Patent GB-1157572-A (GB)
Title: Improvements in or relating to Measuring Gauges.
Inventor: TAYLOR LAURENCE EDGAR
IPC: G01N23/16
Filed: 1966-05-19
Abstract: 1,157,572. Photo-electric measurement apparatus. E.K. COLE Ltd. Aug. 7, 1967 [May 19, 1966], No. 22210/66. Heading G1A. A radiation detector is used to produce pulses whose frequency is representative of a characteristic e.g. the thickness, of a body subjected to penetrative radiation, and which are counted in a circuit arranged to indicate the deviations of the characteristic from a preset value. In one embodiment, Fig. 1, the thickness of a piece of material 2 is measured by detecting the radiation from a radio-active source 1 transmitted by the material, using a scintillation detector 3. Pulses are directed, through a gate G1 provided with amplitude discrimination, to a decimal or binary counter 4. At the same time, pulses from a clock pulse generator 8 are counted by a timer 6. The counter 4 and timer 6 are set by controls 5, 7, respectively, so that if the thickness of the material 2 is the required value they will attain the preset counts simultaneously. Signals over lines L2 and L3 would then be produced to generate a resetting pulse for the counter and timer to initiate another measurement cycle. If the material were too thin, the counter 4 would attain its preset count before the timer, a signal being produced on line L2 only. This results in a signal from gate G2 on line L7 to gate G1 to disconnect the counter 4 from the detector, and in a signal on lead L6 to amplifier 11. At the same time a ramp generator 9 (whose rate of voltage increase is controllable by control 10) is started by a signal on line L8 from G2. The ramp generator output is integrated until the timer 6 attains its preset count, when a signal on line L3 to gate G2 appears, causing a cessation of signals to the amplifier 11 and stopping and resetting of ramp generator 9. The final value of the output of the amplifier when the generator is stopped, is indicative of the amount by which the material is too thin. If the material is too thick, the timer attains its preset count first, causing a signal on line L3. A signal appears on line L6 and the ramp generator 9 started, as before, while the connection between detector 3 or counter 4 is broken and the clock 8 connected to the counter. Thus, clock pulses are subsequently counted until the preset count is attained, when a signal on line L2 appears, to balance that on L3 and cause resetting. In order to indicate which of the timer or counter first reached its preset count and thus whether the material 2 is too thick or too thin, it is arranged for the polarity of the signal on L6 to be negative or positive respectively. The control 7 can be used to compensate for source decay. An integrator is provided in unit 11 to obtain a mean value when a succession of measurements is to be carried out. In a second embodiment, Fig. 2, at the start of a measurement cycle, a preset counter 4 receives pulses from a detector similar to that of Fig. 1, and a preset timer receives pulses from a clock pulse generator 8. While counter and timer are counting they produce output pulses P1 and P2, of lengths equal to the duration of the respective counts. Thus, if the material under test is of the required thickness P1 and P2 will be of equal length and will be fed back through gate G3 and a delay amplifier 13, to reset and restart the counter and timer through bi-stable switches S1, S2. Inequality in the pulse lengths results in a positive or negative pulse being produced on line L7, as a result of subtraction of the pulse P2 from the inverted pulse P2 at junction 15. Such a pulse represents the amount by which the material is too thin or too thick and controls the operation of a ramp generator 19 or 16 whose output is integrated at 20 or 17 and used for indication or operation of an alarm. Instead of transmission of radiation through the test material the backscatter technique may be used. The ramp generator 9 and amplifier 11 may be replaced by a digital indicator reading the value of the unbalance signal.