400ER25U

400ER25U (receiver) is a ultrasonic sensor and it is usually used coupled to 400ET25U (transmitter).

400ET25U

400ET25U (transmitter) is a ultrasonic sensor and it is usually used coupled to 400ER25U (receiver).

250ER25F

250ER25F (receiver) is a ultrasonic sensor and it is usually used coupled to 250ET25F (transmitter).