JPH0312359B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a signal processing circuit for a flame sensor using a spatial filter.

A spatial filter is composed of photoelectric sensors regularly arranged on a plane as shown in Figure 1, and the spatial frequency of the optical image of the object formed on this sensor is the sensor output. Since the frequency characteristics depend on the speed of the object to be detected, etc., it is used as a non-contact speed sensor or distance sensor. In Japanese Patent Application No. 54-135506, the applicant proposed the use of this spatial filter as a flame sensor for a combustion device. This technology directly detects the pulsations in the planar brightness distribution of the flame, so it can be used even when there is a mixture of disturbance light at a direct current level or disturbance light that changes over time in an alternating current manner, such as from fluorescent lights. It has a feature not found in conventional flame sensors in that it can directly detect the flame itself without being influenced by these factors.

FIG. 2 shows a prior art signal processing circuit for a sensor using a spatial filter. In the figure, A and B are the first
This is a photoelectric sensor that constitutes the spatial filter shown in the figure, and converts light into an amount of electricity according to the amount of light incident on the photoelectric sensors A and B. 3 is a differential amplifier that differentially amplifies the optical signal values detected by photoelectric sensors A and B, thereby removing disturbance light components that cause measurement errors and minimizing the effects of temperature drift. There is. 4 is an AC amplifier having a coupling capacitor 4', which removes the DC component contained in the output of the differential amplifier 3 and amplifies only the AC component by AC coupling.
5 is a rectifying element, and the rectified output is integrated by an integrating circuit 6 and then input to a comparator 7, where it is compared with a predetermined level and outputs an ON/OFF output.

When a signal processing circuit having such a configuration is applied to a signal processing circuit of a flame sensor using a spatial filter, the following problems occur. This problem will be explained in detail below with reference to FIG. Through the lens L, the photoelectric sensor A receives the light from the flame A', and the photoelectric sensor B receives the light from the flame B'. These lights consist of a direct current component of the flame and an alternating current component which is a spatial frequency component.
In reality, direct current disturbance light and alternating current disturbance light, which are at almost the same level at photoelectric sensors A and B, are also incident on photoelectric sensors A and B, but these are determined by methods that match the sensitivities of photoelectric sensors A and B. Since it can be removed by the differential amplifier 3 by incorporating the disturbance light, in order to simplify the problem, we will consider here assuming that such disturbance light is not incident.

FIG. 4a schematically shows the output of photoelectric sensor A, and FIG. 4b schematically shows the output of photoelectric sensor B. Further, this figure shows an example in which a change in the state of the flame occurs, and the DC component of photoelectric sensor A rapidly increases, and the DC component of photoelectric sensor B rapidly decreases. FIG. 4c schematically shows the output of the differential amplifier 3, and as the state of the flame changes, the DC component of the output of the differential amplifier 3 also increases rapidly. Figure 4 d shows the output of the AC amplifier 4. In a steady state, only the spatial frequency component of the flame, which is AC, is output, but as shown in Figure 4 c, the output of the differential amplifier 3 suddenly increases. In this case, the output of the AC amplifier 4 will be in a negative saturated state until the coupling capacitor 4' is completely charged. As a result, the output of the rectifying element 5 is set to 0V during this period as shown in FIG. 4e, so the output of the integrating circuit 6 is also reduced to 0V during this period as shown in FIG. Therefore, the comparator 7 outputs an output indicating that there is no flame even though there is a flame. In general, a flame is constantly changing, so as long as such a signal processing circuit is used, it becomes practically impossible to apply a spatial filter as a flame sensor. In addition, when the state of the flame changes such that the output of the differential amplifier 3 suddenly decreases,
Since the output of the AC amplifier 4 is brought into a positive saturated state, no problem occurs because it continues to output flame-present output.

The present invention has been made to solve such problems, and by providing a signal processing circuit that does not output a flameless signal even if a flame state change occurs, it is possible to improve the flame sensor of a spatial filter. The purpose is to make it possible to apply it to

The present invention will be described in detail below based on Examples.

FIG. 5 shows an embodiment of the present invention. The difference from the prior art shown in FIG. 2 is that a full-wave rectifier 8 is used instead of the rectifying element 5. Further, FIG. 6 shows another embodiment of the present invention. The difference from the prior art shown in FIG. 2 is that a window comparator 9 is used instead of the rectifying element 5. Therefore, in FIGS. 5 and 6, parts equivalent to those shown in FIG. 2 are designated by the same reference numerals, and their explanation will be omitted.

According to the embodiment shown in FIG. 5, since the full-wave rectifier 8 takes the absolute value of the output of the AC amplifier 4,
Corresponding to Fig. 4 d and e, the output of the full-wave rectifier 8 becomes as shown in Fig. 7 d-1 and e-1, and as a result, the output of the integrator circuit 6 does not fall to 0V, but instead becomes positive. Since it is converted to a large value, it will no longer indicate the absence of flame. Further, according to the embodiment shown in FIG. 6, the window comparator 9
Since the amplifier 4 is configured to take the HI output when the absolute value of its output exceeds a predetermined value, the output of the window comparator 9 is as shown in FIG. 8 d-, corresponding to FIG. 4 d and e. 2, e-2, and similarly, the output of the integrating circuit 6 does not fall to 0V, but instead is converted to a large positive value, so
It will no longer indicate a no-flame condition.

In this way, the present invention rectifies the output of the AC amplifier of the signal processing circuit of the spatial filter using a full-wave rectifier or a window comparator, which solves the problem when applying the spatial filter as a flame sensor. This makes it possible to eliminate false detections when the combustion state of the flame changes. This makes it possible to apply the spatial filter as a flame sensor, which is extremely effective in practice.

[Brief explanation of the drawing]

Figure 1 is a plan view showing the configuration of the spatial filter, Figure 2 is a circuit diagram of a conventional signal processing circuit for the spatial filter, Figure 3 is an explanatory diagram showing the relationship between the flame and the spatial filter, and Figure 4. are signal waveform diagrams of various parts in the circuit of FIG. 2, FIG. 5 is a circuit diagram of a signal processing circuit according to one embodiment of the present invention, and FIG. 6 is a circuit diagram of a signal processing circuit according to another embodiment of the present invention. 7 is a signal waveform diagram of each part in the circuit of FIG. 5, and FIG. 8 is a signal waveform diagram of each part of the circuit of FIG. 6. A, B...Photoelectric sensor, 3...Differential amplifier, 4
... AC amplifier, 6 ... Integrating circuit, 7 ... Comparator, 8 ... Full wave rectifier, 9 ... Window comparator.

Claims (1)

[Claims] 1. A spatial filter configured by alternately arranging one or more pairs of photoelectric sensors, and a differential amplifier that differentially amplifies the optical signal values detected by the first and second photoelectric sensors, respectively; Remove the DC component included in the output of this differential amplifier,
A signal processing circuit for a flame sensor that includes an AC amplifier that amplifies only the AC component, and a full-wave rectifier or window comparator that is connected to the output side of the AC amplifier and rectifies the output of the AC amplifier.