It flashes in direct proportion to the strength of the sensor's received signal. It offers two ranges in the same sensor model by simply reversing the polarity of the sensor wiring. Long-range mode achieves ranges to 28" for applications involving larger objects; shorter-range mode offers a range of up to 12" for smaller dia objects moving at a faster rate.
Banner Eng. (Minneapolis, MN) has introduced opposed-mode ultrasonic sensors, which can indicate the strength of the sensor's signal. The EZ-Beam ultrasonic sensors use a built-in microprocessor to analyze the signal and control an LED indicator on the back of the readout.