This mode is recommended when detecting objects with round or irregular shapes and non-perpendicular profiles.

The background mode, using a unique secondary echo lockout function, enables the SUPERPROX sensor, with a fixed background target, to operate as a universal, all-materials-type, break-beam detector.

After setting the window limits on the fixed target (See Figure 4), make sure the ultrasonic transmission path between the sensor and the target is clear of obstructions.

Once set, the sensor accepts only the first (primary) ultrasonic pulse echo received from the target within the window limits as shown in Figures 4 and 6a. In this mode, the echo is received and detected as an object not present. Object presence is detected when the object interrupts the sonic pulse transmission path between the sensor and the fixed target, as shown in Figures 5, 6b, and 6c.

As a result of the secondary lock-out function, the sensor is permitted to receive only the primary echo after each sonic pulse. All subsequent secondary echoes are "locked out".

If the first echo received from the object travels a lesser distance than the first echo from the fixed target window, that object is detected as being present.

As shown, if the echo of an object is not received (Figure 6b, object #1),or if the first echo is received from an object that is outside the window limits (Figure 6c, object #2), the object is detected as being present.