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WZS型数字式旋光仪,采用了一种高灵敏过零触发器,触发灵敏度远优于10毫伏,其线路原理如图所示。它是由射极耦合双稳触发器前加一级对数放大器组成。当输入电压趋近于零时,输出电压也趋近于零,反馈二极管处于零偏,相当于开路,此时对数放大器的放大倍数近似等于BG305的开环增益(K_v=100分贝),因此大大提高了过零触发的灵敏度。当对数放大器的输出电压等于反馈二极管的正向箝位电压时,达到全电流负反馈,放大倍数等于1,大大限制了饱和深度。这不仅提高了响应速度,而且实现了增益的自动控制。 (箝位稳压管是2CW7M,稳定电压为23.2～23.4
WZS-type digital polarimeter, using a highly sensitive zero-crossing trigger, the trigger sensitivity is much better than 10 millivolts, the principle of the line as shown. It is composed of an emitter-coupled bistable flip-flop plus a logarithmic amplifier. When the input voltage approaches zero, the output voltage also approaches zero. The feedback diode is at zero bias, which is equivalent to an open circuit. At this time, the logarithmic amplifier gain is approximately equal to the open-loop gain of the BG305 (K_v = 100 dB) Greatly increased the sensitivity of zero-crossing trigger. When the logarithmic amplifier’s output voltage equals the positive clamp voltage of the feedback diode, full-current negative feedback is reached, at a magnification equal to 1, greatly limiting the saturation depth. This not only improves the response speed, but also realizes the automatic gain control. (Clamp regulator is 2CW7M, stable voltage is 23.2 ~ 23.4