JPS61128026A - Safety circuit for combustion controlling device - Google Patents

Abstract

PURPOSE:To provide a safety circuit capable of making a positive supplying of fuel by a method wherein a flow rate monitoring circuit for monitoring the flow rate of fuel in response to a flow rate signal is arranged and when a minimum allowable low rate value is decreased, a valve closing command signal is transmitted from the flow rate monitoring circuit to the fuel valve control circuit. CONSTITUTION:A flow rate signal Sr converted into an electrical signal is sent to a main control circuit 1 monitoring a control over various operations relating to the combustion. This main control circuit 1 is composed of a micro- computer. The flow rate signal Sr from a flow rate sensing circuit 4 is inputted to a flow rate supervising circuit 2 which is independently arranged from the main control circuit 1. In the flow rate monitoring circuit 2, a minimum allowable flow rate value and an actual flow rate are always compared and monitored without having any relation with the main control circuit 1 and when the value is decreased lower than the minimum allowable flow rate value, the valve closing commandsignal Sf is generated, the signal Sf is applied to the fuel valve control circuit 3 and the fuel valve is forcedly closed.

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 a water heater or various combustion equipment that heats running water, and particularly relates to 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 stop when the flow rate of water falls below the minimum allowable value. Concerning safety circuits that enable

(Prior Art) Nowadays, this type of combustion control device operates under the commands of a main circuit that is generally composed of a microcomputer.

That is, the flow rate, supply water temperature, and set temperature at each time of ignition and for the combustion J1 sequence after ignition.

Predetermined calculations are performed on the hot water temperature, etc., and optimal 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. Must be.

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

In other words, if the combustion continues even though the flow rate of water has become extremely low and has fallen below the minimum allowable flow rate, it will result in a so-called "dry cooking" state, 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, the main control circuit sends a valve closing command signal to the fuel valve control circuit to forcibly close the valve. This closes the valve and cuts off the fuel.

In addition to these functions, the main control circuit also monitors the temperature of important points such as the combustion section, heat exchanger, hot water supply pipes, etc., and if an abnormally high temperature becomes unacceptable, the system will immediately respond. Similarly, there is also a system in which a fuel valve closing command signal is sent 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 if the temperature sensor does not provide the correct temperature information, Even if information is given, it becomes completely meaningless.

This is a fatal flaw in the conventional example. Even if the flow rate of 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, Of course, it is not possible to force the fuel valve to close, and 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 valve opening command signal from the main control circuit opens the fuel valve, This is a safety circuit that can be used in conjunction with a combustion control device, which has a fuel valve control circuit that closes the fuel valve in response to a command signal; and a flow rate detection circuit that measures the flow rate of water flowing in a heat exchanger facing a combustion section. Based on the flow rate signal from the flow rate detection circuit, separately from the main control circuit, ! A flow rate monitoring circuit is provided to monitor the flow rate; when the flow rate falls below a predetermined minimum allowable flow rate value, a valve blockage signal is sent from the linear flow rate monitoring circuit to the fuel valve control circuit independently of the main control circuit. A safety circuit for a combustion control device is provided, which is characterized by sending out a command signal.

(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 when the flow rate falls below a predetermined minimum allowable flow rate value. When
Regardless of whether a fuel valve closing command signal is issued from the main control circuit to the fuel valve control circuit, a unique valve closing command signal is sent 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.

In other words, as a safety measure against abnormally high temperatures and fire outbreaks,
Double protection will be provided regarding forced fuel cut-off.

(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 that should be provided with a safety circuit into an appropriate amount of electricity, but commonly used circuits include:
Some use a Hall element or the like in the sensor section to convert the detected flow rate into a pulse width and output the pulse width.

The flow rate signal Sr converted into such an appropriate electric signal is
As in the conventional example described above, the signal is sent to the main control circuit l which controls various operations related to combustion. This main control circuit l is generally composed of a microcomputer.

In the main control circuit 1, when an ignition command is issued, for example, 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 Si with logic "H", for example, is sent to the fuel valve control circuit 3 to open the fuel valve (not shown).

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

As is clear from the above, in general, the signal S1 sent from the main control circuit 1 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. It has become. Therefore, in one drawing, this signal is shown 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 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
is a flow rate monitoring circuit 2 provided separately and independently from the main control circuit 1.
is also entered.

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 4m vessel is determined by the minimum allowable flow rate value. When the flow rate is lower than the flow rate 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 one device is lower than the minimum allowable flow rate value, if the main control circuit 1 is functioning normally, the fuel valve control circuit 3 is connected to the main control circuit 1 and the additional fuel valve control circuit 3 according to the present invention. Valve closing command signals St and SF are sent from both of the flow rate monitoring circuits 2 that have been set.

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 techniques.

On the other hand, even if the main control circuit l 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 sr 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 described above.

In this specific embodiment, it is assumed that the flow rate detection circuit 4 emits an electric signal Sr with a pulse width corresponding to the flow rate of flowing water, and therefore the flow rate monitoring circuit 2 also
This circuit converts the pulse width corresponding to the actual input flow rate into a voltage and monitors it by comparing it with the pulse width at the minimum allowable flow rate value.

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

Therefore, differential pulses are generated at the output of the differential circuit 22 at the rise and fall edges of the flow rate signal Sr, but only for the positive differential pulse, each time the differential pulse appears, the transistor 23 is activated for a certain period of time. turn·
Turn on. In other words, the transistor 23 is turned on for a predetermined period of time per one pulse of the flow rate signal Sr.

Therefore, the capacitor 28, 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 28 and the resistor 25 each time the transistor 23 is turned on as described above. It begins to discharge according to a predetermined time constant. From the above, the frequency of this discharge is determined by the flow rate decreasing and the flow rate signal S
The longer the pulse width of r becomes, the sparser it becomes, and the more the flow rate increases and the shorter the pulse width of flow rate signal S'', the more the flow rate increases.

Therefore, the potential Ec across the capacitor 2B becomes higher as the flow rate decreases.
Define it with a potentiometer/meter consisting of and compare it with this! ! 27, the output provides a signal that discriminates whether the current flow rate is above or below the minimum allowable flow rate value.

In the illustrated embodiment, the reference potential E corresponding to the lowest flow rate value
Since s is applied to the positive input of the comparator 27 and the potential Ec across the capacitor is applied to the negative input, the comparator output that appears when the flow rate falls below the minimum allowable flow rate value is the same as the previous logic "H".
The logic value changes from "L" to logic "L". In this embodiment, the logic "L" signal of the comparator 27 is made significant,
This is used as a valve closing command signal Sf to be sent to the fuel valve control circuit 3.

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

A relay 31 is provided which opens a fuel valve (not shown) when it is magnetized and closes the fuel valve when it is demagnetized, and an npn type switching transistor 32 is arranged in series with the circuit. A valve open/close command signal Si from the main control circuit l is applied.

Similarly, a second but pup-type switching transistor 34 is provided in series with the relay 31, and a third npnm switching transistor 34 whose base can be selectively grounded.
A switching transistor 33 is also 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 becomes a significant valve open signal at logic "H". Therefore, the transistor 32 is turned on.

Also, the valve closing command signal St of the flow rate monitoring circuit 2.

Since it is at the non-significant logic "H", the transistor a3 is turned on, the base of the transistor 34 is grounded, and the transistor 34 is also turned on.

Therefore, the relay at 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 l is operating normally, the valve open/close command signal Si will be a significant valve close command signal at logic "L". This is applied to the base of the transistor 31, so the transistor 31 is cut off and the relay 3 is
1 is released, the fuel valve is shut off, and the supply of fuel is stopped.

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

However, when something goes wrong, the flow rate monitoring circuit 2 installed according to the present invention also issues a logic "L" valve closing command signal SF, which effectively functions to turn off the transistor 33 and turn off the main transistor 34. Since the 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.

In addition, the resistor 2B which is connected between the positive input and the output of the comparator 27 in the flow rate monitoring circuit 2 gives hysteresis to the comparison characteristic by this comparator, as shown in y4.
This is to prevent chattering.

Of course, the illustrated circuit configuration is merely 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 combustion equipment is lower than the allowable minimum flow rate value, even if the main control circuit cannot operate normally due to a failure etc., the fuel Even if a command signal to close the valve cannot be sent, the fuel valve closing command signal can be sent via another route from a flow rate monitoring circuit that is separately provided and can operate independently. , it is possible to provide more ideal safety measures for this type of combustion equipment.

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

Claims (1)

[Scope of Claims] A main control circuit that controls various operations related to combustion; a fuel valve control circuit that opens a 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 safety circuit that can be used in conjunction with a combustion control device, comprising: a flow rate detection circuit that detects the flow rate of flowing water flowing in a heat exchanger facing a combustion section; A flow rate monitoring circuit is provided to monitor the flow rate based on a flow rate signal from the circuit; when the flow rate falls below a predetermined minimum allowable flow rate value, the flow rate monitoring circuit, independently of the main control circuit, A safety circuit for a combustion control device, characterized in that it sends a valve closing command signal to a fuel valve control circuit.