6. In what way is the sensing field of a capacitive proximity sensor different f

Question

6. In what way is the sensing field of a capacitive proximity sensor different from that of the inductive proximity sensor? 7. For what type of target would a capacitive proxim ity sensor be selected over an inductive type? 8. outline the principle of operation of a photoelectric sensor. 9. Name the three most common scan techniques for photoelectric sensors. IIIIIIIIIIIIULIU Mill PART 4 Actuators Relays An actuator, in converts an electrical sense, is device to signal into mechanical that cir relay is a of movement. pile 88 actuator that and Chapter 4 Motor Control Devices

Explanation / Answer

6. Capacitive proximity sensors:

Capacitive transducers work on the principle of change in capacitance. Change in capacitance can be caused by either of the following ways:

1. By changing the area of the plates.

2. By changing the distance between the plates.

3. By changing area of overlap between the plates.

These changes in capacitance can be sensed by output voltage taken across the sensor terminnals. The sensing field is electric field which is applied at the input terminal of the transducer

Inductive proximity sensors:

They work on the principle of change in reluctance path of the flux linking with the secondary winding so that change in induced emf across the output terminal is noted. The sensing field is magnetic field which is produced by the alternating voltage supply at the input terminal.

7.

Capacitive proximity sensors are extremely sensitive and have a higher resolution as compared to inductive sensors.

They also have negligible loading effect higher accuracy and are not affected by stray magnetic field which are the disadvantages of inductive sensors. But capacitive sensors also suffer from several disadvantages such as they are affected by temperature to a greater extent than inductive sensors. Also due to fringing effect non linear characteristics are induced in capacitive sensors.

Hence capacitive transducers should be used where higher accuracy and higher resolution is demanded and change in dispacement is of order of micro seconds.

8. Photoelectric Sensors:

Photoelectric sensors have multiple uses. They are used to detect presence of an object. They are often used for the measurement of speeds of machines,in manufacturing, in theft detector, etc. They work on the principle that when   light( of certain wavelength) falls on a photoelectric material electrons are emitted. When any material comes in between the source and sensor no light will fall on the sensor thereby no current will be recieved at the output terminal confirming the presence of an object. Similarly absentism of an object can also be checked.

9. The three most common sensing techniques are:

1. Thru beam mode

2. Retro reflective mode

3. Fibre optic sensing

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