JP2022065825A - Vibration type densitometer, and bubble mix-in determination method in vibration type densitometer - Google Patents

Abstract

To provide a vibration type densitometer capable of detecting bubbles mixed in a sample cell without repeatedly introducing a sample to be measured into the sample cell.SOLUTION: A vibration type densitometer 1 that measures density of a sample to be measured stored in a sample cell 10, comprises excitation means 20 of exciting vibration in the sample cell 10, measurement means 30 of measuring a vibration cycle of the excited sample cell 10, drive control means 80 of driving the excitation means 20 with first drive force and second drive force smaller than the first drive force, and determination means 90 of determining the presence or absence of air bubbles in the sample cell 10 on the basis of the difference between a first vibration period of the sample cell 10 excited with the first drive force and a second vibration period of the sample cell 10 excited with the second drive force.SELECTED DRAWING: Figure 1

Description

The present invention relates to a vibration type densitometer for measuring the density of a sample to be measured housed in a sample cell, and a method for determining bubble contamination in the vibration type densitometer.

The vibration type densitometer is a device that accommodates a liquid sample to be measured in a sample cell with one end fixed and vibrates it, and calculates the density of the sample to be measured from the vibration cycle (see, for example, Patent Document 1).

The calculation in the vibration type densitometer is based on the following formula (1): where T is the vibration cycle of the sample cell containing the sample to be measured.
ρ _sample = K ₁ x T ² + K ₂ ... (1)
The density ρ _sample of the sample to be measured is obtained by. Here, the calibration parameters K ₁ and K ₂ are constants determined based on the density and vibration cycle when two types of reference substances having known densities are housed in a sample cell at a reference temperature and vibrated. .. Therefore, when the vibration cycle of the sample cell containing the sample to be measured is measured at a temperature different from the reference temperature, an error occurs in the calculated density value.

The vibration type densitometer of Patent Document 1 controls the temperature of the sample cell so as to keep the temperature of the sample cell at the reference temperature by using a temperature control means such as a heat insulating material and a copper block provided with a Pelche element, so that the density of the sample to be measured can be adjusted. It is possible to suppress the occurrence of errors in the calculation.

Japanese Unexamined Patent Publication No. 2011-38810

In the calculation of the density in the vibration type densitometer, not only the measured temperature but also the mixing of air bubbles in the sample cell becomes an error factor. Therefore, conventionally, by repeating the introduction of the sample to be measured into the sample cell and the measurement of the vibration cycle, it has been confirmed that bubbles are discharged from the sample cell when the calculated density does not change.

However, when the introduction of the sample to be measured is repeated, the temperature of the sample cell changes each time. In the vibration type densitometer of Patent Document 1, since it is necessary to wait from the introduction of the sample to be measured until the sample cell reaches the reference temperature, the introduction of the sample to be measured is repeated in order to confirm the discharge of bubbles from the sample cell. There was a problem that the measurement time became long.

The present invention has been made in view of the above problems, and is a vibration type densitometer and a vibration type that can detect bubbles mixed in a sample cell without repeatedly introducing the sample to be measured into the sample cell. It is an object of the present invention to provide a method for determining bubble contamination in a densitometer.

The characteristic configuration of the vibration type densitometer according to the present invention for solving the above problems is
It is a vibration type densitometer that measures the density of the sample to be measured contained in the sample cell.
Excitation means for exciting vibration in the sample cell,
A measuring means for measuring the vibration cycle of the excited sample cell, and
A drive control means for driving the excitation means with a first driving force and a second driving force smaller than the first driving force.
Presence or absence of bubbles in the sample cell based on the difference between the first vibration cycle of the sample cell excited by the first driving force and the second vibration cycle of the sample cell excited by the second driving force. The purpose is to provide a determination means for determining.

According to the vibration type densitometer of this configuration, the exciting means for exciting the vibration in the sample cell, the measuring means for measuring the vibration cycle of the excited sample cell, the first driving force, and the first driving force smaller than the first driving force. (2) Based on the difference between the drive control means that drives the excitation means by the driving force and the first vibration cycle of the sample cell excited by the first driving force and the second vibration cycle of the sample cell excited by the second driving force. By providing a determination means for determining the presence or absence of bubbles in the sample cell, it is not necessary to repeat the introduction of the sample to be measured into the sample cell and the measurement of the vibration cycle in order to confirm the discharge of the bubbles, and the sample cell does not need to be repeated. It is possible to determine the presence or absence of air bubbles while the sample to be measured is contained in the device. Therefore, in the vibration type densitometer of this configuration, the presence or absence of bubbles can be determined in a short time without causing the temperature change of the sample cell a plurality of times due to the repeated introduction of the sample to be measured. As a result, it is possible to shorten the time from the introduction of the sample to be measured to the measurement of the density while preventing the occurrence of an error due to the mixing of bubbles.

In the vibration type densitometer according to the present invention
The second driving force is preferably 1/5 to 1/2 times the driving force of the first driving force.

According to the vibration type densitometer of this configuration, the difference between the first vibration cycle and the second vibration cycle is due to the second driving force being 1/5 to 1/2 times the driving force of the first driving force. Since it becomes remarkable, it is possible to accurately determine the presence or absence of air bubbles in the sample cell.

In the vibration type densitometer according to the present invention
The first vibration cycle is a vibration cycle measured by the measuring means immediately before the driving force of the exciting means is changed from the first driving force to the second driving force.
The second vibration cycle is preferably a vibration cycle measured by the measuring means at an arbitrary time point between 8 and 10 seconds after the driving force of the exciting means is changed to the second driving force. ..

According to the vibration type densitometer of this configuration, the first vibration cycle is the vibration cycle measured by the measuring means immediately before the driving force of the exciting means is changed from the first driving force to the second driving force. The second vibration cycle is the first vibration cycle and the first vibration cycle because the vibration cycle is the vibration cycle measured by the measuring means at any time between 8 and 10 seconds after the driving force of the exciting means is changed to the second driving force. The difference from the two vibration periods becomes more remarkable, and the determination of the presence or absence of air bubbles in the sample cell becomes more accurate.

In the vibration type densitometer according to the present invention
When the difference between the first vibration cycle and the second vibration cycle is 1.5 × 10 ⁻² μsec or more, the determination means preferably determines that the bubbles are present.

According to the vibration type densitometer of this configuration, when the difference between the first vibration cycle and the second vibration cycle is 1.5 × ^10-2 μsec or more, the determination means determines the presence or absence of air bubbles in the sample cell. It can be determined with certainty.

In the vibration type densitometer according to the present invention
The viscosity of the sample to be measured is preferably 200 mPa · s or less.

The higher the viscosity of the sample to be measured, the smaller the difference between the first vibration cycle and the second vibration cycle tends to be. According to the vibration type densitometer of this configuration, since the viscosity of the sample to be measured is 200 mPa · s or less, it is possible to suppress the influence of the viscosity of the sample to be measured and determine the presence or absence of bubbles in the sample cell. ..

In the vibration type densitometer according to the present invention
The sample cell is a U-shaped tube and has a U-shaped tube.
It is preferable that the determination means determines the presence or absence of the bubbles in a section of 1/2 or less from the tip of the U-shaped tube to the fixed end.

In the calculation of the density in the vibration type densitometer, if bubbles are present in the section of 1/2 or less from the tip of the U-shaped tube to the fixed end, the error becomes large. According to the vibration type densitometer of this configuration, the sample cell is a U-shaped tube, and the determination means is practical by determining the presence or absence of bubbles in a section of 1/2 or less from the tip to the fixed end of the U-shaped tube. Above, the density of the sample to be measured can be calculated with sufficient accuracy.

The characteristic configuration of the bubble mixing determination method according to the present invention for solving the above problems is
In a vibration type densitometer that measures the density of a sample to be measured housed in a sample cell, it is a bubble mixing determination method for determining the inclusion of bubbles in the sample cell.
The first excitation step of exciting the sample cell to vibrate with the first driving force,
The first measurement step for measuring the first vibration cycle of the sample cell excited by the first driving force, and the first measurement step.
A second excitation step that excites vibration in the sample cell with a second driving force smaller than the first driving force.
The second measurement step of measuring the second vibration period of the sample cell excited by the second driving force, and the second measurement step.
The present invention includes a determination step of determining the presence or absence of bubbles in the sample cell based on the difference between the first vibration cycle and the second vibration cycle.

According to the bubble mixing determination method of this configuration, the first excitation step of exciting the sample cell with vibration by the first driving force and the first measurement of measuring the first vibration cycle of the sample cell excited by the first driving force. A step, a second excitation step in which the sample cell is excited by a second driving force smaller than the first driving force, and a second measurement step in which the second vibration cycle of the sample cell excited by the second driving force is measured. By including a determination step of determining the presence or absence of bubbles in the sample cell based on the difference between the first vibration cycle and the second vibration cycle, the sample cell is measured to confirm the discharge of bubbles. It is not necessary to repeat the introduction of the sample and the measurement of the vibration cycle, and it is possible to determine the presence or absence of bubbles while the sample to be measured is contained in the sample cell. Therefore, in the bubble mixing determination method of the present configuration, the presence or absence of bubbles can be determined in a short time without causing the temperature change of the sample cell a plurality of times due to the repeated introduction of the sample to be measured. As a result, it is possible to shorten the time from the introduction of the sample to be measured to the measurement of the density while preventing the occurrence of an error due to the mixing of bubbles.

FIG. 1 is a block diagram of a vibration type densitometer according to the present invention. FIG. 2 is a diagram showing the measurement result of the vibration cycle in the measuring means. FIG. 3 is a diagram schematically showing the positions of bubbles in the sample cell. FIG. 4 is a diagram showing a measurement result of a vibration cycle in a sample cell in which bubbles are not mixed in a state where there is a change in temperature after the introduction of the sample to be measured.

Hereinafter, the vibration type densitometer of the present invention and the bubble detection method in the vibration type densitometer will be described. However, the present invention is not intended to be limited to the configurations described in the embodiments and drawings described below.

<Vibration type density meter>
FIG. 1 is a block diagram of a vibration type densitometer 1 according to the present invention. The vibration type densitometer 1 vibrates a sample cell 10 containing a liquid sample to be measured, and calculates the density of the sample to be measured from the measuring unit 100 for measuring the vibration cycle and the measured vibration cycle. It is provided with a calculation unit 200.

<Measurement unit>
The measuring unit 100 includes a sample cell 10, an exciting means 20, and a measuring means 30 housed in a case 52 made of a heat insulating material or the like.

The sample cell 10 is a U-shaped glass tube. A thin plate-shaped permanent magnet 11 is fixed to the tip of the sample cell 10 (the curved tube portion of the glass tube) 10a with an adhesive or the like. The fixed ends (both tube mouths of the glass tube) 10b of the sample cell 10 are fixed by the holder 51, and the holder 51 is fixed to the case 52. One tube port of the sample cell 10 is connected to a sampling tube for introducing the sample to be measured via the holder 51, and the other tube port is connected to a drainage tube for discharging the sample to be measured through the holder 51. It is connected. A resin tube or the like can be used for the sampling tube and the drainage tube, and for introduction and drainage of the sample to be measured into the sample cell 10, for example, a pump (not shown) such as a verista pump is connected to the drainage tube. However, it can be carried out by sucking with this pump. In addition, the sampling tube can also be connected to an automatic sampler in order to continuously and automatically measure many samples to be measured.

A temperature sensor 40 such as a thermistor is arranged near the tip 10a of the sample cell 10. The temperature of the sample cell 10 is set to a predetermined reference temperature by a constant temperature block 53 made of a metal such as aluminum provided with a thermoelectric element such as a Pelche element (not shown) based on the temperature measured by the temperature sensor 40. The feedback is controlled so as to be.

The wall thickness of the glass tube constituting the sample cell 10 is preferably 0.2 mm or less. If the wall thickness of the glass tube is 0.2 mm or less, the thermal conductivity of the sample cell 10 is excellent. Therefore, even when a sample to be measured having a temperature different from the reference temperature is introduced, the sample to be measured The time from introduction to the sample cell 10 reaching the reference temperature is shortened, and the density can be measured in a short time. When the wall thickness of the glass tube exceeds 0.2 mm, the thermal conductivity of the glass tube decreases, and the time from the introduction of the sample to be measured until the sample cell 10 reaches the reference temperature becomes long, so that the density can be measured. It may take a relatively long time. The length L from the tip 10a to the fixed end 10b of the sample cell 10 is preferably 60 to 90 mm. When the length L is within the above range, the vibration cycle in the state where the sample to be measured is housed becomes appropriate, and the accuracy of determining the mixing of bubbles can be improved. If the length L deviates from the above range, the vibration cycle in the state where the sample to be measured is housed may be excessively shortened or lengthened, and the determination accuracy of air bubble contamination may be deteriorated. .. Further, since the vibration type densitometer 1 is used for measuring the density of a sample to be measured in a smaller amount than that of a floating hydrometer or the like, the volume of the sample cell 10 is preferably 1 mL or less.

The exciting means 20 is a drive coil arranged at a position facing the permanent magnet 11. The exciting means 20 excites vibration in the sample cell 10 by causing the permanent magnet 11 to act on a magnetic field change caused by a drive current having a predetermined frequency flowing through the drive coil. The vibration of the sample cell 10 is detected by the measuring means 30 described later, and a drive current synchronized with the vibration cycle of the sample cell 10 is passed through the drive coil based on the detection signal. As a result, the sample cell 10 resonates with the frequency of the drive current flowing through the drive coil and vibrates in the natural vibration cycle. The driving force of the exciting means 20 is changed by controlling the voltage applied to the drive coil or the current flowing through the drive coil by the drive control means 80 described later.

The measuring means 30 includes an LED 31 and a light receiving element 32. The LED 31 and the light receiving element 32 are arranged so as to sandwich the curved tube portion of the U-shaped glass tube constituting the sample cell 10 in the stretching direction. When the sample cell 10 vibrates, the intensity of the light emitted from the LED 31 and transmitted through the sample cell 10 changes according to the vibration cycle. The vibration cycle of the sample cell 10 is measured based on the detection signal that the light receiving element 32 that continuously receives the transmitted light detects the fluctuation of the transmitted light. The measuring means 30 is not limited to the optical measurement, and may measure the vibration cycle of the sample cell 10 by another method. For example, the measuring means 30 may be configured by a detection coil arranged at a position facing the permanent magnet 11 fixed to the tip 10a of the sample cell 10. By detecting the change in the magnetic field caused by the movement of the permanent magnet 11 due to the vibration of the sample cell 10 with this detection coil, the vibration cycle of the sample cell 10 can be measured from the detection signal.

<Calculation unit>
The arithmetic unit 200 is configured to realize a function of controlling the operation of the vibration type densitometer 1 by reading and executing a program recorded in the memory in a computer having a CPU, a memory, a storage, and the like. It can be configured as an integrated circuit that performs some or all of its functions. The calculation unit 200 determines, in addition to the frequency detection means 60 and the calculation means 70, which are means for realizing the density calculation in the conventional vibration type densitometer, the drive control means 80 for driving the excitation means 20, and the presence or absence of bubbles. The determination means 90 is provided. The arithmetic unit 200 further controls the operation of the Pelche element of the constant temperature block 53.

The frequency detecting means 60 calculates the vibration cycle of the sample cell 10 from the detection signal output by the light receiving element 32 of the measuring means 30 with reference to the clock signal from the crystal oscillator (not shown). The frequency detection means 60 outputs the calculated vibration cycle of the sample cell 10 to the calculation means 70 and the determination means 90.

The calculation means 70 calculates the density of the sample to be measured by the above equation (1) using the vibration cycle input from the frequency detection means 60. The density of the sample to be measured calculated by the calculation means 70 is used for display on a display unit (not shown) or for recording in a storage. After completing the calculation of the density of the sample to be measured by the calculation means 70, the calculation unit 200 notifies the pump connected to the drainage tube, the automatic sampler connected to the sampling tube, and the like of the completion of the measurement. As a result, the drainage of the sample to be measured in the sample cell 10 and the introduction of a new sample to be measured into the sample cell 10 are executed.

The drive control means 80 and the determination means 90 have a configuration peculiar to the present invention. In the present invention, the mixing of air bubbles into the sample cell 10 is determined by the operation of the drive control means 80 and the determination means 90.

The drive control means 80 has a function of causing the excitation means 20 to change the driving force that excites the vibration in the sample cell 10. Since the driving force for the exciting means 20 to vibrate the sample cell 10 is proportional to the magnitude of the magnetic field change caused by the driving current flowing through the exciting means 20, the drive control means 80 applies a voltage or a drive to the drive coil. The driving force of the exciting means 20 can be controlled by setting the current flowing through the coil by a digital-to-analog conversion circuit (hereinafter, referred to as “D / A converter”) or the like. The amplitude of the vibration generated in the sample cell 10 also changes in proportion to the magnitude of this voltage or current. The drive control means 80 drives the excitation means 20 with the first driving force during normal operation for measuring the density of the sample to be measured by such control by voltage or current, and determines the mixing of bubbles. Occasionally, the exciting means 20 is temporarily driven by the second driving force from the first driving force. The second driving force is preferably 1/5 to 1/2 times the first driving force. If the second driving force is within the above range, the change in the vibration cycle will be significantly different between when bubbles do not exist in the sample cell 10 and when bubbles exist, and the presence or absence of bubbles is accurate. Can be determined. When the second driving force is less than 1/5 times the first driving force, or when the second driving force exceeds 1/2 times the first driving force, when there are no bubbles in the sample cell 10. The change in the vibration cycle is similar to that when bubbles are present, and there is a possibility that the presence or absence of bubbles cannot be accurately determined.

The determination means 90 includes a vibration cycle (hereinafter referred to as “first vibration cycle”) measured by the measuring means 30 in the sample cell 10 excited by the exciting means 20 driven by the first driving force, and a second vibration cycle. In the sample cell 10 excited by the exciting means 20 driven by the driving force, the vibration cycle measured by the measuring means 30 (hereinafter referred to as "second vibration cycle") is acquired, and the first vibration cycle and the first vibration cycle are obtained. (Ii) The presence or absence of air bubbles in the sample cell 10 is determined based on the absolute value of the difference from the vibration cycle (hereinafter referred to as "vibration cycle difference"). Specifically, the determination means 90 detects the presence of bubbles when the vibration cycle difference between the first vibration cycle and the second vibration cycle is 1.5 × 10 ⁻² μsec or more. Here, the first vibration cycle is preferably a vibration cycle measured by the measuring means 30 immediately before the driving force of the exciting means 20 is changed from the first driving force to the second driving force, and is the second vibration cycle. Is preferably the vibration cycle measured by the measuring means 30 at any time between 8 and 10 seconds after the driving force of the exciting means 20 is changed to the second driving force.

<Foam mixing judgment operation>
FIG. 2 is a diagram showing the measurement result of the vibration cycle in the measuring means 30. FIG. 3 is a diagram schematically showing the positions of bubbles in the sample cell 10. The measurement result shown in FIG. 2A shows the vibration cycle measured in the sample cell 10 containing no air bubbles while the temperature of the sample cell 10 is stable at 20 ° C. using water as the sample to be measured. be. In the measurement result shown in FIG. 2B, water is used as the sample to be measured, and bubbles are mixed in the position of the tip 10a (position A in FIG. 3) in a state where the temperature of the sample cell 10 is stable at 20 ° C. The vibration cycle is measured in the sample cell 10 in the sample cell. In FIGS. 2 (a) and 2 (b), the vibration cycle is measured at a cycle of 1.75 seconds.

In the measurement of the vibration cycle in the sample cell 10 in which bubbles are not mixed as shown in FIG. 2A, the drive control means 80 drives the excitation means 20 with the first driving force until the time t0, and then starts from the time t0. It is driven by the second driving force in the period up to t1 after 8.75 seconds, and is driven by the first driving force again after the time t1. At this time, D so that the current flowing through the drive coil of the exciting means 20 when driven by the second driving force is 1/4 times the current flowing through the driving coil of the exciting means 20 when driven by the first driving force. By setting the output of the / A converter, the second driving force was controlled to 1/4 times the first driving force. Due to such control, in the sample cell 10 in which bubbles are not mixed, the vibration cycle becomes approximately constant until the time t0 when the exciting means 20 is driven by the first driving force, and the driving force of the exciting means 20 becomes the second driving force at the time t0. When the driving force is reduced from the first driving force to the second driving force, the vibration cycle is also temporarily reduced, and the driving force is reduced to about 5 measurement cycles (8.75 seconds) at the time t0 immediately before the driving force is changed. It recovers to a value close to the vibration cycle. When the driving force of the exciting means 20 is increased from the second driving force to the first driving force at time t1, the vibration cycle also temporarily increases, and the increase in the driving force is performed in about 5 measurement cycles (8.75 seconds). It recovers to a value close to the vibration cycle at time t0 again. Due to such a fluctuation pattern of the vibration cycle, in this measurement, the first vibration cycle measured at time t0 immediately before the driving force of the exciting means 20 is changed from the first driving force to the second driving force is used. The vibration cycle difference d1 from the second vibration cycle measured at time t1 8.75 seconds after the driving force of the exciting means 20 is changed to the second driving force is 3.7 × 10 ^-3 μsec. It becomes a small one. As described above, when the vibration cycle difference d1 is less than the threshold value of 1.5 × 10 ⁻² μsec for determining the presence of air bubbles in the sample cell 10, the determination means 90 has air bubbles mixed in the sample cell 10. It can be determined that there is no such thing.

On the other hand, in the measurement of the vibration cycle in the sample cell 10 in which the bubbles are mixed as shown in FIG. 2 (b), the drive control means 80 sets the exciting means 20 at time t0 as in the case of FIG. 2 (a). After being driven by the first driving force, it is driven by the second driving force in the period from time t0 to time t1 8.75 seconds later, and after time t1, it is driven by the first driving force again. By such control, in the sample cell 10 in which bubbles are mixed, when the driving force of the exciting means 20 is reduced from the first driving force to the second driving force at time t0, the sample cell 10 in which bubbles are not mixed is introduced. On the contrary, the vibration cycle temporarily increases. Further, in the sample cell 10 containing no air bubbles, the value recovered to a value close to the vibration cycle at time t0 immediately before the change of the driving force in about 5 measurement cycles (8.75 seconds) after the change of the driving force. In the sample cell 10 in which bubbles are mixed, the vibration cycle continuously increases from the change of the driving force to the time when about 5 measurement cycles (8.75 seconds) have elapsed. Due to such a fluctuation pattern of the vibration cycle, in this measurement, the first vibration cycle measured at time t0 immediately before the driving force of the exciting means 20 is changed from the first driving force to the second driving force is used. The vibration cycle difference d2 from the second vibration cycle measured at time t1 8.75 seconds after the driving force of the exciting means 20 is changed to the second driving force is 2.6 × 10 ^-1 μsec. It becomes a big one. As described above, when the vibration cycle difference d2 becomes the threshold value of 1.5 × 10 ⁻² μsec or more for determining the presence of bubbles in the sample cell 10, the determination means 90 has the bubbles mixed in the sample cell 10. It can be determined that there is.

<Measurement temperature>
The effect of the temperature of the sample cell 10 on the vibration cycle difference was examined. FIG. 4 is a diagram showing the measurement result of the vibration cycle in the sample cell 10 in which bubbles are not mixed in a state where the temperature changes after the introduction of the sample to be measured. In the measurement of the vibration cycle shown in FIG. 4, water is used as the sample to be measured, and the calculation unit 200 controls the Pelche element of the constant temperature block 53 so as to maintain the temperature of the sample cell 10 at the reference temperature of 20.0 ° C. In this state, the sample to be measured at 21 ° C. is introduced into the sample cell 10. The drive control means 80 normally drives the excitation means 20 with the first driving force, but there are five periods from the introduction of the sample to be measured until the temperature of the sample cell 10 reaches the reference temperature of 20.0 ° C. The exciting means 20 was driven by the second driving force for 8.75 seconds each. At this time, D so that the current flowing through the drive coil of the exciting means 20 when driven by the second driving force is 1/4 times the current flowing through the driving coil of the exciting means 20 when driven by the first driving force. By setting the output of the / A converter, the second driving force was controlled to 1/4 times the first driving force.

When the exciting means 20 is driven by the second driving force when the temperature of the sample cell 10 is less than 20.1 ° C., the first vibration measured immediately before the change from the first driving force to the second driving force is performed. The vibration cycle difference d13 between the cycle and the second vibration cycle measured 8.75 seconds after the driving force of the exciting means 20 is changed to the second driving force becomes 6.3 × 10 ^-3 μsec, and the vibration The cycle difference d14 is 0 μsec, and the vibration cycle difference d15 is 3.7 × 10 ^-3 μsec. These vibration cycle differences are less than the threshold value of 1.5 × 10 ⁻² μsec for determining the presence of bubbles in the sample cell 10, and it can be determined that no bubbles are mixed. As described above, in the vibration type densitometer 1 of the present invention, the temperature of the sample cell 10 when determining the mixing of bubbles into the sample cell 10 is preferably less than 0.1 ° C. from the reference temperature. ..

On the other hand, when the exciting means 20 is driven by the second driving force when the temperature of the sample cell 10 exceeds 20.1 ° C., the first measured immediately before the change from the first driving force to the second driving force. The vibration cycle difference d11 between the vibration cycle and the second vibration cycle measured 8.75 seconds after the driving force of the exciting means 20 is changed to the second driving force is 8.4 × ^10-2 μsec. The vibration cycle difference d12 is 3.3 × 10 ⁻² μsec. As described above, when the temperature of the sample cell 10 is higher than the reference temperature by more than 0.1 ° C., the vibration cycle of the first vibration cycle and the second driving force is generated even if bubbles are not mixed in the sample cell 10. The difference is a threshold value of 1.5 × 10 ⁻² μsec or more for determining the presence of bubbles in the sample cell 10. Therefore, in the vibration type densitometer 1 of the present invention, when the difference between the temperature of the sample cell 10 and the reference temperature is 0.1 ° C. or more when the determination of the inclusion of air bubbles in the sample cell 10 is executed, the sample cell is used. It is preferable to set the threshold value for determining the presence of bubbles in No. 10 to be 1.5 × 10 ⁻² μsec larger than the increase value of the vibration cycle assumed by the temperature change.

<Position of bubbles in sample cell>
The influence of the position of the bubble in the sample cell 10 on the vibration cycle difference was examined. Using water as the sample to be measured, the temperature of the sample cell 10 is stable at 20 ° C. in the sample cell 10 in a state where bubbles are present at each of the positions A to E shown in FIG. 3 and in a state where no bubbles are present. Therefore, the exciting means 20 is driven by the first driving force, then driven by the second driving force for 8.75 seconds, and then driven by the first driving force again, whereby the first driving force is driven to the second driving force. Measure the vibration cycle difference between the first vibration cycle measured immediately before the change to and the second vibration cycle measured 8.75 seconds after the driving force of the exciting means 20 is changed to the second driving force. bottom. At this time, D so that the current flowing through the drive coil of the exciting means 20 when driven by the second driving force is 1/4 times the current flowing through the driving coil of the exciting means 20 when driven by the first driving force. By setting the output of the / A converter, the second driving force was controlled to 1/4 times the first driving force. Further, the density was calculated by the calculation means 70 in a state where bubbles exist at each position of A to E shown in FIG. 3 and in a state where bubbles do not exist.

As shown in Table 1, when bubbles are present at positions A, B, or C in a section of 1/2 or less from the tip 10a to the fixed end 10b of the sample cell 10, the density calculated by the calculation means 70 is calculated. Compared with the density calculated by the calculation means 70 when no bubbles are mixed in the sample cell 10, the difference is 2.0 × 10 ^-2 g / cm ³ at the maximum, and an error of 2.0% is obtained. It is happening. When bubbles are present at positions A, B, or C, the vibration cycle difference between the first vibration cycle and the second vibration cycle is 2.5 × 10 ^-1 μsec or more. In this way, when bubbles are present at any of the positions A, B, or C, the vibration cycle difference becomes larger than the threshold value of 1.5 × 10 ⁻² μsec for determining the presence of bubbles in the sample cell 10. .. Therefore, the determination means 90 can detect the presence of bubbles in the sample cell 10 when bubbles are present in a section of 1/2 or less from the tip 10a to the fixed end 10b of the sample cell 10. The density calculated by the calculation means 70 can be treated as if an error has occurred due to the presence of bubbles.

On the other hand, when bubbles are present at positions D and E in a section of 1/2 or less from the fixed end 10b to the tip 10a of the sample cell 10, the vibration cycle difference between the first vibration cycle and the second vibration cycle is 3. It will be 3 × 10 ^-3 μsec or less. Therefore, the determination means 90 cannot detect the presence of bubbles in the sample cell 10 based on the threshold value of 1.5 × 10 ⁻² μsec for detecting the presence of bubbles in the sample cell 10. However, when bubbles are present at positions D or E in the sample cell 10, the density calculated by the calculation means 70 is compared with the density calculated by the calculation means 70 when no bubbles are mixed in the sample cell 10. The difference is 1.4 × 10 ^-3 g / cm ³ or less, and the error is 0.14% or less. Therefore, even if bubbles are present at positions D or E in the sample cell 10, the density calculated by the calculation means 70 can be treated as having sufficient accuracy for practical use regardless of the presence or absence of the bubbles. ..

<Viscosity of the sample to be measured>
The effect of the viscosity of the sample to be measured on the vibration cycle difference was investigated. A viscosity standard solution JS50 having a density of 0.85 g / cm ³ and a viscosity of 42 mPa · s, a viscosity standard solution JS200 having a density of 0.86 g / cm ³ and a viscosity of 172 mPa · s, or a density of 0. Using the viscosity standard solution JS500 having a viscosity of .87 g / cm ³ and a viscosity of 436 mPa · s as the sample to be measured, a state in which bubbles are present at each positions A to E shown in FIG. 3 and bubbles in the sample cell 10. After the temperature of the sample cell 10 stabilizes at 20 ° C. in the absence of, the exciting means 20 is driven by the first driving force, then driven by the second driving force for 8.75 seconds, and then again. By driving with one driving force, the first vibration cycle measured immediately before the change from the first driving force to the second driving force and after the driving force of the exciting means 20 is changed to the second driving force 8 The vibration cycle difference from the second vibration cycle measured after .75 seconds was measured. At this time, D so that the current flowing through the drive coil of the exciting means 20 when driven by the second driving force is 1/4 times the current flowing through the driving coil of the exciting means 20 when driven by the first driving force. By setting the output of the / A converter, the second driving force was controlled to 1/4 times the first driving force. Further, the density was calculated by the calculation means 70 in a state where bubbles exist at each position of A to E shown in FIG. 3 and in a state where bubbles do not exist. Table 2 shows the measurement results when the viscosity standard solution JS50 was used as the sample to be measured, Table 3 shows the measurement results when the viscosity standard solution JS200 was used as the sample to be measured, and Table 4 shows the measurement results when the viscosity standard solution JS200 was used as the sample to be measured. The measurement result when the viscosity standard solution JS500 was used as a sample is shown.

As shown in Table 2, when the viscosity standard solution JS50 having a viscosity of 42 mPa · s is used as the sample to be measured, the positions A and B of a section of 1/2 or less from the tip 10a to the fixed end 10b of the sample cell 10 Or, when bubbles are present in C, the density calculated by the calculation means 70 has a maximum difference of 4 as compared with the density calculated by the calculation means 70 when no bubbles are mixed in the sample cell 10. It is 7.7 × 10 ^-3 g / cm ³ , and there is an error of 0.6%. When bubbles are present at positions A, B, or C, the vibration cycle difference between the first vibration cycle and the second vibration cycle is 4.8 × ^10-2 μsec or more. As described above, when the viscosity standard solution JS50 is used as the sample to be measured, the vibration cycle difference is the threshold value for determining the presence of bubbles in the sample cell 10 regardless of the presence of bubbles at any of the positions A, B, or C. It is larger than 1.5 × 10 ^-2 μsec. Therefore, even when the determination means 90 uses the viscosity standard solution JS50 having a viscosity of 42 mPa · s as the sample to be measured, bubbles are generated in a section of 1/2 or less from the tip 10a to the fixed end 10b of the sample cell 10. If present, it is possible to detect the presence of bubbles in the sample cell 10, and the density calculated by the calculation means 70 can be treated as if an error has occurred due to the presence of bubbles.

As shown in Table 3, when the viscosity standard solution JS200 having a viscosity of 172 mPa · s is used as the sample to be measured, if bubbles exist at the position B of the tip 10a of the sample cell 10, the density calculated by the calculation means 70. Compared with the density calculated by the calculation means 70 when no air bubbles are mixed in the sample cell 10, the difference is 4.0 × 10 ^-3 g / cm ³ , and an error of 0.5% is obtained. It is happening. When a bubble is present at the position B, the vibration cycle difference between the first vibration cycle and the second vibration cycle is 3.5 × ^10-2 μsec. As described above, when the viscosity standard solution JS200 is used, if bubbles are present at the position B, the vibration cycle difference becomes larger than the threshold value of 1.5 × 10 ⁻² μsec for determining the presence of bubbles in the sample cell 10. Therefore, when the determination means 90 uses the viscosity standard solution JS200 having a viscosity of 172 mPa · s as the sample to be measured, if bubbles exist in the vicinity of the tip 10a of the sample cell 10, bubbles exist in the sample cell 10. It is possible to detect that the density is high, and the density calculated by the calculation means 70 can be treated as if an error has occurred due to the presence of bubbles.

On the other hand, when bubbles are present at positions A, C to E, the vibration cycle difference between the first vibration cycle and the second vibration cycle is 8.0 × 10 ^-3 μsec or less. Therefore, when the viscosity standard solution JS200 having a viscosity of 172 mPa · s is used as the sample to be measured, the determination means 90 is based on the threshold value of 1.5 × 10 ⁻² μsec for detecting the presence of bubbles in the sample cell 10. , It is not possible to detect the presence of air bubbles in the sample cell 10. However, when the viscosity standard solution JS200 having a viscosity of 172 mPa · s is used as the sample to be measured, if bubbles are present at positions A, C to E in the sample cell 10, the density calculated by the calculation means 70 is the sample cell. Compared with the density calculated by the calculation means 70 when no air bubbles are mixed in 10, the difference is 1.4 × 10 ^-3 g / cm ³ or less, and the error remains 0.17% or less. .. Therefore, when a viscosity standard solution JS200 having a viscosity of 172 mPa · s is used as the sample to be measured, even if bubbles are present at positions A, C to E in the sample cell 10, the calculation means is used regardless of the presence or absence of the bubbles. The density calculated in 70 can be treated as having sufficient accuracy for practical use.

As shown in Table 4, when the viscosity standard solution JS500 having a viscosity of 436 mPa · s is used as the sample to be measured, the density calculated by the calculation means 70 when air bubbles are present at the position B of the tip 10a of the sample cell 10. Compared with the density calculated by the calculation means 70 when no air bubbles are mixed in the sample cell 10, the difference is 2.6 × 10 ^-3 g / cm ³ , which is a certain amount of 0.3%. There is an error. However, when the viscosity standard solution JS500 having a viscosity of 436 mPa · s is used as the sample to be measured, the vibration cycle difference between the first vibration cycle and the second vibration cycle regardless of the presence of bubbles at any of the positions A to E. Is 6.3 × 10 ^-3 μsec or less, which is extremely close to the vibration cycle difference of 3.0 × 10 ^-3 μsec when there are no bubbles in the sample cell 10, and is based on the vibration cycle difference. It is difficult to determine the presence or absence of air bubbles in the sample cell 10.

From the above examination, when the influence of the viscosity of the sample to be measured on the vibration cycle difference is taken into consideration, the density calculated by the calculation means 70 due to the mixing of air bubbles in the sample cell 10 in the vibration type densitometer 1 of the present invention is obtained. In order to properly detect bubbles in the sample cell 10 when an error occurs, the viscosity of the sample to be measured is preferably 200 mPa · s or less.

As described above, the vibration type densitometer 1 according to the present invention has the first vibration cycle of the sample cell 10 measured by the measuring means 30 when the exciting means 20 is driven by the first driving force, and the exciting means 20. The presence or absence of air bubbles in the sample cell 10 can be determined based on the vibration cycle difference from the second vibration cycle of the sample cell 10 measured by the measuring means 30 after the driving force of the sample cell 10 is changed to the second driving force. Therefore, it is not necessary to repeat the introduction of the sample to be measured into the sample cell 10 and the measurement of the vibration cycle in order to confirm the emission of bubbles prior to the measurement of the density of the sample to be measured, and the sample to be measured is housed in the sample cell 10. It is possible to determine the presence or absence of air bubbles in the state of being in the state. Therefore, the presence or absence of air bubbles can be determined in a short time without causing the temperature change of the sample cell 10 a plurality of times due to the repeated introduction of the sample to be measured. As a result, it is possible to shorten the time from the introduction of the sample to be measured to the measurement of the density while preventing the occurrence of an error due to the mixing of bubbles.

The vibration type densitometer of the present invention can be used for density measurement of various samples such as concentration control of soft drinks.

1 Vibration type densitometer 10 Sample cell 10a Tip 10b Fixed end 20 Excitation means 30 Measuring means 80 Drive control means 90 Judgment means

Claims (7)

It is a vibration type densitometer that measures the density of the sample to be measured contained in the sample cell.
Excitation means for exciting vibration in the sample cell,
A measuring means for measuring the vibration cycle of the excited sample cell, and
A drive control means for driving the excitation means with a first driving force and a second driving force smaller than the first driving force.
Presence or absence of bubbles in the sample cell based on the difference between the first vibration cycle of the sample cell excited by the first driving force and the second vibration cycle of the sample cell excited by the second driving force. A vibration type densitometer provided with a determination means for determining. The vibration type densitometer according to claim 1, wherein the second driving force is 1/5 to 1/2 times the driving force of the first driving force. The first vibration cycle is a vibration cycle measured by the measuring means immediately before the driving force of the exciting means is changed from the first driving force to the second driving force.
The second vibration cycle is a vibration cycle measured by the measuring means at any time between 8 and 10 seconds after the driving force of the exciting means is changed to the second driving force. 2. The vibration type densitometer according to 2. The determination means is any one of claims 1 to 3 for determining that the bubble is present when the difference between the first vibration cycle and the second vibration cycle is 1.5 × 10 ⁻² μsec or more. The vibration type densitometer described in the section. The vibration type densitometer according to any one of claims 1 to 4, wherein the viscosity of the sample to be measured is 200 mPa · s or less. The sample cell is a U-shaped tube and has a U-shaped tube.
The vibration type densitometer according to any one of claims 1 to 5, wherein the determination means determines the presence or absence of the bubbles in a section of 1/2 or less from the tip of the U-shaped tube to the fixed end. In a vibration type densitometer that measures the density of a sample to be measured housed in a sample cell, it is a bubble mixing determination method for determining the inclusion of bubbles in the sample cell.
The first excitation step of exciting the sample cell to vibrate with the first driving force,
The first measurement step for measuring the first vibration cycle of the sample cell excited by the first driving force, and the first measurement step.
A second excitation step that excites vibration in the sample cell with a second driving force smaller than the first driving force.
The second measurement step of measuring the second vibration period of the sample cell excited by the second driving force, and the second measurement step.
A bubble mixing determination method including a determination step of determining the presence or absence of bubbles in the sample cell based on the difference between the first vibration cycle and the second vibration cycle.

Images