JPH0138523Y2 - - 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. Since there is a flow in the test water (for example, in an aeration tank, there is a circulating flow with a flow rate of 1 to 2 m/sec due to aeration), bulky waste does not settle but floats and becomes entangled in the water sampling port of the test water. Therefore, if you prevent bulky garbage from coming into direct contact with water intake ports, etc., 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 the output. Since sample water is constantly 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 output, making it unusable for controlling dissolved oxygen concentration, etc.

Furthermore, in the dissolved oxygen meter shown in JP-A-51-74691, a detection electrode is provided around the periphery of a cylindrical casing with both ends closed, and a window serving as a water sampling section is provided on the periphery of the casing. A bubble generating hole is provided in the casing 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 test water is not sucked in, it can also prevent large debris from getting entangled, but since the test 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. Therefore, when the output signal (dissolved oxygen concentration value) of this dissolved oxygen meter is used in a control system of a sewage treatment plant or the like, the output signal changes suddenly due to bubble cleaning, causing an 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 increased, but it will always cause an output error and the amount of dissolved oxygen cannot be measured accurately, and the control system cannot perform accurate control.

Taking the above points into consideration, the present invention has a good cleaning effect of bubble cleaning on the detection electrode, prevents bulky debris from getting entangled in the water sampling port, and can correct measurement errors caused by bubble cleaning. The purpose is to provide a dissolved oxygen meter.

Embodiments of the present invention will be described below with reference to the drawings.
FIG. 1 shows the overall configuration of the dissolved oxygen meter according to this embodiment, where 1 is a water test source, such as an aeration tank, 2 is the main body of the dissolved oxygen meter shown in FIGS. 2 to 4, and 3 is installed in the main body 2. 4 is a signal line connecting the detection electrode 3 and the signal converter 12, and 13 is a signal line connecting the signal converter 12 and the indicator recorder 14. Further, 5 is an air pipe that connects the electric on-off valve 6 and the main body portion 2, and 7 is an air pipe that connects an air source, for example, an air pump 8 and the electric on-off valve 6.

2 to 4 show the main body 2 of the dissolved oxygen meter, and 51 is 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. At the same time, the lower part is submerged in water. The pipe 51 also serves as an air pipe, and a pipe connection fitting 53 is screwed onto the upper end of the pipe through a lid 9, and the air pipe 5 is connected to the pipe connection fitting 53. The upper part of the joint 21 is screwed onto the outer periphery of the lower part of the pipe 51, the pipe connection fitting 54 is screwed onto the peripheral wall of the joint 21, and a truncated conical part 212 is formed at the lower end of the joint 21. In addition, a protective tube 2 is installed on the outer periphery of the lower part of the joint 21.
2 is screwed onto the upper end of the protective tube 22, and a plurality (four in the figure) of elongated water sampling ports (windows) 23 are provided on the peripheral wall of the protective tube 22. Water can be sampled freely into the protective tube 22 through the water sampling ports 23. and comes into contact with the detection unit 3. Protection tube 22
An electrode holder 24 is screwed onto the lower inner periphery of the electrode holder 24, a support member 10 for supporting the detection electrode 3 is fitted and inserted into the inner periphery of the electrode holder 24, and a cap 25 is screwed onto the lower end of the electrode holder 24. The support member 10 is firmly fixed. An annular groove 242 is formed in the lower part of the electrode holder 24, and a plurality of bubble generating holes 243 are formed in a circumferential arrangement upward from the groove 242. A pipe connection fitting 55 is screwed onto the peripheral wall of the electrode holder 24 so as to communicate with the groove 242.
An air pipe 52 is connected between the connecting fittings 54 and 55. The signal line 4 is connected to the cap 25 and the support member 1.
0 and connect it to the detection electrode 3. pipe 5
1, joint 21, protection tube 22, electrode holder 2
4, etc., and a dust prevention member 101 is attached with screws 102 on the upstream side of the casing with respect to the flow direction of the sample water shown at 100 in FIG.

Further, the signal converter 12 includes a preamplifier 26 and a cleaning error correction circuit 27 as shown in FIG. 5, and the cleaning error correction circuit 27 is configured as shown in FIG. In FIG. 6, 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 with the above configuration, the main body 2 is the water test source 1.
When the sample water is immersed in water, it enters and exits the main body 2 through the water sampling port 23 and comes into contact with the detection electrode 3.
is the amount of dissolved oxygen in the sample water (Do; dissolved oxygen saturation)
is detected, and an electrical signal proportional to the Do value is sent to signal line 4.
Output by 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. Air reaches the groove 242 through the fitting 54, the air pipe 52, and the fitting 55. As a result, the bubble generation hole 2
A group of bubbles is generated from 43, and this group of bubbles rises while touching the surface of the detection electrode 3 while moving chaotically due to buoyancy, hits the truncated cone portion 212, and enters the water sampling port 2.
Go out from 3. Therefore, the surface of the detection electrode 3 is cleaned by air bubbles and adhesion of sludge and the like is prevented.

Also, since the bulky debris that has moved along with the flow of the test water shown by the arrow 100 hits the debris prevention member 101 and is swept away in a direction perpendicular to the flow direction, it does not connect to the protection tube 22 and passes through 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 sample water that has proceeded in the direction indicated by the arrow 100 hits the dust prevention member 101, a part of it changes into vortex energy generated on the rear side of the dust prevention member 101. Due to this vortex, the sample water can freely enter and exit from the water sampling port even though the dust blocking member 101 is provided on the upstream side, and the detection electrode 3 can perform accurate measurements. 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.

Further, during measurement, the electric on-off valve 6 is always open, and bubbles are always generated from the bubble generation hole 243 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. Expressing this relationship in a formula is: 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 3,
This value is determined by the water test source 1. Therefore, it remains constant unless the installation location of the main body 2 is changed. This constant can be easily determined by comparing the outputs using, for example, a portable dissolved oxygen meter. If the true dissolved oxygen saturation is Do (true) and the output of the preamplifier 26 during non-cleaning is V _Dp , then V _Dp = kDo
(true) becomes [volt]. k is a constant. Therefore, the output when cleaning the preamplifier 26 is V _Dp (washing)
Then, V _Dp (Wash) = k {100−Δ ₀ /100Do (True) + Δ ₀ } [Volt...(2). The value of Do (true) ranges from 0 to 100 (%). Therefore, in the cleaning error correction circuit 27 shown in FIG. 6, 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 _Dp (washing)} The output voltage V ₂ of the cleaning error correction circuit 27 is V ₂ = R ₃ /R ₂ {V ₀ (1 − VR ₁ /R ₁ ) +VR ₁ /R ₁ V _Dp ( Wash)} …(3) becomes. Substituting equation (2) into equation (3), we get V ₂ = R ₃ /R ₂ {V ₀ (1-VR ₁ /R ₁ ) +VR ₁ /R ₁ k (100-Δ ₀ /100Do (true) + Δ ₀ )}…(4) becomes. When Do (true) = 0, V _Dp = 0 volts, Do
If (true) = 100, then V _Dp = 1 volt, then k = 1/100. Also, if we set V ₀ = 1 volt and adjust it so that VR ₁ /R ₁ = 100/100−Δ ₀ , equation (4) becomes V ₂ = R ₃ /R ₂ × 1/100Do (true ) [volts], and V ₂ is proportional to Do (true), and cleaning errors can be eliminated. Note that the same function can be obtained by using VR ₁ as a fixed resistor and the two R _1s as variable resistors. This output V ₂ is input to the instruction recorder 14 via the signal line 13 to record the instruction. By monitoring the indicator recorder 14, the monitor can accurately know the amount of dissolved oxygen in the sample water. Furthermore, by connecting the output _V2 to the control system, dissolved oxygen concentration control can be performed accurately without disturbance.

As described above, in the present invention, a detection electrode is provided in the casing, and a bubble generation hole is provided below the detection electrode to constantly generate a group of bubbles that move up while moving chaotically near the detection electrode due to buoyancy. The detection electrode is constantly cleaned by a group of bubbles,
The cleaning effect to prevent sludge from adhering to the detection electrode is enhanced, and sludge adhesion is completely prevented. In addition, oxygen dissolves into the sample water from air bubbles during cleaning, so if constant cleaning is performed, the output of the detection electrode will always include a cleaning error, but a correction circuit is installed on the output side of the detection electrode to correct the cleaning error. The output of the oxygen meter will always show the correct Do value. Furthermore, when cleaning is performed intermittently, the output of the detection electrode changes greatly during cleaning, causing disturbance to the control system and making it difficult to perform accurate control. There are no sudden changes and the output is always accurate, so dissolved oxygen concentration can be measured accurately without any disturbance.
In addition, a water sampling port is provided in the casing so that the sample water can freely enter and exit the casing and come into contact with the detection electrode, and since the sample water is not sucked into the casing due to the air lift effect, large debris may enter the water sampling port. There is little chance that measurement will become impossible due to entanglement.

[Brief explanation of the drawing]

Fig. 1 is an overall configuration diagram of a dissolved oxygen meter according to the present invention, Figs. 2 to 4 are a half-longitudinal front view of the main body of the dissolved oxygen meter according to the present invention, Fig. 2 is a cross-sectional plan view taken along line X-X, and A perspective view, FIG. 5 is a block diagram of the signal converter according to the present invention, FIG. 6 is a circuit diagram of the cleaning error correction circuit according to the present invention, and FIG. 7 is a true Do value in the dissolved oxygen meter according to the present invention. and the output of the detection electrode during cleaning. DESCRIPTION OF SYMBOLS 1... Water test source, 2... Main body, 3... Detection electrode, 6... Electric shut-off valve, 8... Air source, 12...
Signal converter, 14... Indication recorder, 21... Joint, 22... Protection tube, 23... Water sampling port, 24
...Electrode holder, 243...Bubble generation hole, 26...
...Preamplifier, 27...Cleaning error correction circuit, 2
8, 29...Operation amplifier, _VR0 , _VR1 ...Variable resistor, _R1 to _R3 ...Resistor.

Claims (1)

[Scope of utility model registration request] A detection electrode is provided in the casing, and a bubble generation hole is provided below the detection electrode in the casing to constantly generate a group of bubbles that are connected to an air source and move up while moving chaotically near the detection electrode due to buoyancy. In order to provide a water sampling port through which the sample water enters and exits, and to correct the error caused by air bubble washing on the output side of the detection electrode, when the true dissolved oxygen saturation is Do, (100−△o/100) ×Do＋△o
(However, △o is a constant determined by the water source)
A dissolved oxygen meter characterized by being equipped with a cleaning error correction circuit that generates an output proportional to Do.