JP2002022635A - Oscillatory density meter - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a density meter utilizing the fact that the frequency of a piezoelectric oscillator self-oscillating in a gas or liquid is varied depending on the density of the gas or liquid. SOLUTION: Density is measured by oscillating a liquid or gas to be measured and analyzing the response of an oscillator. The oscillator 1 is subjected to free oscillation by a self-excited oscillation circuit 2, the natural frequency thereof is measured by means of a counter 3, and the measurement is converted into a density being measured.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a density meter used for controlling the concentration of abrasive grains in a CMP (Chemical Mechanical Polishing) polishing apparatus or the like in a semiconductor device manufacturing process and measuring the SS concentration of harmful substances in environmental management.

[0002]

2. Description of the Related Art Conventionally, when measuring the density of a liquid, it is performed by sampling the liquid and measuring its volume and mass. However, in order to continuously measure this, conventionally, the attenuation of light and sound in a liquid has been measured. In the method of calculating the density from the attenuation of light and sound, the relationship between the attenuation and the density is determined in advance for each liquid type for which the density is to be measured, and the density is measured using the calibration value. This is because the attenuation of light and sound is not directly related to the density.

For example, when light is used, even if the density is the same, the density of a white substance and the density of a black substance have different attenuation values. In the case of the ultrasonic densitometer shown in FIG.
In particular, the amount of attenuation greatly depends on the temperature in the liquid. Therefore, there is a problem that the calibration curve differs depending on the type of the liquid to be measured.

[0004]

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems, and measures the density according to a principle completely different from that of the prior art. In order to directly measure the mass, a means for moving the liquid or gas to be measured is required. For example, when a vibrator vibrates in water, the liquid near the vibrator vibrates at the frequency of the vibrator,
An effect occurs as if the mass of the vibrator was increased. The liquid also has the effect of increasing the action of the spring.

Therefore, the natural frequency of the vibrator changes. The action of the additional mass and the additional spring is affected by the density of the liquid. Accordingly, it is an object of the present invention to provide an apparatus for measuring the density of a liquid by measuring the unique frequency of a vibrator.

[0006]

The vibration density meter according to the present invention comprises:
This is a density meter that utilizes the fact that when a piezoelectric vibrator that self-oscillates is placed in a gas or liquid, the frequency of the vibrator changes according to the density of the gas or liquid.

[0007] A densitometer utilizing the fact that the impulse response of a piezoelectric vibrator placed on a gas or liquid changes according to the density of the gas or liquid. The density meter is characterized by using a quartz crystal or a ceramic vibrator as the piezoelectric vibrator. The density meter is characterized by using a frequency counter as a method of detecting a frequency change. The density meter is provided with a function of converting the detected frequency change into density or density.

[0008]

DESCRIPTION OF THE PREFERRED EMBODIMENTS In order to measure the natural frequency of a vibrator, it is necessary to make the vibrator eigenvibrate using a self-excited oscillation circuit and measure the frequency, or obtain and analyze the impulse response and frequency response. . In practical terms, the former seems to be advantageous. Here, a block diagram of the embodiment in this case is shown in FIG.
Shown in

In FIG. 1, reference numeral 1 denotes a vibrator.
The vibrator 1 is made of ceramic, but if temperature insensitivity is required, quartz can be used. Reference numeral 2 denotes a self-excited oscillation circuit. A circuit example of the vibrator 1 and the self-excited oscillation circuit 2 is as follows.
It is shown in FIG. Reference numeral 3 is a counter for measuring the self-excited oscillation frequency. Reference numeral 4 denotes a part for converting a self-excited oscillation frequency to a density, and this conversion is performed by a microcomputer. Reference numeral 5 is a density display unit.

FIGS. 3 and 4 are external views of this embodiment. FIG. 3 shows an embodiment in which the present invention is applied to a portable density meter. It operates on dry batteries. FIG. 4 shows an embodiment using the present invention as a densitometer sensor. This is installed in the apparatus and used.

[0011]

Conventionally, when the density of a liquid or gas is continuously measured, a method has been used in which the attenuation of sound or light in the liquid or gas is measured and the density is obtained indirectly. . The present invention is a direct measurement method because it is a method of measuring a density by moving a liquid or gas to be measured. Therefore, it is possible to manufacture a densitometer having characteristics that are less sensitive to the type of the liquid or gas to be measured.

[Brief description of the drawings]

FIG. 1 is a block diagram showing one embodiment of a configuration for implementing a density measuring method according to the present invention.

FIG. 2 is a circuit diagram showing one embodiment of a self-excited oscillation circuit for vibrating a vibrator to generate vibration in a liquid or gas.

FIG. 3 is an embodiment in which the present invention is used for a portable density meter.

FIG. 4 is an embodiment in which the present invention is used for a sensor type densitometer.

FIG. 5 is a typical example of a conventional ultrasonic densitometer.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Transducer (sensor) 2 Self-excited oscillation circuit 3 Frequency counter 4 Frequency density conversion part 5 Density display part 6 Ultrasonic transmission part 7 Ultrasonic reception part 8 Thermometer 9 Density calculation part, density display part

Claims (8)

[Claims] 1. A density meter utilizing the fact that when a piezoelectric vibrator that self-oscillates is placed in a gas or liquid, the frequency of the vibrator changes according to the density of the gas or liquid. 2. A density meter utilizing the fact that the impulse response of a piezoelectric vibrator placed on a gas or liquid changes according to the density of the gas or liquid. 3. A density meter utilizing the fact that the frequency response of a piezoelectric vibrator placed on a gas or liquid changes according to the density of the gas or liquid. 4. The density meter according to claim 1, wherein quartz is used as the piezoelectric vibrator. 5. The density meter according to claim 1, wherein a ceramic vibrator is used as the piezoelectric vibrator. 6. The density meter according to claim 1, wherein a frequency counter is used as a method for detecting a frequency change. 7. A method for detecting a density or a density from a detected frequency change.
The density meter according to any one of claims 1 to 3, further comprising a function of converting the density into a density. 8. The multipoint density meter according to claim 1, wherein a density distribution can be measured by using a plurality of density meters.