Patent GB-1215292-A (GB)
Title: Improvements relating to spectrometric analyzers
Inventor: BROWNING GEORGE WILLIAM
IPC: G01N23/223
Filed: 1966-11-25
Abstract: 1,215,292. Programmed control of testing. ASSOCIATED ELECTRICAL INDUSTRIES Ltd. Nov. 21, 1967 [Nov. 25, 1966], No. 53025/66. Heading G3N. [Also in Division G1]. The operation of a X-ray spectrometer is controlled by instructions pre-recored on a paper sheet or tape or a magnetic tape, drum or disc, etc. The spectrometer itself of the type in which an electrom beam is scanned over the surface of a specimen under investigation to produce X-rays characteristic of the elements encountered by the scanning beam. The characteristic X-rays are passed through a device which selects a particular wavelength or wave band corresponding to an element of interest for delivery to a detector generating electrical pulses in response to the intensity of the received X-rays. The detector circuit includes a pulse height discriminator and a pulse ratemeter or scaler the output of which is a function of the concentration of the element of interest. Control System The instructions for operating the spectrometer are recorded on the recording medium e.g. paper tape in lines of holes one part of each line being reserved for operational information and the remaining part for setting information associated with the operation. The input means, i.e. in the case of paper tape, a tape reader 1, to the apparatus for controlling the spectrometer is especially adapted to read information arranged in this way, it being provided with a number of pick up heads equal to the number of holes in each line. For example, if the instruction is to adjust the selected wavelength band of the spectrometer, the first part of the line of holes relates to the operation itself and the second part of the line to the numerical value of the setting. In some cases, only the operational part of the line is used e.g. in the case of starting the scaler or printer. The tape is advanced line by line through the reader 1 under the control of a control and sequencer unit 2. When a line is read, the operational part is decoded by device 3 and a signal passed through an access gate 6 or 6a to the relevant store 7-12, any setting information in the line being gated subsequently through gate 13 to the same respective store. Once the operation has been carried out the tape is stepped forward to enable reading of the next line. The block of stores 7 is provided to enable the selected wavelength to be set very accurately, this requiring a high number of bits. The setting information in this case occupies five successive lines on the tape. The wavelength setting is carried out by feeding signals from stores 7 and from a digitizer 18, which senses the spectrometer angle i.e. relative orientations of detector and the diffraction crystal, to a comparator 16, which supplies a motor 20 to adjust the spectrometer angle until the decoded digitizer output coincides with the stored valve in 7. As the various operations proceed and measurements are carried out, these are printed out, together with all the tape controlled parameters if required, through printer control 5. Spectrometer details. The electron beam for producing characteristic X-radiation is finely focused and can be scanned over the surface of the specimen point by point in a single line or line by line over a given area. The movement of the beam with respect to the specimens is either by electronic deflection or by mechanical displacement of the specimen holder. A number of specimens e.g. unknown and reference may be mounted in a rotatable drum. To aid setting up for the apparatus, e. g. to choose a particular area to be scanned, an optical microscope or CRT display of the spectrometer output may be utilized. The spectrometer arrangement may be in the Johannson or Johann focusing condition. To cater for different wavelength ranges, two or more different diffraction crystals e.g. mica and lithium fluoride, may be used and are interchangeable. The detector may be a gas flow proportional counter in tandem with a scintillation counter, the first detecting low energy and the second, higher energy radiations. The detector output is amplified by a variable gain amplifier and applied to a scaler and a ratemeter. The scaler output is printed out or used to punch a tape. The ratemeter output is recorded graphically or as a CRT trace. Output information may be fed to a computer with feedback control facilities. Control operations and functions include the following: - (1) Spectrometer angle setting (2) Spectrometer crystal selection (3) Scaler range selection (4) Pulse height analyser threshold level selection (5) Pulse height analyser gate width selection (6) Amplifier gain selection (7) Scaler Start (8) Printer Start (9) Specimen stepping (10) Scintillation counter H.T. supply voltage (11) Selection of detector output to be recorded when two are used (12) Sample selection  (13) Electron beam accelerating voltage (14) Electron beam current (15) Opening and closing of window between specimen and spectrometer (16) Operation of scan recording camera (17) Operation of optical microscope camera.