What is Photoelectric Sensor

Function

-         Sense visible light, IR, UV

-         By Photo bJT, photo diode, photo FET

-         Use to detect object by emit light to the object then capture the reflect light

Type

1. Through Beam
1. Not affected by the color of the object
2. High position detection, repeatability
3. Emitter & receiver are separated. 

2. Reflective
1. Suitable for transparent obj, semi trans, reflective obj
2. Not affected by background 

3. Diffuse
1. Affected by background, obj color
2. Easy to install

4. Limited reflective
1. Limited detectable zone only
2. Not affected by background after sensing zone.

Note

-         Through Beam sensor may face interference from other through beam sensor or other light source

-         Diffuse/reflect wont face these type of interference because they detect the light with their own clock

What is Proximity Sensor

Function

-         Sense distance of object
-     Differential conductive object from others

Principle of operation

1. High-freq oscillation type - use electromagnetic induction
1. Coil produce high-freq magnetic field
2. Object approach, eddy current induce in obj
3. Obj closer, current higher
4. Load on oscillation circuit higher
5. Detection and output
6. *Non-ferrous metal closer, oscillation freq lower, ferrous metal closer, osc freq higher.

2. Magnetic type – use magnetism

3. Electrostatic capacity type
1. sense changes in the electrostatic capacity btw sensing obj & sensor

Factor affecting sensing distance

1. Material of the object
1. Conductivity higher, magnetic induction lower
2. Non-ferrous metal more conductive, sensing distance smaller

2. Size of object
1. Size smaller, detection distance smaller

3. Thickness
1. For non-ferrous < 0.01mm, detection distance = ferrous metal
2. Magnetic metal must > 1mm.