1006 



EXPLORATION GEOPHYSICS 



come at rates that are much too fast for any mechanical device, and their 

 number must be reduced before they can be recorded. The basic scale-of- 

 two circuit is shown in Figure 624. 



The circuit has two stable posi- 

 tions : when triode A is conducting, 

 triode B cuts off, and vice versa. 

 Let us assume that tube A is off. 

 The input pulse passes through the 

 diode to the grids of both tubes A 

 and B. But tube B is already con- 

 ducting, so that the pulse will have 

 no effect on it. Triode A, however, 

 will start to conduct, thus lowering 

 the grid potential of B and cutting 

 it off. The neon lamp will glow and 

 a negative pulse will be transmitted 

 to the diode of the next stage. But 

 the diodes are biased to cut-off so 

 that the negative output pulse has 

 no effect. Nothing is transmitted to the next stage, but the glow of the neon lamp 

 shows that the circuit "remembers" one pulse. 



The second positive pulse arriving at the input affects B, shuts off A, and stops the 

 glow of the neon bulb. A positive pulse is transmitted through the diode to the next 

 stage. Each time the scale-of-two receives a positive pulse, it swings over, emitting 

 alternatively negative and positive pulses. The negative pulses have no effect so that 

 the scale effectively swallows every other pulse. 



Fig. 624. — Basic scale-of-two circuit (the Eccles-Jordan 

 version, modified by Higginbotham). 



Fig. 625.- 



-A, portable decimal scaler and high voltage supply; B, internal view. 

 Berkeley Scientific Company.) 



(Courtesy of 



Scaling circuits frequently have six scales, with a pre-amplifier to feed the first 

 stage and a power amplifier to actuate a mechanical pulse register after the last stage. 

 Such an instrument will register one click for each 64 pulses received at the input end. 

 Decimal scalers also have been developed, and are usually arranged as scales-of-1000 

 (Figure 625). Electronically they are more complicated than instruments based on 



