Patent GB-1423462-A (GB)
Title: Infrared imaging systems
IPC: G01J5/48
Filed: 1973-03-01
Abstract: 1423462 Thermograph SPECTROTHERM CORP 1 March 1973 [6 March 1972] 10089/73 Heading H4F In television type display thermograph, the raster C.R.T. display Fig. 3 shows the infra-red image 95 of the object being scanned in an upper region and a graph 99 showing the temperature variation across a required section 101 in the lower region. Although photographs of the display are best taken, definition-wise at the slow (e.g. 2 sec.) frame scan rate, focus &c. adjustments are best made on a display produced by repetitively-reading out a memory at the standard television rate-e.g. 60 frames sec.- the memory having had an entire frame written into it at the slow scan rate. The object 15, Fig. 2, is line scanned by a hexagon mirror drum 17 through a 30 degree sector of its 120 degree sweeps, a reference temperature bar 31 being scanned before the beginning of each line. A typical video signal for one line is shown at (a) Fig. 9, 143 being the reference level and 145 the object response. Frame scanning of the object is by an oscillating mirror 19 which is also caused to scan across the section 107 after the frame is completed. The video signal from a liquid Nitrogen cooled, Hg.Cd.Te, detector 21 (overheating protection being given by thermister protector 39 and audible and visible alarms 92, 94) is preamplified at 33 and processed at 61. Processor 61 serves to: (a) give D.C. restoration; (b) blank off the video signal when the detector is not scanning the object or reference bar; (c) automatically control brightness of display so that high lights in consecutive frames are at same brightness; (d) plot the temperature profile 99; (e) produce the section line 101; and (f) produce the graticule lines 103. The output of processor 61 i.e. 64 blank lines, 528 picture lines and 129 profile lines, are fed from 65 to video amplifier 67 and display tube cathode, via two way switch 53. In the position shown switch 53 gives the slow 2 sec. scan for photographic and fine definition use. Slow scan, line and frame sync. signals from circuits 51, and produced thereat from signals picked up by light detector 41 from source 45 via the mirror 17, are fed to the display tube deflection means via switch 53. The photograph is by a camera 85 having an electronically opened shutter, opened during the scanning. Additional information on the patient, e.g. left (L) or right (R) profile, the average intensity of the infra red radiations i.e. the scale for the profile, and the patients name, are simultaneously photographed by being contained on a card placed in an exposure section 96 of the camera. The video signal is additionally stored in memory 104, until a whole frame is stored, and, when switch 53 is changed to the fast scan position, the memory is repeatedly read out, e.g. at 60 frames per sec., fast sweep circuits 119 now being operative. Processing circuit 61, Figs. 4 and 5, starts with a D.C. restorer in which an F.E.T. 129 holds the reference level 143, Fig. 9(a) to ground during every reference interval (F). An interscan gating signal (g) stops the video signal from passing F.E.T. 137 when neither the object or bar are being scanned. In the automatic brightness control, the maximum voltage of a picture signal line is stored across capacitor 165 and is then transferred to capacitor 167 to act as a bias on the subsequent picture signal line at amplifier 187. A high (2) and low (1) level video signal are both produced at outputs 191, 197. The low level video signal is fed to the processor output 65<SP>1</SP>, via a switch 255 in the "picture" position V, its other position S being that when the profile is displayed. After the picture has been displayed, the vertical scan signal (C) Fig. 8 for controlling the mirror 19 is stopped and set to a constant voltage so that the object is repeatedly scanned across the section 101. This change is caused by change of switch 283 from the normal sweep signal to the output of potentiometer 269. The resulting repeated video signal 243 from section 101 (a), Fig. 6, is fed to one input of comparator 231 where it is compared with the slowly decreasing (discharging constant current source 235) voltage 241 across capacitor 233. The comparator output (b), representing those parts of the video signal above the capacitor voltage, are differentiated at 245 and the resulting bipolar pulses change to unipolar pulses at 247/251, which are fed to the display to produce to profile. The section line 101 is produced from the voltage from potentiometer 269 by comparing it at 271 with the vertical scan signal and generating a pulse when equality occurs, which, via one shot circuit 265 and OR gate 267 closes switch 277 and momentarily leads a D.C. one line pulse from source 279 to the video output. The graticule lines are similarly produced by pulses resulting from dividing the line sync pulses by 32.