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Text excerpt from page 9 (click to view)
external programming rheostat or potentiometer should be a wirewound device with a temperature coefficient o� 30 ppm or better. The potentiometer must be capable of carrying ? . 3 m a or more. It is also recommended that the programming lead be shielded and the shield connected to the ground of the supply. See Figures 3 and 5 . CAUTION: 1. If the Programming terminals are open circuited the output voltage will rise well in excess of 320 volts and damage to the supply may result if operated in this condition over a prolonged period. 2 A rapid turndown of the programming potentiometer, internal or external, may burn out the potentiometer. It is recommended that the programming potentiometer be turned down no faster than the voltage needle falls on the front panel meter
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SPECIAL CONSIDERATIONS PROGRAMMING RESISTANCE
It has previously been warned that a rapid turndown could damage the programming potentiometer. While it is unlikely that t h e internal programming potentiometer will be burned out by even an instantaneous turndown from 320 volts to zero, it is possible to overheat the lower resistance region of the resistance element and thus cause it to become noisy at the low end. Mrhen the supply is heavily loaded a reasonably rapid turndown will not be detrimental to the potentiometer.
PROGRAMMING RATES
The maximum safe rising programming rate is about 50 volts/ sec. The maximum falling programming rate is determined by the load current and the supply capacitance. A t heavy output currents down programming rates up to 50 volts/second are feasible whereas at low voltage and no load the down programming rate may be as low as 1/2 volt/second.
SHORTING THE SUPPLY
The supply is designed only to sustain a shortcircuit across the load terminals. Inadvertent shorts between one of t h e output terminals and the sensing on the A terminals will result in the failure of the instrument. It is important to insure that the sensing terminals are tight and that the shorting occurs on the output terminal leads and not on the sensing leads.
