JPH0629617Y2 - Water detection anticorrosion circuit - Google Patents

Description

[Detailed Description of the Invention] [Object of the Invention] (Field of Industrial Application) The present invention is a water detection anticorrosion circuit, particularly water detection for a water heater that heats water using oil, gas, electricity, etc. as a heat source. Regarding anticorrosion circuit.

(Prior Art) A conventional apparatus will be described using the hot water supply system in FIG.

Reference numeral 1 denotes a can body, the metal surface of which is enameled, and the water supplied from the water supply port 2 is heat-exchanged by the burner unit 3 to be hot water, which is supplied to the place of use through the hot water supply port 4.

A water detecting / corrosion preventing electrode 5 and a ground electrode 6 are provided on the side wall of the can body 1, and a water detecting / corrosion preventing circuit 7 connected to these electrodes is provided.
In, the presence or absence of water in the can is detected and the anticorrosive potential is applied.

Here, the anticorrosion potential is the potential difference applied to the contact surface between water and metal in the direction of canceling the corrosion potential generated between the can body 1 and water.

Reference numeral 8 is a controller of the burner section. As is apparent from the above configuration, the water detection / corrosion prevention circuit 7 detects water in the can body 1 to prevent the heating by the burner part 3 and at the same time, the can body 1
The anticorrosion potential is applied to the. And the third
The figure shows an example of a conventional water detection anticorrosion circuit.

As shown in FIG. 3, the water resistance R _W is between the electrodes 5 and 6.
There is a fixed voltage V _CC to the Zener diode
The method of applying via ZD is adopted.

Therefore, in a normal state in which water is present in the can body 1, a predetermined voltage reduced by the voltage drop due to the Zener diode ZD and the short-circuit resistance R ₁ is applied as the anticorrosion potential, and the input terminal of the operational amplifier OP is also predetermined. A voltage is applied.

Then, a reference voltage from the power supply E ₁ is applied to the reference terminal of the operational amplifier OP. For example, if the input terminal voltage is lower than the reference voltage, the output V _{0 of the} operational amplifier OP becomes H level, and display etc. is performed by a method not shown. Done. If the water runs out in this state, the voltage at the input terminal becomes higher than the reference voltage, and as a result, the output V _{0 of the} operational amplifier OP becomes L level, which is used as an alarm and other outputs.

(Problems to be Solved by the Invention) In the conventional device having the above configuration, it is necessary to insert the short-circuit resistor R ₁ for protection when the electrode and the ground are short-circuited. In addition, and due to variations due to changes in water quality resistance R _W of water
Changes. For this reason, not only a constant anticorrosion voltage cannot be obtained, but also the characteristics of the entire device become unstable due to further changes due to the temperature characteristics of the Zener diode ZD.

The present invention has been made in view of the above circumstances, and an object thereof is to provide a water detection anticorrosion circuit that can obtain extremely stable characteristics.

[Structure of the Invention] (Means for Solving Problems) The present invention will be described with reference to FIG. 1 corresponding to the embodiment.
By applying a reference voltage by a voltage dividing means to the first and second operational amplifiers OP ₁ and OP _{2 and} using the first operational amplifier OP ₁ so that the voltage of the electrodes becomes constant, a negative return resistance is obtained. An anticorrosive voltage is applied to the electrode 5 provided on the side wall of the can via R ₂ to change the water resistance R _W by the first operational amplifier OP.
The output change of ₁ is detected, and this voltage change is input to the second operational amplifier OP ₂ to derive the detection output.

(Operation) The output voltage of the first operational amplifier OP ₁ is output so that a constant voltage such that the electrode 5 becomes V _refl is applied. Therefore, the current i _B that compensates for the change in the water resistance R _W flows through the negative return ring resistance R ₂ .

Therefore, water detection is detected as a change in the output voltage of the first operational amplifier OP ₁ , which is input to the second operational amplifier OP ₂ and detected as a change in the output of the OP ₂ .

(Examples) Examples will be described below with reference to the drawings.

FIG. 1 is a block diagram of an embodiment of a water detection / corrosion protection circuit according to the present invention.

In FIG. 1, the water detection / corrosion protection electrode 5 is connected to the input terminal (-) of the first operational amplifier OP ₁ via the operational amplifier input offset current compensation resistor R ₁ and also connected to the negative feedback ring resistor R ₂ . Is connected to the output terminal of the first operational amplifier OP ₁ . In this case, the first operational amplifier OP ₁ has a function such that the electrode 5 has a constant voltage V _refl (corrosion protection voltage).

R ₆ , R ₇ , and R ₈ are voltage dividing resistors, and the first reference voltage generated by these resistors is used. Is applied to the reference terminal (+) of the first operational amplifier OP ₁ .

Input terminal (-) of the second operational amplifier (comparator) OP ₂
Is connected to the output terminal of the first operational amplifier OP ₁ via the operational amplifier protection resistor R ₃ , and the reference terminal (+) is connected to the second reference voltage via the resistor R _4. Is applied.

Then, the output of the second operational amplifier OP ₂ is input to the CPU. Note that V _CC is a constant voltage power supply.

Next, the operation will be described.

The reference terminal (+) of the first operational amplifier OP ₁ has the above-mentioned V
_Refl is applied and the electrode 5 is output by the function of becoming a constant voltage (corrosion protection voltage) V _refl . The resistance R ₂ connected to the output end is a negative return resistance, and at the same time, plays a role of causing a current i _B (corrosion protection current) to flow through the water resistance R _W.

Here, it is assumed that the output voltage of the first operational amplifier OP ₁ is V _W. When the resistance R _W changes (increases to + ∞) due to water shortage, the output voltage V _W of OP ₁ is almost the reference voltage V _W.
It becomes _refl .

The anticorrosion voltage is not affected by the resistance value of water, and a constant voltage V _refl is _applied to the terminal 5 and the water resistance R _W.

In this state, the second operational amplifier (comparator)
To the reference terminal (+) of OP ₂ through the resistor R ₄ , the above-mentioned V
_ref2 is applied. Therefore, the output of OP ₂ is always at the L level, but if the water resistance increases (+ ∞) due to water shortage, the output V _{W of} the first operational amplifier OP ₁ becomes V
_Since it becomes _refl and decreases, the input of the second operational amplifier OP ₂ becomes smaller than the reference voltage (because V _refl <V _ref2 ), the output becomes H level and inverted, and the CPU detects this. To do.

The resistor R ₅ is a resistor for hysteresis, and is provided to prevent chattering in the CPU when the output of the second operational amplifier OP ₂ changes due to the change in water resistance.

Here, assuming that the operational amplifier H level voltage is V _CC , the water detection voltage is V _W (ON), and the water absence detection voltage is V _W (OFF), the above-mentioned hysteresis V _H is as follows.

_However, the _{R 6, R 7, R 8} «R 4, R 5.

Therefore, according to the present embodiment, a stable circuit that is not affected by temperature is provided.

[Effect of the Invention] As described above, according to the present invention, the reference voltage generated by the voltage dividing means is applied to the reference terminal of each operational amplifier, and the operational amplifier is used so that the electrodes have a constant voltage. , The anti-corrosion voltage is applied to the electrode provided on the can body through the negative return resistance, and the change in the output voltage of the operational amplifier caused by the change in the water resistance is detected by the comparator in the next stage. It is possible to provide an extremely stable water detection / corrosion protection circuit that is not affected by the above.

[Brief description of drawings]

FIG. 1 is a block diagram of an embodiment of a water detection anticorrosion circuit according to the present invention, FIG. 2 is an example of a general hot water supply system, and FIG. 3 is an example of a conventional water detection anticorrosion circuit. OP _1, OP ₂ ... op V _refl, V _ref2 ... first, second reference voltage R W _... water resistance, 5,6 ... electrode

Claims (1)

[Scope of utility model registration request] 1. A water detection / corrosion protection circuit for providing a single electrode on a side wall of a can body for storing water to perform cathodic protection and water detection in the can body, wherein voltage dividing means is provided for the first and second operational amplifiers. The reference voltage is applied to the electrodes and the first operational amplifier is used so that the voltage of the electrodes is constant. A water detection / corrosion protection circuit characterized in that a change is detected as an output change of the first operational amplifier, and this voltage change is input to a second operational amplifier to derive a detection output.