The PDA has one input and several types of outputs. 

 The input level to the PDA is controlled by a precision 10- 

 turn potentiometer and the level can be in the range from 1 

 volt to 50 volts rms. The frequency range is from dc to 

 10 kc/s and this range should never be exceeded. The in- 

 put level is set with the aid of a true-rms voltmeter. 



There are two analog outputs. The X (amplitude) 

 output is from -10 to +10 volts and corresponds to +5 to -5 

 times the rms input level. The Y (probability density) out- 

 put is from to about 7. 5 volts and corresponds to a PD 

 from to 10. However a meter on the instrument gives a 

 reading of PD on either of two, scales, from to 0.4, or 

 to 1. 0. A PD greater than one can be measured using 

 the digital outputs, of which there are two: al-Mc/s and 

 a 10-Mc/s output. Both digital outputs are on when the in- 

 put signal is inside the amplitude interval Ax, at any 

 selected amplitude. The PD is obtained by counting the 

 number of cycles per second from either digital output. 

 The counting interval can be varied as the occasion demands, 



Another output available on the PDA is the pulse out- 

 put. This particular output gives one pulse each time the 

 signal goes into the amplitude interval, or two pulses for 

 signals exceeding the set-in level (one pulse when signal 

 passes through on the way up and another pulse when it is 

 on the way down). 



Some of the important controls on the PDA are the in- 

 put potentiometer (to determine and set input level), the "X" 

 10-turn calibrated potentiometer (to select the amplitude 

 around which the probability density is to be measured), 

 and the output-damping-sweep time control (to select the 

 averaging time and sweep speed). Other controls deal with 

 the calibration of the PDA and are better described in the 

 PDA manual. 1 



42 



