Sensors

Sensors

sensor,

Definition: a device for sensing a physical variable of a physical system or an environment.

.Sensor Technology – Terminology

•     Transducer is a device which transforms energy from one type to another, even if both energy types are in the same domain.

–     Typical energy domains are mechanical, electrical, chemical, magnetic, optical and thermal.

•     Transducer can be further divided into Sensors, which monitors a system and Actuators, which impose an action on the system.

–     Sensors are devices which monitor a parameter of a system, hopefully without disturbing that parameter.

Classification of Sensors

•      Mechanical quantities: displacement, Strain, rotation velocity, acceleration, pressure, force/torque, twisting, weight, flow

•      Thermal quantities: temperature, heat.

•      Electromagnetic/optical quantities: voltage, current, frequency phase; visual/images, light; magnetism.

•      Chemical quantities: moisture, pH value.

Specifications of Sensor

•     Accuracy: error between the result of a measurement and the true value being measured.

•     Resolution: the smallest increment of measure that a device can make.

•     Sensitivity: the ratio between the change in the output signal to a small change in input physical signal. Slope of the input-output fit line.

•     Repeatability/Precision: the ability of the sensor to output the same value for the same input over a number of trials.

Measurement

Measurement output:

•      interaction between a sensor and the environment surrounding the sensor.

•      compound response of multiple inputs.

Measurement errors:

•      System errors: imperfect design of the measurement setup and the approximation, can be corrected by calibration .

Random errors: variations due to uncontrolled variables. Can be reduced by averaging.