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Optical Sensors - Phototransistors

The SFH 309 FA-4/5 RN18C phototransistor from Siemens is an infrared optical sensor with a range of applications and an interesting working principle. This article will discuss the application field and working principle of the SFH 309 FA-4/5 RN18C.

Application Field

The SFH 309 FA-4/5 RN18C from Siemens is an infraredNPN silicon phototransistor with a sensing distance of up to 0.5 mm and a spectral response from 900 nm to 1100 nm. It is mainly used for detecting small objects in close range without contact and it is particularly suitable for presence detection of small parts in automated assembly processes and for producing optical alarms. The phototransistor has a high degree of sensitivity and a wide ambient light rejection range.

The SFH 309 FA-4/5 RN18C has a small, rugged package design that allows for easy mounting with a variety of standard mounting accessories. The package is also designed to have excellent heat dissipation for improved reliability. The phototransistor also offers excellent signal processing accuracy due to its high linearity and low dark current. The SFH 309 FA-4/5 RN18C has a low power consumption and is well-suited for battery-driven applications.

Working Principle

The SFH 309 FA-4/5 RN18C phototransistor from Siemens works by detecting infrared radiation, or light, using a sensitive collector-base junction. The phototransistor is sensitive to infrared light at a specific wavelength range, from 900 nm to 1100 nm, and can detect small objects and changes in light intensity. This is due to the phototransistor’s ability to convert incoming infrared light into an electrical signal.

The phototransistor consists of two elements: a base and collector. When infrared light strikes the phototransistor’s collector-base junction, it causes a small current to flow through the collector-base junction. This current is then amplified and used to produce an output signal. The output signal can be used to for a variety of purposes such as controlling motors, lighting circuits, and alarms.

The phototransistor also has a wide ambient light rejection range that helps minimize false triggering due to stray light sources. This makes the phototransistor ideal for presence detection applications where false triggering needs to be minimized. The SFH 309 FA-4/5 RN18C also has a high sensitivity and linearity, meaning it can accurately detect small changes in light intensity and provide a reliable output signal.

In conclusion, the SFH 309 FA-4/5 RN18C from Siemens is a reliable and rugged infrared sensing phototransistor. It has a wide application field including automated assembly processes, presence detection, and optical alarms and it works by detecting incoming infrared light and converting it into an electrical signal. The phototransistor also has excellent heat dissipation and low power consumption making it suitable for a variety of applications.

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