| 摘要 |
<p>A controller (16) adapted for coupling a plurality of ultrasonic transducers (12, 14) includes a multiplexer (62) for selecting a transducer (12, 14), signal processing means (50) for processing an output of the selected transducer (12, 14), and controller means (64) for providing operational parameters corresponding to the selected transducer (12, 14). The controller (16) couples to a two wire 4-20 mA communication loop (18) to periodically excite the selected transducer (12, 14). The controller (16) stores power received from the communication loop (18) and excites the transducer (12, 14) by using the stored power to exceed the power available directly from the communication loop (18). The controller (16) provides a wet self-test of the transducer (12, 14) whereby the output level of the transducer (12, 14) is monitored while the strength of the excitation signal provided to the transducer (12, 14) is decreased. The amount of decrease required for the output signal to pass a threshold level is an indication of the usefulness of the sensor (18A, 18B-18N).</p> |
