JP2518169B2 - Liquid level detector - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a liquid level detection device, and more particularly to a liquid level detection level sensor having a structure in which resistors and electrodes are alternately installed to detect a change in the resistance value of a liquid level detection device. The present invention relates to a liquid level detection device that detects the liquid level of a solution.

[0002]

2. Description of the Related Art FIG. 4 shows an example of the configuration of a conventional liquid level detecting device for detecting the liquid level of a solution to be measured containing an electrolyte.

In the figure, an AC voltage is applied from an AC voltage signal source 13 to the resistance sensor 11 (liquid level detection level sensor), and a detection signal V output from the resistance sensor 11 is detected.
When K is input to the signal processing circuit 15, the differential amplifier circuit 1
The signal amplified by 7 and amplified by the terminal 19 is output.

On the other hand, FIG. 5 shows the construction of the resistance sensor 11 used in this liquid level detecting device.

The resistance sensor 11 includes a good conductor electrode 20.
When the liquid surface 24 of the solution to be measured including the electrolyte rises and the electrodes are buried, the buried electrodes 20m are short-circuited. Therefore, the level of the liquid surface 24 of the solution to be measured changes and the terminal 11 is changed according to the change in the number of electrodes buried under the liquid surface 24.
The resistance value between a and 11b changes. Therefore,
By applying a voltage between the terminals 11a and 11b,
When the resistance value between 11b is detected, the liquid level of the measured solution can be detected. Here, since the AC voltage signal is applied to the terminals 11a and 11b, it is possible to maintain the performance of the resistance sensor for a long period of time without the electrode 20 being corroded by the electrolysis of the solution to be measured. ing.

[0006]

However, in the liquid level detection device as described above, since the resistance sensor 11 is integrally formed in the circuit, noise is simultaneously amplified together with an effective signal, which is effective. There was a problem that information could not be obtained.

That is, since the resistance of the resistance sensor 11 is one factor that determines the amplification factor of the differential amplifier circuit 17, the amplification factor changes depending on the level applied here.

On the other hand, such noise is mostly due to a sudden change in voltage (on / off of a switch of a fluorescent lamp).
Since it is OFF, ON / OFF of switches of other devices, etc.), the voltage that drives the resistance sensor 11, the effective information that is extracted, the voltage, and the generated noise are also based on the voltage. It has been difficult to obtain valid information by removing the.

The present invention has been made in view of the above problems, and an object of the present invention is to stabilize a signal obtained from a liquid level detection level sensor so that the liquid level with high measurement accuracy and reliability can be obtained. It is to provide a detection device.

[0010]

In order to achieve the above object, in the liquid level detecting device according to the present invention, the characteristics of the sensor, the sensor drive circuit and the operational amplifier circuit are made independent and the sensor By using a constant current as a driving signal, a stable sensor output can be obtained.

That is, the electrolyte is detected by detecting a change in the resistance value of a liquid level detection level sensor formed by intermittently arranging detection electrodes along the length direction of a pair of resistance coatings installed in parallel. In the liquid level detection device for detecting the liquid level of the measured solution containing, a constant current source for supplying a constant current,
Switching means for periodically inverting the current supplied from the constant current source and supplying it to the level sensor, an amplifier for amplifying the output signal output from the liquid level detection level sensor, and an amplifier output from this amplifier Sample the signal
Sample hold circuit to hold and delay against the inversion
Timing to perform the sampling at the same timing
Comprising a generator, a characterized Rukoto.

[0012]

In the liquid level detecting device of the present invention having the above-mentioned structure, the current supplied from the constant current source becomes a current which is periodically inverted by the switching means and is supplied to the level sensor.

When the liquid level of the solution to be measured containing the electrolyte changes and the number of electrodes buried below the liquid level changes, the level of the output signal output from the liquid level detection level sensor follows this change. data but since the change, which is delayed from the amplified output signal which is output from the liquid level detection level sensor inverted
The liquid level of the solution to be measured can be detected by holding the sample with the imming .

Since the direction of the current supplied to the liquid level detection level sensor is periodically inverted and supplied, the electrodes are not corroded by the electrolysis of the solution to be measured.

[0015]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a block diagram showing the structure of a liquid level detecting device according to the present invention.

In this block diagram, a liquid level detection level sensor A is installed in a container to be inspected, and a constant current is supplied from a constant current circuit B to this sensor A.
Here, the constant current supplied from the constant current circuit B to the sensor A is converted by the signal switching circuit C into a signal whose current direction changes.

Then, the level of the output signal output from the sensor A changes in accordance with the amount of the electrolytic solution filled in the container, and this level is amplified by the analog signal operational amplifier circuit D. The liquid level can be detected by sampling and detecting this in the sample hold circuit E. The timing of the sampling and holding circuit E and the timing of the signal switching circuit C are performed by the timing generating circuit F.

FIG. 2 shows a concrete example of the signal processing circuit in the liquid level detecting device according to the present invention. As can be seen from the figure, this circuit includes a resistance sensor 11
It has a constant current source 33, a switching circuit 35, a differential amplifier circuit 17, a sample hold circuit 39 and a controller 41, and the information obtained from the resistance sensor 11 is output to the output terminal 4
It is possible to obtain from 3.

Further, the switching circuit 35 includes analog switches SW1 to SW4 which are integrated circuits, and these are OS.
It opens and closes based on the signal from C38, while SW5 in the sample-hold circuit 39 is the OS.
It is designed to open and close based on a signal from C40. Then, the controller 41 uses the OSC 38 and the OSC.
40 controls are performed. That is, the controller 41
Is a microcomputer, which determines the timing of signals output by the OSC 38 and the OSC 40 according to a predetermined program.

As is apparent from FIG. 2, the switch SW 1 and the switch SW 4 are interlocked with each other, while the switch SW 1 and the switch SW 4 are interlocked with each other.
And SW 3 and the switch SW 2 is integrated. Since the inverter 35c is included, the switch SW 1
And switch SW 4 are closed, switch SW 2 and switch SW 3 are opened, and switch SW 1 and switch SW
When switch 4 is open, switch SW 2 and switch SW 3
Will be closed, and in the exemplary embodiment, the switch
When SW 1 and switch SW 4 are closed at the same time, arrow X
Current is passed in the direction of, and switches SW 3 and S
When W 4 and W 4 are closed at the same time, current is passed in the direction of arrow Y.

In this way, by applying a current whose direction is periodically reversed to the electrodes, it is possible to prevent the electrodes used in the sensor 11 from being corroded by the electrolysis of the solution to be measured. However, the frequency at this time is preferably 100 Hz to several kHz.
This is because at 100 Hz or less, the electrode is corroded in comparison with the reaction rate of the electrolytic solution used as the conductor, and 10 kH
This is because at z or more, the change in frequency becomes so severe that effective signal processing cannot be performed.

On the other hand, a current in which the direction thus generated is periodically inverted is applied to the sensor 11, and the sensor 1
The output from 1 is amplified in the differential amplifier circuit 17, and of these, either the current flowing in the direction of the arrow X or the current flowing in the direction of the arrow Y is required. . Therefore, in the present embodiment, the voltage when flowing in the direction of the arrow X is detected, and the level of this signal is sampled by the sample hold circuit 39 for detection.

Therefore, as shown in FIG. 3 showing the timing chart in this apparatus, in the switch SW 5 in the sample hold circuit 39, the switch SW
1 and the switch SW 4 are controlled in response to the open / closed state. That is, when the switch SW 1 and the switch SW 4 are closed, the switch SW 5 is closed after a slight time shift, while the switch SW 5 is opened and sampling is performed shortly before the switch SW 1 and the switch SW 4 are opened. It is like this. This is to prevent an adverse effect on the measurement value due to poor current switching, and by operating the switch SW 5 in this manner, a steady-state signal can be captured. Therefore, a stable pulse value can be obtained and effective information processing can be performed.

As described above, by measuring the level of the detected output level, it is possible to accurately detect the level of the electrolyte surface in which the resistance sensor 11 is immersed. .

In this embodiment, all the analog switches are used as the changeover switches of the changeover circuit, but the switches are not limited to this, and relays,
All change-over switches such as change-over circuits using FETs and transistors are used.

[0026]

According to the liquid level detection level sensor of the present invention constructed as described above, the reproducibility is within the accuracy distribution of about 1%, and this kind of measurement is usually about 5%. Considering that, it can be said that the data is quite good.

[Brief description of drawings]

FIG. 1 is a block diagram showing a functional configuration of a liquid level detection device according to an embodiment of the present invention.

FIG. 2 is a block diagram showing a functional configuration of a processing circuit of the liquid surface detection device according to one embodiment of the present invention.

FIG. 3 is a timing chart showing the operation of switches of the circuit of this embodiment used in FIG.

FIG. 4 is a block diagram showing a functional configuration of a signal processing circuit of a conventional liquid level detection device.

FIG. 5 is a diagram showing a configuration of a resistance sensor (liquid level detection level sensor) used in the liquid level detection device.

[Explanation of symbols]

 11 Resistance Sensor (Liquid Level Detection Level Sensor) 17 Differential Amplifier Circuit 33 Constant Current Source 35 Switching Circuit 39 Sample Hold Circuit 41 Controller

Claims (1)

(57) [Claims] 1. A liquid level detection device for detecting the liquid level of a solution to be measured containing an electrolyte, wherein a pair of resistor coatings are provided in parallel on an insulating substrate and along the lengthwise direction thereof. Using a liquid level detection level sensor with intermittent detection electrodes, the length of the liquid level detection level sensor is vertically immersed in the electrolyte to be measured, and the resistance is placed parallel to the solution to be measured. In the liquid level detection device for detecting the liquid level of the electrolytic solution to be measured by detecting the change in the resistance value caused by the body film short-circuiting through the measured solution via the detection electrode, a constant current is applied to the liquid level detection level sensor. A constant current source for supplying a constant current source, switching means for periodically inverting the current supplied from the constant current source and supplying the level sensor, and an amplifier for amplifying the output signal output from the liquid level detection level sensor. And this It is sampled and held signals outputted from the amplifier
Sample hold circuit and the sampling at a timing delayed from the inversion.
Fluid level sensing apparatus according to claim Rukoto and a timing generating circuit to perform.