Patent GB-1491207-A (GB)
Title: Sensors for monitoring the electrical conductivity of electrically conductive fluids
IPC: G01F1/58
Filed: 1973-11-12
Abstract: 1491207 Measuring liquid conductivity temperature and flow electrically UNITED KINGDOM ATOMIC ENERGY AUTHORITY 22 Oct 1974 [12 Nov 1973] 52492/73 Headings G1N and G1U The temperature and/or flow-rate of an electrically conductive fluid (liquid metal in a reactor) is measured by monitoring its conductivity by means of a pair of mutually coupled coils immersed in the fluid, the degree of coupling being dependent upon the conductivity of the fluid. Primary 5 and secondary coils 6 are wound in line on a former positioned in a steel thimble, Fig. 1 (not shown), such that when the thimble is placed in liquid sodium the latter effectively forms a single turn tertiary winding so that as the conductivity of the sodium changes so does the voltage induced in the secondary 6. The induced voltage is fed over transformer 13 to rectifier 31 the output of which is applied to inverting integrating amplifier 32 and non-inverting amplifier 33. The output of amplifier 32 gives a D.C. proportional to the steady conductivity whereas rapid fluctuations in the conductivity are obtained by subtracting the outputs of amplifiers 32, 33. Noise cancellation A voltage proportional to primary current is obtained across resistor 19, which after rectification at 22 is fed to inverting integrating amplifier 23 and non-inverting amplifier 24, the outputs of which are compared and amplified at 28. The output of amplifier 28 is fed via resistor 38 to the input 37 of amplifier 35 to which is also fed the difference signal from amplifier 34. Since the two inputs at 37 are of opposite sign variations in amplitude due to imperfections in driving current and common mode noise cancel out. In a similar manner the outputs of inverting amplifiers 23, 32 are compared and the difference amplified at 71. Stabilized power supply The output of amplifier 23 is fedback to differential amplifier 25 where it is compared with a reference voltage and any error signal produced is used to vary the gain of amplifier 16 to control the primary winding excitation current. Temperature measurements Since the electrical conductivity of fluid 2 depends both on its temperature and flux distortion due to the fluid-flow the component due to the latter must be cancelled for temperature measurement. This is achieved, Fig. 3 (not shown) by dividing the primary winding 5 into two seriesconnected portions 5a, 5b lying on respective sides of the secondary winding. Flux distortions due to fluid movement assist the coupling between 5a and 6 whilst simultaneously reducing the coupling between Sb and 6. Temperature and flow measurements Secondary coil 6 of (Fig. 3) may be provided with a centre tap to provide two coils operating in push-pull. The signals due to different coupling conditions between coils 5 and 6 at each end of coil 5 may be used to provide an indication of the fluid flow-rate. Alternatively a single primary winding may be used with two secondary windings positioned one on either side of the primary, Fig. 4 (not shown), or two secondary and two primary windings may be employed Fig. 5 (not shown). Fig. 6 shows a circuit for measuring both temperature and flow, terminals 50, 51 being connected to the temperature measuring circuit of Fig. 2 and the remaining circuitry of Fig. 6 showing the flow measuring circuit by which steady flow and short term fluctuations can be obtained.