JP5355278B2 - Calibration parameter determination method and density calculation method for vibration type density meter - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for determining the calibration parameter of a vibration type densitometer capable of determining the calibration parameter of the vibration type densitometer at various temperatures without acquiring the enormous data due to two kinds of substances having known densities. <P>SOLUTION: The calibration parameters at various temperatures are calculated from vibration cycles at various temperatures of pure water and air and a fitting function is preliminarily formed on the basis of the relation between the calculated calibration parameters and temperatures. Then, when measurement is started after the cell temperatures and usable optional calibration parameters in the respective measuring steps are selected on a set screen of temperature scanning, the Peltier element of a copper block 12 is controlled so that the temperature detection output of a thermistor 14 may become the set temperatures in the respective measuring steps to measure the inherent vibration cycle of the measuring cell 1. In a case that the calibration parameters are calculated from a fitting formula, the set temperatures are input to the fitting formula to calculate the calibration parameters K<SB>1</SB>and K<SB>2</SB>at a measuring temperature, and the density of a sample to be measured is operated. <P>COPYRIGHT: (C)2011,JPO&amp;INPIT

Description

  The present invention relates to a vibration type density meter, and more particularly, to a method for determining calibration parameters of a measurement cell (vibrator) at different temperatures and a density calculation method.

  The vibration type density meter is a device that vibrates the measurement cell containing the sample to be measured, and calculates and outputs the density of the sample to be measured from the measured natural vibration period. For example, the density of various fluids such as concentration management of soft drinks It is used for measurement.

  This vibration-type density meter has, for example, a glass U-shaped measurement cell, a permanent magnet is fixed to the tip of the measurement cell, and a drive head and a detection unit are built in a position facing the permanent magnet. Is arranged. At the time of density measurement, a sample to be measured is introduced into the measurement cell, and the measurement cell is vibrated by applying a driving current to the driving coil of the measurement head and applying an electromagnetic force to the permanent magnet. The density of the sample to be measured is obtained from the natural vibration period.

The vibration type density meter can be represented by a spring constant k and a mass m as shown in FIG. In this vibration system, when the natural vibration period is T,
T = √ (m / k)
That is,
T ² = m / k
It is.
The mass m is divided into the mass m _glass of the glass tube and the mass m sample of the _sample to be measured.
T ² = (m _sample + m _glass ) / k
Therefore, the mass m _sample of the _{sample to} be measured is
m _sample = k · T ² −m _glass (1)
It becomes.

The above (1) Density [rho _SAMP sample to be measured from the equation, if the capacity of the measuring cell and _{V cell,}
ρ _SAMP = m _sample / V _cell = k · T ² / V _cell -m _glass / V _cell
It becomes. Here, when k / V _cell is K ₁ and −m _glass / V _cell is K ₂ ,
ρ _SAMP = K ₁ · T ² + K ₂ (2)
It can be expressed as

Next, a method for calculating the density of the sample to be measured will be described.
When T _WATER and T _AIR are natural vibration periods of two kinds of substances having a known density, for example, pure water (ρ _WATER ) and air (ρ _AIR ) measured by a measuring cell,
ρ _WATER = K ₁・ T _WATER ²
+ K ₂ (3)
ρ _AIR = K ₁ · T _AIR ² + K ₂ (4)
From the above equations (3) and (4), the calibration parameters K ₁ and K ₂ are
K ₁ = (ρ _WATER −ρ _AIR ) / (T _WATER ² −T _AIR ² ) (5)
K ₂ = −T _AIR ² · (ρ _WATER −ρ _AIR ) / (T _WATER ² −T _AIR ² ) + ρ _AIR (6)
It becomes.
Since the densities ρ _WATER and ρ _AIR at the measured temperatures of pure water and air are known, the calibration parameters K ₁ and K ₂ are calculated from the vibration periods T _WATER and T _AIR measured for pure water and air. The density ρ _SAMP of the sample to be measured can be obtained from the natural vibration period T obtained by measuring the sample to be measured by the above equation (2).

Since the calibration parameters K ₁ and K ₂ calculated as described above are constants determined based on the density and natural vibration period of two specific substances under a certain reference temperature t ₀ , the reference temperature t _When the density of the sample to be measured is calculated based on the natural vibration period obtained by measuring the sample to be measured using a measurement cell having a temperature different from ₀ , an error from the true value occurs.

Therefore, the temperature of the measurement cell is maintained at the reference temperature t ₀ using temperature control means such as a heat insulating material or a thermo module, and the natural vibration period when the temperature of the measurement cell reaches the reference temperature t ₀ is measured. (For example, refer to Patent Document 1).

Japanese Patent Laid-Open No. 6-58862

On the other hand, in industries such as the petroleum industry, density measurement at several measurement temperatures may be required. However, as described above, the calibration parameters K ₁ and K ₂ vary depending on the temperature, so the measurement temperature changes. For example, it is necessary to calculate calibration parameters each time using air and pure water of known density, and a very long restraint time is required for density measurement at different temperatures, including waiting time after temperature change.

For this reason, calibration parameters using two kinds of substances having known densities, for example, pure water (ρ _WATER ) and air (ρ _AIR ), are calculated at various temperatures and stored as tables. By reading the calibration parameters at the measurement temperature, it is possible to calculate the density of the sample to be measured at various temperatures using the above equation (2).
However, in order to prepare calibration parameters at all temperatures, it is necessary to obtain the relationship at theoretically infinite points, and calibration parameters using two kinds of substances having known densities, such as pure water and air, are used. Creating a table is almost impossible.

  The present invention was devised to solve the above problems, and can determine calibration parameters at various temperatures without acquiring enormous data of two kinds of substances having known densities. An object of the present invention is to provide a method for determining a calibration parameter of a vibration type densitometer and a method for calculating a density using the determined calibration parameter.

A calibration parameter determining method for a vibration type densitometer according to a first aspect of the present invention is a calibration parameter determining method for a vibration type densitometer that calculates the density of the sample to be measured from the vibration period of the measurement cell containing the sample to be measured and the calibration parameter. The vibration periods of density 0 and 1 at various temperatures are calculated from the vibration periods of two substances of known density at various temperatures, and the vibration periods and temperatures of density 0 and density 1 at the various temperatures are calculated. A fitting function is created based on the relationship, and vibration cycles of density 0 and 1 at a predetermined temperature are obtained by the created fitting function, and calibration parameters at the predetermined temperature are calculated from the vibration cycle.

According to a second aspect of the present invention, there is provided a vibration density meter density calculation method for calculating a density of a sample to be measured from a vibration period of a measurement cell containing the sample to be measured and a calibration parameter. The calibration parameter at the measurement temperature of the sample to be measured is determined by the calibration parameter determination method according to the first aspect of the present invention, and based on the calibration parameter and the obtained vibration cycle of the measurement cell, The density is calculated.

When a fitting function indicating the relationship between calibration parameters and temperature is created using vibration cycles of air and pure water at multiple temperatures, the fitting function includes temperature changes in the density of air and pure water, and temperature changes in the measurement cell. In particular, since the temperature change of the pure water density has a peak at 4 ° C, the content becomes complicated, fitting is difficult, and in order to improve accuracy, the number of data used to create the relational expression is greatly increased. Need to increase. However, according to the calibration parameter determining method of the vibration type density meter of the invention according to claim 1 , the vibration periods of density 0 and 1 at various temperatures are calculated from the vibration periods at various temperatures of two substances of known density. Then, a fitting function indicating the relationship between the calculated vibration frequency of density 0 and density 1 and temperature is created, and vibration cycles of density 0 and 1 at a predetermined temperature are obtained by the created fitting function, and from this vibration cycle at a predetermined temperature. Thus, the influence of density temperature change can be eliminated, and at least the number of data necessary for creating the fitting function can be reduced.

According to the density calculation method of the vibration type densitometer of the invention according to claim 2 , the calibration parameter at the measurement temperature of the sample to be measured is determined by the calibration parameter determination method of the invention according to claim 1 , Since the density of the sample to be measured is calculated based on the calibration parameters and the acquired vibration period of the measurement cell, the density when changing to any cell temperature without performing calibration with air or pure water at various temperatures Can be measured. For this reason, when the density measurement of the sample to be measured is continuously performed at a plurality of temperatures different from those at the time of calibration with air and pure water, the restraint time required for the measurement can be greatly shortened. It is also possible to perform density calculation at an arbitrary temperature with a density meter having no general temperature control function.

It is a figure which shows the structure of the sensor part of the vibration type density meter of this invention. It is a conceptual diagram of the vibration type density meter which attached the sensor part of FIG. It is an example of the setting screen of a temperature scan. It is the graph which plotted the square of the natural vibration period which measured air and pure water at various temperatures with respect to temperature. It is the graph which plotted the square of the natural vibration period in various temperatures in case of density 0 and density 1 against temperature. It is the figure which modeled the vibration system of the vibration type density meter.

  1A and 1B are diagrams showing the structure of the sensor unit of the vibration type densitometer. FIG. 1A is a side view of the sensor unit, and FIG. 2B is a top view of the sensor unit. This sensor part is composed of a measurement cell 1, a permanent magnet 2, holders 3a and 3b, a temperature sensor 4 and a glass outer cylinder 5.

  The measurement cell 1 is a thin U-shaped tube made of glass having a wall thickness of about 0.2 mm, and a thin plate 2 of a permanent magnet is fixed to the tip of the tube with an adhesive. Further, the base end portion of the measurement cell 1 is fixed to holders 3a and 3b, and the holders 3a and 3b are fixed by projections 6 provided on the outer cylinder 5 as shown in FIG. The temperature sensor 4 has a thermistor inserted in the glass tube, and measures the temperature of the sample. This sensor part is sealed after helium is injected into it through the helium inlet 7 after assembly.

  On the other hand, FIG. 2 is a conceptual diagram of the vibration type density meter to which the sensor unit of FIG. 1 is attached. Is controlled so that the temperature of the sample to be measured in the sensor unit, that is, the measurement cell 1 is maintained at the set temperature. In addition, a measurement head 13 incorporating a drive coil and a detection coil is disposed at a position facing the permanent magnet 2 fixed to the tip of the measurement cell 1.

As shown in the figure, a thermistor 14 is disposed in the glass tube of the temperature sensor 4 and measures the temperature near the tip of the measurement cell 1.
On the other hand, one open end of the measurement cell 1 is connected to a sampling tube 15 for introducing a sample to be measured, and the other open end is connected to a drain tube 16 for discharging the sample to be measured after measurement.

  The control device 17 includes a control unit 21, a drive unit 22, a detection unit 23, a display unit 24, and a storage unit 25. The temperature detection output of the thermistor 14 is input to the control unit 21, and the temperature of the thermistor 14 is measured and set. The Peltier element of the copper block 12 is controlled so that the temperature is reached. The drive unit 22 supplies a drive current to the drive coil of the measurement head 13, and the detection unit 23 detects the output of the detection coil of the measurement head 13 to detect the vibration cycle of the measurement cell 1. Furthermore, the control unit 21 displays the measurement setting screen and the density measurement value on the display unit 24, and stores the measurement condition set by the user, the detected vibration cycle, and the like in the storage unit 25. In addition, the storage unit 25 is provided with a table that stores density data of air and pure water at various temperatures.

Next, a calibration parameter calculation method used for calculating the density of the sample to be measured at various temperatures without performing calibration using pure water and air at the time of measurement will be described.
First, the vibration periods T _WATER and T _AIR of pure water and air at 5 ° C., 20 ° C., 50 ° C., and 70 ° C. are measured with a vibration type _densimeter , and 5 using the above formulas (5) and (6). The calibration parameters K ₁ (t) and K ₂ (t) at ° C., 20 ° C., 50 ° C., and 70 ° C. are set to K ₁ (t) = (ρ _{WATER, t−} ρ _{AIR, t} ) / (T _{WATER, t} ² -T _{AIR, t} ² )
K ₂ (t) = − T _{AIR, t} ² · (ρ _{WATER, t} −ρ _{AIR, t} ) / (T _{WATER, t} ² −T _{AIR, t} ² ) + ρ _{AIR, t}
Ask for. In addition, since the density ρ _{WATER, t 1} , ρ _{AIR, t} of pure water and air at each temperature is known, the vibration periods T _{WATER, t 1} , T _{AIR, t} of pure water and air at each temperature are used. Calibration parameters K ₁ (t) and K ₂ (t) at each temperature can be obtained.

Next, using the calibration parameters K ₁ (t) and K ₂ (t) at 5 ° C., 20 ° C., 50 ° C., and 70 ° C., a relational expression between the calibration parameters and the temperature, that is, the following formula (7) , (8) quadratic fitting functions K _1t and K _2t are created and stored in the storage unit 25 of the control device 17.
K _{1, t} = a ₁ · t ² + b ₁ · t + c ₁ (7)
K _{2, t} = a ₂ · t ² + b ₂ · t + c ₂ (8)
When calculating the density, the calibration parameters K _{1, t 2,} K _{2, and t} at each temperature can be obtained by inputting a predetermined temperature t into the above equations (7) and (8).

Next, the operation when measuring the density of the sample to be measured at a plurality of different temperatures will be described.
When a temperature scan is selected on the function selection screen of the display unit 24 of the control device 17, a temperature scan setting screen is displayed on the display unit 24. FIG. 3 shows an example of a temperature scan setting screen. As shown in FIG. 3, the cell temperature at each measurement step can be input on this setting screen. When the cell temperature at each measurement step is input, the control unit 21 determines a calibration parameter that can be used at the cell temperature and displays it brightly in the “calibration parameter” column.

  That is, parameters that have been calibrated just before using pure water and air (current), parameters that have been calibrated using pure water and air at that temperature in the past (past), and the above fitting equation There are three types of calibration parameters (relational expressions) calculated using, and in the example of FIG. 3, the current calibration parameters can be used at 20 ° C., and calibration has been performed in the past at 30 ° C. and 40 ° C. It shows that the calibration parameters can be used. It should be noted that the date of calibration performed is also displayed brightly in the calibration parameter display field for which calibration has been performed in the past.

  The user can select an arbitrary calibration parameter that can be used from the three types of calibration parameters. In the example of FIG. 3, the current calibration parameter at 20 ° C., the past calibration parameter at 30 ° C., and 40 ° C. And the use of calibration parameters calculated using a fitting equation at 50 ° C. has been selected.

Next, the operation when measuring the sample to be measured after setting the temperature scan as described above on the setting screen of FIG. 3 will be described.
First, the control unit 21 introduces the sample to be measured into the measurement cell 1 through the sampling tube 15, and the Peltier element of the copper block 12 so that the temperature detection output of the thermistor 14 becomes the set temperature of Step 1, 20 ° C. To control. When the temperature detection output of the thermistor 14 reaches 20 ° C., the control unit 21 inputs a drive current from the drive unit 22 to the drive coil of the measurement head 13 to apply an electromagnetic force to the permanent magnet 2, thereby measuring cell 1. To start vibration.

The detection coil of the measurement head 13 detects the vibration at this time, and a detection signal is input to the detection unit 23, and a drive signal synchronized with this vibration cycle is continuously input to the drive coil of the measurement head 13, thereby allowing the measurement cell to 1 is vibrated at a constant period, and the natural vibration period T _{SAMP at 20 ° C.} is measured.
Next, the control unit 21 determines the calibration parameter selected at 20 ° C., and in this case, the current calibration parameters K ₁ (20 ° C.) and K ₂ (20 ° C.) are selected. The density ρ _SAMP of the sample is calculated by the following formula and displayed on the display unit 24.
ρ _SAMP = K ₁ (20 ° C.) × T _{SAMP, 20 ° C.} ² + K ₂ (20 ° C.)

Next, the control unit 21 controls the Peltier element of the copper block 12 so that the temperature detection output of the thermistor 14 becomes the set temperature of step 2, 30 ° C. For example, after a waiting time of 1 hour has elapsed, the natural vibration period T _SAMP of the measurement cell 1 _{and 30 ° C.} are measured in the same manner. Next, the control unit 21 determines the calibration parameter selected at 30 ° C. In this case, since the past calibration parameters K ₁ (30 ° C.) and K ₂ (30 ° C.) are selected, the measurement target The density ρ _SAMP of the sample is calculated by the following formula and displayed on the display unit 24.
ρ _SAMP = K ₁ (30 ° C.) × T _{SAMP, 30 ° C.} ² + K ₂ (30 ° C.)

When the density measurement at 30 ° C. is completed, the control unit 21 next controls the Peltier element of the copper block 12 so that the temperature detection output of the thermistor 14 becomes the set temperature of step 3, 40 ° C. After 1 hour, the natural vibration period T _SAMP of the measurement cell 1 _{and 40 ° C.} are measured. Next, the control unit 21 determines the calibration parameter selected at 40 ° C. In this case, since the “relational expression” is selected, the calibration parameter is calculated from the fitting expression. That is, the control unit 21 inputs 40 ° C. into the fitting equations of the above formulas (7) and (8) read from the storage unit 25, thereby calibrating parameters K1, _{40 ° C} , K2, _{40 ° C} at _{40 ° C.} Is calculated.

And the control part 21 uses said K1, _{40 degreeC} , K2, _{40 degreeC} as a calibration parameter, and uses said _{TSAMP, 40 degreeC} as a vibration period, The density of a to-be-measured sample ρ _SAMP is calculated by the following formula and displayed on the display unit 24.
ρ _SAMP = K _{1 , 40 ° C.} × T _{SAMP, 40 ° C.} ² + K ² _{, 40 ° C.}
Similarly, in step 4, the calibration parameters K ₁ , 50 ° _C. , K ₂ , and 50 ° C. at 50 ° _C. are calculated, and the density ρ _SAMP of the sample to be measured is calculated by the following formula to be displayed on the display unit 24. indicate.
ρ _SAMP = K _{1 , 50 ° C.} × T _{SAMP, 50 ° C.} ² + K ² _{, 50 ° C.}

As described above, the density when changing to any cell temperature can be measured without performing calibration with air or pure water at various temperatures. Can be executed automatically.
That is, normal measurement → temperature change → waiting time (1 hour) → normal measurement → temperature change → waiting time (1 hour) → normal measurement, the density measurement value of the sample with the temperature changed by carrying out the measurement Can be obtained continuously.

  In the above embodiment, the fitting function indicating the relationship between the calibration parameter and the temperature was created, but the fitting function includes the temperature change of the density of air and pure water and the temperature change of the measurement cell. Since the temperature change of 4 has a peak at 4 ° C., the content becomes complicated, the fitting is difficult, and in order to improve accuracy, it is necessary to greatly increase the number of data used for creating the relational expression. For this reason, in this embodiment, vibration cycles of density 0 and 1 at various temperatures are calculated from vibration cycles of pure water and air at various temperatures, and the relationship between the calculated vibration cycles of density 0 and density 1 and temperature. By creating a fitting function indicating the above, the influence of the temperature change of the density is eliminated, and at least the number of data necessary for creating the fitting function is reduced.

Hereinafter, the calculation method of the calibration parameter in the present embodiment will be described.
First, in the same manner as described above, the vibration periods T _WATER and T _AIR of pure water and air at 5 ° C., 20 ° C., 50 ° C., and 70 ° C. are measured with a vibrating _densimeter .
Fig. 4 is a plot of the relationship between the square of the measured vibration frequency of pure water and air and the temperature, where ■ is the pure water (WATER) and ◆ is the vibration cycle when air (AIR) is measured. The curve is a function fitting the relationship between the square of the vibration period and the temperature. This function includes the temperature change of the density of the sample (air, pure water) and the temperature change of the measurement cell. In particular, the temperature change of the pure water density has a peak at 4 ° C, which complicates the contents. , Fitting is difficult. For this reason, calibration parameters K ₁ (t) and K ₂ (t) at each temperature at which the vibration period is measured are calculated, and vibrations at ρ = 0 and ρ = 1 at each temperature are calculated based on the calculated values. By calculating the cycle, the fitting error is reduced.

That is, using the above equations (5) and (6), the calibration parameters K ₁ (t) and K ₂ (t) at 5 ° C., 20 ° C., 50 ° C., and 70 ° C. are expressed as K ₁ (t) = (ρ _{WATER, t-} ρ _{AIR, t} ) / (T _{WATER, t} ² -T _{AIR, t} ² )
K ₂ (t) = − T _{AIR, t} ² · (ρ _{WATER, t} −ρ _{AIR, t} ) / (T _{WATER, t} ² −T _{AIR, t} ² ) + ρ _{AIR, t}
Ask for. In addition, since the density ρ _{WATER, t 1} , ρ _{AIR, t} of pure water and air at each temperature is known, the vibration periods T _{WATER, t 1} , T _{AIR, t} of pure water and air at each temperature are used. Calibration parameters K ₁ (t) and K ₂ (t) at each temperature can be obtained.

Next, the vibration periods T _{ρ = 0, t} , T _{ρ = 1, and t} at 5 ° C., 20 ° C., 50 ° C., and 70 ° C. when _{ρ = 0 and ρ = 1} are obtained using the above equation (2). And
_{Tρ = 0, t} = √ {(ρ−K ₂ (t)) / K ₁ (t)} = √ {−K ₂ (t) / K ₁ (t)}
_{Tρ = 1, t} = √ {(ρ−K ₂ (t)) / K ₁ (t)} = √ {(1−K ₂ (t)) / K ₁ (t)}
Calculated by

FIG. 5 is a graph in which T _{ρ = 0, t} and T _{ρ = 1, and} the square of t is plotted with respect to the temperature t, where ■ is the vibration period of ρ = 1, and ◆ is the vibration period of ρ = 0. It is. From this graph, a relational expression between the square of the vibration period of ρ = 0 and ρ = 1 and the temperature, that is, a quadratic fitting expression of the following expressions (9) and (10) is created and stored in the control device 17. Stored in the unit 25. As can be seen from comparison with the graph of FIG. 4, the graph of FIG. 5 is not affected by the temperature change of the density and is a function having a small error even when approximated by a linear expression, so that the fitting error can be reduced. it can.
T _{ρ = 0, t} ² = a _{ρ = 0} · t ² + b _{ρ = 0} · t + c _{ρ = 0} (9)
T _{ρ = 1, t} ² = a _{ρ = 1} · t ² + b _{ρ = 1} · t + c _{ρ = 1} (10)

When calculating the density, etc., by inputting a predetermined temperature in the above equations (9) and (10), the vibration period when ρ = 0 and ρ = 1 is obtained. ), Ρ = 1 and ρ = 0 are substituted for ρ _WATER and ρ _AIR in (6), and the calibration parameters K _{1, t} , K _{2, and t} at each temperature can be obtained by the following equations. .
_{K 1, t = 1 / (} T ρ = 1, t 2 -T ρ = 0, t 2) ··· (11)
_{K 2, t = -T ρ =} 0, t 2 / (T ρ = 1, t 2 -T ρ = 0, t 2) ··· (12)

Next, the operation in the case of measuring the density of the sample to be measured using a fitting equation of the square of the vibration period of ρ = 0 and ρ = 1 and the temperature will be described.
After the temperature scan setting is set as shown in the setting screen of FIG. 3, when performing measurement in which “relational expression” is selected as the selected calibration parameter, for example, density measurement is performed at 40 ° C. In this case, the control unit 21 controls the Peltier element of the copper block 12 so that the temperature detection output of the thermistor 14 is 40 ° C. For example, after a waiting time of 1 hour has elapsed, the natural vibration period T _SAMP of the measurement cell 1 is measured at _{40 ° C.}

Next, the control unit 21 inputs 40 ° C. into the fitting equations of the above formulas (9) and (10) read from the storage unit 25 so that the vibration period at 40 ° C. when ρ = 0 and ρ = 1. give squared ^{_{T ρ = 0,40 ℃ 2, T}} ρ = 1,40 ℃ 2, this formula (11), input to the (12),
K _{1, 40 ° C.} = 1 / (T _{ρ = 1, 40 ° C.} ²⁻ T _{ρ = 0, 40 ° C.} ² )
^{_{K 2,40 ℃ = -T ρ = 0}} , t 2 / (T ρ = 1,40 ℃ 2 -T ρ = 0,40 ℃ 2)
To calculate calibration parameters K ₁ , _{40 ° C.} , K ₂ and _{40 ° C.} at _{40 ° C.}

And the control part 21 uses said K1, _{40 degreeC} , K2, _{40 degreeC} as a calibration parameter, and uses said _{TSAMP, 40 degreeC} as a vibration period, The density of a to-be-measured sample ρ _SAMP is calculated by the following formula and displayed on the display unit 24.
ρ _SAMP = K _{1 , 40 ° C.} × T _{SAMP, 40 ° C.} ² + K ² _{, 40 ° C.}
As described above, the vibration periods of density 0 and 1 at various temperatures are calculated from the vibration periods of pure water and air at various temperatures, and the fitting indicating the relationship between the calculated vibration periods of density 0 and density 1 and the temperature. By creating the function, it is possible to eliminate the influence of the temperature change of the density, so that the number of data necessary for creating the fitting function can be reduced at least.

  In the above embodiment, the example in which the density of the sample to be measured is measured at a plurality of different temperatures by setting a plurality of measurement temperatures on the setting screen of the temperature scan has been described. The present invention can also be applied when measuring the density of a sample to be measured.

  In the above embodiment, the Peltier element of the copper block is controlled so that the temperature of the thermistor becomes the measurement set temperature. However, the density calculation method of the present invention is a density meter that does not have a general temperature control function, and an arbitrary temperature. The present invention can also be applied to the case where density calculation is performed at, and the case where density calculation at an arbitrary temperature is performed with a density meter having no general temperature control function will be described below. The configuration of the vibration type density meter is the same as that of FIG. 2 except that the heat insulating material 11 and the copper block 12 are not provided in the vibration type density meter of FIG.

At the time of measurement, the natural vibration period T _{SAMP, t} of the measurement cell 1 is obtained, and the temperature t at the time of density measurement is detected from the detection output of the thermistor 14. Assuming that the temperature t at the time of density measurement is 25.02 ° C., the control unit 21 inputs 25.02 ° C. into the fitting equation of the above formulas (7) and (8) read out from the storage unit 25 to obtain 25.02 ° C. The calibration parameters K1, _{25.02 ° C} , K2, and _{25.02 ° C} are calculated, and the density ρ _SAMP of the sample to be measured is calculated by the following formula and displayed on the display unit 24.
ρ _SAMP = K 1, _{25.02 ° C.} × T _{SAMP, 25.02 ° C.} ² + K ² _{, 25.02 ° C.}

On the other hand, when using the fitting function indicating the relationship between the vibration period of density 0 and density 1 and the temperature, the control unit 21 uses the above-described equations (9) and (10) read from the storage unit 25. By inputting 25.02 ° C., the square of the vibration period T _{ρ =} 0, _{25.02 ° C.} ² , T _{ρ = 1, 25.02 ° C.} ² when ρ = 0 and ρ = 1 at _{25.02 ° C.} is obtained. ), (12)
K 1, _{25.02 ° C.} = 1 / (T _ρ = 1, _{25.02 ° C.} ²⁻ T _{ρ = 0, 25.02 ° C.} ² )
K 2, _{25.02 ° C.} = − T _{ρ = 0, t} ² / (T _{ρ = 1, 25.02 ° C.} ² −T _{ρ = 0, 25.02 ° C.} ² )
To calculate calibration parameters K1, _{25.02 ° C} , K2, and _{25.02 ° C} at _{25.02 ° C.}

Then, the control unit 21 uses the above K1, _{25.02 ° C} , K2, _{25.02 ° C} as the calibration parameters, and uses the above T _{SAMP, 25.02 ° C} as the vibration period _{, thereby} the density of the sample to be measured. ρ _SAMP is calculated by the following formula and displayed on the display unit 24.
ρ _SAMP = K 1, _{25.02 ° C.} × T _{SAMP, 25.02 ° C.} ² + K ² _{, 25.02 ° C.}
As described above, it is possible to perform density calculation at an arbitrary temperature even with a density meter having no general temperature control function.

  In the above embodiment, the relationship between the calibration parameter and the temperature and the relationship between the square of the vibration period of ρ = 0 and ρ = 1 and the temperature are fitted by a quadratic function, but pure water, air It is also possible to perform fitting with a polynomial such as a cubic equation or a quartic equation by increasing the number of measurement points of the temperature at which the vibration period is measured.

  Further, in the above embodiment, the vibration type density meter provided with the measurement head including the drive coil and the detection coil arranged to face the permanent magnet attached to the tip of the measurement cell has been described as an example. The vibration type density meter of the present invention can also be applied to other density meters such as the type of vibration density meter detected by the above.

DESCRIPTION OF SYMBOLS 1 Measurement cell 2 Permanent magnet 3a, 3b Holder 4 Temperature sensor 5 Outer cylinder 6 Protrusion 7 Helium inlet 11 Heat insulating material 12 Copper block 13 Measuring head 14 Thermistor 15 Sampling tube 16 Drainage tube 17 Controller 21 Control part 22 Drive part 23 Detection unit 24 Display unit 25 Storage unit

Claims (2)

A calibration parameter determination method for a vibratory densimeter that calculates the density of a sample to be measured from the vibration period and calibration parameters of a measurement cell that contains the sample to be measured,
Calculate vibration cycles of density 0 and 1 at various temperatures from vibration cycles of two substances of known density at various temperatures, and based on the relationship between the calculated vibration cycle of density 0 and density 1 at various temperatures and temperature. A vibration function of the vibration type densitometer is characterized in that a vibration function having a density of 0 or 1 at a predetermined temperature is obtained from the generated fitting function and a calibration parameter at a predetermined temperature is calculated from the vibration period. Calibration parameter determination method. A density calculation method for a vibratory densimeter that calculates the density of the sample to be measured from the vibration period of the measurement cell containing the sample to be measured and the calibration parameter,
The calibration parameter at the measurement temperature of the sample to be measured is determined by the calibration parameter determination method described in claim 1 , and the density of the sample to be measured is calculated based on the calibration parameter and the acquired vibration period of the measurement cell. A density calculation method for a vibratory densimeter, characterized in that

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