Ultrasonic sensors with separate transmitter and receiver are placed directly opposite of each other. In this setup, all shapes of objects can be detected with a switching frequency up to 500 Hz. The ultrasonic transmitter/receiver sensors are available in an M18 or a miniature cube housing. These sensors are ideally suited in applications where normal ultrasonic sensors are not fast enough and where optical sensors are not suitable due to the shape or transparency of the material that has to be detected. Think of applıcatıons such as detecting or counting bottles or plastic packaging on a conveyor belt.