1578 
the output points R, R,- A signal applied to the input them appears as 
@ voltage change across Rj Ry which is measured by the detecting circuit 
consisting of two push-pull amplification stages, using 6J7 (or 6SJ7) 
tubes. 
The detecting circuit is a modified version of an instrument 
described by Lyons and Heller@/ in 1939. The output is read by noting the 
swing of a 50 microampere meter placed across the points AB for low 
‘gain operation or CD for high gain. Various normal operating voltages 
are indicated on the circuit diagram. Any well regulated a.c. operated 
power supply is adequate for the Bt and Bo voltages. 
2e2 This circuit has been found to be very stable and linear in its 
operation. Some typical calibration results are shown in Table IV and 
are compared with measurements made at the Cambridge Thermionic Corporation 
by means of the old microcoulometer. 
Sensitivity 
3-1 The sensitivity of the low gain range of the new instrument is such 
as to give full scale deflection of the meter for an input signal of 0.5V. 
The high gain range gives full scale deflection for an input signal of 
0.05V. 
On the high gain range it would therefore be possible to calibrate 
small gauges having sensitivities of the order of 0.1 micro micro coulomb 
per psi. by using pressure differentials of about 4000 psi. and total 
input capacity of 10,000 micro microfarads. 
3-2 The instrument becomes quite sensitive to pick-up if the input 
capacity is made very low (ca. mtn ce but this difficulty could 
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