Photomicrosensor
Application Guide ～Solution proposal for user’s challenges～

A built-in type Photomicrosensor, also known as a photointerrupter, is a compact optical sensor that senses objects or object positions. The best fit sensors to your applications can be chosen from a wide variety of available options.
Photomicrosensors (photointerrupters) are commonly used for object presence and absence detection, disk rotation counting, positioning of moving objects and rotating direction detection. In order to effectively use a Photomicrosensor, this Application Guide explains the principles, the types and the differences in usage of Photomicrosensors, and introduces actual application cases in detail.

A Photomicrosensor (photointerrupter) is categorized into 2 main types. One is a transmissive (slot) type, the other is a reflective type. The illustration below is a general example of the connection/mounting method of different Photomicrosensors. PCB mounting is the most popular method of sensor attachment. Surface mount (SMD) is effective for downsizing and allows fewer man-hours of assembly. Pre-wired, or connector style is convenient for wiring and maintenance, and is ideal for detecting an object placed far from the main PCB. Omron advises users to choose a sensor that best matches the mechanical structure of the target device/equipment.

SMD

Surface mount

Connector

Screw mounting/snap-in
*Connector with cable is available by separate order

Lead

Through-hole

Pre-Wired

*Detachable connector provided.

Photomicrosensors (photointerrupters) are commonly used for 1) Object presence and absence detection, 2) Disk rotation counting, 3) Positioning of moving objects and
4) Rotating direction detection (for encoder use).
Here are some examples of typical applications using each of the two types of Photomicrosensors: transmissive (slot) type and reflective type.

A basic switch is made of open and closed contacts whereas a Photomicrosensor (photointerrupter) is non-contact switching using an optical beam. A basic switch is available for AC and DC supplies. Since a basic switch does not emit LED, it is ideally suited for applications that require low current consumption such as battery-powered equipment. A Photomicrosensor is superior in durability, sensing position accuracy and response speed.

＊These differences do not necessarily apply to all the available product models. Be sure to check the specification datasheet for details of each product model.

A Photomicrosensor, with its non-contact switching technique, has the advantage of high reliability, eliminating the contact deterioration problem caused by wear and corrosion.
For example, for a switch within machine internals that may remain closed for an extended period of time, the contacts may deteriorate from oxidation and sulphuration due to the surrounding atmosphere, ultimately affecting the switching performance. Using the Photomicrosensor for such applications is ideal without worrying about contact deterioration.

Below are the structural differences and principles of transmissive (slot type) and reflective Photomicrosensors.

A transmissive(slot) Photomicrosensor(photointerrupter) detects objects by passing the target object through the emitted light beam from the aperture. This is ideal for applications of small object detection or accurate position sensing. A reflective Photomicrosensor detects the presence and absence of objects but also detects marked objects. This type is effective for realizing a low-profile design of a device or piece of equipment.
The transmissive (slot type) Photomicrosensor provides stable detection regardless of the object’s surface condition, position or angle. It is recommended to first check if the design of your device/equipment can apply the transmissive Photomicrosensor (for sensing opaque objects). Here are the advantages and disadvantages of the transmissive (slot type) and reflective Photomicrosensors:

With a phototransistor output, the threshold level to turn the sensor on or off is adjusted using an external circuit, whereas with photo IC output, the threshold level is fixed at an internal circuit board. Phototransistor outputs enable users to set an optimum threshold level according to the application. Photo IC output is ideal for applications requiring a fast response time.
The following table explains the differences between phototransistor output and photo IC output. Please use this as a guide when selecting your sensor and check the specification datasheet for product details.