Agilent HP-Bench-Briefs-1987-04-06 free download

File name HP-Bench-Briefs-1987-04-06.pdf

HEWLETT PACKAR D SERVICE INFORMATION FROM HEWLETT-PACKARD A Rotary Pulse Generator is another form of the "variable control" you see so often on schematics. These familiar variable controls are usually desig- nated by components with arrows through them and are used to vary a frequency or power level in order to control an instrument and make it more useable. Some of the problems associated with these variable analog controls are that they tend to get noisy with age, will physically wear out with contin- ued use and have a limited range (stop-to-stop). Figure 1 Enter the rotary pulse generator, a digital variable control that can be the more of a change it imparts to Figure 1shows a typical circuit for a used to adjust power levels or fre- the circuit it is controlling. The RPG rotary pulse generator. It consists of quencies, or manipulate graphics, contributes no noise to the circuit, is a shaft-encoder sending 120 light markers and waveforms. It has no externally programmable and its po- pulses to the phototransistors Q1 and "stops" and can adjust the unit con- sition can be " r e a d by an external Q3 for each full shaft rotation. The tinuously from one end of its range program. This rotary control, in some outputs of Q1 and Q3 are amplified to the other end. It also has variable cases, takes the place of pushbuttons by Q2 and Q4 and squared by two speed, that is, the faster you spin it on a keyboard. Schmitt trigger gates. Figure %isa timing diagram showing how the circuit works to designate clockwise or counterclockwise rota- tion. At the moment output A goes negative, output B will be either positive (clockwise) o r negative Figure 2 (counterclockwise).The shaft encoder is designed so that the A and B transitions are always shifted by 90 degrees. Figure 3 illustrates a typical RPG