Patent GB-814155-A (GB)
Title: Improvements in or relating to viscometers
IPC: G01N11/00
Filed: 1957-06-17
Abstract: 814,155. Viscometers. BATAAFSCHE PETROLEUM MAATSCHAPPIJ N.V., DE. June 17, 1957 [June 18, 1956], No. 19049/57. Class 40 (1). [Also in Groups XIX and XXXVII] The viscosity of a material such as bitumen is measured by pressing a thin film of the material between a pair of plane surfaces, applying a known force to one surface in a direction parallel to the surfaces and measuring the resulting movement in the direction of the force. In Fig. 2 the specimen is pressed between two glass plates 11, 12 and worked until homogeneous as determined by observing the plates over a white light source. The thickness of the layer is found by weighing the plates before and after the addition of the specimen. The two plates are clamped in a frame 57 (construction in Fig. 4, not shown) and lowered by means of a rod 44 into a constant temperature bath 41, where the left-hand plate is clamped. into a fixed frame 50 by means of the lever 55. The rod 44 is suspended by a chain 45 from one arm of a balance beam 17 which can be loaded by a known weight 21 on the other side. To the chain is fixed a follow-up switch 25 which communicates the shearing motion of the plate 25 to a micrometer 26, and this in turn actuates the recorder 46 via the potentiometer 30 (Fig. 3) as described below. The degree of movement can be estimated by visual inspection of the micrometer 26, or the displacement of the contact 25 may be measured optically. To ensure that the effective area of the specimen does not change during the measurement the moving plate 12 can be made smaller than the fixed plate. When the limit of travel has been reached the plates can be turned over and the specimen sheared in the opposite direction. Measurements can be made at different rates of shear by changing the weight 21. Follow-up circuitry (Fig. 3).-Alternating voltage is supplied to the anode of the thyratron 64 via the windings of the motor 31 and to the grid via the transformer 70 and resistors 66, 65; these voltages are anti-phase so that the thyratron is normally cut off. The speed and direction of the motor depend on the currents through the two halves of the left-hand winding, the motor being at rest when these currents are equal or zero. At the start of the operation the switch 63 is closed in the downward position so that current flows in the lower windings and drives the motor until the contacts 27 and 25 touch. When this happens the thyratron grid is earthed, the valve fires and puts an effective resistance across the upper half of the motor windings. The currents are now equal, the motor stops and switch 63 is released. The thyratron remains conducting and moves the motor slightly until the contact resistance between 25 and 27 is such that the grid voltage of the thyratron is sufficient to cut it off. Movement of the contact 25 decreases the contact resistance and starts the motor again to restore the predetermined value of resistance. The motor also drives the potentiometer 30 and thus operates the recorder 46. Alternatively the relative motion between 25 and 27 could vary a capacitance or the diaphragm of a normally balanced transformer, a suitable servo-mechanism being driven therefrom to restore balance.