JPH0212607Y2 - - Google Patents

Description

[Detailed description of the invention] This invention relates to a dissolved oxygen meter, which can be used to measure the amount of oxygen dissolved in sewage (test water), especially in aeration tanks of sewage treatment plants, with long-term maintenance-free accuracy. It is related to a dissolved oxygen meter that can measure well.

Generally, the measurement sensitivity of a dissolved oxygen meter deteriorates if sludge adheres to the surface of its detection electrode or if large particles (hair, etc.) become entangled. Therefore, in order to eliminate such drawbacks, the present applicant conducted various experiments and found the following. By covering the detection electrode with a group of bubbles that rise while moving randomly due to buoyancy, almost 100% of the sludge adhering to the detection electrode can be removed. However, if the bubble group rises away from the surface of the detection electrode, there is not much cleaning effect, so the bubble generation holes are arranged so that the bubble group rises due to buoyancy and evenly touches the surface of the detection electrode. It is necessary to. The above is the principle of bubble cleaning. Because there is a flow in the test water (for example, in an aeration tank, there is a swirling flow with a flow rate of 1 to 2 m/sec due to aeration), bulky waste does not settle but floats and gets entangled in the water sampling port of the test water. Therefore, if a dust prevention member, which will be described later, is provided to prevent bulky garbage from coming into direct contact with the water sampling port, the bulky garbage will not be swept away by the flow and become tangled.

The applicant has already proposed various improved dissolved oxygen meters by taking advantage of the above. First of all, special public service in Showa 54.
-24876, a detection electrode is provided inside a cylindrical casing having openings at the top and bottom, a bubble generation hole is provided in the casing below the detection electrode, and an opening at the bottom of the casing serves as a water sampling port. A dust prevention member is provided on the upstream side of the chamber, and by constantly generating air bubbles from the air bubble generation hole, the sample water is raised from the lower opening by an air lift effect, and the detection electrode is cleaned by the air bubbles. In this dissolved oxygen meter, bubble cleaning prevents sludge from adhering to the detection electrode, and since the sample water constantly rises and new sample water comes into contact with the detection electrode, bubble cleaning does not cause errors in output. However, since test water is constantly being sucked into the lower opening of the casing, bulky debris tends to get entangled in the lower opening, which obstructs water sampling and causes errors in the output, making it unusable for controlling dissolved oxygen concentration, etc.

In addition, in the dissolved oxygen meter shown in JP-A-51-74691, a detection electrode is provided inside a cylindrical casing with both ends closed, and a window serving as a water sampling section is provided on the peripheral wall of the casing. A bubble generating hole is provided below the detection electrode, and a dust blocking member is provided on the upstream side of the casing. In this dissolved oxygen meter, bubble cleaning can prevent sludge from adhering to the detection electrode, and since the sample water is not sucked in, it can also prevent large debris from getting entangled, but since the sample water near the detection electrode is stagnant, air bubbles There is a drawback that the amount of oxygen dissolved into the test water from air bubbles during cleaning increases, causing errors in the output. (However, if the rising speed of bubbles is fast, the effect of dissolved oxygen will hardly appear on the electrode output.) Therefore, the output signal (dissolved oxygen concentration value) of this dissolved oxygen meter can be used to control systems such as sewage treatment plants. When used in a system, the output signal changes suddenly during bubble cleaning, causing undesirable disturbance to the control system. Therefore, continuous cleaning may be considered.In this case, there will be no sudden change in the output signal and no disturbance will be caused to the control system, and the cleaning effect will be greater, but it will always cause output errors and the amount of dissolved oxygen cannot be measured accurately, and the control system cannot perform accurate control.

A cleaning error correction circuit is provided to correct this bubble cleaning error.

Hereinafter, a conventional example will be explained with reference to FIGS. 1 and 2.

Figure 1 shows the overall configuration of a dissolved oxygen meter, where 1 is a water test source, for example an aeration tank, 2 is the main body of the dissolved oxygen meter whose details are shown in Figure 2, and 3 is a detector installed in the main body 2. electrode, 4 is the detection electrode 3 and signal converter 12
A signal line 13 connects the signal converter 12 and the indicator recorder 14. Also, 5
is an air pipe connecting the electric on-off valve 6 and the main body part 2;
Reference numeral 7 denotes an air source, for example, an air pipe connecting an air pump 8 and an electric on-off valve.

Moreover, FIG. 2 shows the main body part 2 of the dissolved oxygen meter, and 5
Reference numeral 1 denotes a pipe supported by a holder (not shown) attached to one end of the aeration tank 1, the upper part of which is above the water test surface, and the lower part of which is submerged in the test water. The pipe 51 also serves as an air pipe, and the air pipe 5 is connected to its upper end via a lid (not shown). The upper part of the joint 21 is screwed onto the lower outer periphery of the pipe 51, and the pipe connection fitting 54 is screwed onto the peripheral wall of the joint 21. Further, the upper end of a protection tube 22 is screwed onto the lower outer periphery of the joint 21, and a plurality of elongated water sampling ports (windows) 23 are provided on the peripheral wall of the protection tube 22. It freely moves in and out of the tube 22 and comes into contact with the detection section 3. An electrode holder 24 is provided on the inner periphery of the lower part of the protection tube 22.
The detection electrode 3 is fitted and inserted into the inner periphery of the electrode holder 24, and the electrode 3 is firmly fixed by screwing a cap 25 to the lower end of the electrode holder 24. A plurality of bubble generating holes (not shown) are formed in the electrode holder 24 in a circumferential arrangement around the electrode 3. A pipe connecting fitting 55 is screwed onto the peripheral wall of the electrode holder 24 so as to communicate with the bubble generating hole, and an air pipe 52 is connected between the connecting fittings 54 and 55. The signal line 4 passes through the cap 25 and is connected to the detection electrode 3. pipe 51, joint 21,
A casing is formed by the protection tube 22 and the like,
A dust prevention member 101 is attached with a screw 102 on the upstream side of the casing with respect to the flow direction of the sample water shown at 100 in FIG.

The signal converter 12 includes a preamplifier 26 and a cleaning error correction circuit 27 as shown in FIG. 3, and the cleaning error correction circuit 27 is configured as shown in FIG. 4. In FIG. 4, 28 and 29 are operational amplifiers, VR ₀ and VR ₁ are variable resistors, and R ₁ to R ₃ are resistors.

In the dissolved oxygen meter having the above configuration, when the main body 2 is immersed in the test water source 1, the sample water is passed through the water sampling port 23 to the main body 2.
The detection electrode 3 detects the amount of dissolved oxygen (DO; dissolved oxygen saturation) in the sample water and outputs an electric signal proportional to the DO value through the signal line 4. On the other hand, the air source 8 is activated and the electric on-off valve 6 is opened to send air into the pipe 51 via the air pipes 5 and 7. Connecting fitting 5 for air
4. A bubble generation hole (not shown) is reached through the air pipe 52 and the connecting fitting 55, and a group of bubbles is generated from this hole, and this group of bubbles moves chaotically due to buoyancy while touching the surface of the detection electrode 3. rise,
It comes out from the water sampling port 23. For this reason, the detection electrode 3
The surface of the tank is cleaned by air bubbles to prevent sludge from adhering to it.

Also, the bulky debris that has moved along with the flow of the test water shown by arrow 100 hits the debris prevention member 101 and is swept away in a direction perpendicular to the flow direction, so it does not come into contact with the protection tube 22 and is removed from the water sampling port 23. It won't get tangled. Therefore, the cleaning function and measurement function are not lost. Further, when the translational kinetic energy of the test water that has proceeded in the direction shown by the arrow 100 hits the dust prevention member 101, a part of it changes into vortex energy that is generated on the rear side of the dust prevention member 101. This vortex causes the water to be tested by the dust prevention member 101.
Although it is provided on the upstream side, the water can be freely entered and exited from the water sampling port, and the detection electrode 3 allows accurate measurement. Furthermore, since the flow of the test water around the detection electrode 3 is mainly vortex motion and translational motion is reduced, the generated bubbles are not swept away and reliably rise around the detection electrode 3, increasing the cleaning effect. It will be done.

During measurement, the electric on-off valve 6 is always open, and bubbles are constantly generated from the bubble generation hole (not shown) to perform continuous cleaning. Although the cleaning effect is improved by this continuous cleaning, oxygen in the bubbles dissolves into the test water, causing an error in the output of the detection electrode 3. As a result of experiments, it was found that this amount of error has a relationship with the true DO value as shown in FIG. This relationship can be expressed as a formula: Electrode output during continuous cleaning ∝100−Δ ₀ /100 × (dissolved oxygen saturation) + Δ ₀ (1). Here, Δ ₀ is a value of about 1 to 8, and is determined depending on the water test source 1. Therefore, unless the installation location of the main body part 2, conditions of flow of water to be tested, etc. are significantly changed, it will be a constant.

True dissolved oxygen saturation DO (true), preamplifier 2
If the non-cleaning output of 6 is V _DO , then V _DO = k _DO (true)
It becomes [volt]. k is a constant. Therefore, if the output of the preamplifier 26 during cleaning is V _DO (wash), then V _DO (wash) = k{100-Δ ₀ /100 DO (true) + Δ ₀ } [volt] ...(2). The value of DO (true) ranges from 0 to 100 (%). Therefore, the cleaning error correction circuit 2 shown in FIG.
In 7, if the voltage on the output side of the variable resistor VR ₀ connected to the power supply is -V ₀ , the output voltage V ₁ of the operational amplifier 28 is V ₁ = VR ₁ /R ₁ {V ₀ −V _DO (Wash)} The output voltage V ₂ of the error correction circuit 27 is V ₂ =R ₃ /R ₂ {V ₀ (1−VR ₁ /R ₁ ) +VR ₁ /R ₁ V _DO (wash)} (3).

Substituting equation (2) into equation (3), V ₂ = R ₃ /R ₂ {V ₀ (1-VR ₁ /R ₁ ) + VR ₁ /R ₁ k (100
−Δ ₀ /100・DO (true) + Δ ₀ }...(4). When DO (true) = O, V _DO = O volts,
When DO (true) = 100, set V _DO = 1 volt,
If adjusted so that VR1/R ₁ = 100/100−Δ ₀ , (4)
The formula is V ₂ = R ₃ /R ₂ × 1/100 (true) [volts], and V ₂ is proportional to DC (true), so cleaning errors can be eliminated.

However, in order to correct this bubble cleaning error, it is necessary to find the value of Δ ₀ shown in FIG. 5 and adjust VR ₁ . As mentioned above, Δ ₀ remains constant unless the conditions at the measurement location change significantly.

To find Δ ₀ , it is necessary to follow the steps below.

Calibrate the zero point and full scale of the detection electrode 3.

The detection electrode 3 is set in the detection section and installed at the measurement location.

The indicator recorder 14 is read when bubble cleaning is not performed.

(If the flow velocity in the sample water is approximately 0.3 m/sec or higher, this reading can be taken as the true DO value).

Increased value Δ when bubble cleaning is performed in this state
Read.

(However, it is assumed that the capacity is large enough that the DO value in the aeration tank does not change due to bubble cleaning.) Estimate the value of Δ ₀ from Figure 5 or Figure 6.

Adjust VR ₁ to the value corresponding to the value of Δ ₀ .

The above cleaning error correction method has the following problems.

The correction procedure is complicated.

The value of VR ₁ corresponding to the value of Δ ₀ must be determined in advance.

If the conditions at the measurement location change significantly, it is necessary to repeat the complicated procedure.

When cleaning is performed intermittently, the cleaning error correction circuit cannot be used.

This idea was made in view of the above circumstances.
It is easy to set the correction value, it is easy to adjust so that no difference appears in the indicated value when the DO value is stable, and the error correction circuit can be used even in the case of intermittent cleaning. The purpose is to be able to provide an oxygen meter.

Hereinafter, an embodiment of the present invention will be described with reference to FIGS. 7 and 8. Identical parts from FIG. 1 to FIG. 4 are denoted by the same reference numerals.

In FIGS. 7 and 8, a first switch S ₁ serving as a first operating circuit is connected to both ends of a variable resistor VR ₁ (for error correction adjustment) provided in the cleaning error correction circuit 27. On the other hand, this first switch _S1 has a second switch that is a second operating circuit that is linked to this first switch S1.
A second switch S ₂ is provided, and this second switch S ₂ is inserted into an electric line 30 that controls the electric on-off valve 6 . 31 is a control power source for the electric on-off valve 6.

The operation of the error correction means due to bubble cleaning in the embodiment of the present invention constructed as described above will be described. In this embodiment, an example will be described in which the electric on-off valve 6 is closed when the second switch _S2 is turned on. First, (1) the zero point and full scale of the detection electrode 3 are calibrated using the indicator recorder 14. (2) Next, set the detection electrode 3 in the detection section and install it at the measurement location. (3) Here, when the first switch _S1 is turned on, the second switch _S2 is also turned on. Since the first switch S ₁ is turned on, the variable resistor VR ₁ is short-circuited, so
Error correction will no longer work. On the other hand, since the second switch _S2 of the electric on-off valve 6 is turned on, the on-off valve is closed. Therefore, bubble cleaning is no longer performed.
At this time, the indication recorder 14 indicates a predetermined indication value. (4) Thereafter, when the first and second switches S ₁ and S ₂ are turned off, the error correction of the value set in the variable resistor VR ₁ is activated. Further, the first and second switches S ₁ and S ₂
When the switch is turned off, the electric on-off valve 6 is opened, and bubble cleaning is performed. At this time, the variable resistor VR ₁ is adjusted so that the indicated value is the same as the indicated value of the indicated recorder 14 when the first and second switches S ₁ and S ₂ are on (case (3) above). This means is illustrated in FIG. 9. In FIG. 9, T ₁ indicates when the first and second switches S ₁ and S ₂ are on, T ₂ indicates when they are off, and arrow 32 indicates the indicated value adjustment position of variable resistor VR ₁ . In this way, the setting operation is completed by setting the correction values for when cleaning is not performed and when cleaning is performed. (However, the condition is that the DO value in the tank at this time is not saturated.) After performing the above adjustment operation, if you keep it in a continuous cleaning state from then on, it will always respond to changes in the DO value. Appropriate value corrections can be made. In addition, for intermittent cleaning, by automatically operating the first and second switches S ₁ and S ₂ using an external signal, the correction can be activated only during bubble cleaning, and the DO value output can be controlled by the automatic control system. It becomes possible to use it as a signal.

As described above, the present invention provides the following effects.

(1) It is no longer necessary to estimate Δ ₀ from the indicated values with and without bubble cleaning.
Setting correction values has become easier.

(2) Conventionally, it is necessary to set the variable resistance to a value corresponding to the determined Δ ₀ , so it is necessary to provide a scale corresponding to Δ ₀ in advance, but in the present invention, the operation of the first and second switches is Since it is only necessary to correct the difference in the indicated value during the measurement, the adjustment becomes easy even when the measurement location is changed. Furthermore, the adjustment means is simple because it simply matches the indicated values.

(3) Since it takes advantage of the other properties mentioned above, such as the fact that bubble cleaning has a large stain prevention effect, the error value due to bubble cleaning is small, and its appearance is constant, correction and adjustment are easy. Become.

[Brief explanation of the drawing]

Figure 1 is an overall configuration diagram of the dissolved oxygen meter, Figure 2 is a perspective view of the main body of the dissolved oxygen meter, Figure 3 is a block diagram of the signal converter, Figure 4 is a circuit diagram of the cleaning error correction circuit, and Figure 4 is a circuit diagram of the cleaning error correction circuit. Figure 5 is a diagram of the relationship between the true DO value in the dissolved oxygen meter and the output of the detection electrode during cleaning, Figure 6 is a diagram of the relationship between the true DO value and the increased output during cleaning, and Figures 7 to 9 The figures show one embodiment of the present invention, in which Fig. 7 is an overall configuration diagram of a dissolved oxygen meter, Fig. 8 is a circuit diagram of a cleaning error correction circuit equipped with the first and second operating circuits, and Fig. 9 8 is an explanatory diagram for explaining the operation of FIG. 8. FIG. 1... Water test source, 2... Main unit, 3... Detection power source, 6... Electric shut-off valve, 8... Air source, 12...
Signal converter, 14...Indication recorder, 26...Preamplifier, 27...Cleaning error correction circuit, 30...Electric circuit, 31...Control power supply, _S1 , _S2 ...1st, 2nd switch, VR ₀ , VR ₁ ...Variable resistance.

Claims (1)

[Scope of utility model registration request] A casing that is immersed in a sample water source, a water sampling port formed in the casing through which sample water enters and exits, a detection electrode provided within the casing, and an air source provided below the detection electrode within the casing. A bubble generation hole that constantly generates a group of bubbles that move up while moving chaotically near the detection electrode due to buoyancy, and an electrically operated opening/closing device installed in the middle of the air piping that connects this bubble generation hole and the air source. a cleaning error correction circuit connected to the output side of the detection electrode and provided with a variable resistor for correcting errors caused by the air bubble cleaning; an indicator recorder for instructing; a first switch connected to both ends of the variable resistor to turn both ends of the variable resistor on and off;
A second switch is interlocked with the first switch and inserted into the electrical circuit that controls the electric on-off valve. A dissolved oxygen meter characterized in that an error correction value is set to a variable resistance based on the value.