Sensor Kapasitif mendeteksi benda bukan logam, cairan, pupur, material granula, dan material melalui dinding kaca atau plastik.

Kekurangan sensor kapasitif:•Jarak yang pendek, karena pengaruh dielektris dari bendaakan hilang pada jarak yang jauh,•Tidak seperti sensor induktif, sensor kapasitif dapat gagal jika terlalu kotor karena kotoran tersebut dapat terdeteksi,•Dapat menimbulkan persoalan bagi material yang memilikikonstanta dialektrik yang sama dengan udara (1,0005),•Sensor kapasitif yang sangat sensitif kadang-kadang dapat tertriger oleh kondisi kelembaban yang tinggi

Capacitive proximity sensorCapacitive proximity sensor  menggunakan medan electrostatic  untuk mendetect ada tidaknya  object  benda padat apa saja,berupa  logam atau bukan logam.Cara kerja :

cara kerja Capacitive Proximity SensorTarget yang bisa dideteksi Logam dan non logam

deteksi logam dan nonlogamSalah satu  penggunaan  capacitive proximity sensor adalah mendeteksi  level cairan dalam botol melalui penghalang . Contoh, air mempunyai  dielectric yg lebih tinggi dari pada plastik .  Sensor dapat membedakan plastic dan mendeteksi cairan.

What is a Capacitive Sensor?

A capacitive sensor is a proximity sensor that detects nearby objects by their effect on the electrical field created by the sensor.   Simple capacitive sensors have been commercially available for many years, and have found a niche in nonmetallic object

detection, but are limited to short ranges, typically less than 1 cm.

Capacitive sensors have some similarities to radar in their ability to detect conductive materials, while seeing through insulating materials such as wood or plastic.   In practice, the differences are considerable; When compared to radar, capacitive sensors:

Are simpler, so are potentially smaller, less expensive and less power-hungry. Are proximity sensors, rather than range sensors.  They do not give a direct

indication of how far away the detected object is.  A more distant strong target can give the same response as a nearby weak target.

Are non-directional and have a short range.

When used for detecting objects all around a vehicle, some of the disadvantages of the capacitive sensor are less problematic.  A practical system has many sensors regularly spaced around the outside of the vehicle.   This means that there is always a sensor close by, so no great range is required, and objects can be roughly localized by which sensor they are detected in. Non-directional response is actually desirable, since it can detect objects that are between sensors but very close to the vehicle.

What Can it Detect?

Due to its non-directional nature, the capacitive sensor measures some capacitance from objects in the environment that are always present and therefore not interesting.  When mounted on a car, the sensor detects the car itself and the ground.  Unknown objects are detected as increases in this background capacitance.

Commercial capacitive sensors typically operate at ranges of 1 cm or less.    At these ranges the object capacitance approaches the background capacitance.   However, at 1 meter the capacitance change is orders of magnitude smaller, and much less than the background capacitance.  It is necessary to determine what this background capacitance is so that it can be subtracted from the measurement.  

Since the background capacitance is large compared to the object capacitance, and is also subject to drift, it is much easier to use the sensor to detect change in the environment than to detect the absolute presence or absence of an unknown object.  The amount of background capacitance change depends on how stable the environment is.  In a relatively poorly controlled environment such as the outside of a

car,  absolute presence detection of a person is probably limited to 30cm or less.

In this change detector mode, the sensor is not so much a presence detector as a change-of-presence detector,  somewhat like a passive infrared motion detector (PIR.)   However, because of its intrinsically short range, a capacitive motion detector can be used in situations where a PIR detector would falsely respond to apparent background changes.   This is true in the suggested vehicle safety application, where motion of the vehicle causes changes in the thermal background

Capacitive proximity sensors working principle

• Capacitive sensors are used for non-contact detection of metallic objects & nonmetallic objects (liquid, plastic, wooden materials and soon). Capacitive proximity sensors use the variation of capacitance between the sensor and the object being detected. When the object is at a preset distance from the sensitive side of the sensor, an electronic circuit inside the sensor begins to oscillate. The rise or fall of such oscillation is identified by a threshold circuit that drives an amplifier for the operation of an external load.

Applications

• Capacitive touch sensors are used in many

devices such as laptop track pads, digital audio

players, computer displays, mobile phones,

mobile devices and others.

• More and more design engineers are selecting

capacitive sensors for their versatility,

reliability and robustness and cost reduction

over mechanical switches.