Patent GB-974535-A (GB)
Title: Improvements in or relating to weighing apparatus
IPC: G01G7/04
Filed: 1962-09-05
Abstract: 974,535. Electric selective signalling. PHILIPS ELECTRONIC & ASSOCIATED INDUSTRIES Ltd. Sept. 5, 1962 [Sept. 8, 1961], No. 34019/62. Heading G4B. In a weighing apparatus, the weight G 1  of the article to be weighed is compared with the force produced by an electric current taken from a generator which produces identical current pulses, and means are provided for varying the number of pulses incorporated in said current during a particular time interval, the said number being counted by a counter. Two current-carrying coils 6, 6<SP>1</SP> are wound on primers 5, 5<SP>1</SP> supported by springs 7, 7<SP>1</SP> in the field of a permanent magnet 2. The primers 5, 5<SP>1</SP> are movable in response to imbalance between the magnetic forces on coils 6, 6<SP>1</SP> and weight G 1  and a reference weight G 0  respectively, producing signals from zero-position indicators 11, 12. In Fig. 2, an A.C. voltage of 100 kc/s produced by an oscillator 20 is converted into a train of positive pulses at 21, shaped at 22, and fed through one of two gates 24, 24<SP>1</SP> depending on the state of a multivibrator 27, optionally smoothed to a mean current at 36 or 36<SP>1</SP>, and then passed through coils 6, 6<SP>1</SP> in series or through coil 6<SP>1</SP> alone. The shaping at 22 is controlled by indicator 12 so that the force on coil 6<SP>1</SP> balances weight G 0 , thus correcting for any change in the field of magnet 2 due to e.g. temperature variations. The output of oscillator 20 is also frequencydivided at 32 to produce a 10 c/s signal which switches the multivibrator 27 every 0.1 second thereby opening gate 24 to allow pulses to enter coil 6, and closing gate 24<SP>1</SP>. The multivibrator 27 is switched back to close gate 24, and open 24<SP>1</SP>, after a time (less than 0.1 second) determined by a control voltage derived from indicator 11 thereby ensuring that the current in coil 6 balances the weight G 1 . The 10 c/s signal is also applied to a ten-output electronic switch 33 each of the outputs of which is thereby pulsed in turn. The first output of switch 33 provides one of the two necessary enabling voltages for a gate 35 which, when open, allows the output of oscillator 20 to enter a counter 30. The other enabling voltage is provided when pulses are passing through coil 6. Hence, those pulses passing through coil 6 during the first tenth of each second are counted, giving a counter reading proportional to weight G 1 . Counter 30 is reset at the end of each second by the tenth output of switch 33. The maximum weight which can be weighed can be altered by altering the value of a resistor 37 across coil 6<SP>1</SP>. Fig. 3 (not shown) shows an alternative embodiment in which pulses pass through coil 6 all the time, the number passing in 0.1 1 second, which is counted, being varied by varying the frequency of the pulse generator in accordance with a control voltage derived from indicator 11. Indicator 12 controls the magnitude of a D.C. current which is passed through coil 6<SP>1</SP>, and the voltage across a resistor in series with coil 6<SP>1</SP> controls the amplification factor of an amplifier through which the pulses to coil 6 pass.