"The Digitec indicators are precision, transistorized, servo-balancing, potentiometer type instruments. In the various ranges offered they are capable of accurately indicating DC voltage digitally from 0.1 MV to 1000 V." (United Systems Corp., Manual I-490)
BRIEF SPECS
| Range | 10 mV ~ 1000 V |
| Readout | 4 digits "odometer" |
| Accuracy | 0.1% |
| Power | 25 watts |
| Weight | 2.5 kg |
| Dimensions | 22 cm x 15 cm x 20 cm |
| Technology | transistor |
| Price (approx.) | $ 300 |
United Systems Corp. was one of the first manufacturers of 'low-cost' dvm's. Operation is based on a closed control loop. The amplified input signal drives a servo motor together with the readout odometer and an precision potentiometer. An known reference voltage is divided by the precision pot, until this voltage is of same quantity than the unknown input. The comparison is made with a chopper (Cambridge Scientific, Maryland, U.S.A., model 225A-1) before the ac- coupled amplifier. Therefore the circuit is fairly stable.
This 'Digitec' instrument is equipped with the optional zener reference. Models with a small standard cell were standard. It was modified to operate at 230 VAC with a new transformer by the preowner.
