GB1233881A - - Google Patents

Abstract

1,233,881. 881. Measurement of viscosity. N.V. TOOLS Ltd. Nov.17, 1969 [Jan. 2, 1969], No.332/69. Headings G1A and G1S. Apparatus for determining the viscosity of a fluid includes a paddle 1 which is immersed in the fluid and oscillated back and forth through the fluid, the viscosity of which is determined from the frequency of reciprocation. The paddle is connected to a rod 3 which constitutes the armature of a magnetic system comprising a small permanent magnet 5 and an electromagnet provided by coil 4. A flexible diaphragm 2 separates the paddle from the armature. The rod 3 carries a shield member such that at each extreme of reciprocation, light from a lamp 7 (plus lens 6) is prevented from reaching one, and completely illuminates the other, of a pair of photo-diodes 9 (and 10). The illuminated diode changes in resistance and causes triggering of a bi-stable circuit (12) Fig.3 (not shown). The state attained by this driver circuit determines the direction of current flow through coil 4 and thus the direction of the magnetic field acting on armature rod 3. Thus, at each extreme of movement of rod 3, it causes a change in the field and itself to change direction. The time for the armature and paddle to move from one extreme to the other is a function of the viscosity of the liquid through which the paddle moves and so the output of circuit (12) is analyzed by differentiating it and passing the voltage spikes produced through a doubling circuit and a capacitor (13) to produce a steady voltage, dependent on the repetition frequency, which is indicated by meter 14. The viscosity may be controlled by monitoring the voltage across the capacitor (13). If it departs from a predetermined value a solenoid valve is operated to add correcting fluid in the required quantity.