Introduction to Capacitive Sensors :
Capacitive sensors are the noncontact devices having potential of high-resolution
measurement of not only position but also change of position of any conductive
target. To measure the position or other properties such as motion, chemical composition, electric field of
nonconductive targets capacitive sensing can be used. Pressure, acceleration, fluid level, and fluid composition are some of the variables which can be measured by capacitive sensors by converting them into motion or dielectric constant. Capacitive sensors are able to detect conductive and non-conductive, transparent,
opaque, metallic, non-metallic, liquid and solid, substances
reliably without the need for contact.
Applicatios :
1.
Flow--Many
types of flow meters convert flow to pressure or displacement, using an orifice
for volume flow or Carioles Effect force for mass flow. Capacitive sensors can
then measure the displacement.
2. Pressure--A diaphragm with stable deflection properties can measure pressure with a spacing-sensitive detector.
3. Liquid level --Capacitive liquid level detectors sense the liquid level in a reservoir by measuring changes in capacitance between conducting plates which are immersed in the liquid, or applied to the outside of a non-conducting tank.
4. Spacing--If a metal object is near a capacitor electrode, the mutual capacitance is a very sensitive measure of spacing.
5. Scanned multiplate sensor--The single-plate spacing measurement can be
6. extended to contour measurement by using many plates, each separately
7. addressed. Both conductive and dielectric surfaces can be measured.
8. Thickness measurement--Two plates in contact with an insulator will measure the insulator thickness if its dielectric constant is known, or the dielectric constant if the thickness is known.
9. Ice detector--Airplane wing icing can be detected using insulated metal strips in wing leading edges.
10. Shaft angle or linear position--Capacitive sensors can measure angle or position with a multiplate scheme giving high accuracy and digital output, or with an analog output with less absolute accuracy but faster response and simpler circuitry.
11. Lamp dimmer switch--The common metal-plate soft-touch lamp dimmer uses 60 Hz excitation and senses the capacitance to a human body.
12. Keyswitch--Capacitive keyswitches use the shielding effect of a nearby finger or a moving conductive plunger to interrupt the coupling between two small plates.
13. Limit switch--Limit switches can detect the proximity of a metal machine component as an increase in capacitance, or the proximity of a plastic component by virtue of its increased dielectric constant over air.
14. X-Y tablet--Capacitive graphic input tablets of different sizes can replace the computer mouse as an x-y coordinate input device. Finger-touch-sensitive, z-axis-sensitive and stylus-activated devices are available.
15. Accelerometers--Analog Devices has introduced integrated accelerometer ICs with a sensitivity of 1.5g. With this sensitivity, the device can be used as a tiltmeter.
2. Pressure--A diaphragm with stable deflection properties can measure pressure with a spacing-sensitive detector.
3. Liquid level --Capacitive liquid level detectors sense the liquid level in a reservoir by measuring changes in capacitance between conducting plates which are immersed in the liquid, or applied to the outside of a non-conducting tank.
4. Spacing--If a metal object is near a capacitor electrode, the mutual capacitance is a very sensitive measure of spacing.
5. Scanned multiplate sensor--The single-plate spacing measurement can be
6. extended to contour measurement by using many plates, each separately
7. addressed. Both conductive and dielectric surfaces can be measured.
8. Thickness measurement--Two plates in contact with an insulator will measure the insulator thickness if its dielectric constant is known, or the dielectric constant if the thickness is known.
9. Ice detector--Airplane wing icing can be detected using insulated metal strips in wing leading edges.
10. Shaft angle or linear position--Capacitive sensors can measure angle or position with a multiplate scheme giving high accuracy and digital output, or with an analog output with less absolute accuracy but faster response and simpler circuitry.
11. Lamp dimmer switch--The common metal-plate soft-touch lamp dimmer uses 60 Hz excitation and senses the capacitance to a human body.
12. Keyswitch--Capacitive keyswitches use the shielding effect of a nearby finger or a moving conductive plunger to interrupt the coupling between two small plates.
13. Limit switch--Limit switches can detect the proximity of a metal machine component as an increase in capacitance, or the proximity of a plastic component by virtue of its increased dielectric constant over air.
14. X-Y tablet--Capacitive graphic input tablets of different sizes can replace the computer mouse as an x-y coordinate input device. Finger-touch-sensitive, z-axis-sensitive and stylus-activated devices are available.
15. Accelerometers--Analog Devices has introduced integrated accelerometer ICs with a sensitivity of 1.5g. With this sensitivity, the device can be used as a tiltmeter.
Key Features :
Contactless
- Reliable object detection with sensing distances up to 30 mm
- No sensor damage due to aggressive media
- Medium is not contaminated by the sensor
No matter what material
- Reliable detection of conductive and non-conductive materials
- Failure-free detection of highly transparent and opaque materials
- Reliable detection even on optically reflecting surfaces
Durable
- Protected installation outside of the container possible
- Closed sensor front increases service life in case of contact with liquids
- High wear resistance of the housing increases sensor service life in case of contact with granules.
Advantages :
- More reliable than mechanical sensor.
- No moving part- there is no wear or tear.
- Less expensive.
- Can detect metal and non-metal.
Disadvantages :
- Dirty or wet environment.
- Large gap between sensor and target isrequired.
- Very sensitive to environment and noise.
Market :
The capacitive sensors market is expected to grow at a CAGR of 15% in
the next five years (2013-2018). Various factors are responsible for
driving the market in the current scenario and the major driver is the
increasing demand for capacitive sensors in the consumer electronics
sector.
The figure below shows the continuous growth of the market in the coming five years from 2013 to 2018.
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| Source : MarketsandMarkets |
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