JPS623379B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a device for measuring the specific gravity of a liquid using ultrasonic waves, and its purpose is to determine the specific gravity value of a sample liquid by comparing the specific gravity of the liquid with a standard liquid. In particular, the present invention provides a measuring device that eliminates temperature-dependent errors in specific gravity that depend on temperature differences in liquids.

The above object is achieved by an apparatus that measures the specific gravity of a sample liquid by propagating ultrasonic waves through the sample liquid, which includes a standard liquid having a known specific gravity and a standard liquid dissolved in the standard liquid. a solute, and a value corresponding to a temperature-dependent characteristic of one of ultrasound sound pressure, transmission time, and transmission sound velocity is known for the standard liquid, and the device transmits ultrasound to the sample liquid. an ultrasonic transmitting/receiving element that receives ultrasonic waves propagated through the sample liquid; and an ultrasonic transmitting/receiving element that measures the temperature of the sample liquid and generates a first signal corresponding to a value corresponding to the temperature-dependent characteristic of the standard liquid. a temperature measuring means; a measuring means for measuring a corresponding one of the sound pressure, the transmission time and the transmitted sound velocity of the ultrasonic wave in the sample liquid by the propagation; and a difference detection means for determining the specific gravity difference with respect to the standard liquid from the difference between the two values and the first signal.

Conventionally, it is well known to measure liquid specific gravity using ultrasound. Ultrasonic waves are transmitted into a liquid, and the transmission time to the received signal is directly read using the sing-around method or other methods, and the specific gravity is directly determined from that time.

However, the measured values show variations due to temperature and other external factors, making it impossible to perform highly accurate measurements. Furthermore, it has been conventional practice to make ultrasonic waves incident on each of a standard liquid and a sample liquid, and to determine the concentration of the sample liquid from the difference in transmission time.

The present invention relates to an apparatus for measuring the specific gravity of a liquid using ultrasonic waves, which improves the drawbacks of conventional hydrometers, and the principle thereof will first be explained below.

When the density of the material is ρ and the speed of sound is C, the acoustic impedance Z is expressed by the following formula.

Z=ρC Now, from the material with acoustic impedance Z, Z _A , Z _B
The difference in sound pressure transmittance when a sound wave is incident on materials A and B is as follows: ΔP=2Z _A /Z+Z _A -2Z _B /Z+Z _B =2Z(
It is expressed as Z _A −Z _B )/(Z+Z _A )(Z+Z _B )...(1). Hereinafter, subscripts A and B will be used in the same way as Z _A and Z _B. Here, consider a case where substances A and B are acoustically extremely similar. For example, in a solid solution or solution B in which one type of solute is slightly dissolved in pure substance A, Z _B = Z _A + ΔZ C _B = C _A + ΔC ρ _B = ρ _A + Δρ, then Z _A ≫ ΔZ, C _A ≫ ΔC, Since ρ _A ≫Δρ holds, ΔP≒−2ZΔZ/(Z+Z _A ) ² ΔZ=C _A Δρ+ρ _A ΔC+ΔρΔC ≒C _A Δρ+ρ _A ΔC ∴ ΔP=2Z/(Z+Z _A ) ² ( _CA Δρ+ρ _A ΔC)
…(2) Furthermore, since a small amount of solute determines the values of ΔC and Δρ under constant temperature and constant pressure,
A proportional relationship holds between the amount and ΔC and Δρ.

Therefore, if the proportionality constant is k, ΔC=kΔρ∝Amount of solute (solution concentration)...(3) Equation (2) is ΔP=-2Z/(Z+Z _A ) ² (C _A +kρ _A )Δρ...
(4) Now, in equation (4), the coefficient of Δρ is temperature, pressure,
It does not change if the type of solvent solute is constant. Thus, by measuring the difference in sound pressure, the difference in density of similar substances can be determined.

By the way, the proportionality constant k naturally depends on the substance. Therefore, it is clear that equation (4) is an equation for the case where there is only one type of solute. The condition for this equation to hold true even when many types of solutes are dissolved is when k is equal for all solutes. Conveniently, when sucrose, lactose, KCl, HCl, etc. are slightly dissolved in water, the value of k is O〓
All values are extremely close to each other within the range of Δρ=0.04.

Furthermore, although the description has been made here regarding transmitted sound waves, the density difference can also be determined for reflected sound waves using essentially the same principle. Furthermore, if there are multiple layers to be reflected or transmitted, there will be reflection and transmission at each interface, and the equation will be complicated.
If this treatment is performed strictly, it is possible to derive an expression proportional to Δρ.

Next, we will show that an expression proportional to Δρ can also be derived for the speed of sound.

The speed of sound when a sound wave passes through a substance is expressed by the following formula.

E: Bulk modulus As in the acoustic impedance method, consider a pure substance A and a substance B containing a small amount of one type of solute.

E _B =E _A +ΔE (E _A ≫ΔE) ρ _B =ρ _A +Δρ (ρ _A ≫Δρ) Since the concentration of solute is completely proportional to Δρ and ΔE, ΔE=k'Δρ...(6) From (5) and (6) Equation (7) corresponds to equation (3) in which ΔC is proportional to Δρ. This proportionality constant is almost unaffected by temperature.

As an example, a graph for a saline solution is shown in FIG. It is clear that the proportional relationship between ΔC and Δρ and the proportionality constant do not depend on temperature in the range of 10°C to 30°C.

Also, considering the case where a sound wave transmits a distance l in a substance in the same way as the speed of sound, the difference between the transmission times t _A and t B of substances A and _B is becomes.

If substance A is the standard liquid and substance B is the sample liquid, the sound pressure difference, the transmission sound velocity difference, or the transmission time difference between the two are proportional to the density difference, as described above, and if a calibration curve is drawn in advance, then , the density difference between both liquids can be determined from these measured values.

By the way, in order to specifically configure a hydrometer based on the above principle, it is actually necessary to equalize the temperatures of the standard liquid and the sample liquid, or to correct errors due to temperature differences. There are several possible ways to do this.

Specific embodiments of the present invention will be described below with reference to the accompanying drawings.

FIG. 2 shows a specific embodiment of the present invention, and shows a block diagram of a circuit of a specific gravity measuring device, and shows a case where transmission time is measured.

This block diagram measures the permeation time of a sample liquid in which a small amount of solute is dissolved in the standard liquid (in other words, the solvents of the standard liquid and sample liquid are the same), and the permeation time of the standard liquid itself (not shown) is measured. This provides a method for inputting the difference as a difference and determining the specific gravity value from the difference in both transmission times. A rectangular wave with a sharp rise of, for example, 1 KHz is transmitted from the transmitter 1, and the voltage is applied to the transmitting ultrasonic transducer 2. The rise time of the rectangular wave is adjusted to match the natural vibration waveform of the oscillating ultrasonic transducer 2. A pulse waveform having a natural frequency of the transducer is transmitted from the transmitting transducer 2 at a period of 1 KHz, and the sample liquid 4
It passes through a sample liquid tank 3 containing a standard liquid (not shown, but it goes without saying that it can be handled in the same way) and the sample liquid 4, is received by a receiving element 5, and is converted into an electrical signal. The received pulse is amplified by a high frequency amplifier 6, shaped into a waveform, and converted into a trigger pulse, which is sent to a gate control circuit 7. A gate opening/closing signal from the transmitter 1 is sent to the gate control circuit 7, and a gate signal is generated in the gate control circuit 7 together with the trigger pulse. The gate 9 is opened and closed in response to this signal, and the clock pulses from the timer 8 are counted by the counter 10, and the value is held for each count.

The above operations are repeated every cycle of the rectangular wave transmitted from the transmitter 1. In this way, the transmission time of the ultrasonic waves propagating through the sample liquid 4 including the sample container 3 is measured.

On the other hand, a thermistor 1 is placed near the sample liquid 4 and changes its low resistance value in accordance with the temperature of the sample liquid 4.
3 and the fixed resistor 12 are connected to a constant current source 11. The terminal voltage of this thermistor 13 and resistor 12 is amplified by a buffer amplifier 14 and then converted to an AD converter 15.
is converted into a digital quantity by This AD conversion operation is performed every cycle of the rectangular wave transmitted from the oscillator 1. The thermistor 13 and fixed resistor 12 are used to electrically substitute these resistance values instead of directly determining the acoustic wave transmission time of the solvent component (standard liquid) of the sample liquid 4. In other words, the output of the AD converter 15 is the solvent component (in addition,
If the sample liquid is urine, the solvent component is water. ) The fixed resistor 12 is selected for the thermistor 13 so that it exactly matches the count value of the transmission time when only the temperature is included, and also changes correctly according to the temperature.

The output of the buffer amplifier 14 is stored in a register 16 as a digital quantity. The ultrasonic transmission time of the sample liquid 4 including the sample container 3 held in the counter 10 and the sample container 3 stored in the register 16
The value equivalent to the ultrasonic transmission time on the side of the solvent component (standard liquid) containing
Input to DA converter 18.

The output of the DA converter 18 is sent to the recorder 20,
On the other hand, it is again converted into an appropriate digital quantity by the AD converter 19 and displayed on the display 21. In this way, the difference in specific gravity between the sample liquid and the solvent component (standard liquid) is measured.

In the above block diagram, sample liquid tank 3
In this method, ultrasonic waves were input into the sample liquid, and the temperature dependence of the sample liquid was apparently compensated for using a thermistor and a resistor.

FIG. 3 shows an embodiment showing the state of a sample liquid tank, which is comprised of a sample liquid tank 3, a container holding portion 22, and a thermistor element 13 between an ultrasonic transmitting element 2 and a receiving element 5.

FIG. 4 shows an embodiment of the specific gravity detection portion when the present invention is implemented in a urine hydrometer. This liquid container 3 is a disposable urine container and allows continuous measurement by connecting upper and lower tubes. A spring 25 is attached to the slidable container holding portion 22 so that it can be tightly attached to the container. A thermistor 13 is fitted into the holding portion 22 as a temperature detection element, thereby making it possible to measure the temperature of the fluid. In order to easily attach such a detection portion to the bedside or the like, it can be attached to the bedside 27 using a mounting member 26 such as double-sided tape or a magnet.

These specific gravity measurements are not limited to urine, but can also be applied to liquids such as general liquids, infusion agents, blood, and dialysate.

Although one embodiment of the present invention has been described above, it goes without saying that these are merely examples and include those that can be easily implemented by those skilled in the art.

Further, although an embodiment using a transmission time difference has been shown, the basic idea of this method can also be realized when using a transmission sound velocity difference method. It is also possible to achieve this by using a sound pressure difference between the ultrasonic waves passing through both liquids.

Next, to make the operation of this device more concrete, the liquid whose specific gravity is to be measured as shown in Figs. 3 and 4 is placed in a container continuously or intermittently, The ultrasonic transmission time of the liquid is measured by adding a substance other than the liquid such as a container. In this case, the ultrasound transmission time is measured by the propagation time between the ultrasound transmitting and receiving elements. Since this time depends on the temperature of the liquid, correction is required. Therefore, in the present invention, instead of directly measuring the ultrasonic transmission time of the standard liquid that is the solvent component of the sample liquid, the AD converter 15 shown in FIG. 2 outputs an output equal to the counted value of the transmission time.
The output is output as a temperature-corrected value using the thermistor 13 and fixed resistor 12.

This ultrasonic reception output and the output of the AD converter are electrically processed as input signals of the block diagram shown in FIG. 2, and as a result, a measurement output responsive to the specific gravity value is displayed.

In this manner, the present device measures specific gravity by measuring only the sample liquid, requires only one measuring circuit, and can measure specific gravity with high accuracy.

Furthermore, the specific gravity of a sample liquid can be measured continuously or intermittently.

[Brief explanation of the drawing]

Fig. 1 shows the correlation between the density difference and sound velocity difference between water and saline, Fig. 2 is a block diagram of the circuit of the specific gravity measuring device according to the present invention, and Fig. 3 shows the container for containing the standard liquid according to the present invention. FIG. 4 is a partially cutaway sectional view of a container portion showing an example in which the ultrasonic hydrometer according to the present invention is used as a urine hydrometer. 2... Ultrasonic transmitting element, 3... Sample liquid container,
4...Sample liquid, 5...Ultrasonic receiving element, 11...
...Constant current source, 13...Thermistor.

Claims (1)

[Claims] 1. A container containing a sample liquid, an ultrasound transmitting element and a receiving element disposed across the container, and means for measuring one of the sound pressure, transmission time, and transmission sound velocity of transmitted ultrasound. , standard value calculating means for measuring the temperature of the sample and electrically generating the value of the selected physical quantity in the standard liquid from known temperature characteristics; A device for measuring the specific gravity of a liquid using ultrasonic waves, comprising means for calculating a difference.