IE52083B1

IE52083B1 - A radiation sensing device

Info

Publication number: IE52083B1
Application number: IE2735/81A
Authority: IE
Original assignee: Deutag Mischwerke & Fertighaus
Priority date: 1980-11-24
Filing date: 1981-11-23
Publication date: 1987-06-10
Also published as: DE3044104A1; IT1139826B; GB2088049B; NL8105307A; FR2494844A1; LU83784A1; IT8125228A0; DK518781A; IE812735L; GB2088049A; FR2494844B1; BE891222A

Abstract

A radiation-sensing device for measuring temperatures in intensely- heated bulk materials or the like has a lens system 3 in a holder 4 and is provided with a shield tube 8 to which an air-supply is fed. The inlet 15 for air is located at a closed inner chamber of the shield tube or holder, said chamber being in close contact with the lens system. The air inlet opens into an internally-open annular chamber. The supply of air into the enclosed chamber of the shield tube, located near the lens system, protects the lens system from dust, vapours and impurities, so that radiation from the heated material can be measured without external influence.

Description

The invention relates to a radiation sensing device for measuring temperatures in intensely-heated bulk materials, particularly dustgenerating and/or vaporous masses of bulk material such as rolling asphalt, pouring asphalt and the like, the device having a radiation sensor set in a holder which is preceded by a shield tube.

There are considerable difficulties involved in the use of conventiona radiation sensing devices for determining temperatures in intensely-heated dust-generating and vaporous bulk materials. In order to enable temperature measurements in the range + 0°C to + 500°C, it must be ensured that the Ten; system of the device, in both intermittent and continuous operation, is exposed to a maximum temperature of only +40°C, and is kept free of fine • dust and dewpoint droplets. In a processing plant for bituminous mixes, for example, knowledge of the correct temperature of the material is an essential prerequisite for its further processing. The measured values are for example used to control burners, and for maintaining precise required values. 'Not inconsiderable measurement errors arise through dust development. The indicated accuracy is also altered by wear on the sensor.

In the case of one known radiation sensing device with a shield tube, a so-called scale breaker is mounted at the free end of the device. Compress air is fed to openings or nozzles on the free end of the shield tube in order to remove scale from the surface to be measured, after which the movable shield tube 1s retracted. This does not eliminate the risk that dus and scale particles might pass into the shield tube as far as the pyrometer. Nor can the shield tube be kept free of dust and vapour. 53083 It is further known, in the case of a measuring head for a device with a measuring cell, a lens system and a shield tube, to locate in the measuring head in front of the lens system an air lock with an air inlet and an air outlet nozzle, said nozzles being oblique to the longitudinal axis of the shield tube. However, this design of radiation sensor does not ensure that dust, vapour and the like are reliably kept away from the lens system. Passing an airflow transversely to the shield tube causes an injector effect which can suck in impurities, dust, vapour and the like, into the measuring device, considerably impairing the measurement, and thus also affecting the control of the processing plant which is derived therefrom.

According to the present invention there is provided a radiation sensing device for measuring temperatures of heated materials, comprising a shield tube for receiving radiation through one end and defining a passageway for the radiation, a radiation sensor mounted with a lens system in a holder at the other end of the passageway, and an inlet for air leading to an annular chamber which communicates with the passageway through an annular gap extending between them, the annular gap being spaced along the passageway from the lens system.

The device preferably ensures that the radiation sensor and lens system are reliably protected from disturbing influences such as dust, dirt layers, condensate and the like, and that correct temperatures can be measured.

The means for achieving this is that the air inlet leads to an enclosed inner space, in close contact with the lens system, of the shield tube or of the holder for the same.

Such a design of the air supply to the radiation sensor, i.e. the measuring unit, means that the lens system can be simply and reliably protected from emanations such as generated dust, vapours and the like which emanate from the heated bulk material and which would otherwise impair the measurements. In this way the radiation emitted by the mixed material and the like can be measured without any disturbing influence. Adjacent the lens system at the end of the shield tube is a baffle space from which there is maintained a constant airflow in the direction of the free end of the shield tube, so that all penetration of impurities, dust and the like is eliminated. The radiation entering the shield tube is passed to the measuring cell, uninfluenced by the air-column flowing in the opposite direction. Thus the measuring space is kept constantly clean and uniform and is unaffected by interference from the material being measured. This helps to eliminate overheating of the mixed material in the control derived from the radiation sensor, enabling considerable energy savings. The air-column in the shield or baffle tube, with constant externally-directed flow pressure, further serves as an equilising column for exhaust residues which can form in the burner chamber or in the drying chamber. The lens system is kept clean and wear is reduced. The exact temperature of the mixed material can be controlled and evaluated.

The inlet preferably opens into an inwardly-opening annular chamber, which equalises the pressure of the incoming air. This annular chamber connects with the inner space of the shield tube by means of an annular gap, or slot.

The holder for the radiation sensor may advantaveously be formed from a two-part housing block having a carrier block and a foreblock. The annular gap may be formed between the carrier block and the foreblock for air passage from the expansion chamber into the interior of the shield B2083 tube. In this way the air-flow entering the shield tube from the chamber of the foreblock can be diverted and stabilised. The expansion chamber equalises the pressure and volume distribution. The incoming air can pass in controlled amounts through the annular gap or slot into the fore5 block chamber and constantly flow towards the outer end of the shield tube.

Sources of disturbances are eliminated in front of the lens system.

A cooling chamber is provided by the spacing of the sensor's lens system and the annular gap or slot. This helps to block off disturbances in the baffle tube, in front of the lens system.

The foreblock and carrier block may be connected together by a flange and screws. The radiation sensor itself may be surrounded by an enclosed protective jacket which may be fixed on the carrier block, for example by means of a screw ring or the like.

The radiation sensing device of the invention may be designed as an enclosed system. Here the free end of the baffle tube can comprise a fixture which is screwed on to a stationary part of a mechanical installation or the like. Thus atmospheric air cannot penetrate at the free forward end of the baffle tube, said free end surface being in direct contact with an opening in the wall of the installation. Such an enclosed system is particularly suitable for attachment to outlet chutes of drum driers or tubular rotary kilns. The correct temperature is determined, in the case of the enclosed system, in the fully-encapsulated path of movement of the medium to be measured.

The device of the invention may also be used in an open system. In . this case the carrier block may be provided with a suspension lug and the device freely suspended at transfer or loading positions. The correct temperature can be accurately determined from the material, for example mixed bituminous material, while it is in free fall, e.g. on the way from a silo to a transporting vehicle or the like. This ensures that the mineral-containing mixed material is delivered to the worksite or the like at the required temperature.

Embodiments of the invention will now be described by way of example with reference to the accompanying drawings, in which: Figure 1 is a diagrammatic longitudinal section of a radiation sensing device of the invention for an enclosed system; and Figure 2 is a diagrammatic longitudinal section of a radiation sensor sensing device of the invention in an open system.

The radiation sensing device 1 in Figure 1 has a sensor 2 with a lens system 3 connected to a holder 4. The holder 4 is in the form of a housing block having a carrier block 5 and a foreblock 6. Connected to the foreblock 6 is a baffle tube 8. The foreblock 6 has a continuous chamber 9 through which radiation 10 from material to be measured can pass to the lens system 3. The carrier block 5 and the foreblock 6 are rigidly connected together by means of flanges 11 and 12 and screws 13.

At the end of the foreblock 6 facing the carrier block 5 is an air entry inlet 15, and between the interfacing surfaces of the carrier block 5 and the foreblock 6 is an annular slot 16 which connected with the air inlet 15. Between the inlet 15 and the annular slot 16 is an annular chamber 17 serving as an expansion chamber, enabling pressure and volume equilisation. Between the lens system 3 and the annular slot 16 is a chamber 18 serving as a cooling chamber, cooling the air before it comes into contact with the lens system 3.

The baffle tube 8 absorbs exhaust residues formed in a combustion chamber or drying chamber from the intensely-heated material. The air column compressed in the baffle tube 8 compensates for such pressure influences, and the entry of air through the inlet 15 causes a counterflow, so that the lens system 3 is kept free of impurities. Thus the temperature of the material can be exactly determined. The length of the baffle tube depends on the circumstances at any time and is a multiple of its diameter, a common length in an enclosed system being about 11 times, and in an open system about 5 times the baffle tube diameter.

The radiation sensor 2 is set in a recess 20 with an interposed damping ring 21, and is secured by a knurled screw 22. The sensor 2 is surrounded by a protective jacket 23 with an enclosed cover-plate 23a. The jacket 23 may be thrust on to the carrier block 5 and tightened thereon by a screw ring 24 in order to protect the sensor from temperature fluctuations and atmospheric influences. The wall 8a of the baffle tube 8 serves not only as a temperature spacer but also substantially as a heat-exchange surface.

When using the measuring device 1 as an enclosed system, the baffle tube 8 can be fitted with a securing ring or flange 26. Accompanying this securing ring 26 is a counter-ring 27 secured, for example by welding, to a wall 28. The wall 28 has an opening 29 corresponding to the diameter of tbe baffle tube 8, so that the radiation 10 can pass from the radiating surface of the heated material inside the wall to the lens system 3. Securing screws 30 attach the radiation-sensor system on the counter-flange 27, with an interposed gasket 31 made for example of asbestos or the like.

The embodiment of Figure 1 provides an entirely closed system between the measuring device and the material passing through the installation.

The device 33 in Figure 2 corresponds generally to that in 5 Figure 1. The carrier block 5 has a suspension lug 34, so that the measuring device 33 may be freely suspended by a lug 34 relative to the radiating surface of the material to be measured. The baffle tube 8 and its jacket 8a is thrust on to the foreblock 9 and clamped thereon by a screw ring 35. The baffle tube 8 is open to the environment at the forward end. The freely-suspended device 33 is oriented and suspended at a distance relative to possibly free-falling material, for example a heated bitumen mix, so that the radiation emitted by the material can be exactly monitored. The lens system of the device in this embodiment is also effectively protected against disturbances emanating from the material.

Claims

1. A radiation sensing device for measuring temperatures of heated materials, comprising a shield tube for receiving radiation through one end and defining a passageway for the radiation, a radiation sensor 5 mounted with a lens system in a holder at the other end of the passageway, and an inlet for air leading to an annular chamber which communicates with the passageway through an annular gap extending between them, the annular gap being spaced along the passageway from the lens system. 10

2. A device according to Claim 1, wherein the holder for the radiation sensor is in the form of a housing block comprising a carrier block and a foreblock.

3. A device according to Claim 2, wherein the annular gap is formed between the carrier block and the foreblock. 15

4. A device according to Claim 2 or 3, wherein the carrier block and foreblock are connected together by flanges and screws.

5. A device according to any one of the preceding claims, wherein the shield tube is in the form of a baffle tube whose length is a multiple of its diameter. 20

6. , A radiation sensing device substantially as hereinbefore described with reference to Figure 1 of the accompanying drawings.

7. A radiation sensing device substantially as hereinbefore described with reference to Figure 2 of the accompanying drawings.