Patent GB-997579-A (GB)
Title: Standardization of radiation-absorption type density gauges
IPC: G01N23/16
Filed: 1963-05-08
Abstract: 997, 579. Radiation detector for measuring density. ELECTRONIC AUTOMATION SYSTEMS Inc. May 8, 1963 [May 14, 1962], No. 18257/63, Heading G1A. The invention relates to a radiation detector arrangement for and a method of measuring the density of a moving material, for example fluid flowing in a pipe, of the kind in which a detector detects unabsorbed radiation from a radio-active source, which has passed through the material, the arrangement including a calibration circuit for the initial calibration of the arrangement and for periodic calibration to eliminate error in measurement due to delay in source output radiation. In the embodiment shown data or gamma radiation from an isotope 2 is directed through the pipe 4 and unabsorbed radiation is detected by an ionisation chamber 3 whose output is fed through a D.C. amplifier 6 and a cathode follower CF in series with a variable resistor P4 to a centre zero meter 7. The probe 3<SP>1</SP> of the ionisation chamber 3 is also connected through a high resistance R 1 , a calibrating switch S 1  and a potentiometer P 2  to ground, the potential at the slider 9 of P2 being in opposition to that at the switch S 1  end of the resistor R 1 . Initially the pipe is emptied and gauged calibration switches S 1 ,S 2  are set at STD No. 1 position. A variable resistor P 1  connected as shown is then adjusted until the meter 7 reads zero and its sensitivity is reduced by adjustment of a resistor P5. The pipe line is then filled with a first standard sample material of known median density represented as density 1.0 for example and the switches turned to OPR position. P2 is then adjusted until the meter again reads zero, this position of P2 being retained for all subsequent operation until a new basic standardization is required. After further emptying and refilling with a second standard material having a known deviation from density 1. 0 such as either - or + 10% the meter 7 is adjusted to read fall scale deflector by adjustment of P4. With the switches at STD No. 2 position a resistor P3 connected between the junction A between resistors P1 and P2 and the switch S2, is adjusted until the meter again reads full scale deflection. This claibrates the meter for full scale deflection for the voltage at point A which is used henceforth as a reference voltage. After this last step the arrangement is ready for normal density measurement and recalibration may be carried out by emptying the pipe, setting the switches to STD No. 1 position and adjusting P1 until the meter is zeroed, and then setting the switches to STD No. 2 position and adjusting P5 until the meter reads full scale deflection, after which with the switches at OPR position normal measuring may be resumed. In another embodiment (Fig. 2 not shown) after initial manual calibration as above, recalibration is carried out automatically by the operation of a programming system which operates relays controlling the switches and servomotors which adjust the resistors P1 and P5. U.S.A. Specifications 2,675,483 and 2,829,268 are referred to.