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Measuring principle of rotational viscometer

- May 19, 2018 -

For double-barrel viscometers, read the instrument manual carefully. Different rotors (inner cylinders) are matched to the corresponding cylinders. Otherwise, the measurement results will be greatly biased. For a single cylinder rotary viscometer, the radius of the outer cylinder is in principle required to be infinitely large. The actual measurement requires that the inner diameter of the outer cylinder, that is, the measurement container, be not less than a certain size. It is required that the measuring beaker or straight container has a diameter of not less than 70mm. Experiments have shown that especially when the No. 1 rotor is used, a large measurement error is caused if the inner diameter of the container is too small.


Construction: Rotating viscometer consists of five parts: motor, constant speed device, transmission, measuring device and bracket box. Constant speed devices and transmissions are collectively referred to as rotating parts. An outer cylinder is fixed on the rotating part, that is, the outer cylinder rotates. The measuring device consists of a measuring spring component, a dial and an inner cylinder. The inner cylinder is fixed to the body by a torsion spring, and a dial is attached to the torsion spring. The outer cylinder is usually called the rotor and the inner cylinder is called the suspension.


Principle: In the measurement, the inner cylinder and the outer cylinder are immersed in the drilling fluid at the same time. They are concentric cylinders with an annular gap of 1.17 mm. When the outer cylinder rotates at a constant speed, it drives the drilling fluid in the annulus to rotate. Due to the viscosity of the drilling fluid, the inner cylinder connected to the torsion spring is rotated at an angle. According to Newton's internal friction law, the angle of rotation is proportional to the viscosity of the drilling fluid, so the measurement of the viscosity of the drilling fluid is converted into the measurement of the rotation angle of the inner cylinder. The size of the corner can be read directly from the dial, so this type of viscometer is also called a direct-reading rotary viscometer.


Measuring principle: 1 relationship between shear rate and speed: 1 rev / min (common rpm is expressed) = 1.703s-1; 2 dial reading q (q is the number of degrees on the circumference, the unit can be omitted) and the shear stress t (in Pa) is proportional to. When the torsion spring coefficient of the design is 3.87 ́10-5, the relationship between the two can be expressed as: t=0.511q(Pa).

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