Type of Sensors in Automation

Sensors is a device used to detect an object, and the result of the detection variable will be processed into an output signal of digital status (ON-OFF) or analog signal.
There are many sensors maker such as Omron, Keyence, Fuji, Siemans, Allan Bradley and so on. The following image is an example of sensor made by Omron:

Photo Electric E3JK by Omron

Especially in the field of automation with PLC, a sensor is functioning as a part of input. These sensors will issue a digital or analog signal to then to be processed by the CPU or PLC program.
There are various kind of sensors based on the following categories:

• Based on the voltage supply:

1. Sensor with AC supply voltage, which means working on AC voltage is usually 100 Volts or 220 volts.
2. Sensor with DC supply voltage, This sensor usually works with voltage 24 volt.

• Based on the output type: 

Especially for the sensor with a DC voltage supply and output signal is digital. This category relates to the connection type used in the PLC input devices:

1. Output PNP, Signal output voltage will be positive (+) 24 volts DC.
2. Output NPN, signal output voltage will be negative (-) 24 volts DC.

• Based on the detected  object or working principle:

1. Limit switch, It's the beginning of sensor that works mechanically (switch).
2. Photo Electric Sensor, Sensor that detect the object by transmitting a beam with intensity that has been determined. The beam can be an infrared or photoelectric. object: metal and non-metal.
3. Laser Sensor, similarly with photo electric, but laser is used.
4. Proximity Sensor, Sensor that detect the object without touching the object being detected. object : metal and non metal.
5. Pressure Sensor, Sensor that detects the pressure both compressor (positive) and vacuum (negative).
6. Temperature Sensor, Sensor To detect the temperature of an object or room.
7. Encoder, Position sensor/Cam Positioner, Sensor is used to calculate position or position angle. It can be 360 degrees or 720 degrees.
8. Touch switch sensor, Sensor that will operate if touched by a particular object. 
9. Vision, Camera sensor, Detecting an image by differentiating the intensity of color, light-dark, paterns and so on.
10. Floatless sensor, Sensor which equipped with electrodes usually to detect the liquid level.
11. Flow sensor, Sensor to detect the flow of liquid.