JPH071190B2 - Water level detector for water heater with bath - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a water level detecting device in a bathtub of a water heater with a bathtub, and in particular, a pressure sensor is used to detect the water level in the bathtub by a pressure change based on the amount of hot water. Regarding the improvement of the device.

[Prior Art] Even though it is a conventional example, a recent hot-water supply device with a bathtub includes an automatic filling function up to the set water level in the bathtub, an automatic reheating function for cold water, and other functions using a microcomputer. A high degree of control is possible. Further, as for the heat exchanger, in addition to the one for hot water supply used at the time of automatic filling of water or the normal tap, shower, etc., there is also one dedicated for reheating.

Naturally, in such a water heater, for example, the user can pour hot water to a set water level that is set arbitrarily or fixed at any of several suitable height positions. It is necessary to detect the water level in the bathtub in order to know whether or not the bath is finished.

However, a classical type of water level detection sensor of this type is a float type that is used by floating in a bathtub. With such a liquid level detector, the water level can be known simply by the geometrical liquid level of the hot water in the bath, but this is not preferred as a recent product. It needs to be attached directly to the bathtub, which not only impairs the design, but also causes injury. Further, generally, it is not possible to continuously detect a change in the water level, and it is only possible to judge whether or not the molten metal surface has reached a predetermined single height position. In order to perform continuous liquid level detection with a float type, for example, a potentiometer is housed in a cylindrical housing, and it is operated in a non-contact manner and variably adjusted according to the movement of the float. I have to say.

Therefore, recently, as the concept is shown in FIG. 4, a method of continuously detecting the water level of the hot water in the bathtub by using the pressure sensor 21 is generally adopted.

For example, when a user's command operation on an operation panel (not shown) requests a filling of water to the microcomputer 23 (simply CPU in the figure) built in the controller of the water heater main body 20, In response, the microcomputer 23 issues an ignition command to a burner (not shown) to heat the heat exchanger 22, and based on the detection information from the temperature sensors (not shown) and the flow rate sensor, the hot water is heated to the set temperature. The bathtub 11
To start hot water supply. The hot water supply port at this time is described as "communication port 12" instead of the hot water supply port in the figure for a reason described later, and is provided at a predetermined height x (cm) from the bottom of the bathtub 11.

While the automatic filling of water into the bathtub 11 is started in this manner, preset water level data is given to the microcomputer 23 in advance. What is set water level data?
Although it is data that specifies which height position of the bathtub 11 the hot water is poured into, this is actually represented by the water pressure data when the set water level is reached after starting to put hot water into the empty bathtub, Therefore, the microcomputer 23 is provided with an appropriate correspondence between the water pressure and the water level for each bathtub to be used, through the attached memory.

That is, first, when pouring or pouring (a representative of pouring) one by one into an empty bathtub 11, the pressure sensor 21 in the case of the figure shows the bottom of the bathtub 11 (this is the standard height position). Since it is located at the same height as the communication port 12 that has a height of x cm from "0", the pressure value detected by this pressure sensor 21 will be the first even if pouring by a Is zero.

Generally, the detection output of the pressure sensor 21 is a voltage output,
In the rest of this document, this will be represented by V _P. However, as shown in FIG. 3, the pressure range to be detected by the commercially available pressure sensor 21 of this kind is positive and negative, so that when the detected pressure is zero. However, a certain constant voltage output V _P x was generated. Therefore, even if pouring starts from an empty state in the bathtub 11, the pressure sensor output voltage V _P remains V _P = V _P x until the water level in the bathtub reaches x cm.

At the place where the pouring was done, a times a times and b times 12
When soaked in hot water, which causes significant pressure on the pressure sensor 21, its output voltage V _P begins to increase. Therefore, the pouring a · b () until such a change in the output voltage V _P of the pressure sensor 21 is first captured is at least at the height position x at which the pressure sensor 21 is located at the bathtub 11 from the bottom of the bathtub. It can be seen that the amount of hot water required to fill the water to (cm) is within the allowable range.

After that, the actual water level, which increases every time a is poured into the bathtub 11, and the output voltage value V _P of the pressure sensor 21 at that time are generally in one-to-one correspondence.

Therefore, by writing such a correspondence relationship in the memory and giving it to the microcomputer 23 when necessary, even if the user subsequently changes the set water level during actual use, the total amount of hot water required up to the changed water level is It can be calculated immediately or, more simply, the water level in the bathtub at that time can be known based on the output voltage value V _P of the pressure sensor 21.

Of course, the output voltage V _P of the pressure sensor 21 is an analog voltage value as shown in FIG. 3, but generally this analog data is used after being converted into a digital value by the microcomputer 23. Therefore, it is necessary to consider the resolution of the water level detection, but as can be seen in the bathtub 11 shown by the solid line in FIG. 4, at the set height position between the pressure sensor 21 and the bathtub 11. Sufficient resolution was obtained as long as there was no big difference and the height difference was within a predetermined allowable range.

For example, taking a concrete example, as shown in FIGS. 3 and 4, the bathtub is moved from the height position x (cm) where the communication port 12 is located.
Maximum height position x + α when pouring hot water inside 11
The water level change range α (cm) in the bathtub up to (cm) is generally about 60 cm, even if it is roughly estimated with some margin. Conversely, a deeper bathtub is usually unthinkable.

On the other hand, the number of bits at the time of analog-to-digital conversion by the microcomputer 23 can be easily and inexpensively obtained at about 8 bits, so that the resolution is 60 (cm) /256=0.2 cm / bit, which is sufficient.

It should be noted that the planned maximum height position x + α in the bathtub 11
The output voltage value V _P of the pressure sensor 21 corresponding to when the hot water is filled up to (cm) is indicated by the symbol V _PM in FIG.

Further, in FIG. 4, the direction of the hot water with respect to the communication port 12 is
Not only the hot water supply direction explained above, but the opposite direction is also indicated by the arrow in parentheses, but this is because the water heater with the reheating function has Hot water is taken in through the inlet, heated through a heat exchanger that is also used for hot water supply or for reheating, and then returned to the bathtub from the hot water inlet again. This is because the sensor 21 may be provided in the flow path communicating with the intake port. Therefore, as in the case of the present invention described later, the "communication port 12" is
It may be a hot water supply port or an intake port. In either case, the pressure sensor 21
Should be provided.

[Problems to be Solved by the Invention] However, as shown in phantom lines in FIG.
In the recent installation form, it is required to allow a case where the installation height position of the bathtub 11 is greatly different from the installation height position of the water heater body 20. For example, the water heater body 20 is arranged at the height position of the first floor of the house, and the bathtub 11 is provided on the second floor of the house, or vice versa.
Or, for example, installing a bathtub in the basement.

Here, in FIG. 4, the bottom of the bathtub 11 indicated by a solid line at a height position substantially the same as that of the water heater main body 20 is set as a reference height position and the origin of height is set to 0 m. The height to the bottom of the virtual line bathtub 11 installed at a high position is + H
₂ (m), and the height to the bottom of a bathtub installed at a low position is -H ₁ (m), those values are easily 2 m respectively.
The degree is conceivable.

In such a case, the pressure sensor 21 built into the water heater body 20
The range of water level change to be detected is not limited to the water level change range α (cm) in each bathtub, but it is natural because it is affected by potential energy. Must also be covered.

In fact, conventionally, in such a case, as shown in FIG. 2, for example, a 5 m width from −2 m to +3 m is set as the water level detection target range, and this can be detected in the output voltage range of 0 to 4 V. I used a different pressure sensor.

However, as will be readily apparent, as in the case of the prior art example, the pressure sensor 21 changes the height change range X + α of the hot water in the bathtub.
Compared to the case where the measurement dynamic range is less than 1 m as a result of being located only inside, when using a pressure sensor with such a wide height range as the measurable area, analog with the same number of bits is used. If the digital-to-digital conversion is performed, the resolution will be significantly inferior.

For example, if it is assumed that the 8-bit A / D convertible voltage range in the microcomputer 23 used, that is, the full scale is 5 V, which is equal to the power supply voltage, the water level change of 5 m is 0
The resolution obtained when using a pressure sensor expressed in the output voltage range of ~ 4V is 500 (cm) / 4 (V) x 5 (V) / 256 = 2.4 (cm) / bit, which is not enough. come. In particular, when the conversion error in the microcomputer 23 is expected to be about 3 bits, the maximum error that can be considered is three times that, that is, the resolution is 7.2 cm, which is too large.

The present invention is intended to solve this problem, and it is expected that the bathtub installation position will change considerably in the height direction with respect to the installation position of the water heater body, and as a result, a wide height range will be detected. If you have to use a pressure sensor such as
An object of the present invention is to provide a water level detection device that prevents the deterioration of the resolution and enables highly accurate detection of the water level in the bathtub.

[Means for Solving the Problems] In order to achieve the above object, the present invention arranges a pressure sensor in a flow path to a communication port communicating with hot water of a bathtub and digitally detects a pressure conversion output voltage detected by the pressure sensor. As an improvement in the device that converts the value into a value and detects the water level of the hot water in the bath based on the converted digital value, the output voltage value of the pressure sensor is converted into an analog input voltage value range within a specific value range. A fixed analog-to-digital converter amplifies the converted voltage value before converting it into the digital value, and a change range of the amplified output voltage value of the pressure sensor is converted into the convertible input voltage value range of the analog-to-digital converter. Before the conversion into the amplification circuit and the conversion into the digital value, the analog-to-digital converter in the change range of the output voltage value of the amplified pressure sensor is used. And an offset voltage adder circuit for adding a negative or positive offset voltage to the amplified output voltage of the pressure sensor in order to select the convertible range. To propose.

[Operation] According to the present invention, due to the convenience of the A / D conversion side, the analog voltage range that can be converted to a digital value is fixed to a certain change width, and A / D conversion is performed with a certain number of bits. Even when it must be done, since the pressure value (output voltage) detected by the pressure sensor corresponding to the water level in the bathtub is amplified,
The change in pressure value per bit, and thus the change in measured water level value per bit, becomes finer and the resolution is increased.

Therefore, for example, only the water level change range less than 1 m,
Unlike the case where it is only necessary to detect it, it is expected that the height position of the bath itself, which should detect the water level of the hot water in the bathtub, will change significantly, for example, ± 2 m and beyond. As a result, the required water level detection resolution in the bathtub does not have to be sacrificed even when a pressure sensor that must measure such a wide height range must be selected.

However, it is easily conceivable that the voltage range that can be converted into a digital value will be exceeded by simply amplifying the output voltage of the pressure sensor.

For example, if there is a pressure sensor that can detect a water level height change of 5 m at 0 to 4 V through pressure change, such as the pressure sensor mentioned above, simply amplifying this to about 5 times will cause a digital change. The voltage range that must be converted is 0 to 20V
It also becomes.

However, the power supply voltage of the control circuit built in the main body of the water heater using a recent microcomputer is about 5V, and therefore, the analog-digital conversion function is equivalently performed by software processing in the microcomputer. Whether the output voltage of the pressure sensor is satisfied or when an analog-digital converter is used as dedicated hardware, the output voltage change range can be converted into a digital signal by simply amplifying the output voltage of the pressure sensor as described above. The analog voltage range (generally equal to the power supply voltage) is exceeded.

However, in the case of the present invention, since a circuit for adding a negative or positive DC offset voltage to the output voltage value of the pressure sensor amplified as described above is provided, one of the ranges of the amplified voltage change range is provided. Only the part needs to be digitally converted.

For example, if -15V (which is a DC voltage value and therefore always constant) is added as an offset voltage, when the pressure sensor output voltage change range amplified as described above is 0 to 20V,
This is shifted from -15 to + 5V. Of course, addition of a negative value in this document has the same meaning as subtraction of a positive value that is equal in absolute value, so the above can be rephrased as subtracting + 15V.

In any case, if such an arithmetic process is performed, when performing analog-to-digital conversion with 0 to 5V as the full scale, the part from -15V to 0V is discarded in the above, and only the part from 0 to 5V is discarded. Since it is subjected to the digital conversion, the measurement dynamics of the pressure sensor used is substantially
1V between 3-4V which is the upper quarter part of the range 0-4V
Only the change width of is amplified 5 times and becomes the measurement target.

Similarly, if -5V is added, the amplified pressure sensor output voltage value change range is shifted to -5 to + 15V.
If the 0-5V part is the target of digital conversion,
Measurement dynamic range of pressure sensor before amplification 0-4V
Regarding, regarding the lower quarter part, 0 to 1V part, and the upper half part, 2 to 4V part, are excluded from the detection target, and only the 1 to 2V part between them is quintupled. It is amplified and set as the change width for digital conversion.

What this means is the height position of the bathtub itself,
For example, when the bottom of the bathtub is used as the reference position, this corresponds to the fact that the variation in height of this reference position can be shifted. That is,
What is finally desired to be detected is not the water level in the bathtub in addition to the reference position of each bathtub with respect to the height origin, but the water level in the bathtub regardless of the height position of the bathtub. Then, the water level itself never shows a change of several meters, and as already mentioned, the change is less than 1 m at the most.

Therefore, as mentioned above, even if it is necessary to use a pressure sensor with a measurement dynamic range of up to 5 m, it is possible to offset the fluctuation of the height of the bathtub, or at least to make it a small effect, and somewhere in it. Only the change range of about 1m can be measured with high resolution.

As will be apparent, the present invention does just that. Amplification of the pressure sensor output voltage change range of the part corresponding to the required water level change width (for example, 1 m) and digital conversion can be performed, and pressure sensor output voltage amplification that makes measurement unnecessary due to the height change of the bathtub itself The minutes can be reasonably discarded.

Of course, when using a type that has a negative output voltage range, such as a differential pressure sensor, if the required digital conversion range is in the negative range and the digitally convertible voltage range is in the positive range, For example, according to the present invention, after the output voltage of the pressure sensor is first amplified, a positive DC offset voltage can be added to expect the same effect as above.

[Examples] Examples of the present invention will be described below with reference to FIG.

In the present invention, as is clear from the above-mentioned object, the arrangement relationship between the water heater main body 20 or the pressure sensor 21 built therein and the bathtub 11 is, as already described with reference to FIG. As shown in the bath line 11 whose height position is shown by the solid line, the height position of the pressure sensor 21 is outside the bath line 11, 11 where the bath line 11 and 11 are shown by virtual lines. As shown in the above, there are cases in which there may be large differences.

In this regard, if the reference position of the height of the bathtub 11 itself in the description here is their bottom, and therefore the position of the bottom of the bathtub 11 shown by the solid line is the height origin 0 (m),
The bathtub height position indicated by the phantom line is + H ₂ ,
The height position of the bathtub 11 shown by a virtual line on the lower side is −H ₁ .

Further, for convenience, in this system, the height range in which the bathtub 11 can be set with respect to the height origin is −H ₁ to + H ₂ . That is, the upper and lower bathtubs shown in phantom in FIG.
11 and 11 are the maximum allowable upper limit position + H ₂ (m)
And the lowest position m).

In addition, a heat exchanger that is inside the bathtub 11 and is built in the water heater body 20.
The height of the communication port 12 that communicates with 22 from the bottom of the bathtub is X
(Cm), and the water level change range in the bathtub 11 to be detected is X + α (cm). The pressure sensor 21 is provided in the flow path communicating with the communication port 12, and the water level change width of the detection target corresponding to the pressure due to this is the allowable height change range −H ₁ to + H with respect to the bath 11. _In addition to ₂ , the maximum water level value X + α in the bathtub 11 located at the allowable upper limit height position + H ₂ is covered.

Further, for convenience of comparison with the conventional example, although shown in different sizes in FIG. 4, respective values H ₁ and H ₂ are equal in absolute value and are 2 m, respectively, and the water level in the bathtub is It is assumed that the detection target change width X + α of 1 is 1 m. However, as described above, the height X of the communication port 12 from the bottom surface of the bathtub is generally about 10 cm, and α is at most 50-60 cm at the most, so it is necessary to measure 1 m. The range of change is not necessary, and although this can be reduced in reality, the above value is used to simplify the description.

Under these conditions, the pressure sensor 21 used in this embodiment is
Has the characteristics shown in the second illustration already described. That is, from -2m corresponding to the height position of -H ₁ ,
The total span of 5m up to + 3m, which corresponds to the height position of (+ H ₂ + X + α), corresponds to the output voltage change range of 0 to 4V. In addition,
With the pressure sensor used in the experiment, the output voltage at the origin of height 0m was almost + 1.7V.

An example of a circuit configuration satisfying the present invention as a water level detecting device for converting the output voltage of the pressure sensor 21 into a digital value and using it for water level detection is as shown in FIG. 1, for example.

Output voltage V _A of pressure sensor 21 (0-4V according to the above promise)
Is applied to the positive phase input (+) of the first operational amplifier 31, and the output voltage V _D of this operational amplifier 31 is applied to the input of the analog-to-digital converter 24.

However, in this embodiment, the analog-to-digital converter (substantially an analog-digital converter (substantially) is processed by software processing by the microcomputer (CPU) 23, which is usually incorporated in the controller of this type of hot water heater recently. It is assumed that a function equivalent to that of the A / D) 24 is incorporated.

Of course, the present invention can be applied to the case where the A / D converter 24 is prepared as dedicated hardware,
In any case, the digital-converted numerical data is, by the microcomputer 23, as described above,
It is used to control this kind of water heater, such as the automatic filling function up to the set water level.

On the other hand, the output of the first operational amplifier 31 and the negative phase input (-)
A feedback resistor R ₂ is provided between them, and the negative phase input is connected to the output of another operational amplifier 32 via the resistor R ₁ .

Therefore, if the output potential of the second operational amplifier 32 is substantially equal to the ground potential, it means that one end of the resistor R ₁ is simply grounded, and if this state is considered, it is clear. That is, the first operational amplifier 31 literally has a normal input voltage amplifying function, and its gain G is G = 1 + R ₂ / R ₁ ...

Here, according to the value in the standard, the resistance value of the resistor R ₂ is 39K _Ω
If the value of the resistor R ₁ is 10 _KΩ , the gain G is G = 4.9.

For the sake of simplicity, the amplification factor G of the first operational amplifier 31 shown in FIG. 1 is rounded to G = 5, but if the output voltage of the second operational amplifier 32 is ground potential, then The variation range of the output voltage V _P of the pressure sensor 21 is 0 to 4 V, the first operational amplifier
The output voltage V _D change width of 31 is expanded five times to 0 to 20V.

Therefore, if the output voltage V _D of the first operational amplifier 31 is directly applied to the input of the A / D converter 24, the A / D converter 24
It is easily conceivable that the voltage range that can be digitally converted in the above will be exceeded. As already mentioned, the power supply voltage of the control circuit built into the main body of the water heater using a recent microcomputer is about 5V, and naturally, of course,
This is because the analog voltage range that can be converted into a digital value (generally approximately equal to the power supply voltage) cannot be exceeded.

Even if an A / D converter 24 capable of collectively converting the input voltage range of 0 to 20 V is prepared, if the number of bits is not significantly increased, it is desired to finally detect, at most, about 1 m. It cannot show high resolution for the water level difference. With about 8 bits, as already mentioned, A / D
Considering the conversion error, the final resolution is 7 cm or more.

However, in the case of the present invention, as seen in the illustrated embodiment, the other end of the resistor R ₁ whose one end is connected to the negative phase input of the first operational amplifier 31 has the other end of the second operational amplifier 32. On the other hand, since the second operational amplifier 32 has a so-called voltage follower structure and is an impedance converter, the second operational amplifier 32 is connected to the output of the second operational amplifier 32.
Depending on the polarity and the absolute value of the analog DC voltage V _A given to the positive phase input of, the output voltage range of the first operational amplifier 31 can be shifted positively or negatively as a whole. That is, according to such a circuit configuration, the output voltage V _D of the first operational amplifier 31 is V _D = G · V _P − (R ₂ / R ₁ ) · V _A. It can be expressed as follows, and as is clear, the first term on the right side of this equation shows the function of simply amplifying the input pressure sensor output voltage V _P by the first operational amplifier 31, but the second term
The term shifts the output voltage V _D of the first operational amplifier 31 to negative or positive by (R ₂ / R ₁ ) · V _A according to the magnitude of the DC voltage V _A and its polarity (positive or negative). Means to get.

Therefore, in the case of this embodiment, the circuit for adding the DC offset voltage as described in the gist of the present application is a circuit including the second operational amplifier 32 and the resistors R ₁ and R ₂ .

Further, in this embodiment, the analog DC voltage V _A given to the input of the second operational amplifier 32 is the microcomputer 23
The value and the polarity are the binary numerical data obtained under appropriate calculation or judgment by the microcomputer 23, which will be described later.
It is assumed that it can be obtained by digital-to-analog conversion by the A converter 25 (by software processing or by separate hardware).

Note that the polarity of the output voltage can be determined simply by using only the numerical data, but of course, only the polarity data may be separately handled by giving it to a separate register (not shown), as in the present embodiment. In the case where only the DC offset voltage of one polarity (in this case, negative) needs to be added, naturally, the selective inversion processing regarding such polarity is not necessary.

How to use such a circuit, in particular, how to determine the DC offset voltage V _A can be as follows, for example.

As described with reference to FIG. 4, if the height of the hot water in the bathtub 11 does not reach the communication port 12, as long as the bottom of the bathtub 11 is at the height origin 0 m, the pressure sensor at that time The output voltage V _P should be some constant value V _PX as shown in FIG.

However, in this embodiment, the water level is detected up to a negative height region with respect to the height origin 0 m, and the pressure sensor 21 having the second characteristic shown in FIG. 1.7V is obtained, and the slope of the characteristic curve is 4 (V) / 5 (m) = 0.8 (V / m), the height X of the flow port 12 is For example, if it is 10 cm,
The above constant value V _PX is (1.7 + 0.08) V (let's assume about 1.8V). Of course, this value can be managed by the microcomputer 23 by storing it in the attached memory as a known value.

Similarly, when the water level detection range is up to 1m in the bathtub 11 at the origin of height 0m (actually, it is not necessary to be so deep, but for convenience of explanation as described above), it is equivalent to the maximum water level. The output voltage V _PM of the pressure sensor 21 is 2.5 V.

Therefore, when the pressure sensor pressure voltage range 1.7 to 2.5V required for the bath at the height origin is amplified by the gain 5, the width becomes 4V of 8.5 to 12.5V.

However, even though the span is suitable at 4V, the voltage range that can be converted into a digital conversion value on the microcomputer 23 side is +0 to + 5V in absolute value depending on the power supply voltage.
If it has been decided that the absolute voltage value + 8.5V at the lower limit of the above span is too high.

Therefore, the value of the second term (R ₂ / R ₁ ) · V _{A on} the right-hand side of the above equation (that is, (R ₂ / R ₁ ) is 3.9 in this embodiment, and henceforth, it is rounded down to 4V _A ). If, for example, it is determined to be 7.5 V, as described above, 8.5 at the height origin 0 m position
The output of the first operational amplifier of ~ 12.5V is +1 to + 5V in absolute voltage value while keeping the same width of 4V as the span.
Microcomputer that can shift up to 23
It will be appropriate as the input voltage range for the A / D conversion on the side, and even if the A / D conversion is applied with about 8 bits as in the conventional case,
Sufficient water level resolution per bit is obtained.

Obviously, the value of V _A can be set to an optimum value as a function of the height position of the installed bathtub, and in that case, the bathtub 11 will in this case be from −2 m +
Regardless of which height position is within the range of 2 m, at each height position, there is always a water level change range of less than 1 m at most.
It can be set as a detection target range.

For example, when there is a bathtub installed at a position of + 1.4m, and therefore the height position to the communication port 12 is + 1.5m, the pressure sensor output voltage at the height to the communication port 12 in the bathtub. Is calculated as 2.9V from the slope 0.8 of the characteristic curve of FIG. 2 and the value 1.7V of the output voltage axis intercept (since the linearity is good, the measured value also agrees well with this).
Then, if this is amplified according to the gain G = 5 by the first operational amplifier 31, it is multiplied by 5 to become 14.5V.

Conversely, as a result of filling the communication port 12 with water (hot water) in a bathtub of a certain height, when the output potential of the second operational amplifier 32 is the ground potential, it is amplified only by the gain of the first operational amplifier 31. If the output voltage V _D becomes 14.5 V, it can be known that the communication port height X of the bathtub is +1.5 m with respect to the height origin 0 m.

Therefore, conversely, without knowing the height of the bathtub each time, if the voltage value of 14.5V is obtained, by giving 13.5V as the shift DC offset voltage value 4V _A , In the bathtub, as in the previous case, the detection range of the water level in the bath can be shifted to the absolute voltage value range of +1 to + 5V. According to the above-mentioned principle, this is possible even if the pressure sensor output voltage at the maximum water level in the bath is not obtained. By the way, at 2.5m up from + 1.5m to 1m, the value after being multiplied by the gain G is 18.5V, and if 13.5V above is subtracted from this, the maximum voltage value to be used for digital conversion is 5
It becomes V.

To put this more generally, the above equation is obtained by substituting G = 1 + R ₂ / R ₁ (equation) according to the above equation, and rearranging it so that V _D = (V _P −V _A ) · (R ₂ / It can be rewritten as R ₁ ) + V _P.

Therefore, if it is desired to set the first operational amplifier output voltage V _D to, for example, 1 V on the basis of the pressure sensor output voltage V _PHX when there is a water level at the position of the communication port 12 in any height H _X of the bath 11, the V _D =
1 (V) is substituted into the above equation and solving for further modification to _{V A, V A = V PHX} - (1-V PHX) · (R 1 / R 2) becomes ‥‥‥, R ₁ Since the term / R ₂ is known, and of course V _PHX can also be known in advance, the value of D /
Binary numerical data is obtained such that the analog DC offset voltage V _A after leaving the A converter 25 is fixed at this value, and this is calculated by the D / A converter 25 (as described above, it is actually a soft value). It can be processed, but it can be given to. Of course, setting V _D above to 1V is merely exemplary.

Thus, the present embodiment has been described in detail in accordance with each specific numerical example, but according to the present invention, if the height position of the bathtub itself, for example, the bottom of the bathtub is the reference position, this reference position Height fluctuations relative to the height origin are canceled or reduced, regardless of the height position of the bathtub, regardless of the height position, the water level in the bathtub is the same number of bits within the voltage range that can be converted to a digital conversion value. Can be detected.

Therefore, as mentioned above, even if it is necessary to use a pressure sensor that extends up to 5 m as the measurement dynamic range, of the part corresponding to the water level change width (for example, 1 m) required depending on the bathtub installation position, Only the change range of the pressure sensor output voltage is amplified and the extracted change range (span)
Can be digitally converted, in other words, due to the height change of the bathtub itself, the pressure sensor output voltage amplification that does not need to be digitally converted is reasonably discarded.

Of course, as a result of using a type that has a negative output voltage range, such as a differential pressure sensor, the voltage range that can be digitally converted is limited to the positive range, but the input voltage range to be converted is If it is in the negative region, the same action as above can be expected by setting the DC offset voltage of an appropriate absolute value, which is added after amplification of the pressure sensor output voltage, to be positive.

However, the origin position related to height can be set arbitrarily, and each parameter only needs to be moved in parallel. For example, in Fig. 2, the -2m point is the origin 0m position, and the range from here to + 5m is the pressure sensor. You can also leave it as 21 measurement targets.

Further, according to the first illustrated circuit, the DC offset voltage value V _A initially set by the microcomputer 23 becomes inappropriate due to the aging of the pressure sensor 21, and a different output voltage V _D is obtained at the position of the communication port 12. In such a case, the correction is simple and can be automated.
This is an effect that is incidental as a result of achieving the object of the present invention, but once obtained, it is also surprisingly large.

[Effect] According to the present invention, the height range of the bathtub that can be installed with respect to the main body of the water heater needs to be allowed to be quite wide, and therefore, the pressure sensor used for detecting the water level in the bathtub also has the pressure detection range. Even if it is necessary to use a wide bathtub, with regard to the bathtub 11 once set at a certain height position, even if the number of bits for analog-to-digital conversion is not increased, the water level in the bath must be highly resolved. It can be detected accurately.

In other words, it is possible to relax the regulation of the height relationship between the water heater main body and the bathtub, and to construct a hot water supply system that is more flexible and has high marketability.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram of a main circuit in an embodiment of a water level detecting device of the present invention, and FIG. 2 uses a pressure sensor that detects a water level in a bath by a change in pressure and generates a corresponding output voltage. Fig. 3 is an explanatory view showing the tendency of the change relation between the water level in the bathtub and the output voltage in the case, Fig. 3 is an explanatory view of a characteristic example of a commercially available pressure sensor capable of detecting a relatively wide water level difference, and Fig. 4 is a water heater body or FIG. 5 is an explanatory diagram showing the relationship between the pressure sensor installation position and the bathtub installation height position. In the figure, 11 is a bathtub, 12 is a communication port, 20 is a water heater main body, 21 is a pressure sensor, 22 is a heat exchanger, 23 is a microcomputer,
24 is an A / D converter, 25 is a D / A converter, 31 is a first operational amplifier,
32 is a second operational amplifier, R ₁ and R ₂ are resistors, V _P is a pressure sensor output voltage, V _D is a first operational amplifier output voltage to be used for conversion into a digital value, and V _A is a DC offset voltage. is there.

Claims (1)

[Claims] 1. A pressure sensor is arranged in a flow path to a communication port which communicates with hot water of a bathtub, a pressure conversion output voltage detected by the pressure sensor is converted into a digital value, and the inside of the bathtub is converted based on the digital value. A device for detecting the water level of hot water; converting the output voltage value of the pressure sensor into the digital value by an analog-to-digital converter having a convertible analog input voltage value range fixed to a specific value range. An amplifying circuit which is previously amplified and has a range in which the output voltage value of the amplified pressure sensor changes exceeds the range of the convertible input voltage value of the analog-to-digital converter; Of the output voltage value of the amplified pressure sensor, the output of the amplified pressure sensor is selected in order to select a range convertible by the analog-to-digital converter. Offset voltage addition circuit and for adding a negative or positive offset voltage to the voltage; water level detecting device tub with water heater comprising a.