JPS6137969Y2 - - Google Patents

Description

[Detailed Description of the Invention] The present invention relates to a flame detection device with a fail-safe function.

When the output of the flame detection device is used for furnace combustion control, etc., if the flame detection device malfunctions and generates a flaming signal when there is no flame, the fuel continues to be supplied to the burner, causing fuel to flow into the furnace. There is a risk of overfilling. Therefore, it is necessary to provide a fail-safe function so that at least a flame signal will not be generated when the flame detection device fails.

An object of the present invention is to provide a flame detection device that has a fail-safe function against failure of all active elements constituting the flame detection device.

The failsafe mechanism of the flame detection device of this invention is
There are two types of display devices and their drive circuits: main and sub. By performing a strobing operation on the signal discriminator, both displays display a matching display when there is no failure, and when a fault occurs, both displays display a mismatch or no flame display.

The present invention will be explained below with reference to the drawings. The figure is an electrical configuration diagram of an embodiment of the present invention. In the figure, BR
is the burner, FL is its flame, and EL is the electrode. A voltage from an alternating current power supply AC is applied between the burner BR and the electrode EL via a capacitor _C1 . The alternating current power supply AC is, for example, a commercial frequency power supply. U ₁ , U ₂ , U ₃ are differential operational amplifiers, Q ₁ , Q ₂ , Q ₃ are transistors, ZD ₁ , ZD ₂ are Zener diodes, D ₁ , D ₂ ,
D ₃ , D ₆ are diodes, D ₄ , D ₅ are light emitting diodes, R ₁ to R ₁₉ are resistors, C ₂ to _{C 9} are capacitors, RL
is a relay.

The voltage generated between burner BR and electrode EL is resistance
The voltage is divided by a series circuit of R ₁ and R ₂ , smoothed by a capacitor C ₂ , and applied to the non-inverting input terminal of an operational amplifier U ₁ . The series circuit of Zener diodes ZD ₁ and ZD ₂ limits the amplitude to prevent the input voltage from becoming excessive. The output voltage of the operational amplifier U ₁ is divided by a series circuit of resistors R ₄ and R ₅ and fed back to the inverting input terminal. As a result, the input voltage is amplified by a gain determined by resistors R ₄ and R ₅ . The output voltage of the operational amplifier _U1 is applied to the guard electrode of the holder of the electrode EL through the resistor _R3 , thereby reducing leakage current. The output voltage of the operational amplifier U ₁ is determined by the resistance R ₆ ,
A twin T circuit consisting of R ₇ , R ₈ and capacitors C ₃ , C ₄ , C ₅ removes the frequency component that is the same as the voltage of the AC power supply, and connects it to the operational amplifier through resistor R _9.
Given to U ₂ and U ₃ . Since the output voltage of the operational amplifier _U1 includes a DC component based on the rectification effect of the flame FL, this DC component is extracted by the action of the twin T circuit. The DC component becomes an electrical signal indicating the presence of flame. This flame signal takes a positive or negative value depending on the type of flame FL.

The operational amplifiers U ₂ and U ₃ are bare amplifiers without negative feedback, and due to their high gains, each operates as a voltage comparator forming a determination circuit. The operational amplifier U ₂ responds to a positive flame signal; the flame signal is applied to its inverting input terminal, and its non-inverting input terminal is connected to an adjustable positive flame signal by means of a circuit consisting of resistors R ₁₂ , R ₁₄ and capacitor C ₇ . A constant voltage is given as a reference voltage. The inverting input terminal and the non-inverting input terminal are connected by a series circuit of a diode _D1 and a resistor _R10 . The operational amplifier U ₃ responds to a negative flame signal, and the flame signal is applied to the non-inverting input terminal, and the adjustable negative flame signal is applied to the inverting input terminal by a circuit consisting of resistors R ₁₃ , R ₁₅ and capacitor C ₈ . A constant voltage is given as a reference value. Both input terminals are connected by a series circuit of resistor R ₁₁ and diode D ₂ . Operational amplifiers U ₂ and U ₃ include transistor Q ₂ for strobin.
is connected. Transistor Q ₂ is an operational amplifier
This is a device that is grounded or floated in the middle of the amplification path of U ₂ and U _3. When it is grounded, transmission of the amplified signal is blocked, and when it is released, signal transmission is restored. Each time the signal transmission is blocked, the output circuits of the operational amplifiers U ₂ , U ₃ are inactive, so that their output terminals are connected in common to the positive voltage applied through the resistor R ₁₆ forming a clamping circuit. become. When signal transmission is restored, the output circuit becomes operational, and the voltage at the output terminal becomes a value corresponding to the amplified output. Transistor Q ₂ is driven by the alternating voltage generated across resistor R ₇ of the twin T circuit, and turns on and off at the same frequency as this alternating voltage. Therefore, the output circuits of operational amplifiers U ₂ and U ₃ also repeat operation and non-operation at the same frequency. This operation at separate intervals is called strobing.

The outputs of operational amplifiers U ₂ and U ₃ are connected to transistors Q ₁ and
Given on the basis of Q ₃ . Transistor Q ₁ is
It is a PNP type transistor, and a load consisting of a resistor _R17, a light emitting diode _D4 , and a relay RL is connected to its emitter. Diode _D3 is for absorbing the back electromotive force of relay RL, and capacitor _C10 is for smoothing the drive current. The light emitting diode _D4 serves as a flame indicator, and the relay RL serves as a condition signal generator for a combustion control device, etc. Transistor Q ₃ is an NPN type transistor, and is AC-coupled to operational amplifiers U ₂ and U ₃ via capacitor C ₉ . diode
D ₆ is for discharging capacitor C ₉ . In the collector of the transistor Q ₃ there is a resistor R ₁₉ and a light-emitting diode D ₅
A series circuit of is connected as a load. Light emitting diode _D5 is a sub-indicator.

The operation of the device configured in this way is as follows. When there is no flame between the burner BR and the electrode EL, the DC voltage generated at the output of the twin T circuit is zero or a small value that does not reach the reference value, so the operational amplifier U ₂ The operational amplifier _U3 produces a positive saturated output voltage in response to a reference voltage applied to its inverting input terminal.
The output circuits of operational amplifiers U ₂ and U ₃ are repeatedly activated and deactivated by strobing by transistor Q ₂ , but their output terminals maintain the saturated output voltage both when activated and when they are not activated. Because there are
The drive signals for transistors Q ₁ and Q ₃ are constant positive DC voltages. Therefore, transistors Q ₁ and Q ₃ are off, light emitting diodes D ₄ and D ₅ do not emit light, and relay RL is also inactive. In other words, no flame is displayed when both the main and sub-indicators are off.

When a flame is present between the burner BR and the electrode EL, a negative DC voltage is generated at the output of the twin T circuit, depending on the type of flame. When this DC voltage is positive and greater than the reference voltage of operational amplifier _U2 , the output of operational amplifier _U2 is inverted and becomes zero.
Further, when the DC voltage is negative and its value is smaller than the reference voltage of the operational amplifier _U3 (the absolute value is large), the output of the operational amplifier _U3 is inverted and becomes zero as well. Therefore, when there is a flame, the output voltage of either operational amplifier U ₂ or U ₃ becomes zero. operational amplifier
Since the output terminals of U ₂ and U ₃ are connected in common and connected to the positive DC power supply through the resistor R ₁₆ , the voltage at the common connection point also becomes zero at this time. operational amplifier
U ₂ and U ₃ are repeatedly activated and deactivated by strobing, and when they are not activated, the voltage at the common connection point rises due to the voltage of the DC power supply, so the voltage at the common connection point is strobed. fluctuates at the same frequency as Every time the voltage at the common connection point becomes zero, the transistor _Q1 is turned on, causing the light emitting diode _D4 to emit light and driving the relay RL. Since the drive currents of the light emitting diode _D4 and the relay RL are smoothed by the capacitor _C10 , continuous lighting and excitation are performed. As the voltage at the common connection point changes at the strobing frequency, the AC-coupled transistor _Q3 is also turned on and off. Therefore, the light emitting diode _D5 blinks, which also appears to the human eye as being continuously lit. Therefore, when there is a flame, both the main and sub-indicators light up to indicate that there is a flame.

In this manner, when each part of the device is operating normally, the presence or absence of a flame is indicated by the simultaneous flashing operations of both the main and sub-indicators D ₄ and D ₅ .

In such a flame detection device, active elements such as operational amplifiers U ₁ , U ₂ , U ₃ and transistors are used.
Various modes of failure can be considered for Q ₁ , Q ₂ , and Q ₃ . The flame detection device of the present invention performs fail-safe operation against any mode of failure of each active element. The fail-safe operation in each case will be explained below. It is not a problem that the display element turns off due to a failure of the active element when there is a flame, since this is a fail-safe measure, but the problem is that both display elements turn on when there is no flame. Therefore, the operation will be explained only regarding failures when there is no flame.

<Failure of operational amplifier U ₁ > Failures of operational amplifier U ₁ include shortening of the output terminal,
There is positive output saturation and negative output saturation.

In the case of a short circuit at the output end, the input to the twin T circuit becomes zero, so the inputs to the operational amplifiers U ₂ and U ₃ are also zero, resulting in a flameless signal. Therefore, the outputs of the operational amplifiers U ₂ and U ₃ become positive saturation voltages, so the transistors Q ₁ and Q ₃ are turned off, and the light emitting diodes D ₄ and D ₅ are turned off, indicating a flameless state.

When the operational amplifier U ₁ has a positive output saturation, a positive DC voltage is applied to the operational amplifiers U ₂ and U ₃ through the twin T circuit, so the output of the operational amplifier U ₂ becomes zero. Since the signal in the twin T circuit does not include an alternating current component, strobing by transistor Q ₂ is not performed, and the output voltage of operational amplifier U ₂ does not pulsate. Therefore, only transistor _Q1 is turned on, light-emitting diode _D4 is lit, and light-emitting diode _D5 is turned off. light emitting diode _D4 ,
A malfunction is indicated because D ₅ are not lit at the same time.

When the output of the operational amplifier U ₁ is in negative saturation, a negative DC voltage is applied to the operational amplifiers U ₂ and U ₃ through the twin T circuit, so that the output voltage of the operational amplifier U ₃ becomes zero. In this case too, no strobing is performed, so only transistor _Q1 is turned on,
Only light emitting diode D ₄ lights up. Therefore, a failure indication is performed in the same manner as in the above case.

<Failure of operational amplifier U ₂ or U ₃ > Operational amplifier U ₂ or U ₃ also has failures such as output end short circuit, output positive saturation, and output negative saturation. When these failures occur, the output becomes a DC voltage at a constant level, regardless of strobing. Also, since there is no flame, the output voltage of the non-faulty side is a positive saturated output.

In the case of a short circuit at the output end, the output voltage is zero, so only transistor Q ₁ is turned on, only light-emitting diode D ₄ is lit, and light-emitting diode D ₅ is off, which indicates a fault. Ru.

In the case of positive output saturation, both transistors Q ₁ and Q ₃ are turned off by this output voltage, so both light emitting diodes D ₄ and D ₅ are turned off, indicating a flameless state.

In the case of output negative saturation, this voltage turns on only the transistor _Q1 , lighting up only the light emitting diode _D4 , and turning off the light emitting diode _D5 . This will indicate a fault.

<Failure of Transistor _Q1 > Failures of transistor _Q1 include short circuit and open circuit. When there is no flame, the outputs of operational amplifiers U ₂ and U ₃ are at positive saturation voltages despite strobing, so transistor Q ₃ is always off, and therefore light-emitting diode D ₅ is always off. There is. Therefore, when a short circuit occurs in transistor Q ₁ , only the light emitting diode D ₄ emits light to indicate a failure, and when an open circuit occurs in transistor Q ₁ , both light emitting diodes go out to indicate a flameless state.

<Failure of transistor _Q2 > Transistor _Q2 also has short-circuit and open-circuit failures. When transistor Q ₂ fails, the strobing of operational amplifiers U ₂ and U ₃ is fixed to either ON or OFF state, but when there is no flame, the output of operational amplifiers U ₂ and U ₃ is positive regardless of strobing. Since the saturation voltage of the transistor is
Since Q ₁ and Q ₃ are both off and the light emitting diodes D ₄ and D ₅ are both off, a flameless state is displayed.

<Failure of transistor _Q3 > Transistor _Q3 also becomes short-circuited or open due to failure. When there is no flame, transistor Q ₁ is off and light emitting diode D ₄ is off, so even if a short circuit occurs in transistor Q ₃ there, the light emitting diode will not turn off.
Only D ₅ lights up, indicating a failure, and when transistor Q ₃ opens, light-emitting diode D ₅ does not light up, indicating a flameless condition.

In this way, according to the present invention, the presence or absence of a flame is displayed using the two main and sub display elements, and when there is no failure, the presence or absence of a flame is displayed by a matching display, and when there is a failure, the display is inconsistent or no flame is displayed. Failsafe can be achieved.

In the above embodiment, the operational amplifier constituting the voltage comparator corresponds to the case where the flame signal is positive and the case where the flame signal is negative.
A pair of U ₁ and U ₂ is provided, but if the type of flame and electrode position are specified and the polarity of the flame signal is either positive or negative, it is also possible to configure one operational amplifier. It is.

[Brief explanation of drawings]

The figure is an electrical configuration diagram of an embodiment of the present invention. BR...burner, FL...flame, EL...electrode,
AC...alternating current power supply, _U1 , _U2 , _U3 ...operational amplifier,
Q ₁ , Q ₂ , Q ₃ ... transistor, D ₄ , D ₅ ... light emitting diode, RL ... relay.

Claims (1)

[Scope of utility model registration request] A discrimination circuit that compares the DC component of a flame signal obtained as a DC electric signal including an AC component with a reference voltage based on the rectification effect of the flame, and generates a flame signal and a flameless signal of different levels, respectively; a strobe circuit that inputs an input and periodically changes the output of the discrimination circuit into an operating state and a non-operation state; a clamp circuit that forcibly holds the output terminal at a level corresponding to a flameless output when the discrimination circuit is inactive; a first display driving circuit that is DC-coupled to the output end of the discrimination circuit and turned on by a flaming output and turned off by a flameless output; and a second display drive circuit that is AC-coupled to the output terminal of the discrimination circuit. A flame detection device equipped with an indicator drive circuit.