RU2440536C2 - Device to measure intensive flame - Google Patents

Abstract

FIELD: power engineering.

SUBSTANCE: device to measure flame intensity in a burner, to which the first alternating signal is sent with the first predetermined fill factor, comprises a flame sensor, which generates ionisation current, proportional to flame intensity in the burner, and facilities to vary fill factor as a function of ionisation current, at the same time the first alternating signal and ionisation current are sent to the input of variation facilities, at the output the variation facility generates an alternating signal, having the second fill factor, which is a function of the ionisation current.

EFFECT: higher accuracy of measurement.

13 cl, 5 dwg

Description

Field of Invention

The present invention relates to a device for measuring flame intensity, having the distinguishing features set forth in the preamble of the main claim.

Technological background

The present invention relates, in particular, but not exclusively, to the field of systems for controlling the gas supply to the burners of heating devices, the flame of which is designed to heat the environment or the intermediate fluid circulating in the boiler plant.

Typical applications are systems that control the gas supply to the burners of boilers for heating residential buildings and / or hot water supply to residential buildings.

In the technical field to which the present invention relates, a solution is known according to which, for safety reasons, the above devices are equipped with devices that detect the presence of a flame by measuring the current flowing in the flame sensor, known in the art as “ionization current”, as described, for example, in US patent No. 5599180, No. 6060719 and in Japanese patent No. 4244922.

However, in this technical field there remains a need to create devices not only for detecting, but also for measuring flame intensity, in order to optimize combustion parameters and, therefore, reduce harmful emissions and fuel consumption.

In this technical field, such devices are required to have sufficient stability characteristics when the temperature changes, at least in the temperature range in which this device is used, when the characteristics of the components are varied and when the supply voltage changes, at the same time without a strong impact on costs, production time and without complicating the design.

Description of the invention

The main objective of the present invention is to provide a device for measuring flame intensity, which constructively and functionally meets the above requirements and, at the same time, eliminates the disadvantages of the prototypes.

These and other tasks, described in more detail below, are achieved using a device for measuring flame intensity in accordance with the attached claims.

Brief Description of the Drawings

Other features and advantages of the present invention are presented in the following detailed description of a preferred embodiment of the invention, given by way of non-limiting example only, with reference to the attached drawings, wherein

1 is a diagram of a preferred embodiment of a flame intensity measuring apparatus of the present invention.

Figure 2 is a diagram of the variation of the duty cycle (in%) of voltage V as a function of ionization current (μA) of five different examples of a flame sensor at a predetermined temperature according to the circuit of Figure 1.

Figure 3 - shows the temperature variation (° C) of the values shown in figure 2.

Figure 4 is a preferred embodiment of the input / output signal to the various components of the device of figure 1.

FIG. 5 is a schematic illustration of a preferred embodiment of a control system of the present invention comprising the device of FIG. 1.

Preferred Embodiment of the Present Invention

As shown in FIG. 1, a flame intensity measuring device configured to, for example, measure flame intensity in burners in accordance with the present invention is generally indicated by 1.

The flame intensity measuring device 1 comprises a flame sensor U1 located in the burner so as to contact the flame when it is present and generate an ionization current proportional to the flame intensity.

The sensor U1 is preferably manufactured using conventional technologies and contains, for example, two electrodes. In a preferred embodiment of the invention, the operation of the flame sensor can be compared to the operation of a current generator connected to an element operating in one-sided mode, for example, a diode connected in series with a resistor (see diode D2 and resistor R10 in FIG. 1): the current generated by the sensor in the result of the presence of flame, in practice flows in only one direction. This, in particular, is due to the fact that in prototype boilers, burners are often grounded, and this leads to the fact that when the current flows in the U1 sensor in the presence of a flame, it "flows" to the ground.

Typically, the currents generated by flame detectors connected to burners known in the art have a force of the order of microamps. For example, in the applications under consideration, the ionization current generated in the sensor U1 preferably ranges from 0.8 μA to 7.5 μA. The device of the present invention, however, can also be used when the ionization currents are of a different order of magnitude.

The term "flame intensity" in the preferred embodiment described below has the following meaning: a "weak" flame is a flame that partially "licks" the sensor when viewed spatially, and a "strong" flame is a flame that completely surrounds the sensor. Various levels of flame intensity, from weak to strong, thus correspond to the state of contact of the flame with a larger area of the sensor assembly, until the flame completely surrounds it.

The device 1 for measuring the flame intensity receives not only a current signal from the sensor U1, but an AC voltage signal V1 having a first predetermined duty cycle, for example, a duty factor of 50% centered on zero. The voltage V can be, for example, the supply voltage from which the constant component is removed by the capacitor C1 (see Fig. 1, in which the resistor R1, the capacitor C1 and two additional resistors R2 and R4 are connected in series, which is one possible embodiment of the present invention ) to obtain a sinusoidal signal having a first duty cycle of 50% and substantially centered at zero (i.e., having an average value substantially equal to zero). Voltage V1 may also be supplied by an alternator or a battery (not shown).

According to the main distinguishing feature of the present invention, the flame intensity measuring device 1 further comprises means 2 for changing a first predetermined duty cycle of the signal V1, to the input of which both the ionization current generated by the sensor U1 after the resistor R6 and the signal V1 of the alternating voltage are supplied. This means 2 generates an AC voltage signal V having a second duty cycle, which is a function of the first duty factor (which is known and specified when the device 1 was installed) and the ionization current U1, as will be shown below. In particular, the second duty cycle of the output signal V increases with increasing ionization current. By measuring the second duty cycle, thus, it is possible to determine the intensity of the flame, since the magnitude of the ionization current is proportional to the intensity of the flame.

Means 2 changes contain a switching element, preferably a transistor Q1, to the base of which a signal V1 and an ionization current are supplied.

A positive supply voltage, which is indicated in FIG. 1 as a constant voltage Vcc, is supplied to the collector of transistor Q1. 1 also shows a collector resistor R5.

The potential difference between the base and the emitter of the transistor Q1 is determined by the input signal on the base (the emitter is preferably connected to ground). The values of the various components of the device 1, the magnitude of the ionization current, and the magnitude of the AC signal V1 having a first duty cycle are such that the input signal based on the transistor Q1 has a value that fluctuates between the saturation level (when the input signal based on the transistor is maximum) and the cutoff level for the transistor Q1, which leads to the work of the latter, essentially, as a "switch".

It should be understood that, operating between saturation and cut-off and not in the linear zone, the transistor Q1 is essentially insensitive to temperature changes, in contrast to the case when the transistor would operate in a linear zone. Moreover, since the gain of the transistor is not an essential parameter, extremely cheap transistors can be used in the device of the present invention.

The measuring device 1 further comprises an optional filtering device 3, by which the AC voltage signal V1 and the current signal from the flame sensor (if a flame is present) are mainly filtered and then fed as input signals to the base of transistor Q1.

The optional filter devices 3 preferably comprise a low-pass filter 3, which is preferably formed by two parallel low-pass filters: a first low-pass filter 4, for example, connected in series with a resistor r8 'and a capacitor C3, and a second filter 5, for example, connected in series with a resistor R9 and capacitor C2. One terminal of capacitor C3 and capacitor C2 is preferably connected to ground.

A low-pass filter 3, containing two low-pass filters 4 and 5, connected in parallel, is an ideal solution for lowering the cutoff frequency of the common signal when using commercially available, cheap and reliable components. The parallel inclusion of two low-pass filters in practice allows the use of smaller resistors and capacitors than in the case of a single low-pass filter. For the same reason, i.e. to reduce the cost and simplify the circuit, the resistor R8 'preferably contains two series-connected resistors R7 and R8.

Obviously, the input signal to the low-pass filter 3 has a negative bias with respect to the signal V1, and this bias depends on the magnitude of the ionization current from the sensor U1 to ground. Therefore, starting from the duty cycle of the signal V1, the signal supplied to the input of the filter 3 and, therefore, to the base of the transistor Q1, has a duty cycle lower than the signal V1 as a result of the ionization current, which, if present, creates a negative bias of the signal V1, those. its “shift” by a certain amount, determined by the strength of the ionization current, to the values of the negative voltage.

The low-pass filter 3 is electrically connected as an output to the base of transistor Q1 by means 6, which regulates the voltage at the base of transistor Q1. The voltage regulating means 6 of the base of transistor Q1, for example, contains a diode D4 connected in parallel with the base, i.e. connecting the base and emitter of transistor Q1 to limit the voltage at the base to a level below the maximum level acceptable for transistor Q1 to prevent damage to the transistor. Preferably, the diode D4 is parallel to the base (although the diode D4 can be connected in series with the base of the transistor) since this inclusion provides the best temperature behavior of the device 1. The diode D4 is further connected in parallel with the resistor R11, which is configured to connect the base to ground.

The transistor Q1 further preferably comprises a collector resistor R5 and has a collector voltage V that represents the output signal of the measuring device 1: this output signal V essentially contains a two-level voltage (for simplicity, known by the short names “high” and “low”), with the second duty cycle, depending on the change in saturation (which corresponds to a "low" voltage V) and cutoff (which corresponds to a "high" voltage V) of the transistor Q1. Since the value of the first duty cycle of the signal V1 remains constant, the duty cycle of the signal V depends on a negative bias proportional to the ionization current generated by the flame sensor U1 in the signal supplied to the base of the transistor Q1.

Advantageously, the resistors R1-R11 are of a type that does not change characteristics with changing temperature, for example, they are transistors of the type of surface-mounted components, in order to ensure, along with the use of transistor Q1 outside the linear zone, the reproducibility of the characteristics of device 1 in a predetermined temperature range, equivalent to the operating range of the burner, for example in the range from -40 ° C to 80 ° C.

For example purposes only, the resistors used have the following values: R1 = 100 kΩ, R2 = R4 = 470 kΩ, R3 = 2.3 MΩ, R5 = R6 = R7 = 1 MΩ, R8 = 22 MΩ, R9 = 15 MΩ, R10 = 47 megohms. The capacitors used have the following meanings: C1 = 2.2 nF, C3 = C2 = 1 nF. And finally, Vcc = 5 V.

The AC voltage signal V1, however, depends on the type of power source to which the device is connected, i.e. in Italy - from a signal with a frequency of 50 Hz. If this value changes, i.e. the network frequency is 60 Hz, all that is needed is a software change, since the device can be used with any supply voltage.

The control system 7 of the present invention, shown in FIG. 5, comprises a device 1 for measuring flame intensity, and means 8 for comparing the second duty cycle of the output signal of the device 1 with a plurality of predetermined levels, in order to assign the flame intensity to a specific value of the second duty factor.

According to a preferred embodiment of the invention, there are four flame levels. Thus, the control function assigns a predetermined level to specific values of the second duty cycle.

According to a preferred embodiment of the invention, the ionization current generated in the sensor U1 can vary in the range from 0.8 μA to 4.5 μA, which leads to a substantially linear change in the second duty factor (minimum - in the absence of flame, and then increasing with increasing ionization current).

The comparator 8 preferably comprises a microprocessor μP, to the input of which a collector voltage V with a high sampling frequency is applied, typically every 64 μs, this value can nevertheless vary and depends, inter alia, on the frequency of the variable signal V1 and ionization current.

Preferably, if the device 1 receives power directly from the mains supply, the control system 7 further comprises an isolation transformer 9 designed to make the signal V1 independent of the mains power supply. The isolation transformer 9 has an auxiliary winding on the secondary winding (not shown), isolating the "high voltage" part of the change circuit 2, which eliminates the need to use optocouplers for docking with the microprocessor.

The device 1 of the present invention operates as follows.

In the absence of a flame, the ionization current does not flow through the flame sensor U1, and therefore, the input and output signals of the filter device 3, which attenuates only the signal amplitude but does not change the duty cycle, are AC voltage signals having a predetermined duty ratio, for example, corresponding to the frequency of the mains power supply. In a preferred embodiment, the first duty cycle is 50%.

Therefore, the potential difference between the base and emitter of transistor Q1 alternates between cutoff and saturation during time intervals depending on the signal V1, and the second duty cycle of the collector voltage V is proportional to the first duty factor and is “inverted” relative to it. In particular, when there is a positive input signal at the base of transistor Q1, the signal V is negative, and when there is a negative signal at the base of transistor Q1, the signal V is positive. In the absence of flame, however, signal V does not have a duty cycle that matches the duty factor of signal V1 due to the presence of resistor R3 (in the preferred embodiment, 2.2 MΩ) to provide a more accurate detection of signal V.

In a preferred embodiment of the device 1 having the output shown in FIG. 2, the duty cycle of the signal V at zero flame is set to 20%, although the duty cycle of the signal V at zero flame can be set arbitrarily.

In the presence of a flame, the ionization current in the flame sensor U1 leads to a negative bias relative to the variable signal V1 at the input of the low-pass filter 3, proportional to the strength of this current: the larger the current, the greater the negative bias, i.e. the "shift" of the signal V1 to negative voltage values and, therefore, the duty cycle of the signal supplied to the base of the transistor Q1 will be proportionally reduced. Refer to figure 4, which shows an example of a signal present as input / output at different points (in particular, at points A, B, C, D and in the absence of flame) of device 1. Although this option illustrates a sinusoidal signal V1 with with a duty cycle of 50%, it is obvious that the signal V1 can be any variable signal with a predetermined duty cycle.

In a first preferred embodiment of the invention, the signal V1 is sinusoidal with a duty cycle of 50%.

In another preferred embodiment, the signal V1 is a triangular signal with a duty cycle of 50%. A triangular signal generator is especially preferred in cases where it is necessary to use an alternating current generator (for example, when it is impossible to connect to the power supply network and, therefore, it is necessary to use an appropriate battery). As a result of the negative bias, the potential difference between the base and emitter of transistor Q1 is such that it cuts off transistor Q1 for a time interval longer than the saturation interval, since the signal applied to the base of the transistor is in the negative voltage region longer than the period during which the base positive voltage is applied. Thus, the output signal V of the device 1 has a "high" state longer than a "low" state, which leads to an increase in its duty cycle (see the signals in Fig. 4). Therefore, the stronger the duty cycle of the input signal on the basis of the transistor Q1 decreases, the stronger the duty cycle of the collector signal (i.e. voltage V) increases.

The second collector voltage factor V of the collector, determined by the passage of the saturation current of the transistor Q1 to the resistor R5, is thus proportional to the detected flame intensity, as shown in Fig. 2: the abscissa shows the ionization current (proportional to the flame intensity), and the ordinate shows the obtained signal fill factor V The larger the current, the greater the duty cycle until saturation is reached (V signal is constantly at a "high" level). The various curves shown in FIG. 2 relate to many different devices 1, in particular, containing different sensors U1 to ensure that their behavior is similar.

The device 1 is sized appropriately so that a saturation value is reached for the maximum flame levels typically found in burners in which the device is used.

As a result of the use of surface-mounted components and the fact that the Q1 transistor does not work in the linear zone, the applicants were able to verify that when the temperature changes from -40 ° C to + 80 ° C, the maximum change in the signal duty cycle V is 2%, which makes device 1 is substantially insensitive to temperature in the normal operating temperature range. Figure 3 presents a diagram similar to figure 2, obtained for three different operating temperatures of the device 1, comprising -25 ° C, 25 ° C and 70 ° C (in this case also, for each temperature, models of different devices 1 having different sensors).

In the control system 7, the voltage V is sampled at a high frequency and the obtained discrete values are compared in the microprocessor with predetermined levels of the control function.

Thus, the present invention achieves the objectives and provides the above advantages compared with solutions known from the prior art.

It should be understood, in particular, that a device for measuring flame intensity does not change characteristics when the temperature changes, when the characteristics of the components are spread, and when the supply voltage changes.

Claims (13)

1. Device (1) for measuring the intensity of a flame in a burner, to which a first alternating signal (V1) with a first predetermined duty cycle is supplied, characterized in that it contains:
- a flame sensor (U1) generating an ionization current proportional to the intensity of the flame in the burner;
- means (2) for changing the first duty cycle as a function of the ionization current, while the first alternating signal (V1) and ionization current are supplied to the input of the means (2), and an alternating signal (V) having a second duty factor is generated at the output, which is a function of the ionization current, wherein the change means (2) comprise at least one switching element (Q1), the input of which is supplied with a second alternating signal having a negative bias with respect to the first alternating signal (V1), while this is the bias depends on the value of the ionization current flowing to the ground, wherein
the switching element (Q1) contains a transistor, and a second alternating input signal is supplied to the base of this transistor (Q1), and the second alternating input signal based on the transistor (Q1) is such that the potential difference between the base and the emitter of the transistor (Q1) alternates between the saturation values and cut-off, and the output signal (V) of the means (2) changes corresponds to the voltage at the collector of the transistor (Q1) having a second duty cycle, depending on the alternation of saturation and cut-off of the transistor (Q1) under the influence of the aforementioned about bias. 2. The device according to claim 1, in which the second duty cycle increases with increasing ionization current. 3. The device according to claim 2, in which the second duty cycle increases with increasing ionization current, essentially linearly in at least one area. 4. The device according to claim 1, in which the means (2) changes contain filtering means (3), the input of which is supplied with a second alternating signal, and the output of which is connected to the base of the switching element (Q1). 5. The device according to claim 4, in which the filtering means (3) contains at least one low-pass filter (4, 5). 6. The device according to claim 5, in which the low-pass filter (3) comprises two low-pass filters (4, 5) connected in parallel. 7. The device according to claim 1, in which the output of the filtering means (3) is electrically connected to the output of the transistor (Q1) through the voltage regulator of the base of the transistor (Q1), which limits the voltage at the base to a level below the maximum limit allowed for the transistor (Q1 ) 8. The device according to claim 7, in which the base voltage regulator (6) comprises a diode (D6) connected between the base and the emitter of the transistor (Q1). 9. The device according to claim 1, in which a constant voltage (Vcc) is supplied from the generator to the means of change (2) supplied to the collector of the transistor (Q1) and the means of change (2) contain a resistor (R5) on the collector of the transistor (Q1). 10. The device according to claim 1, in which the means (2) changes contain resistors of the type that does not change characteristics when the temperature changes. 11. A system (7) for controlling flame intensity, comprising:
- a device (1) for measuring flame intensity according to one or more of claims 1 to 13, generating at the output an alternating signal (V) having a second duty cycle;
- means (8) for comparing the second duty cycle of the output signal (V) of the measuring device (1) with many levels predetermined by the control function. 12. The system according to claim 11, containing an isolation transformer (9), an insulating power source. 13. System (7) according to claim 11, in which the comparison means (8) comprise a microprocessor (μP), at the input of which a collector voltage is applied.

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