JPH0151741B2 - - Google Patents

Description

Detailed Description of the Invention <Field of Industrial Application> The present invention relates to a safety circuit that can be used incidentally to a combustion control device for various types of combustion equipment that heats running water, such as water heaters. Even if the main control circuit in the control device becomes uncontrollable due to failure or other factors, the fuel supply to the combustion section will be reliably cut off and combustion will be stopped when the flow rate of water falls below the minimum allowable value. Concerning safety circuits that enable shutdown.

<Prior Art> Nowadays, this type of combustion control device operates under the commands of a main control circuit generally composed of a microcomputer.

In other words, the flow rate, supply water temperature, set temperature,
Perform predetermined calculations regarding the hot water temperature, etc.
Optimum control is achieved based on the results.

However, in addition to the main control related to combustion as described above, these combustion control devices also have appropriate safety measures to prevent damage to combustion equipment and even major accidents such as fire. need to be.

One of these is the monitoring of the water flow rate by the main control circuit.

In other words, if combustion continues even though the flow rate of running water has become extremely low and has fallen below the minimum allowable value, it will result in a so-called "dry cooking" condition, which will cause abnormally high temperatures. The main control circuit constantly monitors the flow rate signal obtained from the flow rate sensor, and if the flow rate falls below the minimum allowable flow rate value, a valve closing command signal is sent from the main control circuit to the fuel valve control circuit to forcibly close the valve. The valve closes to cut off the fuel.

In addition to these functions, the main control circuit also monitors the required temperatures of the combustion section, heat exchanger, hot water pipes, etc., and if an abnormally high temperature that cannot be tolerated occurs, the same Some systems send a fuel valve closing command signal from the main control circuit to the fuel valve control circuit to cut off the fuel supply.

<Problems to be Solved by the Invention> As is clear from its principle, the safety measures in the conventional example described above are based on the premise that at least the main control circuit always operates normally.

Therefore, if the main control circuit breaks down for some reason and does not operate normally, no matter how much correct flow rate information is provided from the flow rate sensor, or even if the temperature sensor does not provide the correct temperature, Even if information is given, it becomes completely meaningless.

This is a fatal flaw in the conventional example. Even if the flow rate of running water becomes extremely low and a signal to that effect is given from the flow rate sensor, if the main control circuit that processes this is disabled, it is of course impossible to forcibly close the fuel valve. As a result, it is easy to imagine that combustion would continue and a dangerous situation would occur.

This is a similar drawback even when temperature sensors are used at key locations to detect abnormally high temperatures.

The present invention has been made to eliminate the drawbacks of the conventional example described above, and even if the main control circuit happens to be out of order when the flow rate of flowing water falls below the allowable minimum flow rate value, The purpose is to provide a safety circuit that can reliably cut off the fuel supply.

<Means for Solving the Problems> In order to achieve the above object, the present invention includes: a main control circuit that controls various operations related to combustion;
a fuel valve control circuit that opens the fuel valve in response to a valve open command signal from the main control circuit and closes the fuel valve in response to a closure command signal; a flow rate detection circuit that detects the flow rate of flowing water in the heat exchanger facing the combustion section; A safety circuit that can be used in conjunction with a combustion control device having: a flow rate monitoring circuit that monitors the flow rate based on a flow rate signal from the flow rate detection circuit, separate from the main control circuit; Combustion characterized in that when the flow rate falls below a predetermined minimum allowable flow rate value, the flow monitoring circuit sends a valve closing command signal to the fuel valve control circuit independently of the main control circuit. Provides safety circuits for control devices.

<Function> According to the present invention, the flow rate monitoring circuit provided separately and independently from the main control circuit monitors the flow rate separately and independently from the main control circuit, and prevents the flow rate from falling below the planned minimum allowable flow value. When the main control circuit turns on, it sends a unique valve closing command signal to the fuel valve control circuit, regardless of whether a fuel valve closing command signal is issued from the main control circuit to the fuel valve control circuit.

Therefore, even if the main control circuit is unable to function due to a failure or other factors, the flow rate monitoring circuit can back up its function and reliably close the fuel valve to stop combustion.

That is, as a safety measure against abnormally high temperatures and the occurrence of fire, double protection is provided regarding forced fuel cutoff.

<Embodiment> FIG. 1 shows a schematic configuration of a basic embodiment of the present invention.

The flow rate detection circuit 4 may be any type as long as it can convert the flow rate of flowing water flowing through the combustion equipment to which this safety circuit is applied into an appropriate amount of electricity, but commonly used ones include a sensor section. Some use a Hall element or the like to convert the detected flow rate into a pulse width and output it.

Flow rate signal converted into such suitable electrical signal
Sr is sent to the main control circuit 1, which controls various operations related to combustion, as in the conventional example described above. This main control circuit 1 is generally a microcontroller.
Consists of a computer.

In the main control circuit 1, when, for example, an ignition command is issued by a command operation from a user via an operation unit (not shown), an ignition signal is sent to an ignition circuit (not shown), and a flow rate signal Sr is Only when the flow rate value range is indicated, a significant valve opening command signal is sent to the fuel valve control circuit 3, for example, at logic "H".
Si is sent out to open a fuel valve (not shown).

In addition, after the start of combustion, the flow rate signal
If Sr falls below the minimum allowable flow rate value, a significant valve closing command signal Si with logic "L" is sent to the fuel valve control circuit 3 to close the fuel valve and supply fuel to the combustion section. cut off.

As is clear from the above, in general, the main control circuit 1
The signal Si sent from the fuel valve control circuit 3 to the fuel valve control circuit 3 is such that a logic "H" indicates a command to open the valve, and a logic "L" indicates a command to close the valve. Therefore, this signal is shown in the drawings as a valve open/close command signal. Of course, the above logical value relationship may be reversed, and in some cases, two signal lines may be used to individually represent a valve open command and a valve close command. In any case, the peripheral circuit configuration regarding this main control circuit 1 may be the same as before.

In the present invention, the flow rate signal Sr from the flow rate detection circuit 4 is also input to a flow rate monitoring circuit 2 provided separately from the main control circuit 1.

The flow rate monitoring circuit 2 constantly compares and monitors the minimum allowable flow rate value and the actual flow rate, regardless of the main control circuit 1, and the actual flow rate flowing through the device is determined by the minimum allowable flow rate. When the value falls below the value, a valve closing command signal Sf is independently issued, and this is applied to the fuel valve control circuit 3 to forcibly close the fuel valve.

Therefore, when the actual flow rate flowing through the device falls below the minimum allowable flow rate value, if the main control circuit 1 is functioning normally, the fuel valve control circuit 3 will have the main control circuit 1 and the present invention. Valve closing command signals Si and Sf are sent from both flow rate monitoring circuits 2 added.

Of course, the fuel valve control circuit 3 is configured to close the fuel valve in accordance with the command, regardless of whether a fuel valve closing command signal is sent from either the main control circuit 1 or the flow rate monitoring circuit 2. The circuit configuration itself for responding to both signals can be very easily constructed by those skilled in the art using known electronic circuit technology.

On the other hand, even if the main control circuit 1 has stopped its function due to some factor, when an undesirable situation occurs in which the flow rate falls below the minimum allowable flow rate value, the flow rate monitoring circuit 2 provided according to the present invention is activated. On the other hand, since the valve closing command signal Sf is issued independently regardless of a failure in the main control circuit, the fuel valve can be closed as expected via the fuel valve control circuit 2.

FIG. 2 shows an example of the configuration of the flow rate monitoring circuit 2, and also shows a simple modification to the known fuel valve control circuit 3, as mentioned above.

In this specific embodiment, the flow rate detection circuit 4 generates an electrical signal with a pulse width corresponding to the flow rate of flowing water.
Therefore, the flow rate monitoring circuit 2 also converts the input pulse width corresponding to the actual flow rate into a voltage by comparing it with the pulse width at the minimum allowable flow rate value. It is a circuit that monitors the

The flow rate signal Sr is input to the base of the first stage transistor 21 of the flow rate monitoring circuit 2, and its collector output is given to a differentiating circuit 22 consisting of a capacitor and a resistor.

Therefore, at the output of the differentiating circuit 22, differential pulses are generated at the rising and falling edges of the flow rate signal Sr, but only with respect to the positive differential pulse, the transistor 2 is activated each time it appears.
3 turns on for a certain period of time. In other words, the transistor 23 is turned off once per pulse of the flow rate signal Sr for a predetermined period of time.

Therefore, the capacitor 26, which was charged by the power supply voltage via the resistors 24 and 25 when the transistor 23 was in the off state, is charged between the capacitor 26 and the resistor 25 every time the transistor 23 is turned off as described above. It begins to discharge according to a predetermined time constant. And the frequency of this discharge is
From the above, as the flow rate decreases and the pulse width of the flow rate signal Sr becomes longer, the sparse becomes more sparse, and as the flow rate increases and the pulse width of the flow rate signal Sr becomes shorter, the pulse width increases.

Therefore, the potential Ec across the capacitor 26 becomes higher as the flow rate decreases. Therefore, the potential Es corresponding to the minimum allowable flow rate value is determined by a potentiometer consisting of resistors 29a and 29b as shown in the figure. If the comparator 27 compares this with the flow rate, a signal that discriminates whether the current flow rate is above or below the minimum allowable flow rate value is obtained at its output.

In the illustrated embodiment, the reference potential Es corresponding to the minimum flow rate value is applied to the positive input of the comparator 27, and the capacitor both-ends potential Ec is applied to the negative input, so that when the flow rate falls below the minimum allowable flow rate value, The comparator output that appears changes from the previous logic "H" to logic "L". In this embodiment, the logic "L" signal of the comparator 27 is made significant and is used as the valve closing command signal Sf sent to the fuel valve control circuit 3.

The fuel valve control circuit 3 can be configured as follows, for example.

A relay 31 that opens a fuel valve (not shown) when energized and closes the fuel valve when demagnetized is provided, and an npn switching transistor 32 is arranged in series with this circuit, and a main control circuit is provided at the base of the relay 31. A valve open/close command signal Si from circuit 1 is applied.

Similarly, a second but pnp type switching transistor 34 is provided in series with the relay 31, and a third npn type switching transistor 3 whose base can be selectively grounded.
3 will also be provided.

After the start of combustion, if the flow rate exceeds the minimum allowable flow rate value, as described above, the valve open/close command signal Si from the main control circuit 1 is at logic "H" and is a significant valve open signal. Transistor 32
is in the on state.

In addition, the valve closing command signal Sf of the flow rate monitoring circuit 2 is also
Since it is at non-significant logic "H", the transistor 33
turns on, the base of the transistor 34 is grounded, and the transistor 34 also turns on.

Therefore, the relay 31 is energized, the fuel valve is opened, and fuel is supplied to a combustion section (not shown).

During combustion, if the flow rate falls below the minimum allowable flow rate value for some reason, if the main control circuit 1 is operating normally, the valve open/close command signal Si will be a logic "L" and a significant valve close command signal. So this is transistor 3
1, so the transistor 31 is cut off, the relay 31 is deenergized, the fuel valve is shut off, and the fuel supply is stopped.

However, if main control circuit 1 is out of order,
Even if the flow rate is below the minimum allowable flow rate value, the valve open/close command signal Si from the main control circuit 1 may remain at logic "H".

However, in such a case, the valve closing command signal Sf, which is significant at logic "L" and is issued from the flow rate monitoring circuit 2 provided in accordance with the present invention, effectively functions to turn off the transistor 33 and turn off the transistor 34.
Since the main current line, that is, the emitter-collector line is also cut off, the relay 31 is reliably demagnetized and the fuel valve is definitely closed.

The resistor 28 in the flow rate monitoring circuit 2 and connected between the positive input and output of the comparator 27 is
As is well known, this comparator provides hysteresis to the comparison characteristics to prevent chattering.

Of course, the illustrated circuit configuration is only one embodiment of the present invention, and various other modifications can be made in accordance with the gist of the present invention.

<Effects of the Invention> According to the present invention, when the flow rate of flowing water to be heated in a combustion device falls below the allowable minimum flow rate, even if the main control circuit cannot operate normally due to a failure etc. Even if the command signal to close the fuel valve cannot be sent out, it is possible to send out the command signal to close the fuel valve via another route from a flow rate monitoring circuit that is installed separately and can operate independently. Therefore, it is possible to provide a more ideal safety measure for this type of combustion equipment.

[Brief explanation of drawings]

FIG. 1 is a basic schematic configuration diagram of an embodiment of the present invention, and FIG. 2 is a circuit diagram of a more specific embodiment configured in accordance with the basic configuration shown in FIG. 1. , is. In the figure, 1 is the main control circuit, 2 is the flow rate monitoring circuit, and 3
4 is a fuel valve control circuit, and 4 is a flow rate detection circuit.

Claims (1)

[Scope of Claims] 1. A main control circuit that controls various operations related to combustion; and a fuel valve control circuit that opens the fuel valve in response to a valve open command signal from the main control circuit and closes the fuel valve in response to a close command signal. ; a flow rate detection circuit for detecting the flow rate of water flowing in the heat exchanger facing the combustion section; and; A flow rate monitoring circuit is provided to monitor the flow rate based on the flow rate signal from the detection circuit; when the flow rate falls below a predetermined minimum allowable flow rate value, the flow rate monitoring circuit issues a signal independently from the main control circuit. A safety circuit for a combustion control device, characterized in that it sends a valve closing command signal to the fuel valve control circuit.