Types of Sensors
- An active sensor or self-generating sensor is one that can generate a signal without the need of any external power supply.
- Examples of active sensors are Photovoltaic cells, thermocouples, piezoelectric device.
- A passive sensor is one which requires external power supply to generate the signal.
- The typical example for this type of sensor is diaphragm used to convert the pressure or velocity oscillations of sound waves into movements of a solid sheet.
Resolution in sensors:
The resolution of a sensor measures its ability to detect a change in the sensed quantity. It is usually quoted in terms of the smallest change that can be detected.
Errors in sensors:
The sensing of any quantity is liable to error. The errors can be static or dynamic.
- A static error is the type of error that is caused by reading problems like the parallax of a needle on a meter scale(which causes the apparent reading to vary according to the position of the observer’s eye).
- Interpolation error is another error of this type. It arises when a needle is positioned between two marks on a scale, and the used has to make a guess as to the amount signified by this position. When the scale is linear, the interpolation error is least.
- A typical error of this type is difference between the quantity as it really is and the amount that is measured, caused by the loading of the measuring instrument itself.
- An example for this type of error is the false voltage reading measured across a high-resistance potential divider with a voltmeter whose input resistance is not high enough.
- All forms of sensors are liable to dynamic errors if they are used for sensing only.
- If they are used for measurement, both static and dynamic errors will occur.