JPS6145175B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a vibrating density meter that utilizes the fact that the resonance frequency of a mechanical vibrator changes depending on the density of the fluid surrounding the mechanical vibrator.

SUMMARY OF THE INVENTION An object of the present invention is to provide a vibrating density meter that can be used on a bench in a laboratory or laboratory and is easily calibrated.

As a conventionally known density meter, for example, the
As shown in Publication No. 26012, a fluid to be measured is introduced into a pipe vibrator formed in the shape of an acoustic pipe, and the density is determined from the transverse free frequency generated in this vibrator, or Tokuko Showa 51-16794
As shown in the above publication, there is a method in which a fluid to be measured is caused to flow inside and outside a cylindrical resonator, and the density is determined from the annular frequency of the cylindrical resonator.

The former requires a sampling pump, etc. to introduce the fluid to be measured into the pipe vibrator, and the latter requires a cylindrical resonator to be installed in the pipe through which the fluid to be measured flows. The disadvantage is that it is difficult to install and operate. Furthermore, neither method is capable of measuring the density of a minute amount of fluid, such as a sample collected in a test tube.

Here, the present invention aims to realize a vibrating density meter that is easy to handle and capable of measuring the density of a minute amount of fluid.

The device according to the present invention has a structure in which at least one end is open and a fluid to be measured flows in from the open end, and the inside is filled with the fluid to be measured. It has a measuring instrument main body that includes a microprocessor that inputs signals related to the resonant frequency of the resonator and signals related to temperature and performs predetermined calculations, and the cylindrical resonator and the measuring instrument main body are connected by a cable. There is one feature of the structure.

FIG. 1 is a conceptual diagram of the external appearance of a device according to the present invention. In the figure, SE indicates the detection end, which is composed of a cylindrical resonator with one end open and into which the fluid to be measured flows. This detection end is entirely shaped like a thin rod.
As shown in the figure, measurements can be made by inserting the device into a fluid to be measured collected in a beaker, for example. CA is a cable extending from this detection end SE and is connected to the measuring instrument main body ME. The measuring device ME has a display ID ₁ that digitally displays the measured density and a display that digitally displays the measured temperature.
ID ₂ and a key KY for instructing calibration.

FIG. 2 is a sectional view showing an example of the detection end used in the device shown in FIG. 1, and FIG. 3 is a perspective view showing the structure partially in section.

In these figures, 1 is a cylindrical resonator, and one end is provided with a flange portion 11, the other end is provided with a flange 12, and a bottom portion 13 that closes the other end.
A through hole 14 is formed in the flange 12 on the other end side, through which the fluid to be measured that has entered through the opening on the one end side flows out. 2 is an excitation means for the cylindrical resonator 1 attached to the stepped portion of one flange 12, and 3 is a vibration detection means for the cylindrical resonator 1 also attached to the stepped portion of the flange 12. Here, in both cases, PZT is used. is shown. 41 and 42 are covers with the same diameter, and the cover 41 has flanges 11 and 12 at both ends.
The cover 42 is connected to the flange 12 at one end to form an elongated handle, and the lead wire 21 is connected to the excitation means 2 and the vibration detection means 3. It covers 31. Reference numeral 5 denotes a temperature detection means attached to the bottom 13 of the cylindrical resonator 1, which uses, for example, a thermistor or a transistor, and detects the temperature of the fluid to be measured that has flowed into the cylindrical resonator 1. This temperature detection means is used for temperature correction.

The chamber 15 formed between the cover 41 and the cylindrical resonator 1 is filled with gas at atmospheric pressure or constant pressure (including vacuum).

The detection end configured in this way has an elongated rod shape as a whole, and this detection end is connected to the first
As shown in the figure, it has the advantage that it can be inserted into a sample collected in a beaker, for example, and density measurement can be performed. In addition, if the sample collected is hygroscopic,
If the material easily evaporates, measurements can be taken by placing a stopper between the handle and the beaker. A cylindrical resonator 1 is attached to the tip of the rod, and when this is inserted into the sample to be measured (fluid),
The sample flows into the inside of the cylindrical resonator 1 from the tip opening as shown by arrow a and flows out from the through hole 14, filling the inside of the cylindrical resonator 1. In this state, a self-excited oscillation loop (not shown) formed including the excitation means 2 and the vibration detection means 3 causes the cylindrical resonator 1 to vibrate in an annular manner. here,
The resonant frequency of the cylindrical resonator 1 changes mainly in relation to the density D of the fluid to be measured filled inside the cylindrical resonator 1. Note that the influence of the pressure difference between the inside and outside of the cylindrical resonator 1 can be eliminated by making the pressure of the fluid to be measured equal to atmospheric pressure or maintaining it at a constant pressure, and the influence of temperature can be eliminated by This can be eliminated by performing a predetermined calculation using the signal from the detection means 5.

When the inside of the cylindrical resonator 1 is filled with the fluid to be measured and subjected to circular vibration, its resonant frequency d
and the density ρ of the material to be measured have a relationship as shown in the following equation.

However, ₀ : Resonance frequency at density 0 (in vacuum) K: Constant determined by the diameter, thickness, etc. of the cylindrical resonator 1 According to the detection end configured in this way, the density detection part is a rod-shaped tip. Since it can be made into an elongated structure, it is easy to handle and can be inserted into even a minute amount of sample, and there is no need to install a sampling pump or the like. Further, the density detection section can be easily cleaned by supporting the handle part by hand and immersing the tip part in an organic solvent, for example. Furthermore, only the detection end SE portion can be easily replaced.

Figure 4 shows the measuring device main body ME in the equipment shown in Figure 1.
FIG. 2 is a configuration block diagram showing an example of the circuit of FIG.

In this figure, OSC is an oscillation circuit, and the detection terminal
The signal from the vibration detection means of the SE is input, and its output is applied to the excitation means, forming a self-excited oscillation loop including the cylindrical resonator 1, which causes the cylindrical resonator 1 to vibrate at the resonant frequency. ing. TEP is a temperature conversion circuit which inputs a signal from the temperature detection means of the detection end SE and outputs a signal T related to temperature. CU is a counter that counts the frequency signal from the oscillation circuit OSC via the isolator IS.
MPX is a multiplexer that outputs the oscillation amplitude signal V from the oscillation circuit OSC, the temperature signal T from the temperature conversion circuit TEP, and the setting signal e ₁ set by the analog signal (voltage dividing resistor output) in the coefficient setting circuit KS.
Select e ₂ and e ₃ and input them to the A/D converter AD. μP is a microprocessor that receives signals from the counter CU and the D/A converter AD, and includes random access memory RAM.
and read-only memory ROM are combined. ID ₁ is an indicator that indicates density, ID ₂ is an indicator that indicates temperature, and both are microprocessor μ
Connected to P. KY is a key that instructs calibration, and inputs a signal for interrupt processing to the microprocessor μP. Note that here, the amplitude signal V from the oscillator OSC and the temperature signal T from the temperature converter TEP are applied to the A/D converter AD via the multiplexer MAX to be converted into digital signals. /
An F converter may be provided to convert the amplitude signal V and temperature signal T into frequency signals, which are counted by a counter to obtain a digital signal. Furthermore, the oscillation amplitude signal V is used in calculations to eliminate the influence of the viscosity of the fluid to be measured, and may be omitted if the influence of the viscosity is not considered.

The operation of the circuit configured in this manner will be described next.

First, with the detection end SE left in the air, press the calibration key KY to perform calibration. In such a calibration state, the microprocessor μP first reads the digital signal related to the frequency signal ₀ from the counter CU and switches the multiplexer MPX to determine the oscillation amplitude of the cylindrical resonator in the oscillating state in the air. Digital signals related to the signal V ₀ and the temperature signal T ₀ are sequentially read, and the density ρ ₀ of the air at the temperature T ₀ is calculated using each of these data. And each of these data ₀ , V ₀ ,
T ₀ and ρ ₀ are random access memories respectively
Stored in RAM.

Next, release the calibration key KY and enter the measurement state. In this measurement state, the detection end
Insert the SE into the fluid to be measured. In such a measurement state, the microprocessor μP reads the digital signal related to the broken lap number signal from the counter CU, as in the calibration state, and switches the multiplexer MPX to generate vibrations in the fluid to be measured. Oscillation amplitude signal V, temperature signal T, and each coefficient setting signal of the cylindrical resonator in the state
Digital signals related to e ₁ , e ₂ , and e ₃ are read in sequence. Next, the microprocessor μP uses each data read during calibration and each data read into the measurement state to perform, for example, (1).
The density of the fluid to be measured is calculated by performing calculations as shown in equation (2). Note that this calculation formula and calculation procedure are performed according to a program stored in advance in the read-only memory ROM.

x=/ ₀ −1 (1) ρ=A [x ² +Bx+C(x+1) ² (V ₀ /V
-1)] ・[1+(T-T ₀ )]+ρ ₀ [1+β(T-
T ₀ )] (2) where A, B, C: constants α, β: temperature coefficient of cylindrical resonator ρ ₀ : air density ₀ , V ₀ , T ₀ : frequency during calibration, oscillation amplitude, Temperature, V, T: Frequency at the time of measurement, oscillation amplitude, temperature ρ: Density of the fluid to be measured The density ρ obtained by calculation is the one in which the influence of the temperature and viscosity of the fluid to be measured has been removed, and this is the indicated value. Digitally displayed on total ID ₁ . Furthermore, the temperature T is also digitally displayed on the indicator ID ₂ .

In such a device, in principle, calibration only needs to be performed once before measurement, but over long-term use, the natural frequency ₀ , V _0, etc. of the cylindrical resonator may change. , causing errors. Therefore, for long-term use, sometimes press the calibration key KY to enter the calibration state.
₀ , _V0, etc. can be updated. Note that this calibration state is processed by applying a signal from the key KY to the microprocessor μP as an interrupt signal.

In addition, with this device, read-only memory
In addition to the program, the ROM stores various constants such as temperature coefficients α and β of the cylindrical resonator.
Therefore, when the cylindrical resonator (sensing end) SE is replaced, the various constants related thereto also need to be changed at the same time. In this device, a read-only memory ROM is removable from the device, and various constants for each detection end are stored for each detection end.
If you prepare ROMs in pairs and install the appropriate ROM each time you replace the detection end, you can easily ensure compatibility of the detection end.

Furthermore, in this device, the concentration D of the fluid to be measured can be determined by causing the microprocessor μP to perform calculations such as equation (3). The calculation results are digitally displayed on indicator ID ₁ as necessary.

D=-N/M (3) where M and N are constants. Here, it is desirable that the concentration D of the fluid to be measured is indicated by converting it to the reference temperature of the fluid to be measured. For this purpose, the reference temperature Tc of the liquid to be measured, 1
Although it is necessary to provide data on various constants such as the next and second order temperature coefficients r ₁ and r ₂ during calculation, these constants can be provided by setting them in the coefficient setting circuit KS.

This allows the concentration or specific gravity of the fluid to be measured to be known in terms of the reference temperature.

According to the device configured in this way, a density meter that can carry out calibration using air, is easy to handle, and can measure the density of a minute amount of fluid can be realized. Furthermore, a densitometer can be realized in which the detection end can be easily replaced and exchanged, and the density or specific gravity can also be measured.

Note that in the above explanation, the oscillation amplitude signal V is input from the oscillation circuit OSC and this signal is used in calculations to eliminate the influence of viscosity, but the influence of viscosity is not taken into account. Not necessary in some cases. Further, although the main body of the measuring device is provided with an indicator for indicating the temperature, this may be omitted.

As described above, according to the present invention, it is possible to realize a vibrating density meter that is easy to handle and capable of measuring the density of a minute amount of fluid.

[Brief explanation of the drawing]

Fig. 1 is a conceptual diagram of the external appearance of the device according to the present invention;
The figure is a cross-sectional view of the configuration of an example of the detection end used in the device shown in Figure 1, Figure 3 is a perspective view of the configuration partially shown in cross section, and Figure 4 is a circuit diagram of the main body of the measuring instrument in the device shown in Figure 1. FIG. 2 is a configuration block diagram showing an example. SE...detection end, CA...cable, ME...measuring instrument, 1...cylindrical resonator, 2...excitation means, 3...
...Vibration detection means, OSC...Oscillation circuit, TEP...
Temperature conversion circuit, MPX...Multiplexer, μP
...Microprocessor.

Claims (1)

[Scope of Claims] 1. A cylindrical resonator having a structure in which at least one end is open so that a fluid to be measured flows into the resonator and the inside thereof is filled with the fluid to be measured, and includes a temperature detecting means; The measuring instrument body includes a microprocessor that inputs a signal related to the resonant frequency of the cylindrical resonator and a signal related to the temperature from the temperature detection means and performs predetermined calculations. The cylindrical resonator is left in the air, and the microprocessor inputs a signal related to the resonance frequency ₀ in this state and a signal related to the temperature T ₀ and calculates the air density ρ ₀ . The cylindrical resonator is inserted into the fluid to be measured, and the microprocessor generates a signal related to the resonant frequency and a temperature T in this state.
an operation of inputting a signal related to the fluid, performing a predetermined calculation to determine the density of the fluid to be measured using these data and each data obtained in the calibration state, and displaying the calculation result. A vibrating density meter characterized by: 2 Prepare multiple types of detection ends and prepare a read-only memory (ROM) that stores constants specific to each detection end in pairs with each detection end, and select one of the multiple types of detection ends. 2. The vibratory density meter according to claim 1, wherein the read-only memory paired with the detection end is mounted so as to be coupled to the microprocessor. 3. The cylindrical resonator has flange portions at each end thereof, and the patent claim is provided with a cover that is coupled to each flange portion and covers the outside of the cylindrical resonator, and an elongated handle that is coupled at one end to the cover. Range 1
Vibrating density meter as described in section.