INFRA-RED DETECTOR CELLS

• Document Type: CREST
• Collection: General CIA Records
• Document Number (FOIA) /ESDN (CREST): CIA-RDP78-03300A001600050012-5
• Release Decision: RIPPUB
• Original Classification: C
• Document Page Count: 7
• Document Creation Date: December 22, 2016
• Document Release Date: February 8, 2012
• Sequence Number: 12
• Content Type: REPORT

Declassified in Part - Sanitized Copy Approved for Release 2012/02/08: CIA-RDP78-0330OA001600050012-5
CONFIDENTIAL
INFRA-RED DETECTOR CELLS
ORIGINAL CL 9,'(
^ DECL 17f REM ON
[E^XT SYND 6 YRS BY
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DOCUMENT NO.
NO CHANGE IN CLASS. ^
^ DECLASSIFIED
CLASS. CHANGED TO: TS C
NEXT REVIEW DATE:
AUTH: HR 70-2
DATE: --REVIEWER: 010956
CONFIDENTIAL
Declassified in Part - Sanitized Copy Approved for Release 2012/02/08: CIA-RDP78-0330OA001600050012-5
 Declassified in Part - Sanitized Copy Approved for Release 2012/02/08: CIA-RDP78-03300A001600050012-5
T
1. SSRI. Type OBS - PbS
An evaporated lead sulphide layer in an evacuated glass cell. Spectral
sensitivity to 3.511 at room temperature and 4.511 at -180?C (liquid
air).
II. SSRI. Type OBS - PbTe
An evaporated lead telluride layer in an evacuated glass cell. The cell
has a ground glass stopper fitted to a special Dewar flask for cooling
with liquid air.
Spectral sensitivity from 211 to 611 at -180?; 50% transmission at 511.
III. SSRI. Type OBS - PbSe
An evaporated lead selenide layer in an evacuated glass cell. This unit
has a spectral sensitivity to 4.511 at room temperature.
IV. SSRI. Type OBS - ChPb
A chemically precipated lead sulfide layer in an evacuated glass cell.
Spectral sensitivity to 4.211 when cooled to -180?C (liquid air).
Declassified in Part - Sanitized Copy Approved for Release 2012/02/08: CIA-RDP78-03300A001600050012-5
 Declassified in Part - Sanitized Copy Approved for Release 2012/02/08: CIA-RDP78-0330OA001600050012-5
INFRA-RED DETECTOR SSRI. Type OBS - PbS
An evaporated lead sulfide detector unit mounted in an evacuated glass cell.
CELL SIZE
SENSITIVE AREAS
Outside Diameter 29
? 2.0 mm
11 x 4 mm
Inside Diameter
16
? 0.5 mm
5 x 5 mm
Length
45
? 2.5 mm
4 x 4 mm
3 x 3 mm
TEST CONDITIONS
Target Temperature: 3000 C (Black Body)
Detector Temperature: 20? C
Chopping Frequency: 400 c.p.s.
Polarizing Voltage: 100 volts
Amplifier: Band Pass: 50-5000 c.p.s.
Gain: 106
NOTES:
1. The distance between the detector cell and the black body is 80 cm. This gives
0.3 watts/mm2 of the total 300?C black body radiation on the sensitive target
area.
2. The black body orifice is 1 cm2.
3. The charge resistance is usually 1 megohm.
4. In the measurement of the signal to noise ratio an amplifier with a band
pass of 50 to 5000 cycles is used. This wide band is chosen so that the
amplifier will allow the passage of all types of noise. If the detector has a
substantial flicker noise, discernible at low frequencies, the signal to noise
ratio will be low and the cell is rejected.
5. A chopping frequency of 400 c.p.s. is used for the testing procedure. The
optimum chopping frequency for the detector is 800 c.p.s. The low chopping
frequency, coupled with the broad band amplifier is used so the cell can be
tested under its poorest conditions. The curve below indicates the effect of
chopping frequency on noise.
EFFECT I
CHOPPING
FREQUENCY
I JOHNSON NOISE
90 500 800 1000
TEST RESULTS FOR A TYPICAL CELL AT 20?C
8 x 11 mm Sensitive Area
1. Internal Impedance 100,000 ohms
2. Time Constant 10-4 seconds
3. Signal : Noise Grade A 500:1
Grade B 400:1
Grade C 300:1
Declassified in Part - Sanitized Copy Approved for Release 2012/02/08: CIA-RDP78-0330OA001600050012-5 .3
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Declassified in Part - Sanitized Copy Approved for Release 2012/02/08: CIA-RDP78-0330OA001600050012-5
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INFRA-RED DETECTOR CELL AMPLIFIER
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Declassified in Part - Sanitized Copy Approved for Release 2012/02/08: CIA-RDP78-0330OA001600050012-5
 Declassified in Part - Sanitized Copy Approved for Release 2012/02/08: CIA-RDP78-0330OA001600050012-5
Spectral Sensitivity of PbS Cells
evaporated cell
- - - - chemical cell
I temperature 20?C
II temperature 80?C
III temperature 180?C
(Source: black body at 300?C. Modulated
at 400 cps., band pass of the amplifier
50 to 5000 cps.)
6' Wave /e ft~'t T,-77-tu.,
Declassified in Part - Sanitized Copy Approved for Release 2012/02/08: CIA-RDP78-0330OA001600050012-5
 Declassified in Part - Sanitized Copy Approved for Release 2012/02/08: CIA-RDP78-0330OA001600050012-5
.CONFIDEMO96/vfl
INFRA-RED DETECTOR SSRI. Type OBS - PbTe
An evaporated lead telluride detector unit mounted in an evacuated
glass cell. This unit is designed to operate at liquid air temperatures of
-180?C. The cell has a ground glass stopper fitted into a specially designed
Dewar flask. When the Dewar flask is filled with liquid air (approximately
200 cc) the cell will operate for 1 hour without recharging.
Outside diameter . . . 24 ? 2.0 mm.
Length . . . 120 mm ? 5.0 mm.
Sensitive area 8 x 4 mm.
Target Temperature: 300?C (Black Body)
Detector Temperature: -180?C (Liquid air)
Chopping Frequency: 400 c.p.s.
Polarizing Voltage: 50 volts
Amplifier: { Band pass: 50 - 5000 c.p.s.
Gain: 106
Internal Impedance: 100,000 ohms
Time constant: 10' seconds
Signal to noise ratio: 300 : 1
Total Radiation on cell area from Black Body: 0.3 watt/mm2
Declassified in Part - Sanitized Copy Approved for Release 2012/02/08: CIA-RDP78-0330OA001600050012-5 7
 Declassified in Part - Sanitized Copy Approved for Release 2012/02/08: CIA-RDP78-0330OA001600050012-5
Spectral Sensitivity of a PbTe Cell
---- -- - -- ----
Cell at - 180?C thin glass window
at 400 cps., band pass of the amplifier
50 to 5000 cps.
- --------- -- ------
(Source: black body at 300?C. Modulated
v
Wave/eM9t4 ; .~[~
Declassified in Part - Sanitized Copy Approved for Release 2012/02/08 : CIA-RDP78-0330OA001600050012-5