Detector To Indicate Burning Or Glowing Particles

Abstract

A detector to be utilized in processes where inflammable material is transported in conduits at a high speed. Then the detector will indicate glowing particles, as sparks and fire flakes, which may appear within a risk zone or are rapidly being transported through such a zone. Said detector includes a transducer suitable disposed within the system, as on the tube wall of a transport conduit. Said transducer gives signals in the form of a pulse train when such a particle passes through the visual field thereof.

Description

SUMMARY OF THE INVENTION

This invention refers to a detector to indicate hot, namely burning or glowing, particles in connection with the transport of a mass of particles. As an example of a field within which the invention is applicable we can mention the pneumatic transport of inflammable particles, as cellulose fibers, in conduits in connection with the handling or the drying of the material. In that connection said particles can be so heated that they will form sparks or fire flakes within a risk zone or will be transported through such a zone by the carrier gas. If such glowing particles comprise sufficient quantities of energy they will initiate fire or explosion, causing serious damages with associated shut-downs. The intention of the invention is undoubtedly to detect such glowing particles even if the speed thereof is high and to produce remedies within the shortest possible time, as milliseconds, to isolate said risk area and/or to supply fire-fighting or choking means prior to the initiation of said fire or explosion. This is essentially obtained by a transducer, having at least two mutually separated sensing zones within the visual field of the particles, said zones in different positions of the hot particle and during the movement thereof and thus at successive moments supplying the radiation of heat of said particles to light-sensitive elements co-operating with each zone, so that signals sent from said zones form a train of pulses, which via an amplifier is then used to eliminate said particles. By using at least two zones effected by the glowing particle within a very short time interval the activation of an alarm is eliminated in connection with non-dangerous light or heat changes within the visual field, for example by the switching on of lamps, the opening of shutters for the day-light or the like.

DESCRIPTION OF THE DRAWINGS

The invention will be described below more in detail with reference to the accompanying drawings, which as an example disclose an embodiment thereof and in connection therewith also other features of the invention will be set forth.

FIG. 1 shows an embodiment of a detector having a transducer arranged in a conduit.

FIGS. 2-4 show enlarged sections through three embodiments of the transducer.

DESCRIPTION OF THE INVENTION

In FIG. 1 reference number 10 discloses a conduit through which a material in the form of particles, such as cellulose fibers, is transported by a gas medium, such as a mixture of air and combustion gases. On said conduit there is a transducer, generally designed by 12, shaped in accordance to one of FIGS. 2-4. In the embodiment according to FIG. 2 a plate 14 is arranged on a housing 16 forming a number of cells 18, in this case six cells, mutually separated by partitions 20 and at the top covered by a roof 22 formed as a raster. Said roof 22 includes mutually parallel and straight grooves or openings 24, one for each cell 18. The roof is covered by a light or heat permeable layer 25 eliminating the penetration of strange particles into said cells 18. Said grooves 24 extend perpendicular to the length of said conduit 10. The separated cells 18 are shielded from each other and with the exception of grooves 24 also shielded from the surroundings. At the bottom of each cell, suitably at the center of the cells, which are oblong similar to the grooves, there is a light-sensitive element 26, such as a photocell, which within the sensing zone or within a small space angle v limited by planes 28, 30, can catch heat and light radiation, respectively, supplied from the inside of said conduit. Thus, each sensing zone perpendicularly to the plane of the drawing forms a groove limited by planes 28, 30. According to FIG. 2 the zones are separated from each other, and thus in case the glowing particle 32 passes through said conduit according to the drawn line 33 it will be within the visual field of the light sensitive element of the first sensing zone from position 32 to position 32'. Then the effect of the particle on transducer 12 will be eliminated until said particle reaches the limit line 28 of the next sensing zone where the next light-sensitive element 26 receives heat radiation while said particle passes through this sensing zone to position 32' and so on. Thus, said glowing particle 32 will successively and for separate moments give its heat radiation to the successively arranged light sensitive elements 26.

The elements 26 are connected to one or more amplifiers 34 in a control equipment 36. The signals supplied from the separate light-sensitive elements as a train of pulses then pass a filter unit 38 so formed that it will only accept pulses, the slop of which (the front of the pulse) exceeds a set value contributing to make the detector insensitive to irrelevant disturbances. Then said train of pulses passes a pulse shaper 40, a counter unit 42 and an alarm unit 44, from which alarm signals are sent. In order to start an alarm in the embodiment according to FIG. 2, six successive light-sensitive elements 26 have to be subjected to the radiation of the glowing particle. Then the intention is to eliminate incoming light effects which are not dangerous but which in spite of this affect the light-sensitive elements and are not filtered out by the filter unit 38. The number of accepted pulses is counted by the counter unit 42 which automatically resets said detector to zero in case the set number of pulses has not entered within the normal time, whereby a false alarm is prevented.

Normally the radiation from the glowing particles lies within the infrared area. By the selection of the light-sensitive element said transducer can be made insensible to normal day-light and to light for example from fluorescent lamps. By the fact that only incoming pulses having a high slope are accepted said filter unit ensures that irrelevant disturbances cannot start an alarm. Thus, said detector is in several respects designed to prevent false triggering. On the other hand said detector responds to glowing particles also when the speed of flow within the visual field, as in conduit 10, is very high and thus the control equipment 36 will have time to quickly interrupt the process prior to the initiation of a fire or an explosion within the system.

FIG. 3 discloses a transducer having three light-sensitive elements 46 arranged in a chamber 48 the roof 22 of which functions as a raster. Said roof 22 has the shape of a semisphere and includes grooves 50 extending in parallel and cutting into said semi-sphere to the level of the light-sensitive elements 26. By utilizing a semi-sphere the length of the grooves 50 extending perpendicular to the path 33 of the particles will vary. Thus, the centre groove 50 will be more lengthy than the grooves situated at the sides. A particle 32 passing centrally of the conduit will pass the grooves of the sensing zone three times. Each time a light-sensitive element is subjected to radiation from the particle a pulse will pass to the control equipment 36 according to FIG. 1 in the same way described above. The embodiment according to FIG. 3 is independent of the direction of transport of the particle.

In the embodiment according to FIG. 4 said transducer 12 by means of a partition 52 is divided and applied in two sensing zones separated from each other and each extending through a relatively large space angle v'. Each zone includes a light-sensitive element 54. The transducer is closed by a dome-shaped transparent covering 56. In this case the transducer is acted upon twice during the passage of the glowing particle 32 past the raster with an interruption over a distance determined by the separation 52.

A field within which the invention can be advantageously utilized is the drying of cellulose fibers produced by one or more grinding processes. The damp fibers are then by the gas flow and by suitable blowers brought to a cyclone where the dried fibers are separated from the gas and the large part of the water contents. The inventive detector is then arranged in the conduit between the drier and the cyclone to prevent fiber particles heated to glowing in said drier passing to the cyclone or to dust filters applied after the same, respectively. Hereby the otherwise great risk of fire and explosion will be eliminated by the fact that said detector will practically immediately interrupt the drying process or supply fire eliminating means, respectively, into the system.

Of course this invention is not limited to the disclosed embodiments but can be widely modified within the scope of the invention. By selecting different types of light-sensitive elements or by utilizing different types of filters the transducer can be made sensitive to radiation of any wanted frequency.

Claims

What I claim is:

1. In a detector of the type which is adapted to be mounted in a tubular conduit through which air-borne glowing particles may pass, and having

a housing,

at least two light-sensitive elements mounted in said housing,

means within said housing separating said light-sensitive elements from one another to form separate sensing zones in said housing,

a light-permeable covering member extending over said elements, and

means including an amplifier connected to said detector to form a chain of pulses from said light-sensitive elements for use in eliminating said particles,

the improvement wherein said covering member is semi-spherical in shape.

2. A detector as claimed in claim 1, wherein said covering member has a plurality of openings therethrough which are so spaced from one another that when the detector is mounted in a tubular conduit they will be spaced longitudinally of the conduit, said light-sensitive elements are in registry with said openings and said openings are arcuate so that each of said zones covers the total cross section of said conduit.

3. A detector as claimed in claim 2 having a single transparent cover disposed over said covering member.

4. A detector as claimed in claim 2, wherein said openings are of different length.

5. A detector as claimed in claim 2, wherein said openings are parallel and define the sensing zones.