometer yields a velocity signal, and a second integration results in a position signal. However, these processes are not without challenges. Differentiation often amplifies noise, particularly at higher frequencies, and integration can introduce drift due to offset integration. The quality of signal processing greatly impacts the accuracy of the final measurement.