| 摘要 |
PURPOSE:To make it possible to obtain accurate data at all times by a method wherein the converter side and the transmitter side are connected by means of optical fibers, a dead-zone detector is provided in said optical path, and when a dead zone is detected, the optical path is shut off and an alarm is produced. CONSTITUTION:A transmission command signal ST is converted into an optical signal in a light emitting element 12 and sent through an optical fiber 4b to a photoelectric transducer 20 in a transmitter 2. The output thereof is sent through an ultrasonic wave generator 21 and a signal switching device 22 to a transmitter-receiver 23, from which an ultrasonic wave is sent to the liquid level to be measured. Through an amplifier 24 and a light-emitting element 25, the reflected wave signal is sent through an optical fiber 4a and a photoelectric transducer 11 to a time difference/voltage converter circuit 10, which outputs a voltage signal V corresponding to the time differece between the signal ST. On the other hand, when the measurement enters a dead zone, floats 31 having magnets 30 of a dead-zone detector 3 rise, and consequenty a mirror 34 mounted on a permanent magnet 33 rotates to shut off the optical path, so that the voltage V reaches the maximum value and an alarm is issued from an alarm circuit. Thereby, accurate data can be obtained at all times. |
