Device for the purposes of the compensation of a hyperbolic a function of the amplitude of in a detector for roentgenquanten voltage pulses generated

摘要

1,256,028. Feedback amplifiers; gain control. SIEMENS A.G. 12 Dec., 1969 [12 Dec., 1968], No. 60863/69. Headings H3Q and H3W. [Also in Division G1] In an X-ray spectrophotometer of the linear type, in which the direction, of the radiation from the specimen which is analysed, is maintained the same (during changes in the analyser crystal orientation which change the wavelength investigated) while displacing the analyser crystal along a line in the particular direction (the location of the detector being adjusted accordingly to maintain it on the Rowland circle -Fig. 1, not shown), the hyperbolic relationship between the amplitude of the detector output and the distance b between the specimen and the crystal is compensated for by the use of a potentiometer whose tap is coupled to the crystal movement and which modifies the characteristics of an amplifier in the detector circuit in accordance with this movement. The potentiometer may be a linear potentiometer whose slider is connected to the crystal mount, Fig. 2 (not shown), a circular or helical potentiometer whose tap is rotated by the screw drive for the crystal mount, Fig. 3 (not shown), or a contact-less magneto-resistive device. In one circuit arrangement, Fig. 4, the potentiometer P1 is connected across the output of a preamplifier VV which receives the counter tube Z1 output via a coupling capacitor C2. Base gain is provided by resistor R 0 . The effect of the potentiometer is to multiply the amplifier output by the above mentioned distance b and thus give a proportional relationship. Alternative locations for the potentiometer are before or within the amplifier VV or within the main amplifier HV, whose output connects via a pulse height discriminator a counter. Magneto-resistors may be used in the connection of the potentiometer to the amplifier circuit so as to reduce noise. In one arrangement, Fig. 5 and Fig. 6 (not shown), the magnet yoke carries two coils, one coupling a voltage derived from the potentiometer; to modify a magneto resistor in the feedback loop of the main amplifier, the other controlling the operating point of this resistor. The latter coil can also effectively introduce resistors to represent changing of the analyser crystal and of the order of diffraction, or this may be done by relays switching in appropriate resistors as in Fig. 5. In another arrangement, Figs. 7, 8 (not shown) the output of the preamplifier contains a voltage divider arrangement of two magneto-resistors one acted on by the sum and the other by the difference of the premagnetization field of a permanent magnet and the potentiometeractuated coil. Further coils provide for crystal and order of diffraction change.