PHOTOELECTRIC DETECTORS 



lead-sulphide cell which is enclosed in a transparent Dewar flask which may 

 be filled with sohd carbon dioxide to reduce the temperature to — 78°C. 



100 200 300 AOO 500 600 

 Black body temperature 'C 

 Figure 28.43b Effect of temperature on the performance of a Mullard 61 SV 



lead-sulphide cell 



CO 



-150 



100 



50 





-12 



- 8 



Lo 





c 

 gi 



to 



-1200 



- 800 



- ^00 



Radiation from a 200''C (^73°K)black-body 

 source situated 20cm from cell and observed 

 throjgh an aperture of diameterSmmC^-Q ixW ) 

 Interruption frequency = 800 c/s 

 Amplifier band-width r50c/s 

 Room temperature: 21 'C 



50 100 150 200 250 



( 7-5 ^A) (15pA) (22 5 p,A) (30 ^i, A) (37-5 p/ A) 

 Voltage across cell in series with IMSi load 



volts 



Figure 28.44 Effect of applied voltage on performance of Mullard 61 SV lead-sulphide cell 



The variation of signal, noise and signal-to-noise ratio with applied voltage 

 is shown in Figure 28.44. 



375 



