JPH09257682A - Viscosity sensor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To constitute a simple circuit by shortening a measuring time by obtaining the viscosity based on the voltage level obtained from a turning fork type piezoelectric vibrator vibration in material to be measured. SOLUTION: A tuning fork type piezoelectric vibrator 1 is dipped in material to be measured, the electrode of a first piezoelectric element 9 is connected to the output terminal of a first operational amplifier 21 via a resistor 15, and the electrode of a second piezoelectric element 11 is connected to the inverting input terminal of the amplifier 21 via a resistor 19 to constitute a Wien bridge oscillator 13. The one end of a coupling capacitor 33 is connected to the connecting point 31 of the other electrode of the element 11 to the resistor 19, and the other end of the capacitor 33 is connected to a voltage follower 35. A full-wave rectifier 3, a smoothing circuit 39 and a differential amplifier 41 are sequentially connected in series with the output terminal and the later of the follower 35. The voltage level to the viscosity of the material to be measured is obtained from the output terminal 43 of the amplifier 41. A reference power source 45 which can regulate the offset voltage is connected to the amplifier 41.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a viscosity sensor for determining the viscosity of an object to be measured at a voltage level.

[0002]

2. Description of the Related Art A viscosity sensor for determining the viscosity of an object to be measured is:
For example, it is described in JP-A-60-170741.
This viscosity sensor obtains the viscosity of an object to be measured by vibrating a tuning fork type piezoelectric oscillator or a crystal oscillator in an object to be measured and counting the vibration frequency of the tuning fork type piezoelectric oscillator or a crystal oscillator. .

For example, when the resonance frequency in air is 1575H
When the viscosity of light oil is obtained using a tuning fork type piezoelectric vibrator of z, when the viscosity of light oil is 1.8 CP, the count value of the tuning fork type piezoelectric vibrator is 1269 per second, and the viscosity of light oil is 4.1 CP. Sometimes the count was 1261 per second.

[0004]

In this case, while the change in the viscosity of light oil is 2.3, whereas the change in the count value per second is 8, the viscosity of the light oil in this range is reduced. In the case of obtaining in increments of 0.1 CP, a measurement time of about 3 seconds is required. Note that the measurement time of about 3 seconds does not include the time until the tuning fork type piezoelectric vibrator stably vibrates in the object to be measured. For example, the count value is obtained every 3 seconds. Since the first three seconds include a count value due to unstable vibration until the tuning-fork type piezoelectric vibrator stably vibrates, the viscosity of the measured object is determined by the count value output after six seconds. become.

FIG. 4 shows the relationship between the count value and the viscosity.
There is a non-linear relationship as shown in, the change amount of the count value corresponding to the change in viscosity when the viscosity is high is considerably smaller than the change amount of the count value corresponding to the change in the viscosity when the viscosity is low. . Therefore, in order to accurately obtain the viscosity of the measured object over a wide range, it is necessary to extend the measurement time to, for example, about 10 seconds. In addition, since the relationship between the count value and the viscosity of the measured object becomes non-linear, it is necessary to calibrate the obtained count value using a calibration table or the like to determine the viscosity of the measured object.

SUMMARY OF THE INVENTION It is an object of the present invention to solve the above-mentioned problems and to provide a low-cost viscosity sensor that has a short measurement time and that responds almost linearly to a change in viscosity of an object to be measured.

[0007]

According to the present invention, there is provided a viscosity sensor comprising:
A tuning fork type piezoelectric vibrator to be immersed in an object to be measured, and a win bridge oscillation circuit having a resistor connected in series with the tuning fork type piezoelectric vibrator connected between an inverting input terminal and an output terminal; The viscous voltage level of the measured object is output from the connection point between the piezoelectric vibrator and the resistor.

Further, the viscosity sensor of the present invention may include a rectifier circuit for rectifying the viscosity voltage level.

[0009]

FIG. 1 is a schematic perspective view of a tuning fork type piezoelectric vibrator 1 used in an embodiment of a viscosity sensor according to the present invention. For example, in this embodiment, a tuning-fork type piezoelectric vibrator 1 (TFC type manufactured by Iwata Electric Co., Ltd.) having a resonance frequency in air of 1575 Hz is used.

The tuning-fork type piezoelectric vibrator 1 includes a base 3, an elongated plate-shaped first vibrating piece 5, and a second vibrating piece 7 having the same shape as the first vibrating piece 5. I have. First vibrating piece 5
The second vibrating piece 7 and one end of the second vibrating piece 7 are fixed to the base 3 so that their plate faces face each other in parallel. A plate-shaped first piezoelectric element 9 is attached to one end of the first vibrating piece 5, and a second piezoelectric element 9 similar to the first piezoelectric element 9 is attached to one end of the second vibrating piece 7. The piezoelectric elements 11 are attached and each is grounded to the base 3. Further, electrodes are formed on the outer surfaces of the first piezoelectric element 9 and the second piezoelectric element 11, respectively.

FIG. 2 is a circuit diagram of a viscosity sensor according to an embodiment of the present invention. The tuning-fork type piezoelectric vibrator 1 is replaced with one of two capacitors constituting the win-bridge oscillation circuit 13, and the electrode of the first piezoelectric element 9 is connected to the output terminal of the first operational amplifier 17 via the resistor 15. The electrode of the second piezoelectric element 11 is connected to the first operational amplifier 17 via a resistor 19.
Is connected to the inverting input terminal. Also, the first operational amplifier 1
7 is grounded via a capacitor 21 and a resistor 23 connected in parallel with the capacitor 21. Further, a capacitor 25 and a resistor 27 are connected in parallel between the non-inverting input terminal and the output terminal of the first operational amplifier 17, and a capacitor is connected between the non-inverting input terminal of the first operational amplifier 17 and the ground. The resistor 29 is connected.

The other electrode of the second piezoelectric element 11 and the resistor 1
9 is connected to one end of a coupling capacitor 33. The other end of the coupling capacitor 33 is connected to the voltage follower 3
5 is connected. After the output terminal of the voltage follower 35, a full-wave rectifier circuit 37, a smoothing circuit 39, and a differential amplifier 4
1 are sequentially connected in series. And the differential amplifier 41
, A voltage level corresponding to the viscosity of the object to be measured is obtained from the output terminal 43. Note that a reference power supply 45 that can adjust the offset voltage is connected to the differential amplifier 41.

When the viscosity sensor is operated, the tuning fork type piezoelectric vibrator 1 is immersed in light oil, and the viscosity of the light oil is set to 1.8 to 4.1.
When changed within the range of CP, from the connection point 31 to 0.
An alternating voltage varying between 46 and 0.34 V was obtained. This AC voltage changes in a linear relationship with the change in the viscosity of light oil, as shown by the broken line A in the graph of FIG. Then, by processing this AC voltage in the above-described circuit after the connection point 31, as shown by the solid line B in the graph of FIG. A voltage level was obtained. The dashed line C indicates the offset voltage applied to the differential amplifier 41.

As described above, the viscosity sensor converts the viscosity of the object to be measured into a voltage level. Therefore, the waiting time until the viscosity of the object to be measured is obtained requires a stable vibration of the tuning-fork type piezoelectric vibrator. Only a short time to do it.

Although the embodiment of the viscosity sensor of the present invention has been described above, the viscosity sensor of the present invention obtains the viscosity of the object to be measured as a voltage level, so that the viscosity of the object can be measured by various measuring instruments such as a voltmeter and an oscilloscope. The viscosity of the measured object can be easily obtained. In addition, since the measurement time is short, there is little response delay when various control devices are controlled using this voltage level. In addition, this viscosity sensor not only detects the viscosity of the liquid, but also
The viscosity of a solid can also be detected.

Further, the shape of the tuning-fork type piezoelectric vibrator is not limited to the illustrated one, and the shape of the vibrating reed, the interval between a pair of vibrating reeds, and the like may be changed according to the characteristics of the device under test.

[0017]

According to the viscosity sensor of the present invention, the viscosity of the object to be measured is obtained based on the voltage level obtained from the tuning fork type piezoelectric vibrator vibrating in the object to be measured. The measurement time is shorter than that of a conventional device in which the frequency is counted to determine the viscosity of the object to be measured.

Further, since the voltage level obtained from the tuning-fork type piezoelectric vibrator changes linearly with the change in the viscosity of the object to be measured, the voltage can be measured with a simple circuit configuration without using an additional circuit such as a correction circuit or a calibration circuit. The viscosity and the change in viscosity of the measured object can be detected.

[Brief description of the drawings]

FIG. 1 is a schematic perspective view of a tuning-fork type piezoelectric vibrator used in a viscosity sensor of the present invention.

FIG. 2 is a circuit diagram of the viscosity sensor of the present invention.

FIG. 3 is a graph showing a relationship between a voltage obtained from each part of the circuit shown in FIG. 2 and a viscosity of light oil.

FIG. 4 is a graph showing a relationship between a count value of a tuning fork type piezoelectric vibrator and a viscosity of light oil by a conventional viscosity sensor.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Tuning fork type piezoelectric vibrator 13 Win bridge oscillation circuit 15 Resistance 31 Connection point 37 Rectifier circuit

Claims (2)

[Claims] 1. A tuning-fork type piezoelectric vibrator immersed in an object to be measured and a win-bridge oscillation circuit having a resistor connected in series with the tuning-fork type piezoelectric vibrator connected between an inverting input terminal and an output terminal. A viscosity sensor that outputs a viscous voltage level of the object to be measured from a connection point between the tuning fork type piezoelectric vibrator and a resistor. 2. The viscosity sensor according to claim 1, further comprising a rectifier circuit for rectifying the viscous voltage level.