| 摘要 |
A voltage indicating meter is connected between the outputs of two high impedance operational amplifiers, the first of which receives an input signal to be measured through a range setting resistance dividing network and having a gain which can be set to one of a plurality of different values. A zero control network applies a bias voltage to the inverting input of the second operational amplifier for zeroing the meter. The non-inverting input of the second amplifier can be connected either to the output of the first operational amplifier or to a source of reference potential. When, during operation, the non-inverting input of this amplifier is connected to the source of reference potential, the one terminal of the meter is clamped to the bias level and the other receives a voltage proportional to the voltage of given polarity being measured and the meter needle swings in a given direction. When the non-inverting input of the second amplifier is connected to the output of the first operational amplifier, the meter still reads in the same direction for input voltage opposite in polarity to the given polarity.
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