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7A13: Difference between revisions
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In the older version, the comparison voltage is generated from a precision zener supplied from either positive or negative 50 V rail, followed by a 10-step switched divider made of 0.1% resistors to select the first digit. For the lower three digits, a ten-turn potentiometer with a mechanical digital readout is used. | In the older version, the comparison voltage is generated from a precision zener supplied from either positive or negative 50 V rail, followed by a 10-step switched divider made of 0.1% resistors to select the first digit. For the lower three digits, a ten-turn potentiometer with a mechanical digital readout is used. | ||
In the newer version, the zener-derived reference voltage is always positive. A 10-turn pot for coarse selection combines with a single-turn pot for fine control. The resultant voltage is displayed on a 4-digit DVM built around a [[Fairchild 3814]] DVM controller. | In the newer version, the zener-derived reference voltage is always positive. A 10-turn pot for coarse selection combines with a single-turn pot for fine control. The resultant voltage is displayed on a 4-digit simplified DVM built around a [[Fairchild 3814]] 4½ digit DVM controller. For negative values of V<sub>C</sub>, an opamp polarity inverter circuit is switched in. | ||
===Repair issues=== | ===Repair issues=== | ||