JPH0658862A - Temperature compensation for oscillating density meter - Google Patents

Abstract

PURPOSE:To provide a temperature compensation means for oscillation cycle in a oscillating density meter requiring shorter period for density measurement of an object fluid. CONSTITUTION:A oscillating density meter introduces an object fluid 11 into an oscillation cell 12, and then, based on the specific oscillation cycle of the oscillation cell 12, measures density of the object fluid 11 at a specified reference temperature K0. Then, based on the temperature difference DELTAK (=K-K0) between the temperature K of the oscillation cell 12 after introduction of the object fluid 11 and the reference temperature K0 and the specific oscillation cycle TK of the oscillation cell 12 at the current temperature K, specific oscillation cycle T0 at the reference temperature K0 is obtained.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a vibrating densitometer, and more particularly to a temperature correction method for a vibrating densitometer.

[0002]

2. Description of the Related Art A vibrating densitometer is a device for vibrating a vibrating cell containing a fluid to be measured, and calculating and outputting the density of the fluid to be measured from the measured natural vibration period. It is used to measure the density of various fluids.

FIG. 2 is a conceptual view of the essential part of the above-mentioned vibration type densitometer. As shown in FIG. 2, the U-shaped vibrating cell 12 has its base end fixed to the support tube 14, and one opening end of the vibrating cell 12 has an inlet tube 1 for introducing the test fluid 11.
2a, and the other open end is arranged inside the support pipe 14 so as to be connected to a discharge pipe 12b for discharging the measured fluid 11 whose measurement has been completed. A magnet 13 is fixed to the tip of the vibrating cell 12, a head 3 having a drive unit 31 and a detection unit 32 is disposed at a position facing the magnet 13, and a temperature sensor 41 is provided in the vicinity of the head 3. It is arranged.

In order to keep the inner space of the support tube at a predetermined reference temperature K ₀ for the reason described later, the constant temperature medium 21 is provided with a temperature sensor 42 for measuring the temperature of the constant temperature medium 21, and the outer surface of the heat insulating material 23. And is temperature-controlled based on the output of the temperature sensor 42.

In the measurement, first, the introduction pipe 12a is used.
The fluid to be measured 11 is introduced into the vibrating cell 12 through and the driving current is input to the driving unit 31 from a control device (not shown), whereby electromagnetic force acts on the magnet 13 and the vibrating cell 12 starts vibrating.

The vibration cycle at this time is detected by the detection unit 32, the detection signal is input to the control device, and a drive signal synchronized with the vibration cycle is continuously input to the drive unit 31 to output the vibration cell. 12 is vibrated at a constant cycle, and the natural vibration cycle is obtained.

Let the natural vibration period be T, and the fluid to be measured 11
Let ρ be the density of, then ρ can be obtained by the following equation (1).

[0008]

[Equation 1]

Note that P is the vibration constant of the vibration system, V is the volume of the fluid to be measured 11 (volume of the vibration cell 12), M is the mass of the vibration cell 12 and the magnet 13, and each of the P, V and M is the structure of the measuring part. Is a constant determined by

[0010]

[Equation 2]

Then, it can be expressed by ρ = AT ² -B (2) Where the known density (ρ _w , ρ _a )
_Let T _w and T _a be the natural vibration periods at this measuring part obtained from two types of substances having, for example, pure water and air.
Equations (3) and (4) are satisfied.

Ρ _a = AT _a ² −B (3) ρ _w = AT _w ² −B (4) Therefore, the constants A and B are determined from the above equations (3) and (4) as follows. It

[0013]

[Equation 3]

From the above equations (5) and (6), the equation (2) is expressed as the following equation (7), and the density of the test fluid 11 is obtained.

[0015]

[Equation 4]

By the way, the constants A, since B is a constant determined based on the density and the natural vibration period of the two specific materials under a certain reference temperature K _0, the reference temperature K ₀
There is an error in the true value of the density of the test fluid 11 that is output based on the natural vibration period of the vibration cell 12 having a different temperature.

Therefore, as described above, the temperature inside the support tube is maintained at the reference temperature K ₀ by using the temperature control means such as the heat insulating material 23, the constant temperature medium 21, the temperature sensor 42, etc. The temperature 12 is measured by the temperature sensor 41, and the density at the time when the temperature reaches the reference temperature K ₀ is measured.

[0018]

However, even if the inside of the support tube is kept at the reference temperature K ₀ by using the temperature control means, the temperature of the fluid to be detected 11 introduced into the vibrating cell 12 depends on the ambient temperature. Therefore, immediately after the introduction, the temperature does not match the reference temperature K ₀ . Therefore, the temperature of the vibrating cell 12 is different from the reference temperature K ₀ for a while immediately after the introduction, and normally, from the introduction of the fluid to be measured 11 into the vibrating cell 12 until the vibrating cell 12 reaches the temperature equilibrium. It was necessary to wait for a fixed time (for example, about 2 to several minutes).

As a result, the time required for each measurement of the density must be expected to be about 10 minutes in total, for example, from the introduction of the test fluid to the discharge of the fluid or the washing of the inner surface of the vibrating cell. In measuring, for example, sugar concentration (density) measurement in a juice factory requires a lot of time.

The present invention has been proposed in view of the above conventional circumstances, and provides a temperature correction method for a vibration period in a vibration type densitometer that realizes a reduction in the time required for measuring the density of a fluid to be measured. With the goal.

[0021]

In order to achieve the above object, after introducing a fluid 11 to be measured into a vibrating cell 12 as shown in FIG. The present invention employs the following method in a vibrating densitometer that outputs the density of the test fluid 11 at the reference temperature K ₀ .

That is, the temperature difference ΔK between the temperature K of the vibrating cell 12 and the reference temperature K ₀ after the test fluid 11 is introduced.
= K−K ₀ and the natural vibration period T _K of the vibration cell 12 at the current temperature, the temperature correction method approximates the natural vibration period T ₀ at the reference temperature K ₀ .

Specifically, for example, T ₀ = T _K × (1-a
It is possible to use a first-order approximation formula of ΔK) [a: constant].

[0024]

In the above structure, the temperature K of the vibrating cell 12 is
However, when the temperature is higher than the reference temperature K _{0, the} natural vibration period T _K measured under the temperature K is the natural vibration at the reference temperature K ₀ because the volume including the vibration cell 12 expands. When the temperature K is shorter than the period T ₀ and conversely the temperature K is lower than the reference temperature K ₀ , the measured natural vibration period T _K becomes longer than the natural vibration period T ₀ .

[0025] Thus, the difference in natural vibration period T _K at the current temperature K and the natural vibration period T ₀ at the standard temperature K ₀ is
Depending on the temperature difference ΔK between the reference temperature K ₀ and the temperature K, if an appropriate approximate expression: F (T _K , ΔK) is selected, then T ₀ = F (T _K , ΔK) (*) Let the measured natural vibration period T _K be the natural vibration period T
_{It is possible} to correct to ₀ and output the density with less error.

Here, the above approximation formula: F (T _K , ΔK) =
It may be _{T K × (1-aΔT)} .

[0027]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a flow chart of an embodiment according to the present invention. This embodiment is applied to a vibration type densitometer having the structure shown in FIG. 2, and the details of the structure are as described above. Therefore, detailed description is omitted.

For the density measurement by this vibrating densitometer, the test fluid 11 is introduced through the introducing pipe 12a, and the vibrating cell 12 is introduced.
Is started when the test fluid 11 is filled. First, the temperature K ₀ of the constant temperature medium 21 is measured based on the medium temperature detection signal output from the temperature sensor 42 in the constant temperature medium 21 (F1), and is output from the temperature sensor 41 arranged near the vibration cell 12. The temperature K of the vibrating cell 12 is measured based on the cell temperature detection signal (F2), and the difference between the temperature K and the temperature K ₀ is set to ΔK (F3).

During this period, the vibrating cell 12 is driven by the driving unit 31 incorporated in the detection head 3 at its natural vibration period T _K , and the detecting unit 32 of the detection head 3 drives the vibration cycle at the temperature K. _TK is measured (F4).

In general, when the temperature K of the vibrating cell 12 is higher than the reference temperature K _{0, the} natural vibration measured under the temperature K is increased because the volume including the vibrating cell 12 expands. period T _K is shorter than the natural vibration period T ₀ at the reference temperature K _0, the temperature K conversely, the reference temperature K ₀
When it is lower than the above, the measured natural vibration period T _K becomes longer than the natural vibration period T _0. Therefore, the temperature difference ΔK and the temperature K can be set to an appropriate approximate expression: F (T _K , ΔK). Substituting the natural vibration period T in
_K is approximated to the natural vibration period T ₀ at the reference temperature K ₀ (F5).

In the present invention, the above approximate expression: F (T_K, Δ
K) but not limited to the natural vibration period T _KTo the temperature difference ΔK
It has been confirmed experimentally that it changes almost linearly
There is. Therefore, the approximate expression: F (T_K, ΔK) = T_KX (1
-AΔK) [a: constant] is a linear expression that
Vibration cycle T_KFrom the above reference temperature K₀Natural vibration in
Motion cycle T₀Are seeking. The constant a is the vibration density.
The optimum value is determined based on the structure of the meter.

Then, the above approximate expression: F (T _K , ΔK) =
From the value obtained as T ₀ , the density ρ is calculated using the following formula (2), which has been conventionally adopted (F6). ρ = AT ² −B (2) In this embodiment, when the absolute value of the temperature difference ΔK is relatively large, for example immediately after the introduction of the fluid 11 to be detected, the approximation is performed in step F6. Formula: F
With (T _K , ΔK), a good approximation value of the natural vibration period T ₀ cannot be obtained. Then, as shown in the figure, step F6
In the latter stage, a step for ensuring the accuracy of the density ρ is provided.

That is, in the first measurement, the obtained density ρ is once stored in a predetermined storage means as the density ρ ′ (F7YES → F9), and the process returns to step F1. Then, the density ρ obtained by the second measurement is compared with the density ρ ′, and if there is a difference, the density ρ obtained by the second measurement is set as the updated density ρ ′ (F7NO → F8
YES → F9), and returns to step F1 again. The third and subsequent measurements are similarly performed to compare the density ρ and the density ρ ′ and terminate the measurement when the difference becomes zero (F8YES).

FIG. 4 is a graph showing the change over time in the density value when the density of pure water was measured according to this example and the conventional example. In the figure, C1 is the density curve of the example, and C2 is the above temperature correction. It is a density curve of the conventional example which does not perform. For reference, the temperature curve of the vibration cell is shown as C3 at the same time. In this experiment, the temperature of pure water before introduction was 25 ° C, the temperature in the measurement space was 1
The temperature is 5 ° C and the amount introduced is 2 cm ³ .

As is clear from the figure, the time required to obtain the theoretical density value (0.9991 g / cm ³ ) of pure water at 15 ° C. is about 1.5 minutes in the embodiment, whereas it is about 1.5 minutes in the prior art. It took 5.5 minutes, and when the present invention was applied, the time required to display a reliable density value could be greatly shortened.

As another experiment, an outside air temperature of 28 ° C. was measured.
Temperature in constant space 20 ℃, introduction amount 20cm ³And 4 types of cover
When the test fluid was used, the results shown in Table 1 below were obtained.
It was. As shown in Table 1, for all test fluids
The measurement time could be shortened. In addition, depending on each substance
Although the time taken to shorten by the
It can be presumed to be due to the unique physical properties of.

[0037]

[Table 1]

[0038]

As described above, according to the present invention, after introducing the fluid to be measured into the vibrating cell, the density of the fluid to be measured at a predetermined reference temperature is measured based on the natural vibration period of the vibrating cell. In the method, based on the temperature difference between the reference temperature and the vibrating cell, the obtained vibration cycle is approximated to the natural vibration cycle under the reference temperature. Therefore, from the introduction of the test fluid to the measurement of the density. The time can be shortened. As a result, it is possible to measure the density of many samples.

[Brief description of drawings]

FIG. 1 is a flow chart according to an embodiment of the present invention.

FIG. 2 is a main part configuration diagram of an apparatus to which the present invention is applied.

FIG. 3 is a graph showing the concept of an approximate expression in the above embodiment.

FIG. 4 is a graph showing changes with time of the density obtained in the above-mentioned example and the conventional example.

[Explanation of symbols]

11 fluid to be tested 12 vibration cell K ₀ reference temperature K temperature of vibration cell ΔK temperature difference T ₀ natural vibration cycle at reference temperature T _K natural vibration cycle ρ density a proportional constant

Claims (3)

[Claims] 1. A test fluid (11) at a predetermined reference temperature (K ₀ ) based on a natural vibration period of the vibration cell (12) after introducing the test fluid (11) into the vibration cell (12). In the vibrating densitometer for measuring the density (ρ) of the
(K) and the temperature difference (ΔK = KK ₀ ) between the reference temperature (K ₀ ) and the vibration cell
Based on the natural vibration period (T _K ) at the current temperature (K) in (12), the temperature correction in the vibration type densitometer characterized by obtaining the natural vibration period (T ₀ ) at the reference temperature (K ₀ ). Method. 2. The vibration according to claim 1, wherein the natural vibration period (T ₀ ) at the reference temperature (K ₀ ) is obtained by a first-order approximation formula of T ₀ = T _K × (1-aΔK) [a: constant]. Method for temperature compensation in a densitometer 3. The density obtained by performing the above measurement a plurality of times
The temperature correction method for a vibrating density meter according to claim 1, wherein the measurement is terminated when the difference between (ρ) and the density (ρ ′) obtained in the previous measurement becomes zero.