| 摘要 |
The safety installation opens circuit relays (53,73) if a light beam (46) between a transmitter (40) and receiver (60) is interrupted. An oscillator (25) pulse train is supplied to the transmitter and to two test units (45,65) respectively coupled to the transmitter and receiver. - Each unit compares the pulse train with that (61) operated by the receiver (60). If the compared trains have the same frequency, and an inverted or phase reversed signal pattern, with or without phase displacement, the test unit outputs maintain the relays (53,73) closed. |
