JPH03250309A - Ph controller - Google Patents

Abstract

PURPOSE:To attain the stable pH control by providing a control means which inputs the signal received from a piecewise linear function circuit and outputs a control signal to a valve and an instruction means which produces an instruction so as to secure an automatic mode when the signal received from a pH sensor is kept out of a prescribed upper/lower limit range. CONSTITUTION:A 1st pipeline 3 is provided to supply an acid liquid into a tank 1 containing a liquid 2 to be neutralized together with a 2nd pipeline which supplies a basic liquid, and the 1st and 2nd valves 5 and 5. A piecewise linear function circuit 9 converts the signal received from a pH sensor 7 into a signal that secures pH7 as long as the signal received from the sensor sensor 7 is equal to about pH7. An instruction means 10 inputs the signal received from the sensor 7 and sets a controller 8 in a manual mode when the pH value is kept within a prescribed range and then sets the controller 8 in an automatic mode if the pH value exceeds the prescribed range. The controller 8 closes two valves 5 and 6 in a manual mode and outputs the control output based on the signal received from the circuit 9 in an automatic mode respectively. Thus it is possible to minimize the amounts of both acidic and basic liquids to be supplied and to quickly neutralize the pH value of the liquid 2 to pH7.

Description

[Detailed Description of the Invention] <Industrial Application Field> The present invention relates to a pH control device that controls the pH value of a liquid stored in a tank by flowing an acid or a base into it. The present invention relates to a PH control device in which a valve disposed in a conduit for supplying base and a valve disposed in a conduit for supplying base are split control valves, and these valves are controlled by the output of a controller.

<Prior Art> FIG. 4 is a configuration block diagram showing an example of a conventional PH control device. In the figure, 1 is a storage tank, and 2 is a liquid filled in the storage tank, such as factory waste liquid, and PH sub-control is performed to neutralize this liquid.

3 is a pipe line to which an acidic liquid is supplied, 4 is a line g to which a base liquid is supplied, and a valve 5.6 is installed in each pipe line.

7 is a PH sensor, and 8 is a controller that inputs a signal from the PH sensor 7 and controls the opening degree of each valve 5, 6.

Here, each valve 5.6 is a split control valve.

<Problem to be solved by the invention> In the control device with this convenient configuration, the P of the liquid 2 in the tank 1
When adjusting the H value to pH 7 (neutralizing), in an actual process, the process gain is quite different between pH 6 and pH 8 and above or below, so for example, valve 5 for supplying acid must be opened. Even if the pH sensor detects pH 7 and closes the valve 5 to stop the acid supply, the liquid in the tank becomes a strong acid and cannot be neutralized, so the valve 6 is opened to supply the base solution. After that, similar actions were repeated.

For this reason, there was a problem in that a large amount of acidic liquid or base liquid was required for neutralization. In addition, if the agitation of the liquid in the tank 1 is poor, the detection response from the P1 sensor is delayed, further reducing controllability.

The present invention was made in view of this important point, and its purpose is to minimize the amount of acidic and basic liquids supplied and to quickly neutralize the pH value of the liquid to pH 7. The object of the present invention is to provide a PH control device with good controllability.

Means for Solving the Problems> The present invention for solving the above-mentioned problems comprises: a tank in which a liquid to be neutralized is stored; a first pipe line for supplying an acidic liquid into the tank; a second pipe line that supplies a base solution; a first valve and a second valve that are installed in the first pipe line and the second pipe line respectively and perform split control operations on each other; and a liquid in the tank. A PH sensor that detects the PH value of
A broken line function circuit that inputs a signal from a sensor and outputs a signal such that the pH value indicates pH 7 when the signal includes pH 7 and indicates a value around it, and a signal to this broken line rWJ several times. and enter the first,
A control means for outputting a control signal to a second valve; and a signal from the PH sensor is input, and when the signal is within a predetermined upper and lower limit set value range, the control means is set to manual mode and manual output is performed. and an instruction means for instructing to set the value to 50%, and for instructing to enter automatic mode when the value is outside the upper and lower limit ranges.

Function> When the signal from the PH sensor is around pl (7), the polygonal function circuit converts it into a signal that sets the pH to 7.

The instruction means inputs a signal from the PH sensor, and instructs the controller to enter manual mode if the PH value is within a predetermined range, and to enter automatic mode if it exceeds the predetermined range.

In manual mode, the controller provides a manual output such that the two valves are activated, and in automatic mode, it provides a control output based on the signal from the linear function circuit.

<Example> Embodiments of the present invention will be described in detail below with reference to the drawings.

FIG. 1 is a block diagram showing an embodiment of the present invention. In the figure, reference numeral 1 denotes a tank in which a liquid 2 to be neutralized is stored, for example a waste liquid, which is neutralized here and then discharged into a river or the like.

3 is a first pipe line that supplies an acidic liquid into the tank 1, 4 is a second pipe line that supplies a base liquid into the tank 1, and 5 is a line between the first pipe line 3 and the second pipe line 4. The first one installed respectively. This is the second valve. These two valves 5 and 6 are commonly given the control output MV from the controller 8, and are configured to perform a split control I-roll operation with respect to this control output as shown in FIG. It has become. That is, the first valve 5 operates so that its opening gradually increases in accordance with the control output in the range of 12 mA to 20 mA with respect to the control output 4 to 20 mA from the controller 8, and the second valve 6 teeth,
When the control output is 4 mA, the opening degree is 1.0%, and then the opening degree gradually decreases according to the control output, and at 1.2 mA or more, the opening degree is closed.

7 is a PH sensor that detects the pH value of the liquid in the tank 1, 9 is the input signal P from this PH sensor 7, and this signal P
When v includes pH 7 and indicates a value around it, it is a broken line function circuit that outputs a signal such that the pH value indicates pH 7 and applies it to the controller 8.

FIG. 3 is a diagram showing the functional characteristics of the broken line function circuit 9. FIG. In this example, the signal P■ from the PH sensor 7 is pH5
In the range showing PH9, the output signal is output as a signal showing PH7.

10 inputs the signal PV from the PH sensor 7, and when this signal is within a predetermined upper and lower limit setting value, for example, pH 5 to pH 9, the controller 8 is set to manual mode (MAN) and the manual output is set to 50%. It is an instructing means that instructs the automatic mode (AUTO) to be set when the value is outside the upper and lower limit set value ranges. The controller 8 is, for example, a PIDi moderator that inputs the signal from the linear function circuit 9, and can operate as a sample PI controller in addition to manual mode and automatic mode based on instructions from the indicating means 10. It is configured to do so.

The operation of the device configured in this way will be explained next. Let us now assume that the pH value of the liquid in W41 has shifted toward the base side, that is, the signal P from the PH sensor 7 has changed from around pH 8 to pH 9.

In this case, a signal indicating that the pH value of the liquid 2 in the tank 1 is pH 7 is applied to the controller 8 via the linear function circuit 9. Further, since the signal from the pH sensor 7 is within a predetermined upper and lower limit set value, for example, pH 5 to pH 9, the instruction means 10 outputs an instruction to set the controller 8 to manual mode.

Upon receiving such an instruction signal, the controller 8 outputs a manual output value of 50% (2 mA) to the first and second valves 5.6. This leads to the first. The second valves 5.6 both have an opening degree of 0% and are maintained in a closed state.

If this condition is maintained, the pH of the liquid 2 will eventually increase further, and the signal P■ from the PH sensor 7 will exceed the upper limit setting value (PH9>).

Then, the instruction means 10 issues an instruction to set the controller 8 to automatic mode. Upon receiving this instruction, the controller 8 switches to automatic mode, opens the first valve 5 in response to the signal from the polygonal function circuit 9 so as to approach pH7, and pours the acidic liquid into the pipe #I3.
It flows into tank 1 through .

Here, since the controller 8 receives the signal that has passed through the linear function circuit 9, the opening degree of the first valve 5 is kept very small. Therefore, the pH value of the liquid in the tank 1 gradually changes towards acidity. Then, when the signal Pv from the PH sensor 7 becomes smaller than the upper limit setting value (PH9>), the instruction means 10 issues an instruction to set the controller 8 to manual mode.

Upon receiving this instruction, the controller 8 changes to manual mode and outputs a manual output value of 50% (12 mA).

This leads to the first. Both the second valves 5 and 6 have an opening degree of O
% and becomes closed.

As a result, the liquid in the tank 1 will be maintained at around pH 7.

If the pH value of the liquid in tank 1 changes to the acidic side, that is, the signal P from the PH sensor 7, or the pH value changes from around pH 6 to p.
The operation is similar in the case where the change is in the direction of H5.

In addition, W! If the agitation in the sample 1 is poor, the response of the signal from the PH sensor will be slow, or under such a situation, stable control can be achieved by having the controller 8 perform the sample P2 operation.

<Effects of the Invention> As explained in detail above, according to the present invention, P
In the case of neutralizing H7, there were cases where repeated operations such as opening two valves alternately were performed, but it is necessary to prevent such defective control and perform stable P I can do it.

Further, the amount of acidic liquid or base liquid for neutralization can be greatly reduced.

[Brief explanation of drawings]

FIG. 1 is a configuration block diagram showing one embodiment of the present invention, and FIG.
Figure 1. FIG. 3 is a diagram showing the characteristics of a polygonal function circuit, and FIG. 4 is a block diagram showing an example of a conventional PII control device. 1... Tank 3... First pipe line 56... Valve 8... Controller 10... Indicating means 2... Liquid 4... Second pipe line 7... P H sensor 9... broken line function circuit

Claims (1)

[Scope of Claims] A tank in which a liquid to be neutralized is stored; a first pipe line for supplying an acidic liquid into the tank; and a second pipe line for supplying a base liquid into the tank; The first and second valves are installed in the first pipe line and the second pipe line, respectively, and perform split control operation on each other; a PH sensor that detects the pH value of the liquid in the tank;
A signal from the sensor is input, and when the signal includes pH 7 and indicates a value around it, a broken line function circuit outputs a signal such that the pH value indicates pH 7, and a signal from this broken line function circuit is input. , the first and second
an adjusting means for outputting a control signal to the valve; and a signal from the PH sensor is input, and when the signal is within a predetermined upper and lower limit set value range, the adjusting means is set to manual mode and the manual output is set to 50%. and an instruction means for instructing to set the automatic mode when the pH is outside the upper and lower limit ranges.