Patent GB-1059411-A (GB)
Title: Voltage or current comparator
IPC: G01R1/28
Filed: 1964-02-10
Abstract: 1,059,411. Measuring temperature electrically. HOKUSHIN ELECTRIC WORKS Ltd. Feb. 10, 1964 [Feb. 13, 1963], No. 5534/64. Heading [Also in Divisions G3 and H3] A voltage or current comparator, Div. H3, comprising a second harmonic type magnetic modulator which is made to perform parametric oscillations by applying a high frequency current across a non linear resistance in the output circuit thereof may be used in a temperature control and an alarm apparatus performing an on-off operation. In Fig. 4 a temperature sensitive resistor 71 for measuring the temperature of the controlled object denoted by a square of solid lines is connected in a D. C. wheatstone bridge with resistors 72, 73, 74, resistor 72 being variable for setting reference temperatures for the ON-OFF control. In operation the unbalance voltage of the bridge is fed to input windings 8, 9 of the magnetic modulator 6, 7 so that an alternating current output voltage of O phase or # phase is produced by the even harmonics when the apparatus acts as a second harmonic type modulator, the phase being determined by the polarity of the D. C. input current from the bridge. Following the magnetic modulating operation a high frequency current from circuits B, C is applied across non-linear resistance 17 and the circuit comprising the output windings 12, 13 capacitor 16 and resistor 17 begins to perform parametric oscillations the phase of which is the same as that produced by the modulating operation. The parametric oscillations last as long as the high frequency current is applied and are not dependent upon subsequent changes of the D.C. input polarity. The output signal from terminals 18, 19 is amplified by transistor 78 and then passed to a phase discriminating circuit 88 whose reference voltage is a voltage composed mostly of the second harmonic obtained from rectifier 108. Only when the phase of the output from terminals 18, 19, and the phase of the reference voltage accord will there be an output on the secondary windings 85, 86 while for those phases differing by # from each other there will be no output. The output signal from winding 85 fires S.C.R. 91 causing the electric source 92 of heater 93 to be turned on or off in dependence upon the polarity of the unbalance output voltage of the Wheatstone bridge. In order to discriminate whether or not the measured temperature exceeds the upper setting limit or the lower setting limit a small current is fed to windings 76, 77 from source 75 so that further comparisons may be made producing an output in winding 86 when the measuring temperature is lower than the reference setting temperature, higher than the upper limit setting temperature and lower than the lower limit setting temperature. An output signal in winding 86 causes lamp 102 to be struck and operate an alarm connected to terminal 106. Before each monitoring operation the circuit is reset by means of a pulse applied to 103. In the arrangement of Fig. 5 (not shown), source 75 of Fig. 4 is replaced by two separate sources, providing lower and upper limit reference settings and two lamps are provided one being activated when the upper limit is exceeded and the other when the lower limit is exceeded. Although only one magnetic modulator is shown the arrangement of Fig. 1 (not shown) provides a plurality of such comparison circuits.