GB2114363A

GB2114363A - Measurement transducer arrangements

Info

Publication number: GB2114363A
Application number: GB08138994A
Authority: GB
Inventors: Laszle Kortvelyessy
Original assignee: Individual
Current assignee: Individual
Priority date: 1981-07-10
Filing date: 1981-12-24
Publication date: 1983-08-17
Also published as: GB2114362A

Abstract

Two or more measurement sensors are enclosed in protective tubes 3,4 which extend parallel side-by-side from a common measurement head 1. The sensors may be thermocouples, thermistors or oxygen probes. Comparison of temperature measurements from the sensors in each tube can be used to indicate the presence of a leak in one tube. <IMAGE>

Description

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I GB 2 114 363 A 1

SPECIFICATION

Measurement transducer arrangements

5 This invention is related to the improvement of the exactness and reproducibility of the temperature measurement and -control. Two or more protection tubes are suggested, which are fixed in one thermocouple head side by side and not one tube in the 10 other tube as before.

Usually a protection tube is fixed in another protection tube and both together into a thermocouple head, which contains the electric terminals of the thermocouple wires. These protection tubes are 15 made of different materials to damp the thermal stress of the internal protection tube (or of the coils of the resistivity thermometer). The other goal of this coaxial construction is to get an advantageous atmosphare for the thermocouple wires and to get a 20 neutral protection tube for the process.

To simplify this description only the thermocouples are mentioned below, but the same description is valid also for resistivity thermometers with protection tube.

25 Also wellknown is the construction in which one protection tube of a thermocouple contains two thermopairs in a four bore capillary tube or as a double compacted thermocouple (with ceramic powder isolation).

30 This construction was developped to separate a temperature controller from a recorder.

A new development is to fix a protection tube into the head with two times diameter. The goal of this construction is to fulfil only the half part of the 35 protection tube by the built in thermopair. By this way control thermocouple can be inserted into the same protection tube, and so the temperature can be controlled during the run of the furnace.

Disadvantages of these constructions are fol-40 lowing:

1. Two thermopairs in one protection tube are very common, but broken protection tube makes it possible that all the thermocouple wires get the same disadvantageous gas (or fluid) and therefore

45 their thermal emf will aged similarly. The controlling of a thermocouple with the aid of the other thermocouple is therefore not possible in spite of the theoretical independance of the two thermopairs. This construction can be hard controlled during the 50 run.

2. The controlling thermocouple with the double diameter protection tube will cooled down if a control thermocouple is inserted. This cooling down causes an overheating of the furnace as long as the

55 control thermocouple reaches the same temperature as before the controlling. If the charge is sensitive this controlling is not possible in spite of the existing place for the inserted thermocouple.

The thermocouples for the recording instruments 60 and for the security controllers can be checked theoretically by this method, but these thermocou-pler shall be cooled down in the practice by some 100 K. During this controlling process a disturbing of the temperature curve is caused on the recording 65 chart. This cooling down of the temperature curve can be hardly explained later. This controlling process consumes a lot of time.

Another disadvantage of this thick protection tube (for example with a diameter of 24 mm) is its very large dimension. It has a large thermal lag because of its large mass and because of the large gap between the wall of the protection tube and the thermopair.

The idea of the invention is to fix two or more protection tubes side by side, but mainly parallel into one thermocouple head. This group of protection tube enables the temperature measuring quicker and more reliable.

This invention is shown in Figure 1\

1 is the thermocouple head with the electric terminals of the thermocouple wires which can contain an adaptertube (2), the protection tubes are (3) and (4) which are fixed into the thermocouple head advantageously gas-tight.

To simplify the describing the word "thermocouple head" is used here as the construction element of the thermocouple which can be seen from the built in thermocouple: in Figure 1 the "thermocouple head" contains two parts -1 and 2 together.

The advantages of this new thermocouple are following:

1. The protection tubes side by side are thinner than 10 mm and therefore they have time constante of 40% than usual. This little time constante enables very smooth temperature curve. In a concrete case the two-point controlling oscillated between 879,3 °C and 880,0 °C (the set-point was 880 °C). The amplitude was ± 0,35 K which could not be achieved before.

2. The protection tubes in the same thermocouple head have the same temperature with a tolerance of ± 0,1 K in industrial furnaces measured. Therefore the thermocoupler show the same temperature.

3. In an empty protection tube the otherthermo-couplerof the group can be controlled each time without the cooling down of them. Waiting of a longer soaking time for this controlling is not necessary anymore.

4. If one of the protection tubes in the group breaks and therefore for example the recording is disturbed, the empty protection tube can be used for the protection of the recording thermopair. The process can be led up to the end. The empty protection tube is not only a control tube but also a reserve protection tube.

5. An old feeding-through in an existing furnace can be used now to insert two or more thermocouples instead of the only one thermocouple before. The completing of the temperature measuring is possible for example by security controlling.

6. Much less protection gas streams out in the case of a broken protection tube in the group compared to the old one. The new protection tubes are thinner than the old ones and they are more fulfilled.

7. The thin protection tubes of the invention are more elastic and not sensitive against thermal stress. They can work in such furnaces which are vibrated by motors and pumps. These thin protec70

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Claims

I 2 GB 2 114 363 A 2 tion tubes are cheaper and they can be made from very pure and expensive alumina of 99 to 99,7 %. These very pure protection tubes can be used up to 1500 °C (up to 2300 °C in the case of berylia) without 5 banding. In a concrete case a very little drift of 0,7 K was found after 17 months at 1050 °C. This drift was exactly the same for both thermopairs in the group. 8. If a protection tube breaks because of a wrong 10 moving of a charge or because of other factors, the thermocouple wires in this broken protection tube will be poisoned and therefore they indicate on other temperature than the thermocouple wires in the not broken tube. As long as two or more temperature 15 indications at this multiple thermocouple are identical the temperature measuring or -control is reliable. The thermocouple head - the cavities (1) and (2) -can unify not only protection tubes with the same diameters, but also protection tubes with different 20 diameters. It is possible, that a thin protection tube covers a thermopair, a thick one, however, an oxygen probe. By this way the multitube thermocouple enables the improvement of a furnace with protective atmosphere. The old feeding-through can 25 be used within minutes to fix a new high quality thermocouple group and an oxygen probe at once. Optimally the thermopairs are made in the thin protection tube and in the oxygen probe from the same roll of thermocouple wires. The thermocouple 30 indication from the oxygen probe can be used to control the temperature indication from the thin protection tubes by the same way as shown in point 8. Two oxygen probes fixed in one head make 35 possibleto control not only the temperature, but also the measuring of the quality of the protection atmosphere. The electrical terminals of the thermocouples and of the oxygen probe(s) have the important advan-40 tage to be in the same head and therefore in the same cavity getting the same temperature. A continual controlling of the two or more thermocouples and/or oxygen probes in one head is inventionally also possible. 45 The idea of this additional invention is to accept an indication only if a second independent indication is identical with it. Normally nobody is sure if only one indication of a sensor exists, it can be correct or erroneous. 50 Even two or more such sensors in one furnace cannot give security because the temperature or oxygen content can be different in different points of a furnace. Figure 2 shows an inventional solution of this 55 problem. In Figure 2 the numbers are between 1-4 the same as in Figure 1:1 is the head, 2 is the holding pipe, 3 is one protection tube - in this case of zirconia (Zr02) - 4 is the second protection tube. The other numbers are: 5 the wall of the furnace, 6 an 60 instrument, 7 is the comparator which produces alarm, if the difference between two indications is over a limit, say over ± 3 K, 8 is a horn, 9 is the other temperature indicator (controller), 10 is the voltage indicator (controller) of the oxygen probe, 11 is the 65 thermopair in the oxygen probe, 12 is a leading of it, 13 is a larger protection tube, 14 is the thermopair in the tube (4). In an inventional multi-tube-thermocouple and/or -oxygen probe (Figure 2) the sensors are in a very 70 near position in the furnace. They get the same temperature or the same oxygen content. Further the erroneous thermoelectric potentials of these sensors at the terminals ("+" and in Figure 2) in the same head are also eliminated 75 because of isotherm temperature distribution in this head. Therefore, if two or more indications are nearly identical-as in Figure2: 930°Cand 931°C-thetwo or more sensors can have only no error or the same 80 errors. The same errors for two or more sensors are possible, but only theoretically. In the practice it is impossible, that the zirconia tube (3) of the oxygen probe and the alumina tube 85 (4) of the thermocouple have in the same time the same leak causing the same error of say - 30 K. (The real temperature would be in this case 960 °C.) Even the good function of both indicators (controllers) is practically assured, if the two indications are 90 nearly identical, as shown in Figure 2. The inventional solution is not more expensive than the conventional one. The safety rules demand a second independent temperature controller to prevent overheating. A high limit must be set on f.e. 95 1050 °C (Figure 2). Present invention prevents allready an overheating of + 3 K (933 °C - Figure 2) also a too low temperature of - 3 K (927°C). It is more sensitive and in both directions of deviation. 100 Normally the safety-controller controls the first one, but inventionally also the first controller controls the safety controller. Each part in one circuit controls each part in the other electric circuit. It is impossible to forget to set the high limit 105 because this is set automatically on +3K. No deviation more than 1 K was observed in the range of 0-1050 °C during many experiences over one year. The difference between the two indications is allways zero or f.e. 1 K. In the practice the 110 comparator (7) is not necessary, if the temperature range is low. A little deviation over 1 K can be detected immediatelly and the real temperature in the empty protection tube can be tested. 115 CLAIMS

1. Thermocouple or resistivity thermometer consisting head with electrical terminals and protection tubes and thermopairs - or perphaps without ther-

120 mopairs - having inventionally two or more protection tubes side by side, mainly parallel each with other fixed in one head with electrical terminals,

2. thermocouple or resistivity thermometer defi-nited in claim 1 having inventionally an empty

125 protection tube for enabling control measurings,

3. thermocouple or resistivity thermometer defi-nited in claim 1 having inventionally high purity alumina protection tubes,

4. thermocouple or resistivity thermometer defi-

130 nited in claim 1 having inventionally in one or in

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GB 2 114 363 A

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more protection tube(s) oxygen probe(s).

5. Thermocoupie(s) and/or oxygen probe(s) in one head - as in claim 4 described inventionally defined by two or more instruments connected on 5 these sensors with automatic or not automatic comparing of these indications of said two or more instruments.

Printed for Her Majesty's Stationery Office, by Croydon Printing Company Limited, Croydon, Surrey, 1983.

Published by The Patent Office, 25 Southampton Buildings, London, WC2A1 AY, from which copies may be obtained.