Patent GB-1112823-A (GB)
Title: Egg blood detection
Inventor: HIRT EDWIN RICHARD
IPC: B07C5/34
Filed: 1966-03-24
Abstract: 1,112,823. Egg blood detection. FOOD SYSTEMS Inc. March 24, 1966, No. 13096/66. Heading G1A. In apparatus for detecting the presence of blood in eggs radiation is passed through the eggs and detected by two multiplier photo-tubes, one of which is sensitive to radiation of a frequency which is substantially unaffected by the presence of blood in the egg while the other is sensitive to radiation of a frequency which is affected by the presence of blood in the eggs. The multiplier tubes are supplied with operating potential via a circuit controlled by the output of the multiplier tube which is insensitive to the presence of blood to maintain the sensitivity of the device to the presence of blood relatively constant irrespective of the colour and density of the egg. The apparatus, Fig. 1, comprises a conveyer 10 which delivers the eggs to the "candling" stage 24, the eggs rolling continuously through the stage and their presence at the inspecting point being detected capacitively to cause the detecting mechanism to be energized. A good egg passes through the detector and straight along conveyer 34. An egg containing blood causes the detector to operate a solenoid 46 which lowers a guide wall 39 and causes the bloody egg to be deflected onto conveyer 38. Fig. 6 shows the detector apparatus comprising a filament lamp source 50 the light from which after traversing the egg is split by a half silvered mirror into one beam which passes through a filter 55 to be focused on photo-multiplier tube 57, and a second beam which passes through a filter 59 to be focused on photo-multiplier tube 61. Filter 59 passes a wavelength about 575 millimicrons, a wavelength affected by the presence of blood, while filter 55 passes a wavelength of about 600 millimicrons which is substantially unaffected by the presence of blood. Circuit details Fig. 8. Entry of an egg to the detecting stage either causes operation of a mechanical switch 84 which, via a delay circuit to allow the egg to be positioned in the exact detecting position, fires a monostable trigger 81, or the position of the egg in the detecting position causes an electronic switch 83 to be operated again firing monostable trigger 81, which operates pulse generator 77 and causes valve 69 to be turned on to apply operating voltage across the multiplier tubes 57 and 61. Multiplier tube 57, the tube which is insensitive to blood, is connected in a feedback circuit with the grid of valve 69 which tends to maintain the current through this tube constant by varying the voltage applied across the tube. Since this voltage is also applied to the other tube 61 the output of this tube is also compensated for variations in the density of the eggs inspected. Tube 61 is however sensitive to the presence of blood in the egg and therefore the anode current of this tube is monitored and fed to an integrator 82 and if the anode current changes by more than a predetermined amount, indicating an unacceptable egg, monostable trigger 91 is fired to operate the egg reject mechanism. Resistor 74 is made variable to compensate variation of photo-tube gains, and resistor 75 may be a Zener diode which, together with resistor 67 gives an optimum sensitivity characteristic for the device.