JPH077281B2 - Safety circuit for remote controlled water heater - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a safety circuit used by accommodating various water heaters for heating running water, and more particularly to a combustion unit, a hot water supply system, and a micro controller for controlling them.・ A remote control type water heater that contains a computer in a base unit and can issue control commands to the microcomputer by operating a momentary switch installed in a remote unit installed at a remote location. The present invention relates to a safety circuit for detecting a contact abnormality of the momentary command switch and preventing the microcomputer from unexpectedly operating due to this abnormality.

[Prior Art] Recently, in the remote control type water heater of this kind, a microcomputer as a main control circuit is incorporated in the base unit in both the combustion section and the piping section around the combustion section, and the combustion and hot water discharge are exclusively performed. It has come to control under the command. In other words, at the time of ignition as well as the continuation of combustion after ignition, the microcomputer performs predetermined calculations on the flow rate, feed water temperature, set temperature, hot water temperature, etc., and optimizes the results. I am trying to control it.

On the other hand, various commands such as a command to start operation, a command to start filling water, and a command to start additional cooking are issued to such a microcomputer by a remote controller provided at a position convenient for the user, apart from the base unit.・ It is often a momentary type command switch installed in the unit.

That is, when the user presses the momentary operation start switch, the microcomputer detects that the switch has been turned on once and enters the operation start mode, and the user then twists the tap, for example. And, while taking into account the temperature conditions and flow rate conditions at that time and performing optimal control, combustion and tap water are automatically started.

Similarly, with this type of hot water supply these days, not only can you supply hot water from a single faucet, but when you press the hot water filling switch, which is also configured as a momentary type, the hot tub automatically fills the bathtub with a predetermined amount of hot water. The water is stored, or when the additional cooking switch is pressed, the cold water in the bathtub can be replenished.

In addition, it is no longer necessary to set the desired hot water temperature by operating the operation knob command provided in the remote unit.However, the present invention is not of direct interest for those other than the momentary switch. Not shown,
Omit it.

However, as mentioned above, it is not an alternate type switch to give a command from the remote unit to the built-in microcomputer in the base unit,
The use of the momentary type switch is not only a principle requirement but also operability and a kind of safety.

First of all, in terms of operability, the adoption of this type of momentary switch is almost indispensable to the product value when it is actually supplied to the market as a product and used in general households. To contribute.

The relatively early ones do not have the water filling function or the additional cooking function,
Since there were only operating switches, most of them adopted an alternate switch, but this is an obstacle to creating a high-class feeling because of the feeling that they are operated by the switch both on and off. As various types of switches such as tension switches and additional cooking switches have been added, the operation panel surface of the remote unit has become complicated and it has become difficult to actually operate.

In the first place, in principle, this type of alternate switch cannot be used regardless of the operation switch. For example, as mentioned above, when the water heaters of recent years are also equipped with a predetermined amount of automatic water filling function, it seems that the alternate switch may be used for the automatic start command of this water filling, but it is automatically stopped. I have a problem later. After the water filling is completed, it will not be possible to return to the initial state for the next use unless you put it with an alarm and require the user to always switch back. , It becomes extremely inoperable. There is no convenient way to press the momentary type command switch only when you want hot water.

Furthermore, in the alternate switch, if you forget to return the contact to the off state, the microcomputer is turned on and the power-on reset circuit normally provided in this kind of circuit system has a predetermined reset time. As soon as the reset of the microcomputer is released after
There is also a risk that the operation commanded by the alternate switch that has been forgotten to return may unexpectedly start.

For this reason, in hot water heaters of recent years, it has been proposed to use a momentary type for various command switches.Therefore, the command for the switch is generally to change the potential once the switch is turned on. The data is converted into the data and sent to the microcomputer, and the data is decoded by the microcomputer and the corresponding control is performed.

[Problems to be Solved by the Invention] As described above, it has been understood that the switch operated by the user in this type of water heater is preferably of the momentary type.

However, regarding the alternate type switch, when it was forgotten to return it while mentioning the malfunction, when turning off the power switch of the system once or turning it on again or inserting the power plug into the outlet, Normally, the power-on reset circuit, which is built in for this kind of control circuit, forgets to return after releasing the reset after the power-on reset of the microcomputer for a predetermined time from the power-on. There is a danger that the operation commanded by the switch that is performed immediately occurs even though the user does not intend it.

However, if this state is carefully considered, it can be seen that even when a momentary type command switch is used, a similar situation occurs if a contact abnormality occurs in this switch.

In other words, if the non-dissociation failure (ON failure) occurred when the momentary switch contacts did not come off when the system was turned off and then on again or after the first power-on after shipment, After the initial reset is released by the on-reset circuit, the microcomputer immediately causes the on-failure momentary
If an operation corresponding to the command type of the switch occurs, for example, if it is a hot water switch, the power is turned on but the user is not doing anything, but hot water starts to be supplied to the bathtub. Accidents such as being lost will occur.

The present invention has been made in view of this point, and when the power supply to the microcomputer is turned on, the contact states of various momentary type command switches are also monitored and detected, and in the case where an ON failure occurs Prevents the microcomputer from operating so that unexpected movements do not occur,
Therefore, this is one of the safety measures for this kind of water heater.

[Means for Solving the Problems] In order to achieve the above object, the present invention normally uses a power-on reset circuit used in a control circuit of this type, while still being capable of restricting its operation. To provide.

In other words, as is well known, the power-on-reset circuit has a function of sending a reset signal to the microcomputer for a predetermined time that has been set since the power was turned on, as is well known. A reset release blocking circuit is provided which prevents the power-on reset circuit from releasing the reset when it is issuing a release blocking command.

In other words, as long as the reset release blocking circuit continues to output the release blocking signal, the power-on reset circuit continues to output the reset signal even after the predetermined time has elapsed after the power was turned on. To do so.

The reset release blocking circuit issues the release blocking signal when the momentary type command switch has already failed to turn on when the power is turned on.

That is, in the present invention, a switch monitoring circuit is provided,
This switch monitoring circuit can monitor the contact state of the momentary type command switch at least immediately after the power is turned on.If this is on, for example, the potential of the line including this switch is off. Based on the fact that it is different from the case where there is a failure, the presence or absence of the ON failure is judged, and if it is judged to be the ON failure, an abnormality detection signal is issued and the reset release prevention circuit described above is activated by this abnormality detection signal. Prevents the reset release of the power-on reset circuit.

Therefore, conversely, if this switch monitoring circuit does not detect the ON failure of the momentary type command switch and the contact state is off and it is normal, the reset release blocking circuit does not work, so The on-reset circuit performs its original function and causes the reset signal sent to the microcomputer to be lost after the lapse of the predetermined time after the power is turned on.

In the present invention, once the micro
After the computer is started up, the operation of the switch monitoring circuit or the reset blocking release circuit is invalidated thereafter, that is, the abnormality detection function according to the present invention is invalidated.

This is because even if the legitimate momentary command switch is operated after the system has been normally started up, a potential change appears on the line including this switch for at least a moment. This is because unless one of the circuits has its function disabled, the contact closure based on the normal switch operation may be mistaken as an ON failure.

Further, preferably, even if the momentary type command switch is turned on when the power is turned on, if this is a transient failure and the contact is turned off after a while after the power is turned on, the predetermined command is given from this point. Allow the power-on reset to be released after a lapse of time.

[Operation and Effect] In the present invention, if a power switch as a hot water supply system is provided, this switch is operated, or if not provided, a power plug is inserted into an outlet, immediately at the beginning. The contact state of the momentary type command switch is inspected by the switch monitoring circuit.

In this type of water heater, the momentary type command switch is, for example, an operation start switch, a hot water filling switch, or a reheating switch.
In other words, the switches to be monitored in the present invention are all switches that are not turned on by simply starting up the microcomputer, and after the startup of the microcomputer, the user's intention The contact is closed once for the first time by a simple pressing operation.

As a matter of fact, turning on and off between the contacts depends on the fact that the potential of the line including the contact in series is different depending on whether the contact is on or off at either contact position. Since it is usually taken in as command data and decoded, the existing technology is also used in the switch monitoring circuit of the present invention, and the potential at one contact of this switch is immediately measured when the power is turned on. You can read and determine if it is on or off.

Here, in the normal case, the momentary command switch should be off immediately after the power is turned on as described above.
Nevertheless, when the switch monitoring circuit recognizes that the contact is ON, naturally the switch has an ON failure, and therefore the switch monitoring circuit outputs an abnormality detection signal.

When the switch monitoring circuit issues an abnormality detection signal, it acts on the reset release blocking circuit, which also limits the original function of the power-on reset circuit, and when the power is on normally A power supply that invalidates the reset signal of the microcomputer that was being issued when the power was turned on after the lapse of a fixed time.
Change the on-reset function to the state where it continues to send the reset signal.

Normally, the reset signal to the microcomputer can be defined as a significant logic "L", so the above operation is performed by the power-on reset circuit even if the above-mentioned predetermined time has elapsed after the power was turned on. The signal applied to the input can be embodied in such a state that it does not become a logic "H" forever, and therefore the specific circuit configuration itself for realizing such operation is left to the design of one skilled in the art. obtain. The present invention is characterized by the principle configuration in which the power-on reset circuit is used to satisfy both the original function and the reset blocking function at the time of abnormality detection.

Since it is like this, even if the momentary type command switch has an ON failure, the inconvenience that the water filling starts or the additional cooking starts without turning the power on Can be prevented.

On the other hand, as a matter of course, if the switch monitoring circuit does not detect the ON failure of the contact, the reset release blocking circuit does not work, so the power-on reset circuit has the original power-on reset function. The microcomputer is kept in the reset state until the predetermined time elapses after the power is turned on, but after the predetermined time elapses, the reset is automatically released, and then the microcomputer is started up and the existing hot water supply of this type is started. Like the system, it may be in a state of waiting for a user's operation command.

In the present invention, once the micro
After the computer is started up, the operation of the switch monitoring circuit or the reset blocking release circuit is disabled thereafter, that is, the abnormality detection function is lost.

This is because even if the legitimate momentary command switch is operated after the system has been normally shut down, a potential change appears on the line containing this switch for at least a moment. This is because unless the function of one of the circuits is disabled, the normal switch operation may be mistaken for an ON failure.

In addition, in this way, in principle, no major modification is required to a known circuit system or a program for determining the presence / absence of switch operation in a microcomputer, and simply by adding the constituent parts of the present invention to the present invention. You can enjoy safety measures based on it.

Further, as described above, preferably, even if the switch monitoring circuit is in the ON failure detection state for a while after the power is turned on, if the switch monitoring circuit is in the normal OFF state, the power is turned on from this point. It is also a good consideration to configure and place the microcomputer so that it can be started after the reset circuit has performed its original operation. This is because even if the momentary command switch is turned on when the power is turned on, this may be a temporary failure. Of course, even if this failure eventually leads to a continuous failure, it can be surely detected at least at the next power-on of the microcomputer.

Although not directly related to the present invention, with respect to the ON failure of this type of switch during the operation of the microcomputer, since the ON signal is generally continuously issued to the microcomputer, it is comparatively possible. You can easily know such a failure.

Therefore, if we dare to say that there are such facts, the present invention has focused its attention on preventing an unexpected operation from occurring immediately after the power-on reset is released when the power is turned on. Of.

[Examples] FIG. 1 shows a schematic configuration of a basic embodiment of the present invention, and FIG. 2 shows an operation example thereof.

In the case shown in the figure, the momentary type command switch to be monitored by the present invention is located in the remote unit 25 surrounded by a virtual line frame and substantially burns through the microcomputer 11. Operation switch S ₁ for instructing the start of the hot water supply, the standby state for starting hot water supply, the water filling switch S ₂ for instructing the operation of automatically collecting a predetermined amount of hot water in the bathtub, and the hot water spouted in the bathtub. Although three of the additional cooker switches S ₃ for fixing are shown, any switch has the same meaning in that it is a target for detecting an on-failure according to the present invention, and therefore, hereinafter, unless particularly distinguished, These momentary type command switches will be described with the symbol "S ₁ " representing all of them.

Naturally, the momentary type command switch S _i to be monitored according to the present invention is not limited to these three, and other remote control type water heaters of this type can be used.
Anything provided for the unit 25 can be similarly monitored by the present invention.

Further, the remote unit 25 may have a built-in volume, for example, so that the hot water temperature can be specified by the user, as described above, but since it is not the subject of monitoring in the present invention, Illustration and description of these are omitted.

One of the contacts of each momentary type command switch S _i is commonly grounded, and the other end is input to each dedicated terminal of the microcomputer 11.

Further, in the case shown, the switch monitoring circuit 21 is shown to be provided in the switch monitoring circuit 21, but similarly in the hot water supply systems up to now, similarly to the one connected to each dedicated terminal of these microcomputers 11. The other end of each switch S _i is connected to the power supply potential V _cc via a pull-up resistor R _i (= R ₁ , R ₂ , R ₃ ).

Therefore, when the momentary command switch S _i in a state where the micro-computer 11 is risen is pressed by the user, in FIG. 2, the Yo shown by reference numeral "P _x" in the key point, the switch S _i the potential of the pull-up resistor R _i side of the line including in series transiently falls to the ground level or low level, which is decoded by the microcomputer 11 as an instruction data P _x for each switch, a combustion system (not shown) And acts on the hot water supply system to start a predetermined operation.

In a sense, the switch monitoring circuit 21 provided in the base unit according to the present invention also uses a similar state when the switch operation data is sent to determine the ON failure of the switch. If the switch S _i has already turned on and failed when the power was turned on, the potential on the pull-up resistor R _i side of the failed switch S _i should be at a low level immediately when the power is turned on. Is.

The operation of the present invention when the power is turned on will be described below.
In FIG. 2, the left half starting from the power-on time T ₁ is when the ON failure has not occurred in any momentary type command switch S _i, and the right half starting from the power-on time T ₃ is
Shows a main part waveform to main section state of the first in illustrated circuit when the ON failure in the momentary command switch even one any has occurred, the further the time T ₄ after, as discussed last, momentary The on-failure has occurred in the mold command switch S _i , but this is transient, and the self-recovery is shown. .

At time T ₁ , when the power supply V _cc is turned on as shown in the uppermost row of FIG. 2, unless all the momentary switches S _i have the contact-on failure, all the momentary switches S _i are not damaged. The contact potential on the pull-up resistor R _i side with respect to S _i becomes a high level (substantially the power supply level).

Therefore, in the switch monitor circuit 21 shown in FIG. 1, all the diodes D _i (= D ₁ , D) whose cathodes are connected to the contacts on the pull-up resistor R _i side of all the momentary switches S _{i. 2} , D ₃ ) is turned off because there is no significant potential difference between the commonly connected anode side and the relevant cathode, and it is equivalently removed from the circuit system. The npn transistor Q _{1 in} this case, whose base is connected through the same, is turned on because it is in the same state as being simply subjected to a predetermined base bias.

Here, the waveform at the anode end of the diode D _i is the second waveform.
The switch status signal is shown in the second row of the figure
Immediately after T _1, it is at a high level corresponding to the scale of switch state “off”.

Therefore, the output of the switch monitoring circuit 21, which is the collector terminal of the transistor Q ₁ that is turned on in accordance with this, is at a low level indicating a normal state, and
Stay low.

In Fig. 2, this signal also shows the scale "abnormal" and "normal". Similarly, the upper scale also has a logical "H".
Or high level, the lower scale represents a logical "L" or low level.

This also applies to the output signal of the power-on reset circuit 22, which will be described later. In the figure, the scale "release" indicates a high level and the "reset" indicates a low level.

In any case, when the contact of the momentary switch S _i is opened as it is when the power is turned on, the output of the switch monitoring circuit 21 becomes “L” and becomes a significant normal signal, and this normal signal is reset. It constitutes the release blocking circuit 26.
Given to the base of npn transistor Q ₂ , keeps it turned off.

Here, since the emitter-collector of the transistor Q ₂ is connected to both ends of the capacitor 23 in the illustrated case, the fact that the transistor Q ₂ is in the off state means that the capacitor 23 is Transistor like
Equivalent to Q ₂ not connected.

On the other hand, the capacitor 23 is the same as the power-on reset circuit 22 used in this embodiment.
It has the role of setting the time length of the reset signal when exhibiting the reset function, that is, the predetermined time for maintaining the microcomputer in the reset state after the power is turned on.

In other words, the power-on reset circuit, which is often used in this type of control circuit system, uses the charging time constant of the capacitor to set the predetermined time from power-on to reset release. and of the type which, although it is to those utilizing the discharge time constant, in the present embodiment has a gentle and of the type which utilizes the charging time constant of the capacitor, therefore, when the power is turned at time T ₁ If there is no abnormality in all the momentary switches S _i as described above, the power-on reset circuit 22 exhibits its original power-on reset function as follows.

When the power is turned on at time T ₁ in FIG. 2, the power supply voltage V _cc is also applied to each internal circuit element of the power-on reset circuit 22.

Then, the threshold value V set by the fixed voltage divider
_th is applied almost immediately to the negative phase input of the comparator 24. As shown in the fourth row in FIG. 2, the anti-phase input of the comparator 24 is shown by the waveform of a virtual line.

On the other hand, the positive voltage input of the comparator 24 is supplied with the divided voltage of the capacitor 23 and the resistor described above, so that this voltage is almost supplied with the full charge of the capacitor after the power is turned on T _1. By the time it rises to the potential V _cc , an integrated waveform with a delay occurs due to the time constant related to the charging path of the capacitor 23 and the resistor. Therefore, the voltage relationship between the negative phase and positive phase inputs of the comparator is the above time constant and the above Until the time T ₂ determined by the set threshold value V _th on the negative phase input side, the potential on the negative phase side remains higher.

As a result, the power that can be captured as the output of the comparator 24
The output of the on-reset circuit 22 is
"L" level to maintain, and it up to the time T _2, the microcomputer 11 maintains the reset state.

As is clear from such an operation, when all the momentary switches S _i are normal, when the power is turned on T ₁
From power-on reset circuit for a predetermined time set in the _{24 t d (= T 2 -T} 1), After the initial resetting is applied, the power-on reset circuit output at time T _2, after The rising to the "H" level (falling as the reset signal) puts the microcomputer 11 into the operable state.

On the other hand, when any one of the momentary switches S _i has an on-failure, that is, a non-dissociation anomaly in which contacts cannot be separated at the beginning of power-on,
In FIG. 2, the power-on time T ₃ which is the first change point in the right half
As will be shown below, the circuit system of the present invention takes the following measures.

That momentary switch even one any from the initial power-on is on the inside of the diode group provided in the input stage of the switch monitoring circuit 21, at least any one of the diode D _i Power It means that it becomes a forward bias with turning on and turns on immediately.

This way, the diode logic is operated, the switch status signal appearing at its output point is different from the normal previous, "H" without rising to the level at time T ₃ after also the "L" level maintain.

Therefore, the transistor Q ₁ provided on the output side of the switch monitoring circuit 21 does not turn on, and the output of the switch monitoring circuit defined as this crector end has one end at the collector of the transistor Q _1. Through the connected pull-up resistor, it is almost pulled up to the power supply potential V _cc and becomes "H" level, and this is given to the base of the transistor Q ₂ constituting the reset release blocking circuit 26.

Therefore, this transistor Q ₂ turns on and shorts both ends of the capacitor 23. In this case, in FIG.
Almost at the same time as the power is turned on at time T _3, the power-on
A fixed threshold voltage _Vth is immediately given to the negative phase input of the comparator 24 in the reset circuit 22 by a fixed resistance voltage dividing circuit, but the positive phase input is short-circuited at both ends of the capacitor 23. Therefore, it will not rise from the ground level or "L" level forever.

Therefore, the output of the power-on reset circuit 22, which is defined as the output of the comparator 24, is different from the original power-on reset signal in the normal state, and is always at the “L” level after the power is turned on after T _3. As a result, the microcomputer 11 is held in the reset state.

In this way, according to this circuit, when the momentary switch S _i has an ON failure, it is well detected, and the possibility of unexpected operation even if the power is turned on is avoided.

In addition to these basic operations, this circuit also performs the following operations.

One of them is the function of the abnormality detection disabling circuit 27.

In the case of the first illustrated embodiment, this abnormality detection invalidation circuit 27
It is turned on by the reset release signal generated by the comparator 24 or the power-on reset circuit 22, that is, the "H" level signal, and the output of the transistor Q ₁ on the output side of the switch monitoring circuit 21 is forced to the ground. It consists of a short-circuiting transistor Q ₃ . From some perspectives, it can be said that it is composed of a transistor Q ₃ forcibly short-circuiting the input of the reset release blocking circuit 26.

Therefore, in FIG. 2, the time used to explain the normal condition is first described.
Power-on reset circuit as shown after T ₂
22 performs its original power-on-reset function,
The reset signal has a non-significant logic level after the lapse of a predetermined initial reset time t _d . If you launch the "H" level, this receives a high level signal to Besu input transistor Q ₃ is turns on, and therefore, or later is momentary switch S _i is also turned on, it does not detect this , Will be disabled.

This is because when the transistor Q ₃ is on, the momentary switch S _i is turned on, the switch state signal becomes “L” level, and the switch monitoring circuit 21 has already been described. The same as when detecting an abnormality
Even if the operation to turn off the transistor Q ₁ occurs,
This is because the collector of the transistor Q ₁ is forcibly pulled to the ground by the transistor Q _{3 and} thus this detection operation is substantially invalidated.

This can also be seen as an invalidating operation for the reset release blocking circuit 26. Transistor Q ₃ turns on,
Transistor in input stage of reset release blocking circuit 26
Fixing the base of Q ₂ to a low level is substantially the same as the state of this reset release blocking circuit 26 under normal conditions, and therefore the power-on reset circuit 22
On the other hand, no significant command is sent.

Such an abnormality detection disabling circuit 27 is provided so that when the user operates the momentary switch S _i as a normal operation after the microcomputer 11 is normally started up, in FIG. , The data P _x , the contact potential on the pull-up resistor R _i side drops to a low level, even though it is transient, as in the case of the ON failure, and this transition is caused by the output of the diode logic. This is because it also appears in dots. It is clear that it is uncomfortable to consider that the low level generation caused by such a normal switch command operation is abnormal.

In other words, because of this, in order to fetch and decode the command data P _x based on the operation of the momentary switch S _i in the microcomputer 11, it is necessary to change the existing program in this type of system. It doesn't matter if it doesn't.

Next, in the present circuit, at the moment the power is turned on, at least any one of the momentary switches S _i has an ON failure as described after time T _{3 in} FIG. Therefore, even after this circuit has performed the above-mentioned desired abnormality detection operation and fixed the output of the power-on reset circuit 22 to the “L” level, which is the continuous output state of the reset signal, the momentary When the ON failure in the switch S _i is transient and self-recovers, the operation accompanying the power-on at that time can be normally started from there.

That is, as shown at time T ₄ in FIG. 2, when the momentary switch S _i that has been turned on returns to the normal off state for some reason, the power switch
Since the significant "L" level reset signal was continuously sent from the on-reset circuit 22, the abnormality detection invalidation circuit 27
Since the switch state monitoring function of the switch monitoring circuit 21 is still enabled, the switch S _i returns to the normal OFF state at time T _{4 when} the output of the diode D _{i on} the anode side is output. When the inversion of the switch status signal to "H" level representing the normal OFF state is generated, the abnormality detection state by this circuit is released.

That is, when the switch state signal is the logic "H" inversion, which is the normal state, the operation is exactly the same as that described for the operation after the time T ₁ when it was normal from the beginning of power-on, and at this time T ₄ Then, the switch monitoring circuit 21 starts to output a significant normal signal at a low level, so that the transistor Q ₂ is turned off and the capacitor 23 is charged, and thereafter, the capacitance value of the capacitor 23 and the threshold value V after a lapse of time equal to a predetermined initial reset time t _d set by _th, the reset release signal from the comparator 24 to the power-on reset circuit 22, i.e.,
A significant release signal is sent at "H", and the microcomputer 11 becomes operable.

Therefore, from this time, similarly, the abnormality detection invalidation circuit 27 operates, and similarly to the above, the normal command data P _x associated with the pressing operation of the momentary switch S _i by the user after the time T ₅ is the micro command.・ It is taken in normally by the computer 11.

In fact, the momentary switch may cause a transient ON abnormality for some reason rather than an unrecoverable failure. Therefore, it is convenient to be configured as in this circuit.

Of course, the next time the power is turned on, this circuit will be turned on by monitoring the switch status, so it is safe even if such an ON abnormality leads to a serious failure. Further, normally, a switch abnormality during the operation of the microcomputer is easily detected by the microcomputer itself. In a normal program, the microcomputer repeatedly checks the state of each switch at a predetermined cycle, and therefore such a failure can be detected in the form of continuation of an ON signal for an abnormally long cycle.

Note that it is a matter for a person skilled in the art to arbitrarily design such that an audible alarm and a visual alarm are generated by the output signals of the switch monitoring circuit 21 and the reset release blocking circuit 26.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram of essential parts of a preferred embodiment of a hot water supply safety circuit to which the present invention is applied, and FIG. 2 is an explanatory diagram of the operation of the first illustrated circuit. In the figure, 11 is a microcomputer, 21 is a switch monitoring circuit, 22 is a power-on reset circuit, 23 is a capacitor, 24 is a comparator, 25 is a remote unit, 26 is a reset release blocking circuit, and 27 is an abnormality detection. The invalidation circuit, S _i is a momentary type command switch.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (56) Reference JP-A-57-83693 (JP, A) JP-A-61-283901 (JP, A) JP-A-58-70304 (JP, A) Actual development Sho-61- 42601 (JP, U)

Claims (2)

[Claims] 1. When a momentary command switch provided in a remote unit is operated, a microcomputer incorporated in a base unit provided at a remote place responds to the operation, and the microcomputer is incorporated in the base unit. Of the remote control type water heater whose combustion and hot water discharge mechanism is controlled in accordance with the above command; power-on for sending a reset signal to the microcomputer for a predetermined time after the microcomputer is powered on. A reset circuit; from the time of turning on the power to the microcomputer,
Monitor the contact status of the momentary command switch,
A switch monitoring circuit that continues to output an abnormality detection signal when the power is turned on as long as the contact is closed; and a power-on reset circuit that outputs the abnormality detection signal as long as the switch monitoring circuit continues to output the abnormality detection signal. Even if the reset signal exceeds the predetermined temperature,
A reset release blocking circuit that keeps sending; and an abnormality that disables at least one of the function of the switch monitoring circuit and the reset release blocking circuit after the power-on reset circuit releases the reset of the microcomputer. A safety circuit for a remote-controlled water heater, which comprises a detection invalidation circuit; 2. The reset release prevention circuit is a power-on circuit when an abnormality detection signal from the switch monitoring circuit is lost.
A signal similar to that at the time of power-on is sent to the reset circuit, so that the power-on reset circuit cancels the reset of the microcomputer after the lapse of the predetermined time from the time when the abnormality detection signal is lost. The remote control type water heater safety circuit according to claim 1, wherein: