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在质谱计及其它一些仪器中,为了测量微小的离子电流,常采用电子管静电计直流电流放大器,也称做离子流放大器。这种高内阻信号源的缓变微小电流的测量的典型电路方案是:第一级采用输入阻抗不低于10~(14)～10~(15)Ω的静电计电子管做放大器的输入级,随后是两级直流电压放大器(用电子管或晶体管),末级用阴极输出器。整个电路加有从放大器输出端经过10~(10)～10~(12)Ω高值电阻到静电计输入端的100％负反馈。
In mass spectrometry and other instrumentation, a tube electrometer direct current amplifier, also called an ion current amplifier, is often used to measure minute ion currents. The typical circuit scheme for measuring the slowly varying small current of a high resistance signal source is as follows: The first stage uses an electrometer tube with an input impedance of not less than 10-14 (10) ohms to the input stage of an amplifier , Followed by a two-stage DC voltage amplifier (using a tube or a transistor) and a cathode outputter at the final stage. The entire circuit plus 100 ~ 100% negative feedback from the amplifier output through the 10 ~ (10) ~ 10 ~ (12) Ω high resistance to the electrometer input.