Short Answer:
Active transducers generate their own electrical energy when exposed to a physical quantity, such as temperature, pressure, or force. They do not require an external power source. Examples include thermocouples and piezoelectric sensors.
On the other hand, passive transducers do not generate their own energy; instead, they rely on an external power source to operate. They measure changes in physical quantities by altering electrical properties like resistance, capacitance, or inductance. Examples of passive transducers include strain gauges and thermistors.
Detailed Explanation:
Active Transducers
Active transducers are devices that convert a physical quantity into an electrical signal without needing any external power source. They generate their own electrical energy in response to a change in the measured physical property. For example, when a thermocouple is exposed to a temperature difference, it generates a voltage proportional to the temperature change, and this voltage can be measured and used for further analysis. Similarly, a piezoelectric sensor generates an electrical charge when subjected to pressure or mechanical stress.
Active transducers are typically used when high sensitivity and accuracy are required. These devices are self-powered and do not require any additional energy input, making them simple to use in certain applications. They are widely used in temperature sensing, pressure sensing, and other applications where converting physical properties to electrical signals is necessary.
Key Characteristics of Active Transducers:
- Self-powered: They generate electrical signals without the need for an external energy supply.
- Higher sensitivity and accuracy: Since they generate their own energy, they are typically more sensitive.
- Requires no external power source: Useful for applications where powering the device would be cumbersome or impractical.
Examples:
- Thermocouples: Measure temperature and generate a small voltage proportional to the temperature.
- Piezoelectric sensors: Convert mechanical stress into electrical energy.
- Photovoltaic cells: Convert light energy into electrical energy.
Passive Transducers:
Passive transducers, unlike active transducers, do not generate their own electrical energy. Instead, they rely on an external power source to operate. They typically measure a physical quantity by altering electrical properties like resistance, capacitance, or inductance. For example, a strain gauge measures deformation by changing its resistance when it is stretched or compressed. The change in resistance is then measured by passing a known current through it.
Because passive transducers rely on external power sources, they are often simpler and more cost-effective than active transducers. However, they are generally less sensitive and less accurate than active transducers. The use of passive transducers is widespread in industrial applications, where they are used for measuring mechanical forces, pressure, displacement, and temperature.
Key Characteristics of Passive Transducers:
- Require external power: These devices cannot function without an external power source.
- Changes in electrical properties: They work by altering physical quantities like resistance, capacitance, or inductance.
- Generally less sensitive: They typically offer lower sensitivity compared to active transducers.
Examples:
- Strain gauges: Measure strain by changing resistance.
- Thermistors: Change resistance based on temperature variations.
- LVDTs (Linear Variable Differential Transformers): Measure displacement by detecting changes in inductance.
Conclusion
The primary difference between active and passive transducers lies in the need for an external power source. Active transducers generate their own electrical energy and are typically more sensitive and accurate, while passive transducers require external power to operate and work by altering electrical properties. Both types of transducers play crucial roles in measuring and converting physical quantities into electrical signals, and the choice between the two depends on the specific application and requirements.