| 摘要 |
<p>An onoard power supply and metering unit is connected, via an overboard cable e.g., 1000 meters long, to an underwater light-pulse projecting unit and a fluorescence-sensing receiver unit. The operating power is transmitted to the underwater units by an onboard constant-current source, instead of a voltage source. Likewise, the output signal of the receiver unit is transmitted through the cable in the form of a current, not a voltage. The current of the receiver's photodiode is integrated, the peak value of the integral determined and held, this held value logarithmized, the logarithmized value sampled and held, and the held voltage converted to a current constituting the output signal. The peak detector and log amplifier used are zeroed automatically, by a balancing signal applied during pulse measurements, but derived between pulse measurements. The balancing signal is derived by integrating a signal derived from the log amplifier's output signal, and is applied to the input of the peak detector, with the peak detector converted to simple voltagefollower operation during the deriving of the balancing signal.</p> |
