Patent GB-1158834-A (GB)
Title: Electronic Servo-Type Multiplication and Division Apparatus
Inventor: TAKADA KEISUKE
IPC: G06G7/163
Filed: 1967-08-14
Abstract: 1,158,834. Electromagnetic induction flowmeters. TOKYO SHIBAURA ELECTRIC CO. Ltd. Aug. 14, 1967 [Aug.18, 1966; Oct.8, 1966; Oct. 15, 1966], No.37243/67. Heading G1N. [Also in Division G4] A multiplier and divider circuit Fig. 1 comprises a fixed resistor in series with a variable resistor R whose valve is responsive to a parameter operating through a control element Ro ; the resistor comprising a light sensitive photoresistor or photo-transistor; a heat sensitive themistor, a magnetically variable resistor, or a voltage sensitive field effect transistor, Signals V 1  at frequency f 1  V 11  at frequency f 11  V 12  at frequency f 12  V 13  at frequency f 13  V 14  at frequency f 14  are supplied to one terminal of the resistance chain and a signal VF 1  at the junction is filtered out and compared with the input V 0  at frequency f 1  in comparator C, and the error is amplified to energize control element of resistor R to zeroize the error so that V 0  = V F1 , and if G is the division ratio of the resistors #, R; VF 1  = GV 1  and G V0/V1 so that bandpass filters F 11  to F 14  produce from the junction of #, R the signals VF11=GV11=V0V11/V1 at frequency f 11 , VF 12 = GV 12  = V0V12/V1 at frequency f 12  VF 13 =GV13=V0V13/V1 at frequency V 13  VF 14 = GV 14 = V0V14/V1 at frequency V 14  In a modification Fig. 2 (not shown) the variable resistance Rk is connected as one arm of a bridge completed by two equal resistors R A  and two resistors Rn, Rm in series; an input signal V 0  at frequency f 1  being applied to the junction. An amplifier and control element for the variable resistor are connected to one diagonal, and the other receives signals V 1  at f 1 , V 11  at f 11 , V 12  at f 12 , V 13  at f 13  &c. producing corresponding currents I 1  I 11  , I 12  , I 13  &c., it being shown that inputs VF 11  at f 11 = G A I 11 = -G B  I0I11/I2 V F12  at f 12 = G A I 12 = -G B  I0I12/I1 V F13  at f 13 =G A I 13 =-G B  I0I13/I1 where G A  = R A (R n  + R m  - R k  / 2R A  + R n  + R m  + R k  G B  =2R A R m  / 2R A  + R n  + R m  + R k    and G A  / O B  = I 0  / I 1  In a further modification (Fig. 3) a field effect transistor R k  is connected in bridge with equal resistors R A  and series resistors R n , R m , and signals V 1  at frequency f 1  and V 11  at frequency f 11  are applied over resistors R 2 , R 3  to produce corresponding current I 1 , I 11  while a signal V 0  at frequency f 1  produces a current I 0  through resistor R 1  to the junction T of R n  and R m . Bridge unbalance voltage at diagonal PQ is amplified at A 0  from which output signals at frequencies f 1  and f 11  are extracted by selective amplifiers A 1 , A 11 . The former signal is applied to the gate electrode of R K  over resistance R 4  and the latter is applied to produce a voltage signal V F11  at f 11  and a current I 011  over resistor R 6  to junction T of R n , R m . The bridge output at f 11  is zeroized and G A I 11  + G B I 011  = 0 I 011  = I 0 I 11 /I 1  VF 11  = V 0 .V 11  / V 1    The junction of R 4  and the gate of R K  is grounded over series resistor R 5 , diode D 11  and voltage source E 1  operating as a limiter to compensate the non-linear characteristic of R k  Fig. 4 (not shown). Plural parallel limiters producing a piecewise linear fuction may be used. In a further modification (Fig. 5) an electromagnetic flowmeter 20 having excitation winding 24 and electrodes 22 is push-pull amplified at 25 to produce signal V 0  at frequency f 1  = k 1  v# where k 1  is constant, v=velocity flow, # = magnetic flux and the corresponding current I 0  is applied to junction T or resistors R n , R m  of bridge 27 also containing equal resistors R A  and resistor Rk varied by control element 36. Transformer 28 in the supply to excitation winding 24 produces a signal V 1  at frequency f 1  applying current I 1  to the bridge, also receiving a current I 11  at frequency 11 from voltage output V 11  of modulator 32 energized by a signal E 11  representing fluid density, temperature, or other parameter. The bridge output from diagonal P, Q is amplified and divided into signals at frequencies f 1  and f 11  by selective amplifiers 34, 35; the former of which is supplied to control element 36 to balance the bridge while the latter is rectified and applied as a D. C. voltage E 0  at input O. This is modulated at 37 by frequency f n  and applied as current I 011  to function T of R n , R m . Then E 0  = V 0 E 11 /V 1 = kv E 11  so that it represents the flow rate compensated for variations of magnetic excitation for E 11  = constant flow mass if E 11  represents density, and temperature compensated flow rate if E 11  represents temperature.