How can I use Photomicrosensors(photointerrupters) for stable object detection over long periods of time?

1. Select the dynamic range of S/N.
   In order to use built-in Photomicrosensors (phototransistor output) to stably detect objects over time, an appropriate signal value (when there is an object) and noise value (when there is no object) should be determined. Photomicrosensors detect objects by comparing the level of signal and noise, so it’s important to ensure the dynamic range of S/N with the appropriate design of the device/equipment for each application.
2. Select appropriate threshold values.
   Once device/equipment design has been successfully optimized and the dynamic range of S/N has been set, it is important to identify any change in signal/noise during operation. Factors that can cause variation include: object material, positional displacement of objects, degradation of LED, temperature change, dust, disturbing external light, etc. Predict the worst values of signal and noise. The most appropriate threshold value is the center of the maximum signal value and the minimum noise value.

Dynamic range of S/N
Transmissive Photomicrosensors detect opaque objects that completely block the light emitted from the slit of the sensor. Thus, a great range of S/N ratio is ensured without optimization of device/equipment. However, in some cases, the light from the slit may not be blocked. That is why we recommend that evaluations be conducted using actual samples in advance. It is best to prevent any light disturbance during the evaluation.
Reflective Photomicrosensors are likely to be affected by product (object) variations (shape, size, reflection ratio, surface conditions, etc.), positional/angle displacement, and background. Reflective Photomicrosensors have more variable factors than transmissive ones, so it’s critical to ensure a dynamic range of S/N. Select appropriate signal and noise threshold values according to the applications.

■Background is present in FOV: Reduce the noise value.

• [ Remove the background ]
  If the background is a frame of the device/equipment, it is recommended to change the device/equipment design.
• [ Reduce reflective light from the background ]
  Make the surface of the background low reflective (paint in black/change to rough-surfaced) or apply low-reflection sheet.
• [ Reduce reflective light from the background ]
  Create an incident angle to prevent the reflective light from entering to the slit. If the surface of the object is rough-surfaced, change the angle of the Photomicrosensors. Changing the angle can reduce the reflective light from the background.
• [ Change sensor ]
  Use a different sensor has a smaller detection range (EE-SY1200).
• [ Change sensor ]
  Use a limited reflective sensor (B5W-LB).

■ Objects: Increase the signal value.

• Referring to “Detection distance characteristics” (see the graph below), select the peak distance for the object to receive the light from the sensor.
• Use an object that is larger than the spotlight from the sensor.

■If a small object is used: Increase the signal value.

• [ Change sensor ]
  Use a sensor with smaller spotlight from the sensor (EE-SY169A(B)).