JPH0321508Y2 - - Google Patents

Description

[Detailed Description of the Invention] This invention relates to a flame detection device in which a flame sensor is a spatial filter constructed by combining a plurality of photoelectric sensors.

As flame sensors, UV tubes, which are phototubes with sensitivity in the blue to ultraviolet region, have been widely used. UV tubes are used for
This is to avoid erroneously detecting that there is a flame due to infrared rays from the red-hot furnace wall of the combustor even after the flame has disappeared. Misdetection of flame is extremely dangerous because it may lead to a situation where fuel gas or the like continues to be supplied even though there is no flame.
In conventional technology, in order to further increase the reliability of detection, a mechanical shutter is placed in front of the UV tube, the photodetection signal is chopped into pulses, and this pulse is detected by a pulse detection circuit with a fail-safe function. This prevents false detection not only in the UV tube but also in the circuitry.

On the other hand, flame sensors using spatial filters have also been proposed. A spatial filter is composed of one or more pairs of photoelectric sensors regularly arranged on a plane, and the spatial frequency of the optical image of the object formed on the photoelectric sensor is the same as that of the object. Since it depends on speed, etc., it is used as a non-contact speed sensor or distance sensor. When such a spatial filter is used as a flame sensor, since it directly detects the pulsations in the planar brightness distribution of the flame, it detects disturbance light at a direct current level and changes in alternating current over time like that of a fluorescent light. It has a feature that other flame sensors do not have in that it can detect the flame itself without being affected by ambient light even if it is mixed with ambient light. Furthermore, since the output of the sensor itself has pulse characteristics, there is no need to provide a mechanical shutter such as a UV tube.

This invention utilizes the above-mentioned advantages of a flame sensor using a spatial filter, and also provides an extremely reliable flame detection device by connecting it to a pulse detection circuit with a fail-safe function. The purpose is

An embodiment of this invention will be described below with reference to the drawings. In Fig. 1, A and B are flame sensors consisting of spatial filters constructed by alternately arranging one or more pairs of photoelectric sensors that convert the amount of incident light into an amount of electricity, and 1 is a differential amplifier. By differentially amplifying the signal values detected by the flame sensors A and B, disturbance light components that cause measurement errors are removed, and the influence of temperature drift is minimized. 2 is an AC amplifier that cuts the DC component of the output of the differential amplifier 1 and amplifies the AC component. The comparator 3 functions to slice the output of the AC amplifier 2 at a slice level Vth and convert the alternating current component, which is a spatial frequency component of this output, into a pulse signal. This comparator 3
The pulse output of is supplied to the base of transistor Q to turn it on and off. That is, as the output of transistor Q, only when there is a flame
A Hi/Lo pulsed output is provided, and if there is no flame or if any circuit component, including transistor Q, is faulty, the output of transistor Q will maintain its Hi state to Lo state. It becomes tama-tama.

This Hi/Lo signal is supplied to a pulse detection circuit having a fail-safe function as shown in FIG. This pulse detection circuit consists of a resistor R1, a diode D1, and a capacitor C connected across the power supply.
1, a second series circuit of diode D2 and relay K connected in parallel with diode D1, and a third series circuit of capacitor C2 and resistor R2 connected in parallel with relay K. The output is output as the opening/closing of the contact K1 of the relay K.

When the input of this pulse detection circuit is Hi, a charging current flows from the power supply to the capacitor C1 through the resistor R1 and the diode D1, and the capacitor C1
is charged. Then, when the input becomes Lo,
The charge on capacitor C1 is discharged through diode D2, relay K, points A and B, and relay K is energized by this discharge current. At this time, capacitor C2 is also charged at the same time. Next, when the input becomes Hi again, the capacitor C
1 will be charged again, but during this period, the charge in the capacitor C2 is discharged through the relay K and the resistor R2, and this discharge current maintains the energized state of the relay K. Similarly, the relay K is maintained in the energized state while the Hi/Lo pulse is being input. However, if the input remains in the Hi or Lo state, after capacitor C2 has discharged for a predetermined time constant, relay K is deenergized and a flameless output is provided. Also, if there is an abnormality in the circuit shown in Figure 1 and the output of transistor Q remains Hi or Lo, an output without flame will be output.
Fail safety is maintained.

Note that the circuits shown in FIG. 1 and FIG. 2 may be provided on the same circuit board, or may be configured separately and connected together via a cable.

As described above, according to this invention, by combining a flame sensor with a spatial filter and a pulse detection circuit with a fail-safe function, false detection including the circuit part can be prevented without providing a mechanical shutter, etc., and reliable Flame detection can be performed, and the effect of ensuring phase safety can be obtained.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram of a flame detection section of a flame detection device according to an embodiment of this invention, and FIG. 2 is a circuit diagram of a pulse detection circuit. A, B...Photoelectric sensor, 1...Differential amplifier, 2
...AC amplifier, 3...comparator, K...relay, K1...contact.

Claims (1)

[Scope of utility model registration request] A flame sensor consisting of a spatial filter configured by alternately arranging one or more pairs of photoelectric sensors and the alternating current component of the signal obtained by taking the difference in photocurrent between the photoelectric sensor and the above photoelectric sensor are pulsed. a charging circuit that supplies charging current to the first capacitor when the input based on the pulse signal obtained from the pulse signal is Hi; and a charging circuit that supplies the charging current to the first capacitor when the input changes from Hi to Lo. The relay is energized by the discharge current from the first capacitor, and the relay is charged by the discharge current of the first capacitor, and after the input changes from Lo to Hi, it goes back to Lo.
a second capacitor that discharges during the period of time and supplies a holding current to the relay, and has a fail-safe function that outputs a flame detection signal only while the pulse signal is being output. Equipped with flame detection device.