The present invention relates to a device and method for the control and detection of the flame of a gas burner. In particular the present invention is used in atmospheric or pre-mixed burners. The fuel is preferably gas, but it could be any combustible fuel in gaseous or liquid form (e.g. diesel oil, kerosene, etc.). Purely by way of example, a possible use of the burner according to the present invention is in the field of boilers for heating/sanitary use and water heaters.

More precisely, the present invention relates to the flame signal amplification circuit which is detected via an ionisation electrode inserted in a region where the flame is present. This circuit is normally used for detecting the presence or not of the flame and/or the variation thereof over time so as to regulate the quantity of air and/or gas to be supplied to the burner.

In the prior art, a common control device for combustion of a burner comprises:

• shut off and modulating means (preferably a valve) which regulates the fuel supply flow;
• supply and regulating means of a comburent active towards the burner for providing the comburent to the burner;
• detecting means of a presence of a flame associated, in use, to the burner (preferably defined by an ionisation electrode);
• a control unit operatively connected to the shut off and modulating means, to the comburent supply means for controlling functioning thereof.

The comburent supply means preferably comprises a fan which supplies air. In other words, the comburent preferably comprises air, but might include any other type of comburent different to air.

In particular, it is to be noted that the control unit has substantially two tasks:

• mainly that of guaranteeing a "non-toxic" combustion so as not to generate exhaust gases (mainly carbon monoxide) damaging for the health of individuals. Still more in particular, this control is carried out by taking as a reference a curve in the ionisation current realised as a function of the excess air index. It should be noted that, as is well known, the excess air index is defined by the ratio between the quantity of comburent air and the quantity of fuel used and is denoted by symbol 1 (lambda);
• secondly, the task of regulating the quantity of fuel and comburent according to the energy demand by the user.

For these reasons, an amplification circuit of the flame signal is used, generated by the ionisation electrode for the purpose of constantly monitoring the status of the flame.

In fact, the flame signal is usually a weak signal which is to be amplified. There exist many known types of amplification circuits, all having in common the fact that a direct or alternating current is usually added to the flame signal, followed by an amplification stage (usually by an operational) and a filtering upstream of the amplification stage. Some examples of these systems are described in document US 9651255 or US 9062882.

Other known technologies are described in prior art documents DE 195 02 901, WO 2007/132 484, US 2002/004186. WO 2007/132484 discloses a control device for control and detection of a burner flame employing a flame rod. The flame rod may be connected to a triangular type voltage signal.The resulting signal passes a low pass filter to generate a duty cycle having a square wave output.

However, this known technology has some drawbacks.

In fact, this type of circuit normally generates in output an analog signal which varies slowly with respect to the variation of the flame. Therefore, delays can be generated in the subsequent control of the supply of comburent/fuel.

Further, often this analog signal has a low resolution from which it is difficult to deduce how the flame is changing in real-time.

In this situation, the object of the present invention is to realise a method and a device for controlling the combustion of a burner which obviates the above-cited drawbacks.

An aim of the present invention is to realise a device and method for control of the flame of a gas burner which is able to generate a flame signal with a reduced delay with respect to the variation of the flame. Additionally, an aim of the present invention is to realise a device and method for control of the flame of a gas burner which is able to generate a flame signal with a greater resolution.

The indicated aims are substantially attained by a method and a control device of the combustion of a burner according to what is described in the appended claims.

Further characteristics and advantages of the present invention will more clearly emerge from the detailed description of a preferred but not exclusive embodiment of a device and a method for controlling the flame of a gas burner illustrated in the appended drawings, in which:

• figure 1 schematically illustrates a management apparatus of the burner comprising the device 1 for control of the flame of a gas burner according to the present invention;
• figure 2 is a block diagram of the device 1 for control of the flame of a gas burner according to the present invention; and
• figures 3a, 3b, 3c illustrate the trend of the square wave output signal of the device for control of the flame of a gas burner according to the present invention.

The appended figures illustrate an apparatus 100 for management of a burner 200 and a control device 1 for control of the flame of the burner 200.

In particular, figure 1 is an illustration of an apparatus 100 for managing a burner 200 comprising:

• valve means 101 interposed along a conduit for supply of fuel to the burner 200;
• regulating means 102 interposed along a supply conduit of the comburent for supplying comburent to the burner 200.

Further, the apparatus 100 comprises a control device 1 having an ionisation electrode 2 and an amplifier 3, 7, 11 of the flame 300 ionisation signal deriving therefrom. Lastly, the apparatus 100 comprises a command unit 103 which manages the valve means 101, the regulating means 102 taking values from the control device 1 with the purpose of regulating the quantity of fuel and comburent and the relative ratio for maintaining a correct combustion and/or for monitoring the status of the flame 300.

In greater detail, the ionisation electrode 2 is arranged at a region in which the flame 300 of the burner 200 is present. In particular, the ionisation electrode 2 is configured to generate an ionisation current Ion as a function of a status of the flame. For the sake of simplicity, the ionisation electrode 2 is represented in figure 2 by a rectangular node. The signal generated by the flame 300 is instead represented electrically by a resistance R and a diode D arranged in series.

According to the present invention, the control device 1 comprises an electric circuit 3 for generating a triangular voltage signal Vtr having a triangle wave form. The electric circuit has an input branch 3a connectable to a direct current source 4 (usually 24 Vdc) and an output branch 3b connected to the ionisation electrode 2 via the node 2a.

The circuit 3 for generating the triangular voltage signal Vtr preferably comprises a DC-DC voltage elevator 5 (preferably of the boost type) and a control group 6 of the triangular voltage signal Vtr, connected to one another so as to generate said triangular voltage signal Vtr. The control group 6 is preferably realised as a feedback circuit for controlling the wave form of the triangular signal generated.

Further, the DC-DC voltage elevator 5 is preferably configured to transform a voltage signal in input usually having a value of about 24 Volts in an output voltage signal having a value comprised between 100 Volts and 400 Volts (preferably 250 Vdc).

Further, a capacitor C is interposed (upstream of the node 2a) between the circuit 3 for generating the triangular voltage signal Vtr and the ionisation electrode 2 so as to reduce or eliminate the direct component of the triangular voltage signal Vtr. In practice the triangular voltage signal Vtr is set to level "0" of the y axis (figure 3a) downstream of the node 2a.

As already mentioned, the circuit 3 for generating a triangular voltage signal Vtr is connected to the ionisation electrode 2 in such a way that on varying the ionisation current Ion the average value of the triangular voltage signal Vtr also varies.

In other words, the presence of the flame 300 generates a current which modifies the average value of the triangular voltage signal Vtr by raising or lowering it with respect to level "0" of the y axis.

Further, the device 1 comprises a first output circuit 7 connected downstream of the circuit 3 for generating the triangular voltage signal Vtr (and downstream of the capacitor C) and comprising a low-pass filter 8 for filtering said triangular voltage signal Vtr so as to obtain in output an analog signal 9 representing the average value of the triangular voltage signal (Vtr).

The first output circuit 7 preferably comprises a signal amplifier 10 configured to amplify said analog signal 9 as a function of the ionisation current Ion of the flame. Said signal amplifier 10 is preferably arranged downstream of the low-pass filter 8.

The signal amplifier 10 preferably comprises at least one operational amplifier and/or a transistor amplifier group according to needs.

The first output circuit 7 advantageously enables obtaining an analog signal 9 in output which is relevant in regard to safety standard EN298. In fact, this signal enables determining, with certainty, the presence and the value of the ionisation signal of the flame signal.

Further, the device 1 comprises a second output circuit 11 connected to the circuit 3 for generating the triangular voltage signal Vtr and comprising an electronic group 12 for generating a duty-cycle as a function of the triangular voltage signal Vtr.

The electronic group 12 for generating the duty-cycle is in particular configured to generate a square wave output signal 13 (or PWM) representing said duty-cycle wherein the amplitude of the square wave 13 is a function of the amplitude of the part of positive triangular voltage signal Vtr (greater than "0"). This signal enables a certain determination of whether the combustion is correct or not.

In practice, the second output circuit 11 substantially generates a digital signal which enables rapidly determining how the flame 300 is changing. The displacement of the triangular wave form (being composed of oblique segments) advantageously enables obtaining a rapid variation of the square wave signal 13 so as to obtain a rapid response to how the flame is changing.

Figures 3a-3b-3c include some examples in which:

• in figure 3a the digital signal detects that there is no flame and in this case the duty-cycle is about 50% (the mean of the triangular voltage signal Vtr is about "0");
• in figure 3b the digital signal detects that there is a flame and the duty-cycle is reduced;
• in figure 3c the digital signal detects that there is a flame with an ionisation current Ion that is greater with respect to figure 3b and the duty-cycle is reduced even more with respect to the case illustrated in figure 3b.

Further, the second output circuit 11 comprises a resistor R5 arranged in series with the electronic group 12 for generating the duty-cycle.

In greater detail with reference to the control device 1, the first output circuit 7 and the second output circuit 11 are arranged in parallel to one another and said ionisation electrode 2 is arranged between the circuit for generating the triangular signal and the first 7 and second output circuit 11.

The first output circuit 7 is directly connected to the circuit for generating the triangular signal in order to receive said triangular voltage signal Vtr.

Further, the first output circuit 7 and the second output circuit 11 are connected to one another upstream of the low-pass filter 8 and the group 12 for generating the duty-cycle via a circuit branch comprising a resistor R3.

It should be noted that in the management apparatus 100 of the burner 200, the control unit 103 is operatively connected to the control device 1 to the valve means 101 and to the regulating means 102 and is configured to:

• receive said analog output signal 9;
• receive said square wave output signal 13;
• control the valve means 101 and the regulating means 102 according to the contents of said signals 9, 13 as a function of a predefined fuel/comburent ratio so as to ensure a correct combustion.

The presence of two output circuits 7, 11 advantageously enables having a greater control on the flame 300. In this matter, the command unit 103 is configured for comparing the contents of the analog 9 and square wave form 13 output signals so as the verify the uniformity of the data contained therein.

Further, the command unit 103 is configured to:

• receive the analog output signal 9 and generate an alarm signal according to the contents of said analog output signal 9 in such a way as to satisfy the safety requirements according to standard EN 298;
• receive said square wave output signal 13 and regulate the valve means 101 and the regulating means 102 according to the contents of said output signal 13.

The present invention further relates to a method for the control and detection of the flame of a burner 200 which derives directly from what is described above in relation to the device 1 and the apparatus 100 which is referred to below.

In particular, the method includes receiving the ionising current Ion signal as a function of a status of the flame from said ionising electrode 2. Further, the method comprises a step of generating a triangular voltage signal Vtr having a triangle wave form by means of an electric circuit for generating connected to the ionisation electrode 2 in such a way that on varying the ionisation current Ion the average value of the triangular voltage signal Vtr also varies.

In addition, the method includes generating the analog output signal via a first output circuit 7 connected to the circuit 3 for generating the triangular voltage signal Vtr and comprising a low-pass filter 8 for filtering said triangular voltage signal Vtr so as to obtain in output said analog signal 9 representing the average value of the triangular voltage signal Vtr.

Further, the method comprises a step of generating a square wave output signal 13 via the second output circuit 11 connected to the circuit 3 for generating the triangular voltage signal Vtr and comprising the electronic group 12 for generating a duty-cycle as a function of the triangular voltage signal Vtr wherein said square wave output signal 13 is representative of said duty-cycle.

The present invention obtains the following advantages.

Primarily the device and detecting and control method enable obtaining in output two signals (one analog and one digital) by means of which safety standard requirements can be satisfied (analog signal) and verifications can be performed on the flame with an improved resolution (digital signal) with respect to the prior art and with a larger-scale range.

In particular, the square wave form signal enables more reactively detecting the variations in the flame and therefore the combustion which take place in the burner.