JPH08327527A - Capillary type viscometer - Google Patents

Abstract

PURPOSE: To measure viscosity a wide range with high accuracy by applying a constant differential pressure system when the viscosity of liquid specimen is equal to or above a preset value, and adopting a constant flowrate system when the viscosity is less than the preset value. CONSTITUTION: Measurement fluid is sent to a measurement capillary on the operation of a determination pump. The pressure drop of the liquid at both ends of the capillary in this case is sent to a differential pressure sensor 1 through a pressure transmission tube via a pressure receiving diaphragm for measuring differential pressure across the capillary. Also, a differential pressure signal from the sensor 1 is transmitted to a differential pressure control device 8, and the speed of a servo motor 6 is determined, so as to keep the differential pressure at the preset value. In addition, a signal selector 9 determines whether a signal from the device 8 or from speed setting unit 10 are transmitted to a servo motor speed control device 11. When a signal set in the device 11 is selected, the servo motor 6 begins to rotate at constant speed, and thereby, the viscometer becomes a viscometer of constant flowrate system. Also, differential pressure measurement value and speed measurement value are transmitted to a viscosity calculation circuit 13 for conversion into a viscosity value.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a viscometer capable of measuring the viscosity of a fluid with high accuracy over a wide measuring range. The present invention provides a polymer of a polymer which requires highly accurate viscosity measurement over a wide measuring range. It became possible to manufacture polymers that could not be manufactured until now, such as automation of control.

[0002]

2. Description of the Related Art A conventional thin tube viscometer has a constant pressure difference method in which the differential pressure of a fluid flowing through the thin tubes at both ends of the thin tube is fixed and the viscosity is measured by measuring the flow rate of the fluid. There is a constant flow rate method in which the viscosity of the fluid is measured by measuring the differential pressure between both ends of the thin tube while keeping the flow rate of the flowing fluid constant. The accuracy of these viscometers is determined by the accuracy of the differential pressure sensor or the flow rate sensor, ignoring the accuracy of the control system. In the case of the constant flow rate method, the error of the differential pressure sensor directly affects the measurement error of the fluid viscosity. Since the measurement reproduction error of the current differential pressure sensor is about 0.2% FS, even if the error is allowed up to 2% of the measured value, the measurement range is 1:10.

In the constant differential pressure system, the control error of the control system for controlling the constant differential pressure and the error of the flow rate sensor influence the measurement error of the fluid viscosity. In order to control the differential pressure to be constant, it is necessary to control the flow rate of the fluid, and as a method for this, there are a method using a control valve and a method controlling the rotation speed of the metering pump. The control range of the fluid flow rate by the control valve is about 1: 5, and in the case of the rotational speed control it is about 1: 20, but it takes a measurement time when the flow rate decreases, so the measurement range is realistically about 1: 10. Is the limit.

As described above, the practical limit of the measurement range is 1:10 in both the constant differential pressure method and the constant flow rate method. However, in order to use it for controlling the polymerization of the polymer, 1:50
It requires a certain measuring range, and conventional viscometers cannot control polymerization.

[0005]

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and an object of the present invention is to provide a capillary viscometer capable of realizing a wide measurement range and high measurement accuracy.

[0006]

The capillary viscometer of the present invention comprises a differential pressure constant control system for making constant the differential pressure of the fluid flowing through the measuring capillary at both ends of the measuring capillary, and the fluid flowing through the measuring capillary. Constant flow rate control system for making the flow rate constant, means for automatically switching between the constant differential pressure control system and the constant flow rate control system when the fluid in the measurement thin tube reaches a predetermined viscosity, and the measurement A metering pump for sending a fluid to a thin tube, a means for measuring the number of revolutions of the metering pump, a means for measuring the flow rate of the fluid flowing into the measuring tube from the number of revolutions, a fluid flowing through the measuring tube at both ends of the measuring tube And a means for measuring the differential pressure of, thereby achieving the above object. The capillary viscometer of the present invention may further include means for dividing the differential pressure of the measuring capillary by the flow rate of the fluid flowing through the measuring capillary and multiplying it by a coefficient to obtain the viscosity.

The present invention will be described in detail below.

The relationship between the viscosity of a certain fluid, the differential pressure of the fluid flowing in the capillary at both ends of the measuring capillary (hereinafter referred to as the differential pressure across the measuring capillary), and the flow rate of the fluid flowing in the measuring capillary is Hagen. It is expressed by the formula (1) from the Poiseuille's formula.

M = k · dp / q (1) m; viscosity k; constant dp; differential pressure before and after the measuring thin tube q; flow rate of fluid flowing through the measuring thin tube In the present invention, a constant pump such as a gear pump. In order to obtain the flow rate of the liquid from the number of revolutions of, when the discharge amount per revolution of the metering pump is f and the number of revolutions is n, equation (1) is m = k · dp / f · n = kl · dp / n (2) kl; becomes a constant.

In the present invention, when the viscosity of the fluid to be measured is a predetermined value or more, the constant differential pressure method is used to measure the viscosity, and when the viscosity is less than that, the constant flow rate method is used. To measure the viscosity. The accuracy in this case will be described below.

In the case of the constant differential pressure system, from the above formula (2),
The accuracy of the measured viscosity is determined by the reproducibility of the differential pressure sensor and the measurement accuracy of the rotation speed of the metering pump. The reproducibility of the differential pressure sensor is usually about ± 0.2% FS. Since the balance point of the differential pressure is taken near the upper limit of the measurement range for accuracy, the measurement error of the differential pressure sensor is ± 0.2%.
About.

Further, the measurement accuracy of the rotation speed of the metering pump is
Since it can be measured with extremely high accuracy by a rotary encoder or the like, it can be ignored as long as an error of ± 0.2% is a problem.

Therefore, when the constant differential pressure method is used, the measurement error is ± 0.2% of the measured viscosity, which enables measurement with extremely high accuracy. However, in order to control the differential pressure to be constant, it is necessary to increase the rotation speed of the metering pump as the viscosity of the fluid decreases, but of course there is a limit, and it is practical to control with a servomotor or the like. The limit is a ratio of the minimum rotation speed to the maximum rotation speed of about 1:10 to 1:20.

Another important problem of the constant differential pressure system is that it takes time to feed the fluid into the measuring thin tube when the flow rate of the fluid decreases, so that the measuring time increases as the viscosity of the fluid increases. It has the drawback. Therefore, the practical measurement range of the constant differential pressure system is about 1:10 by comprehensively judging the measurement time delay and the control limit.

In the case of the constant flow rate system, the accuracy of the measured viscosity is determined by the accuracy of the differential pressure sensor. The reproducibility of the differential pressure sensor is about ± 0.2% FS. In case of constant flow rate method,
Assuming that the measurement error is within ± 2% of the viscosity value at that time, the measurement range is about 1:10. The accuracy of the constant flow rate method is considerably worse than that of the constant differential pressure method, but unlike the constant differential pressure method, there is no drawback that the measurement time becomes long when the viscosity of the fluid to be measured is high.

In the present invention, the constant differential pressure method and the constant flow rate method are combined, and the constant differential pressure method is adopted when the viscosity of the fluid to be measured is more than a predetermined value, and the constant flow rate method is adopted when the viscosity is less than that. To measure the viscosity of the fluid.

Specifically, when considering a viscometer having a maximum measured viscosity mx, a constant differential pressure method is used for viscosities up to p% of mx, and a constant flow rate method is used for viscosities less than that.

Xp = mx · p / 100 m ≧ xp constant pressure differential method m <xp constant flow rate method (3) The value of p is usually about 10% to 20%. To be elected.

The advantage of doing so will be described with reference to FIGS.

In FIGS. 1 and 2, the value of p is calculated as 10%. In FIG. 1, the viscometer of the present invention is
From the viscosity mx to 0.1 mx, the constant differential pressure method, the viscosity 0.
A constant flow rate method is used from 1 mx to 0.01 mx (shown by line (a)). Therefore, from the viscosity mx to the viscosity of 0.1
The measurement reproduction error up to mx is as high as 0.2% of the measured viscosity. When the viscosity is 0.1 mx or less, the measurement reproduction error is 0.2% FS, and the measurement reproduction error linearly increases as the viscosity decreases, and when the viscosity is 0.01 mx, it becomes 2% of the measured viscosity.
The measurement repeatability error of the conventional constant flow rate viscometer is 0.2
% FS (shown by the line (b)), and as shown in FIG. 1, the error of the viscosity mx increases linearly from 0.2% to 2% at 0.1 mx 0. 20% at 01mx
Becomes worse. For this reason, the measurement range in the case of the conventional constant flow rate method is 1:10, while allowing an error of 2%. On the other hand, the viscometer of the present invention has a viscosity of 0.01 mx
Until then, the error is kept below 2%, so the measurement range is 1: 100.

In the case of the conventional constant pressure differential system, the line (c) in FIG.
As shown by, the measurement reproduction error from the viscosity mx to 0.1 mx is 0.2%, and the same high accuracy as in the present invention can be obtained. However, the control range of the control system is, as described above,
Since it is about 1:10, it is impossible to measure in a range further than this. Therefore, the measurement range is 1:10 even with the constant differential pressure method.
It is a degree.

From the above, according to the present invention, a highly accurate viscometer can be realized over a very wide range of 1: 100. If a conventional viscometer is used to measure viscosity in such a wide range, 10 viscometers are required for each viscosity, and the construction cost required for that is enormous, and 10 viscometers are required. There is also the problem of how to install this viscometer, which is virtually impossible. This also shows that the effect of the present invention is great.

[0023]

The present invention combines the constant differential pressure method and the constant flow rate method, adopts the constant differential pressure method when the viscosity of the fluid to be measured is more than a predetermined value, and adopts the constant flow rate method when the viscosity is less than that. Then, the viscosity of the fluid is measured.
Therefore, by measuring the fluid viscosity by the constant differential pressure method or the constant flow rate method according to the viscosity of the measured fluid, the advantage of the constant flow rate method, which is relatively excellent in measurement accuracy, and the measurement time even in the measurement of high viscosity liquids. The measurement range can be increased by combining the advantage of the constant differential pressure method that is relatively short.

The viscosity is obtained by dividing the differential pressure before and after the measurement thin tube obtained above by the flow rate of the fluid flowing through the measurement thin tube and multiplying it by a certain coefficient.

[0025]

Embodiments of the present invention will be described with reference to FIGS.

In FIG. 3, the measuring fluid is sent to the measuring thin tube 4 by a metering pump 5 such as a gear pump. At this time, the pressure drop of the liquid at both ends of the measurement thin tube is measured by the pressure transmission pipe 3 through the pressure receiving diaphragm 2 and the differential pressure sensor 1
And the differential pressure before and after the measuring capillary is measured.

In FIG. 4, the differential pressure signal from the differential pressure sensor 1 is sent to the differential pressure control device 8 to determine the rotation speed of the servo motor 6 so that the differential pressure becomes a predetermined value. The determined rotation speed signal of the servo motor 6 is sent to the signal selector 9. The signal selector 9 determines whether to send the signal from the differential pressure control device 8 or the signal from the rotation speed setting device 10 to the servo motor rotation speed control device 11. The selection is performed by the above equation (3). That is, when the measured viscosity of the fluid is larger than the predetermined value, the signal from the differential pressure control device 8 is passed, and when it is less than that, the signal from the rotation speed setting device 10 is selected.

The rotation speed setting device 10 is a device for sending a predetermined constant signal to the servo motor rotation speed control device 11,
When this signal is selected, the servomotor 6 has a constant rotation speed, and the flowmeter is a constant flow rate type viscometer. The servo motor rotation speed control device 11 receives the rotation speed command signal from the differential pressure control device 8 or the rotation speed setting device 10 so that the rotation speed command signal and the signal from the rotation speed detector 12 of the servo motor coincide with each other. , Control the servo motor 6. The differential pressure measurement value from the differential pressure sensor 1 and the rotation speed measurement value from the rotation speed detector 12 are sent to the viscosity calculation circuit 13, and the viscosity value is calculated based on the above equation (2).

The calculated viscosity value is output as a viscosity signal and is also sent to the signal selector 9 to be used for selecting a signal.

[0030]

The present invention combines the constant differential pressure method and the constant flow rate method, adopts the constant differential pressure method when the viscosity of the fluid to be measured is more than a predetermined value, and the constant flow rate method when the viscosity is less than that. Is used to measure the viscosity of the fluid,
A highly accurate viscometer over a very wide range of about 1: 100 can be obtained, and it can be effectively used for polymer polymerization control.

[Brief description of drawings]

FIG. 1 is a constant differential pressure method from viscosity mx to 0.1 mx,
It is a figure which shows a measurement reproduction error at the time of viscosity 0.1mx to 0.01mx when measuring a fluid viscosity with the viscometer which took the constant flow rate system.

FIG. 2 is a diagram showing a measurement reproduction error when fluid viscosity is measured by a conventional viscometer of a constant differential pressure type.

FIG. 3 is a schematic view showing a mechanism for measuring the differential pressure of the liquid in the measuring thin tube and controlling the rotation speed of the metering pump by the servo motor.

FIG. 4 is a block diagram showing a control system of a servo motor.

[Explanation of symbols]

 1 Differential Pressure Sensor 2 Pressure Receiving Diaphragm 3 Pressure Transmission Pipe 4 Measuring Capillary 5 Metering Pump 6 Servo Motor 7 Control System 8 Differential Pressure Control Device 9 Signal Selector 10 Rotation Speed Setting Device 11 Servo Motor Rotation Speed Control Device 12 Rotation Speed Detector 13 Viscosity Arithmetic circuit

Claims (1)

[Claims] 1. In a thin-tube viscometer, a differential pressure constant control system for making constant a differential pressure of a fluid flowing through the measuring thin tube at both ends of the measuring thin tube, and a constant flow rate of the fluid flowing through the measuring thin tube. A constant flow rate control system, a means for automatically switching between the constant differential pressure control system and the constant flow rate control system when the fluid in the measuring capillary reaches a predetermined viscosity, and the fluid is sent to the measuring capillary. A metering pump, a means for measuring the number of revolutions of the metering pump, a means for measuring the flow rate of the fluid flowing through the measuring capillary from the number of revolutions, and a differential pressure of the fluid flowing through the measuring capillary at both ends of the measuring capillary. And a capillary tube viscometer.