Capacitive Proximity Sensor

What is Capacitive Proximity Sensor?

       Capacitive proximity sensors are similar to inductive proximity sensors. The main different between the two types is that capacitive proximity sensors produce an electrostatic field instead of an electromagnetic field. Capacitive proximity switches will sense metal as well as nonmetallic materials such as paper, glass, liquids and cloth.

        The sensing surface of a capacitive sensor is formed by two concentrically sharped metal electrodes of an unwound capacitor. When an object nears the sensing surface it enters the electrostatic field charges the capacitance in an oscillator circuit. As a result, the oscillator begins oscillating. The trigger circuit reads the oscillator’s amplitude and when it reaches a specific level the output state of the sensor changes. As the target moves away from the sensor the oscillator’s amplitude decreases, switching the sensor output back to its original state.

       In the experiment, We try to use many types of material. We will see the different displacement value that can make capacitive proximity sensor response. 

Objective

       1.To study the working of capacitive sensor.
       2.To compare the material that capacitive sensor response.

Experiment apparatus

1. Capacitive sensor experiment kit 
2. material
-  steel
-  aluminum
-  30x30mm copper
-  21x30mm copper
-  ceramic
-  10x10mmPCB
-  76x31mmPCB
-  80x20mmPCB
-  30x20mmPCB
-  20x20mmPCB
-  40x20mmPCB
-  50x20mmPCB
-  Plastic
-  Wood
-  Oil
-  Sugar
-  Salt
-  Antacids
-  Water
-  5mm thick sheet of PVC
-  3mm thick sheet of acrylic
-  3mm thick sheet of fellic
-  Foam

Procedure

1.Set up the capacitive sensor by adjusting the sensitivity.2.Move the material closer to capacitive sensor until the LED is turned on.3.Measure the distance between capacitive sensor and material.

Experiment Result

Table 1 The materials and displacement between object and sensor.

Discussion

      We had the error from the experiment that is the capacitive sensor detected our hand and we had to repeated the same step.
     From the experiment,the easiest material that we detected was water and antacid because it has a highest dielectric constant.The worst case was foam,we couldn't detect foam from because it has very low dielectric constant.

Conclusion

      The capacitive sensor use the electrostatic field to detect the object that come across this field and easily detected depends on the dielectric constant. The higher dielectric constant can detect by the sensor easier.





Notice : The data in the experiments maybe inaccurate or incorrect. Therefore, the results may be different on other trials or a distortion of the theory.