JPH01252859A - Safety circuit for hot water supply device - Google Patents

Abstract

PURPOSE:To make it possible to shut of the supply of fuel immediately, by comparing a conversion electric signal obtained based on the detection of an output hot water temperature detecting element with a reference electric quantity signal and closing a fuel valve which supplies fuel to a burner when an output hot water temperature exceeds an allowable maximum temperature corresponding to the reference electric quantity signal. CONSTITUTION:A voltage signal which changes with an output hot water temperature is obtained at a connection point between a thermistor 21 and a resistor 23. Therefore, if a detected voltage is always compared with a reference voltage, it can be judged whether or not the present output hot water temperature is below the allowable maximum temperature. In the case that the output hot water temperature is lower than the allowable maximum temperature, a valve ON/OFF command signal transmitted from a main control circuit 11 or a valve shut off command signal transmitted from a minimum flow rate detecting circuit 12 works effectively. A drive relay RV of a gas solenoid valve is selectively operated in response to these signals. When the output hot water temperature exceeds the allowable maximum temperature, a power supply line to the gas relay RV of the gas solenoid valve is opened separately and independently of the output signals transmitted from the main control circuit 11 or the minimum flow rate detecting circuit 12 and the combustion is stopped.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a safety circuit used in various types of water heaters that heat running water, and in particular, the present invention relates to a safety circuit that is used in conjunction with various water heaters that heat running water. This circuit relates to a circuit that promptly and reliably cuts off the fuel supply to the combustion section to ensure safety when the temperature exceeds the maximum allowable temperature and reaches an abnormally high temperature.

[Prior Art] Currently, this type of water heater is generally equipped with a main control circuit composed of a microcomputer, and operates exclusively under the instructions of the main control circuit.

In other words, for ignition and for the continuation of combustion after ignition, this microcomputer performs predetermined calculations on the current flow rate, water supply temperature, set temperature, hot water temperature, etc., and then performs calculations based on the results. This is designed to achieve optimal control.

However, in these water heaters, not only the main control related to combustion in normal cases as described above, but also the possibility of equipment damage, water leakage, or In addition, appropriate safety measures must be taken to prevent accidents involving the release of raw gas or other fuel.

One of these is monitoring the hot water temperature.

For example, even though the amount of hot water that comes out is extremely small and falls below the minimum allowable flow rate, the main control circuit may not make the correct decision due to a runaway program, resulting in a failure that causes combustion to continue. This results in a situation that is very close to what is called "dry cooking," and the hot water that is dispensed becomes abnormally high.

This is not only dangerous for the user, but may also cause damage to the equipment. The hot water that comes out may boil and damage the pipes, causing water leaks, or in severe cases, the burner may even explode due to abnormally high temperatures inside the equipment.

Therefore, conventionally, as shown in Fig. 2, a bimetal 10 is used as a so-called high limit switch regarding temperature, and by placing it at an appropriate position in the tap water path, the temperature of the hot water can be determined. This was a final safety measure.

In the case of this second illustration, it is assumed that gas is used as the fuel, and therefore a drive relay 1 (,) is shown that selectively drives the gas solenoid valve as the fuel fF, but under normal usage conditions, this gas The bimetal lO inserted in series in the power line from the power source 1B to the electromagnetic valve driving relay L is electrically closed because the temperature of the hot water at the outlet is within the permissible temperature range.

On the other hand, as already disclosed by the present applicant in JP-A-61-128026, the main control circuit II is
There is also a proposal to forcibly cut off the power supply to the gas solenoid valve drive relay Rv when the amount of hot water falls below a preset minimum flow rate, and this figure also shows a conventional method configured according to this previously filed invention. As an example, the minimum flow rate detection circuit 12 and the pn transistor Q2 which is selectively turned on and off according to this output are shown, but the tapped water flow rate is also within the normal range, and - If the minimum flow rate value or more is secured, the minimum flow rate value detection circuit 12
A significant normal signal at a high level is emitted from the transistor Q2, which also turns on the transistor Q2.

Note that, in reality, one transistor Q+ and Q2 is used, and this is driven by the AND logic result of the selection drive signal from the main control circuit 11 and the selection drive signal from the minimum flow rate detection circuit 12. It is often composed of
Since this is an explanation of the principle, the transistors are shown as separate transistors connected in series for ease of understanding.

In any case, as mentioned above, both the hot water temperature and the hot water flow rate,
Within the range where both are recognized as normal, the gas electromagnetic valve drive relay Itv is controlled exclusively based on the valve opening/closing command signal output from the main control circuit (microcomputer) 11.

In other words, in the case where the main control circuit 11 is shown, it exists at a high level.
When the abrasive valve open command signal is issued, the npn transistor paste is turned on, and the gas solenoid valve drive relay R is activated.
When power is applied to V to open the gas solenoid valve, supplying fuel to the combustion section, and conversely emit a significant valve closing command signal at a low level, transistor q2 turns off and drive relay 1 (, The gas is deenergized, the gas solenoid valve is closed, and combustion stops.

However, due to some failure factor, the temperature of the hot water at the outlet becomes abnormally high, causing the contact of the bimetallic IO to open.
Regardless of the command voltage/V from the main control circuit 11, as is clear from the illustrated circuit example, the gas solenoid valve drive relay 1
(The power supply to v is forcibly cut off, and the fuel supply is stopped.

Similarly, when the flow rate of hot water falls below the allowable minimum a value, normally the 1 control circuit 11 also detects this and issues a valve closing command to the transistor Q1 to turn it off. Even if the microcomputer used as the main control circuit 11 does not work properly due to program runaway, etc., this main control circuit 1
The minimum flow rate detection circuit 12, which is provided separately from the transistor Q2, operates and sends a forced turn-off signal to the transistor Q2, so as to avoid a situation similar to dry cooking. It has become.

[Problems to be Solved by the Invention] The safety measures in the above conventional example have a problem in that they rely only on the bimetal 10 rather than the use of the bimetal IO to monitor the temperature of the hot water. .

First, as a well-known fact, the bimetal itself, its shape,
Temperature characteristics may be inferior depending on the material or due to manufacturing or other reasons. Products with the same loft may even exhibit different operating temperatures.

This basically means that it is extremely difficult to manually create a bimetal with temperature characteristics equal to the maximum allowable temperature set in the design, and if used as is even if it is from the same lot, the bimetal used Because the temperature characteristics of the burner were shifted to the higher side, this also means that an accident such as boiling or high heat damage to the burner part may occur before abnormally high temperatures are detected and the burner opens.

Furthermore, the maximum allowable temperature to be set is limited to the operating temperature of the bimetal, which is set only in stages, and there is also the drawback that it is not possible to set the temperature arbitrarily.

In practice, this lack of design freedom can even lead to inefficient use of equipment. In reality, it may be possible to tolerate a slightly higher temperature, but since there is no bimetal with an appropriate operating temperature, and in addition to this, there is a large variation as mentioned above, so the maximum temperature that can be supplied by the equipment is limited. Sometimes you have to be very restrictive.

Although safety is the first priority above all else, it is better to have a product that can utilize the maximum combustion capacity of the equipment, including its maximum hot water temperature, as long as safety is maintained. There isn't.

Moreover, this kind of bimetallic movement is generally quite slow. It goes without saying that it is desirable to close the fuel valve as soon as an abnormally high temperature is detected, so it is not a very desirable element in that respect. Self-recovery after the abnormality factor is removed also takes time.

Such concerns regarding the use of bimetals cannot be resolved even when the minimum flow rate detection circuit 12 is used in combination, as seen in the above-mentioned conventional example.

Indeed, since the applicant proposed the adoption of this minimum flow rate detection circuit 12, the safety factor of this type of water heater has further increased.

However, for example, even if the minimum flow rate detection circuit 12 does not detect that the minimum flow rate has been reached, if the amount of hot water drops to a value extremely close to this minimum flow rate, it is still possible to avoid the possibility of an abnormally high temperature state occurring. In such a case, one would eventually have to rely solely on the bimetallic IO as a temperature monitoring element.

In view of these circumstances, the present invention has been made to eliminate the drawbacks of the above-mentioned conventional examples.As a precaution, bimetal may be used in combination, but basically it does not rely solely on bimetal and can be used with considerable freedom. For the maximum allowable temperature that can be set,
The objective is to provide a safety circuit that can compare the current outlet hot water temperature and cut off the fuel supply as quickly as possible if the outlet hot water temperature exceeds the maximum allowable temperature.

[Means for Solving the Problems] In order to achieve the above object, the present invention first uses a hot water temperature detection element that detects the temperature of the hot water that is currently being poured, and detects the current temperature detected by the hot water temperature detection element. Converts the tapped water temperature into a predetermined electrical quantity signal (the easiest to handle is a voltage signal).

On the other hand, a reference electricity quantity signal (similarly, it is easiest to use a reference voltage signal) corresponding to the maximum allowable temperature is set in advance, and a converted electricity quantity signal obtained based on the detection of the above-mentioned outlet hot water temperature detection element is set. and this reference electric quantity signal.

As a result of this comparison, if it is determined that the temperature of the hot water at that time has reached the maximum allowable temperature corresponding to the reference electricity quantity signal, fuel is supplied to the combustion section that is burning to boil the water. Block the fuel valve.

Desirably, such a circuit system is provided separately from a main control circuit such as a microcomputer, if the water heater is provided with a main control circuit.

[Operations and Effects] There are various types of hot water temperature detection elements referred to in the present invention, and any of them can be used, but even when considering the most common thermistor, the variation is considerably greater than that of a bimetal. It is small and can be obtained by converting the current tapping temperature into an electrical quantity signal such as impedance value, current value, voltage value, etc. that is continuous and has a high correlation with the tapping temperature.

Therefore, the maximum permissible hot water temperature corresponding to this, that is, the maximum allowable hot water temperature within a range that can guarantee safety, can also be set quite freely as the standard electricity quantity value converted to the corresponding electricity quantity value. Furthermore, the comparison between this reference electricity quantity value and the current outlet hot water temperature conversion electricity quantity value can be done relatively easily and accurately by using known and existing electronic circuit technology. .

For this reason, when considering the water heater as a whole, product tolerances are smaller compared to conventional systems that rely only on bimetals to manage the hot water output temperature, and the optimum maximum hot water temperature can be achieved with a high degree of design freedom. It is possible to reliably limit the upper limit of the hot water temperature.

Therefore, it is possible to improve the efficiency of the equipment, and unlike bimetals, there are no mechanical moving parts involved, so not only are there essentially fewer causes of failure, but the fuel can be cut off after abnormally high temperatures are detected. Operation can also be faster and the safety circuit can exhibit exactly the desired functionality.

Further, when this circuit is incorporated into a modern water heater that uses a microcomputer as a main control circuit, it is most desirable that it is configured as hardware separate from the microcomputer. This is because even if there is an accident such as the microcomputer going out of control, combustion can be stopped independently of the microcomputer when an abnormally high temperature occurs.

Furthermore, this does not preclude its use in combination with a conventional bimetal to form a so-called double safety mechanism.

[Embodiment] Fig. 1 shows a schematic configuration of a basic embodiment of the present invention, and this circuit is different from the conventional configuration shown in Fig. 2 to a maximum temperature detection circuit according to the present invention. 20 sections are shown added.

Therefore, constructors with the same reference numerals as in FIG. The explanation will begin with these conventional components.

As abbreviated as "micro CPU" in the figure,
The main control circuit 11, which is generally configured as a microcomputer, sends an ignition signal to an ignition circuit (not shown) when, for example, an ignition command is issued by a user's command operation via an operation unit (not shown). , only when the hot water output signal indicates an appropriate flow rate value range.
In this example, the transistor Q is configured as an npn type.
1, which sends a high level significant valve open command signal to the base of NPN transistors Q2 and Q3, which are turned on, and which, as will be understood from below, are both turned on at this time. Power is supplied to the gas solenoid valve drive relay Rv via the closed bimetal 10 to open the gas solenoid valve (not shown).

After the start of combustion, if the amount of hot water falls below the minimum allowable flow rate, the main control circuit 11
n) A low level signal is applied to the base of transistor q1, turning it off and causing the gas solenoid valve drive relay R,
deenergizes and closes the gas solenoid valve.

On the other hand, as mentioned earlier, as already disclosed by the present applicant in JP-A No. 61-+28Q, No. 26, the amount of hot water dispensed can be set at a preset minimum flow rate independently from the main control circuit 11. Minimum flow rate detection circuit 1 for forcibly cutting off the power supply to the gas solenoid valve drive relay Rv when the value falls below the value
2 is also provided in this example, and when the hot water 1 falls below the minimum flow rate value, this circuit 12 also sends a valve closing command signal of level 5 at a low level to make the transistor Q2 non-conductive. Output.

However, as described above, when the main control circuit II is operating normally, the valve closing command signal (low level signal) from the main control circuit 11 causes the transistor Q+ to become inoperable, and the power supply line is opened. Therefore, it can be considered that the valve closing command signal from the minimum flow rate detection circuit 12 does not have a substantially significant effect.

However, when the actual flow rate flowing through the equipment falls below the predetermined minimum allowable flow rate value, the microcomputer that forms the main control circuit 11 happens to stop functioning due to a runaway or some other reason. When I was
The fact that the minimum flow rate detection circuit 12 is provided as separate hardware serves as a major backup element, and the gas solenoid valve can be reliably closed regardless of a failure of the main control circuit 11.

However, as mentioned above, this alone is still not a complete safety measure. Although the minimum flow rate detection circuit 12 does not detect it, if the flow rate is very close to the detected value and there is an accident such as the microcomputer going out of control, combustion may continue at a very small flow rate. This is because this may lead to accidents such as damage to the equipment and bursting of pipes due to boiling of water or abnormally high temperatures.

In the end, the most reliable way is to directly monitor the temperature of the hot water itself, regardless of the flowmeter, and for this reason, the present invention has been made, and the above-mentioned configuration can be used to monitor the hot water temperature itself directly. The maximum hot water temperature detection circuit 20 is provided to achieve the above-mentioned effects.

However, in the embodiment shown in the first figure, bimetallic IO, which has been conventionally employed, is also used.

However, this is only used as a precautionary measure as a double safety measure, and this bimetallic IO never plays a leading role in this embodiment as in the conventional example.

In other words, in the present invention, such a bimetal! 0
Although it is essentially not necessary, even if it is provided, the operating temperature of this bimetal In does not determine the maximum hot water temperature of this water heater as in the conventional example, and as described below, The maximum allowable temperature defined by the maximum hot water temperature detection circuit 20 configured according to the present invention is significant, and the temperature set for the bimetal IO is set higher than this.

In other words, the bimetal 10 is selected with respect to its operating temperature so that the bimetal 10 will not operate before the maximum hot water temperature detection circuit 20 configured according to the present invention performs the fuel cutoff operation. Should.

Now, in this embodiment, the thermistor 21 is selected as the outlet hot water temperature detection element 21 mentioned in the gist of the present invention, as it is the most easily available element and can obtain a necessary and sufficient integral. There is.

Of course, this is a device that is placed at an appropriate location in the hot water path from the heat exchanger in the combustion section to the hot water outlet, and detects the temperature of the hot water actually being tapped from the water heater, but as is well known, In addition, this type of thermistor has a negative slope in terms of temperature versus resistance value characteristics, and the higher the temperature to be detected, the lower the resistance value between both ends.

Such temperature versus resistance value characteristics become extremely easy to handle when converted into voltage value information.

This is also the case in this embodiment, and the power supply voltage is controlled by the resistor 2.
By dividing the voltage between the resistor 23 and the thermistor 21, a converted electricity quantity signal whose voltage value decreases as the temperature rises is obtained as a potential with respect to the ground at the connection point between the resistor 23 and the thermistor 21.

However, strictly speaking, as will be described later, the feedback resistor 26 is required to provide hysteresis in the operation of the comparator 22 beyond the set maximum allowable temperature, and the comparator used is bipolar oven collector type or C. -Logic “H” that can be defined in high impedance state in case of MOS type
The pull-up resistor 27, etc. used to convert " to a high voltage level state also contributes to the slope of the temperature vs. converted voltage characteristic by being connected in parallel to the resistor 23 that is in series with the thermistor 21, so these are not included in the design. Also consider the value of

However, as mentioned above, at the connection point between the thermistor 21 and the resistor 23, a voltage signal that decreases in level as the tapped water temperature rises is obtained, so the voltage signal that is obtained when the allowable maximum tapped water temperature is reached is obtained. By setting a voltage of a value equal to 100% as a reference voltage and constantly comparing it with this voltage, it is possible to judge whether or not the current hot water temperature is below the maximum allowable temperature.

Therefore, the above reference voltage value, that is, the allowable maximum temperature information converted into an electrical quantity called voltage, is set in advance by design using a voltage dividing circuit consisting of a resistor 24 and a resistor 25 that divides the power supply voltage ÷ B, and the comparator 22 On the other hand, outlet hot water temperature information obtained by converting the current outlet hot water temperature into an electrical quantity called voltage is provided to the positive phase input of the comparator 22.

As is clear from the above, when the current outlet temperature is lower than the maximum permissible temperature, the resistance value of the thermistor 21 is necessarily higher than the resistance value that can be exhibited when the permissible maximum temperature is reached. Therefore, the voltage value obtained at the connection point with the resistor 23 will be higher than the value set at the negative phase input terminal of the comparator 22 as the reference voltage, and therefore the current outlet water temperature will be as shown above. As long as it is within a normal range below the maximum allowable temperature, the output of the comparator 22 is pulled high via the pull-up resistor 27.

Therefore, if this state continues for a predetermined period of time or more, the diode 28, which is in the forward direction at this time,
For the reason described below, the electrolytic capacitor 30, which is a component of the timer circuit that is preferably provided, is in a fully charged state, so that a significant base bias is applied to the npn transistor Q3 inserted in series with the power supply line. is maintained in a conductive state.

Therefore, under such conditions, as mentioned above,
The valve opening/closing command signal from the main control circuit 11 and the valve closing command signal from the preferably provided minimum flow rate detection circuit 12 can act significantly, and in response to these signals, the drive relay Rv of the gas solenoid valve is activated. Selectively activated.

However, due to some reason, such as a large drop in hot water output,
When the current outlet hot water temperature reaches or exceeds the temperature set as the maximum allowable temperature, a level inversion relationship occurs at the input end of the comparator 22, and the inverse phase power may become higher.

Naturally, the output of the comparator 22 falls to a low level (substantially near the ground level), and the comparator output side of the pull-up resistor 27 is also connected to ground, so that the fully charged capacitor 30 also starts discharging as a result of the creation of a discharge path through the resistor 29 in parallel with the diode 28 which is in the opposite direction when viewed from the side of the capacitor 30 and is turned off.

Then, eventually, after a period of time according to the time constant set in the discharge path has passed, the potential across the capacitor 30 drops below the potential obtained by applying an on-bias to the base of the transistor q3. This transistor Q3 is then forced to be turned off.

In this way, the maximum temperature detection circuit 20 performs its intended function. If the hot water temperature exceeds the maximum allowable temperature, the gas solenoid valve drive relay R
Forcibly open the power supply line to v and cut off the fuel supply,
It is possible to stop combustion.

Note that the feedback resistor 26 provided regarding the comparator 22
As is well known in this type of threshold technology, this is to prevent hunting operation near the threshold, and when the current outlet temperature exceeds the maximum allowable temperature and the output of the comparator 22 becomes low. When the level is reached, the return resistor 26 is connected in parallel to the thermistor 21, so that even if the temperature of the hot water drops below the maximum allowable temperature, the voltage across the thermistor obtained at that time will be lower than before. Therefore, comparator 2
In order to reverse the state of 2 again, the temperature must be lower.

Similarly, the timer circuit, which is simply constructed with a capacitor 30 and a resistor 29, is also intended to avoid substantially too strict operation.

As mentioned above, based on the inversion of the output of comparator 22, transistor Q3 is configured to be forced to turn off after a suitable period of time, e.g., -seconds to two seconds, after capacitor 30 begins to discharge. , conversely, within the time determined by the time constant of the discharge path,
The output of the comparator 22 returns to high level again, and the capacitor 3
This means that if recharging starts at zero, transistor q3 will not turn off. Even if the temperature exceeds the maximum allowable temperature, this is to be tolerated.

In fact, the fact that capacitor 3θ starts recharging before the timer circuit expires means that after such a short period of time, the current outlet water temperature has returned to below the original normal allowable maximum temperature. Since it is guaranteed, it will not lead to major accidents, and is rather desirable in preventing too frequent power on/off operations.

In addition, in the above-mentioned embodiment, as in the conventional example shown in the second figure mentioned above, the command signal for opening/closing the fuel valve (gas electromagnetic valve) output from the microcomputer 11 exemplified as the main control circuit 1.1 is used. , an npn l-transistor Q+ which is selectively turned on and off, and an np transistor which is selectively turned on and off by the minimum flow rate detection circuit 12 described above.
The transistors Q2 and Q2 are shown as separate dedicated transistors, but as described above, these transistors Q1. Q2 is actually a common, single transistor, and is driven by the AND logic of the selection drive signal from the main control circuit II and the selection drive signal from the minimum flow rate detection circuit 12. It's okay.

In Fig. 1, separate transistors Q,
, shown in Q2.

In addition, it is understood that the npn transistor Q3 used in the maximum hot water temperature detection circuit 2o of the first illustrated embodiment constructed according to the present invention can also be used in common with these transistors from the above-mentioned function. , valve opening/closing command signal from main control circuit 11, minimum flow rate detection circuit 1
In addition to the valve closing command signal from 2, the output of the comparator 22 or the signal obtained at both ends of the capacitor 30 is also added, and the AND logic of the three is performed to drive this common, single transistor. I know it's okay to do it.

However, in the case shown in the figure, since the most basic form is shown as above, this transistor Q3 is also similar to the other transistor Q.
1. There is a meaning in showing it as a separate transistor in series with Q2, but contrary to this, even in actual products there are actually transistors dedicated to each control signal: Q+, Q2, Q3.
There is also the idea of providing each separately and independently. In this way, even if any one transistor fails to turn on, the other transistors can reliably open the power line when the gas solenoid valve should be closed, increasing the safety factor of the water heater.

Note that the converted electricity quantity signal that is correlated with the tapped water temperature is not limited to the above-mentioned voltage. Any other type of current that is easy for a person skilled in the art to design may be adopted.

[Brief explanation of the drawing]

FIG. 1 is a basic schematic configuration diagram of an embodiment of the present invention, and FIG.
The figure is an explanatory diagram of a conventional hot water temperature monitoring method. In the figure, 10 is a bimetal, 11 is a main control circuit or microcomputer, 12 is a minimum flow rate detection circuit, 20 is a maximum hot water temperature detection circuit, 21 is a thermistor, 22 is a comparator, 23 , 24 , 25 , 26 , 27 , 29 is a resistor, 28 is a diode, 30 is an electrolytic capacitor, Q+
, Q2, and Q3 are transistors that can selectively open and close the power supply line, and 1 (9 is a drive relay that selectively opens and closes the fuel valve).

Claims (1)

[Scope of Claims] A main control circuit that controls various operations related to combustion for boiling and dispensing hot water, and a fuel that selectively supplies fuel to the combustion section according to instructions from the main control circuit. valve and
A safety circuit for a hot water heater, comprising: a hot water temperature detection element provided in the hot water supply path for detecting the hot water temperature; and one for converting the temperature detected by the hot water temperature detection element into a predetermined electric quantity signal , by setting a reference electricity quantity signal corresponding to a predetermined maximum allowable temperature, and comparing the converted electricity quantity signal obtained based on the detection of the outlet hot water temperature detection element with the reference electricity quantity signal, the standard electricity quantity signal is determined. A safety circuit for a water heater, comprising: a maximum discharge hot water temperature detection circuit that closes the fuel valve when the discharge hot water temperature reaches the allowable maximum temperature corresponding to the electricity quantity signal.