| 摘要 |
<p>The preampiifier for a voltage measuring instrument provides for noninteracting span and zero adjustments. Two voltage follower circuits are used and employ differential amplifiers (16) and (42) with negative feedback. The first produces a current througt the output resistor (58) of the preamplifier proportional to the voltage being measured while the second produces a current through the output resistor proportional to a fixed reference voltage + REF. The proportionality of the first amplifier (16) is adjustable by a potentiometer (20) which modifies the feedback. This adjusts the span. The proportion of the reference voltage used as input to the second amplifier (42) is adjustable by a potentiometer (36) to adjust the zero. The feedback for the second amplifier is via a potential divider (46, 48) which may be connected to + REF to achieve negative or positive zero offsets. </p> |
