What Is a BGS (Background Suppression) Sensor? Operating Principle & Recommended Models | OPTEX FA

What Is a BGS (Background Suppression) Sensor?

What Is a BGS Sensor?

BGS stands for background suppression, and this type of reflective sensor operates on the principle of triangulation. Whereas normal diffuse-reflective type sensors operate by increasing or decreasing the received light amount, BGS sensors operate by determining distance, providing stable detection with advanced resistance to influences from object color, gloss, or tilting.

Operating Principle of BGS Sensors

The distance to the object is determined by forming a triangle between the emitter, receiver element, and object.
When the distance to the object changes (green arrow), the position of the reflected light on the receiver element also changes (blue arrow). In other words, the distance to the object can be determined based on the position of the light on the receiver element.

When to Use a BGS Sensor

The object's reflectance is low (the object is dark).
The object is available in various colors.
The distance between the object and the background is small (minimal step height).
The object has a glossy surface.
The object's detection surface is tilted.

Effective for objects with low reflectance
Effective for objects with various colors

Key Points for Selecting a BGS Sensor

Hysteresis (Minimum Detectable Step)

This graph shows the minimum detectable step for each object color. After confirming the object color and distance (horizontal axis), multiply the distance by the hysteresis value (vertical axis) to determine the minimum step that the sensor can reliably detect.

For stable detection, a value of 2x the hysteresis is recommended.

Number of Control Outputs

This refers to the number of outputs available when a BGS sensor determines the distance to an object.
The number of control outputs affects the range of applications the sensor can support. For example, with a single output, the sensor can indicate either that the object is closer than the set distance or farther than the set distance. With two outputs, however, both conditions can be distinguished and output separately, allowing a single sensor to perform applications that previously required two sensors.

FGS Mode

While BGS ignores backgrounds located beyond the object, FGS mode (Foreground Suppression) uses light reflected from the background and detects an object when it interrupts the reflected light path. This enables stable detection of challenging targets, such as thin, dark objects and objects with uneven or glossy surfaces that are difficult to detect with BGS.

Note:

A light-colored background is required when using FGS mode.
FGS mode is referred to by different names depending on the series:
ZA-B Series: FGS 1-point
BGS-HL Series: Zone
BGS-HDL Series: FGS

Object	Not Present	Tall	Low-reflectance	Glossy and uneven
Output	OFF	ON	ON	ON
Explanation	Light reflected from the background is received only at a specific position on the receiver element (red area). The output remains OFF only when light is received at this position.	When a tall object is present, the reflected light is received at a position other than the red area on the receiver element, causing the output to turn ON.	For low-reflectance objects, such as black objects, the amount of reflected light reaching the receiver element is insufficient, causing the output to turn ON.	For glossy objects with uneven surfaces, reflected light may not reach the receiver element due to diffuse reflection, causing the output to turn ON.