The double-cylinder rotary viscometer has two cylinders, which can be divided into two types: the inner cylinder rotary type and the outer cylinder rotary type.
Inner cylinder rotary viscometer
As shown in the figure, the outer cylinder is a container for the liquid to be measured, which is fixed , and the inner cylinder is a hollow cylinder immersed in the fluid to be measured and rotated , coaxial with the outer cylinder . The shell of the miniature synchronous motor used for driving is installed in a suspended type , and the inner cylinder is driven to rotate at a certain speed through the rotating shaft. body deflection , the motor casing is connected with two metal hairsprings installed one positive and the other reversely installed , when the casing deflects , the hairspring will be twisted, and when the torque of the hairspring and the viscous resistance torque reach a balance , it will be connected with the motor casing The pointer will indicate a certain value on the dial . This value is proportional to the viscous resistance experienced by the drum . Therefore , the scale reading is multiplied by 1, and the specific coefficient F (ie, the drum factor) is expressed as the value of the viscosity coefficient .
The inner cylinder rotary viscometer is a common rotary viscometer . From its structure and operation mode , it is generally used for off-line measurement of fluid viscosity , such as measuring the viscosity value of sampled fluid in the laboratory .
Because there are many factors that affect the viscosity measurement , in order to obtain a more accurate viscosity value as much as possible , the off-line measurement needs to be carried out in an artificially specific environment , such as a given temperature , pressure and flow rate, etc. , and even needs to provide a shear value similar to the original fluid. shear force or shear rate . In the qualitative analysis of a certain solution or the experiment that does not require high , temperature is still an important factor that cannot be ignored . Experiments have proved that : when the temperature deviation is 0.5 °C , the deviation of the viscosity value of some fluids exceeds 5 % , so the temperature deviation has a great influence on the viscosity , and the temperature increases and the viscosity decreases . In order to solve this problem , a constant temperature Water Bath is generally used to control the temperature of the sampled fluid , so as to ensure that the temperature of the sample is consistent with that of the measured fluid , and then obtain a more accurate viscosity value .
As shown in the figure, when measuring, both the inner and outer cylinders are immersed in the measured fluid , and the motor drives the outer cylinder to rotate at a certain speed . The inner cylinder is viscous due to the measured fluid between the two cylinders. The deflection occurs due to the action of force , and the restoring moment generated by the twisting of the wire connected to is opposite to the direction of the viscous moment . When the restoring moment and the viscous moment of the tensioning wire are balanced , the deflection angle e of the inner cylinder The size is proportional to the viscosity coefficient n that causes the viscous moment . From this, the functional relationship between the viscosity coefficient n and the deflection angle e is deduced [ n= f(e)] , and the viscosity coefficient value n can be calculated by measuring the deflection angle e of the inner cylinder .
As with the single-circle rotary viscometer , manual calculations for direct readings are cumbersome .
Lu Zejian proposed a single-chip microcomputer control measurement method .
As shown in the figure , the 8751 single-chip microcomputer controls the motor speed through the 0832D/A conversion chip , and the motor drives the outer cylinder , and the inner cylinder is connected with an elastic element fixed on the casing at one end . The CTC counting method in the CPU is used to measure the rotational speed of the outer cylinder and the torque of the inner cylinder through the optical coupler , and input the results into the microcomputer to calculate and display the viscosity value of the fluid .
This method adopts CTC counting, realizes the digital display of torque, and is easy to use; single-chip control can also collect data conveniently, realize fast calculation of data, and obtain the final viscosity value. It can be better used in the measurement where the environmental requirements are not too high.
