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Title: Standardization of penetrating radiation testing system
Claims: What is claimed is: 1. In an apparatus for inspecting product samples to determine whether each of said samples has a measured quantity of a physical property within predetermined limits, said apparatus comprising means for conveying said samples along a predetermined path through an inspection station; irradiation means disposed adjacent said inspection station for directing a beam of penetrating radiation transversely to said path so that at least a portion of each of said samples is exposed to said beam; detector means adapted to receive radiation scattered by each sample irradiated by said beam; signal generating means responsive to said detector means for generating an electrical signal representative of the amount of radiation received by said detector means in accordance with a predetermined signal gain; and means for determining the quantity of said physical property of each sample irradiated by said beam as a function of said electrical signal; wherein the improvement comprises: means for periodically exposing at least a portion of a reference object having a predetermined quantity of said physical property to said beam of penetrating radidation, so that (1) said detector means receives radiation from said reference object, and (2) said signal generating means generates a stabilization signal representative of the amount of radiation received from said object by said detector means; means for providing a predetermined reference signal; comparison means for comparing said stabilization signal with said reference signal; means responsive to said comparison means for generating a difference signal representative of the difference between said stabilization and reference signals; means for integrating said difference signal so as to provide an integrated signal; and means for adjusting said signal gain in response to said integrated signal. 2. Apparatus in accordance with claim 1 wherein said means for conveying said products includes means for conveying said reference object through said inspection station. 3. An apparatus in accordance with claim 2 wherein said reference object is periodically conveyed through said inspection station between two of said samples. 4. An apparatus in accordance with claim 1 wherein said detector means is positioned so as to receive scattered radiation from each of said samples or said reference object irradiated by said beam and said electrical and stabilization signals are representative of the mass of the portion of said sample and said reference object, respectively, from which scattered radiation is received by said detector means. 5. An apparatus in accordance with claim 1 wherein said electrical and stabilization signals are analog signals. 6. An apparatus in accordance with claim 1 further including monitoring means for indicating when said signal gain is not being adequately adjusted. 7. An apparatus in accordance with claim 1 further including means for providing a supply voltage for said detector means, wherein said means for adjusting said signal gain includes means for adjusting said supply voltage level. 8. An apparatus in accordance with claim 1 wherein said means for determining the quantity of said physical property of each of said samples includes means for determining whether said quantity is within a predetermined range. 9. An apparatus in accordance with claim 8 further including sorting means for sorting said samples whose measured quantity of said physical property is within said predetermined range from those samples whose measured quantity of said physical property is outside of said predetermined range. 10. An apparatus in accordance with claim 8 wherein said means for determining the quantity of said physical property is only operative when a sample is positioned in said inspection station and said comparison means is only operative when said reference object is positioned in said inspection station. 11. An apparatus in accordance with claim 10 further including means for distinguishing at said inspection station between said reference object and said product samples and for generating a second electrical signal indicative of the distinction between said reference object and said product samples, and switching means responsive to said second electrical signal for mutually exclusively (1) directing said first mentioned electrical signal representative of the amount of radiation received by said detector means to said means for determining the quantity of said physical property when said each product sample is irradiated by said penetrating beam and (2) directing said stabilization signal to said comparison means when said reference object is irradiated by said penetrating beam. 12. An apparatus in accordance with claim 1 wherein said electrical and stabilization signals are digital signals. 13. An apparatus in accordance with claim 12, wherein said electrical signal and said stabilization signal are each a series of pulses, the pulse repetition rate of each of said series being dependent on the amount of radiation received by said detector. 14. An apparatus in accordance with claim 13, further comprising a counter for counting said pulses of said series of pulses and a time gate for transmitting each of said series of pulses for a predetermined period of time from said detector means, wherein said means for adjusting said signal gain includes means for applying said integrated signal to said time gate so as to adjust said predetermined period of time so that substantially the same number of pulses are transmitted through said time gate each time said reference object is exposed to said beam. 15. An apparatus in accordance with claim 13 further including amplitude discrimination means for excluding from said series of pulses those pulses whose amplitudes are outside of a predetermined limit. 16. A method of stabilizing the signal output of an apparatus for inspecting product samples to determine whether each of said samples has a measured quantity of a physical property within predetermined limits, said method comprising; conveying said samples along a predetermined path through an inspection station; directing a beam of penetrating radiation transversely to said path so that at least a portion of each of said samples is exposed to said beam, detecting radiation scattered by each sample irradiated by said beam, generating an electrical signal representative of the amount of scattered radiation detected in accordance with a predetermined signal gain, wherein the improvement comprises: periodically exposing at least a portion of a reference object having a predetermined quantity of said physical property to said beam of penetrating radiation; detecting radiation from said reference object radiated by said beam, generating a stabilization signal in response to the detected radiation from said reference object; providing a predetermined reference signal; comparing said stabilization signal with said reference signal; generating a difference signal representative of the difference between said stabilization and reference signals; integrating said difference signal so as to provide an integrated signal; and adjusting said signal gain in response to said integrated signal. 17. A method according to claim 16 wherein said reference object is periodically conveyed through said inspection station between two of said samples. 18. A method according to claim 16 wherein the radiation detected from each of said samples and said reference object when irradiated by said beam is scattered radiation and the electrical and stabilization signals are representative of the mass of the portion of said sample and said reference object, respectively, from which scattered radiation is detected. 19. A method in accordance with claim 16 further comprising determining the quantity of said physical property of each of said samples. 20. A method in accordance with claim 19 wherein determining the quantity of said physical property includes determining whether said quantity is within a predetermined range. 21. A method in accordance with claim 20, further comprising sorting said samples whose measured quantity of said physical property is within said predetermined range from those samples whose measured quantity of said physical property is outside said predetermined range. 22. A method in accordance with claim 16 wherein said electrical and stabilization signals are each a series of pulses, the pulse repetition rate of each of said series being dependent on the amount of radiation detected. 23. A method in accordance with claim 22 further comprising counting said pulses of said series for a predetermined period of time and modifying the predetermined period of time in response to said integrated signal. 24. In an apparatus including a source of penetrating radiation, irradiation means for directing a beam of said penetrating radiation toward at least a portion of an exposed sample, detector means positioned relative to said beam and sample so as to receive radiation from said sample when said sample is exposed to said beam and for generating an electrical signal representative of the amount of radiation received by said detector means in accordance with a predetermined signal gain and as a function of a measured quantity of a physical property of said exposed sample, an improved signal stabilization system comprising: means for exposing to said beam at least a portion of a reference object having a predetermined quantity of said physical property, so that said detector means receives radiation from said reference object and generates a stabilization signal representative of the amount of radiation received by said detector means from said reference object; means for providing a predetermined reference signal; comparison means for comparing said stabilization signal with said reference signal and for generating a difference signal representative of the difference between said stabilization and reference signals; means for integrating said difference signal so as to provide an integrated signal; and means for adjusting said signal gain in response to said integrated signal. Other info: Inventors: Wiley, Philip A. (Boxboro, MA, US) Aronson, Herbert L. (Newton, MA, US) Application Number: 792061 Filing Date: 1977-04-28 Publication_date: 1979-05-15 Assignee: Bedford Engineering Corp. (Bedford, MA) Primary Class(es): 378/89 209/589, 209/592, 209/905, 250/252.1 Other Classes: US Patent Ref:
Other Refs: Primary Examiner: Rolla, Joseph J. Assistant Examiner: Attorney: Schiller & Pandiscio |
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