IMPROVEMENTS IN OR RELATING TO HEAT METERING

Abstract: In a device for the transfer and metering of thermal energy between a supply main and a consumer system, thermal contact between fluids flowing in supply and receiver ducts is effected by means of one or more thermosiphons (30), each containing a working fluid in contact with its vapour, and each having a condenser area (34) in the receiver duct, and an evaporator area (35) in the supply duct. Liquid condensate returns from the condenser area to the evaporator area through a liquid passage (42) which contains a flowrate meter (46) providing a pulsed output in which each pulse represents a quantum of fluid flow therethrough. The pulses are received by a counting and display device (48) calibrated to provide a direct reading of the quantity of thermal energy supplied. Each thermosiphon can have a plurality of separate condenser areas (34) and a plurality of separate evaporator areas (35) arrayed respectively across the receiver and supply ducts. Alternatively the supply duct and/or the receiver duct can be split into a plurality of distinct portions which pass through the thermosiphon vessel to effect heat exchange therewith in the manner of a shell and tube boiler or a plate evaporator. Two or more independent thermosiphons can be provided with their evaporator areas disposed successively along the supply duct and their condenser areas disposed successivily along the receiver duct. Similar arrangements can be provided for metering consumption of refrigerant.

Description: IMPROVEMENTS IN OR RELATING TO HEAT METERING 1 This invention relates to the transfer of thermal energy between a source and a consumer, and in particular to means by which the quantity of thermal energy transferred can be measured. District heating schemes are coming increasingly into being, in vhich thermal energy generated centrally is supplied to individual consumer systems, for example to individual dwellings where it can be used for heating the interior thereof, and for the supply of hot water. Similar schemes operate on an industrial scale where the consumer might be a factory or other industrial undertaking. Such schemes have a number of advantages, in that a constant ready supply of thermal energy can be available to the consumer, and especially in that low-grade thermal energy can be utilised which might otherwise be wasted. In the latter respect, the so-called combined heat and power schemes are particularly economical, in which heat produced as an incidental to power generation can be put to useful effect instead of creating a disposal problem. It is also possible that refrigerant could be supplied from a c ntral source to individual consumer systems from which heat is to be abstracted, and the invention is also useful in relation to such arrangements. In the most usual method of distribution, thermal energy is ' supplied to users by a system of main pipes carrying hot water, often under relatively high pressure. Of course, other heat transfer media such as steam can be used instead of water. In order to provide a fair basis for charging related to consumption, the thermal energy transferred between the main and the cons mer needs to be measured. The direct method of approach involves measurement of supply and return temperatures of heat O PI transfer medium and its flowrate. The thermal energyconsumed can then be calculated from the product of three factors, ie the temperature difference, the flowrate, and the time interval. An instrument which provides a reading of thermal energy consumed in this way is called a true heat meter. In most practical cases the temperature difference and/or the flowrate will vary with time, and the instrument must then be capable of calculating the aforesaid product over short successive time intervals and summating the results. This makes for a relatively complex instrument, which can be simplified to some degree by keeping one or more factors constant (ie flowrate, and/or supply temperature, and/or return temperature). However, this in itself introduces further complexity as well as imposing constraints on the system which may have practical disadvantages. Such meters always need some foim of flowrate meter which is required to measure the flowrate of a hot heat transfer medium which is usually impure and carrying dirt in suspension, tost flov?rate meters are unsuitable for -such an environment, and this gives rise to frequent failures. In many cases the flowrate meter is required to measure a range of flowrates down to a very low rates. For this purpose a very sensitive meter is required, but such a meter is particularly unsuitable for use with hot, dirty liquids. As an alternative to the true heat meter, there are known a number of different types of "apportioning meter" which do not themselves measure heat consumption, but employ some means of indication which varies in accordance with the heat emission from a heat exchanger. If each consumer has a similar meter, the total quantity of heat used by a group can be apportioned among the individual consumers. Some physical phenomena commonly exploited in this type of meter are evaporation of a liquid, metallic creep, thermocouple e. .f. and variation with temperature of the resistance of certain electrical resistors. These devices still require some measurement of the total quantity of heat consumed by the gro.ip and tend to be rather rough and ready in their apportionment• In addition, there are also known proportional meters in which a proportion of the hot liquid drawn from the supply main by a consumer is diverted into a measuring system. Such proportional meters are described for example, in UK Patent Nos 1199311; 701832; 672*+76 and 192610. These meters are very prone to inaccuracy because they rely upon a constant proportion of the hot liquid being diverted to the measuring system. This is exceedingly difficult to achieve where the flowrate of liquid drawn from the main is variable. In each of these proportional meters the heat in the diverted liquid is simply wasted, and hence to minimise this serious disadvantage it is important to keep the proportion diverted to the meter as small as possible. This compounds the difficulty of ensuring that a constant proportion is diverted. The meters described in UK Patent ϊlos 1199311; 67.2^76 and.192610 are all of a calorimetric type which cannot operate continuously and in which the quantity of hot liquid which can be metεred at any one tapping is limited by the capacity of the meter. The meter must be allowed time to return, to ambient temperature before a further tapping takes place, or further inaccuracy will result. In UK Patents Nos tøθδ21; and 251379, there are disclosed systems in which heat is distributed from a central source through a main which carries steam. Each consumer is provided with a heat exchanger which heat is provided to the consumer's heating system. A liquid flowmeter measures the volume of liquid condensed from the main as the result of heat supplied to the consumer through his individual heat exchanger, and the volume of condensate can be related to the heat consumed. Such systems, however, suffer from a number of disadvantages. In order to provide an accurate indication, the steam supplied and the water returned must be at kno n, preferably constant temperatures, otherwise an un-metered flow of heat will take place as a result of unknown variations in supply and return temperatures. Another difficulty is that the flow meter must be capable of registering accurately over a wide range of flowrates. Available meters capable of meeting this requirement are not normally sufficiently r g e d to withstand working with hot, dirty liquids such sis would be encountered in a steam main. A need therefore exists for a true heat meter of reasonably simple form which is capable of reasonably accurate measurements, and which avoids the difficulties associated with requiring a sensitive flowmeter to measure the flowrate of hot dirty heat transfer medium. In many instances, it is desirable to isolate the main from the consumer's heating system, especially where the main is at high,pressure, and this is commonly done by employing a heat exchanger through which heat is transferred from the main to the consumer's system without any fluid communication occurring between the two systems. The Applicant has appreciated that by use of a particular form of heat exchanger, a very advantageous method of heat metering is ©ade possible. " According to the present invention, a device for the transfer and metering the total quantity of thermal energy transferred between a supply main and a consumer system includes at least one thermosiphon comprising a hermetically sealed vessel containing a liquid in contact with its vapour and having a first heat transfer area of the vessel wall adapted to make thermal contact with a supply fluid which can flow in the supply main, and a second heat - transfer area of the vessel wall adapted to make thermal contact with the heat sink a consumer fluid which can flow in the consumer system, a vapour passage through which the vapour can flow between the first and second heat trsnsfer areas, a liquid passage through which a return flow of liquid condensate can occur between the first and second heat transfer areas, and means for measuring the quantity of the liquid which flows through the liquid passage. In the envisaged application of the invention the device will normally comprise a supply duct for connection into the supply main and a receiver duct for connection into the consumer system, said first heat transfer area being located adjacent the supply duct and said second heat transfer area being located adjεcant the receiver duct. In one useful arrangement the first heat transfer area of the vessel wall constitutes an evaporator area in which the liquid within the sealed vessel can be evaporated and the second heat transfer area of the vessel wall constitutes a condenser area in which vapour within the sealed vessel can be condensed. Conveniently, the device comprises a thermosiphon having a plurality of separate evaporator areas and a plurality of separate condenser areas, the evaporator and condenser areas being connected, by a common liquid passage, the separate evaporator areas of each thermosiphon being arranged, to extend transversely with respect to the direction of flow in the supply duct, ana the separate condenser areas of each thermosiphon being arranged to extend transversely with respect to the direction of flow in the receiver duct. The evaporator and condenser areas can also be connected by a common vapour passage if deslre-lt, Th another advantageous arrangement, the supply duct is split into a plurality of distinct supply duct portions which pass through the sealed vessel, each supply duct portion being defined at least in part by a wall which seals the interior of the portion from the interior of the sealed vessel and constitutes a part of the evaporator area. The receiver duct can similarly be split into a plurality of distinct receiver duct portions which pass through the sealed vessel, each receiver duct portion being defined at least in part by a wall which seals the interior of the portion from the interior of the sealed vessel and constitutes a part of the condenser area. The hot and cold fluids can be arranged to flow in any desired way through the supply duct portion and receiver duct portions respectively, ie in series or in parallel or in any desired combination of series and parallel groupings. Advantageously there are provided two or more mutually independent thermosiphons having the evaporator areas of independent thermosiphons arranged successively along the intended direction of flow in the supply duct ar.ά the condenser areas of independent thermosiphons arranged successively along the intended direction of flow in the receiver duct. The invention will now be described by way of example only with reference to the accompanying drawings, of which Figure 1 is a schematic longitudinal sectional elevation of a heat e_5_hanger comprising a plurality of thermosiphons, Figure 2 is a schematic end elevational view in section of the heat exchanger shown in Figure 1, Figure 3 illustrates graphically the temperatures obtaining in the fluids when the heat exchanger of Figures 1 and 2 is operated, in counter«-current fluid flow, Figure k is a schematic end elevational view in section of a device for the transfer and metering of thermal energy in accordance with the invention, Figure 5 illustrates graphically the temperature distribution obtaining in a less preferred embodiment of the invention, Figure 6 is a sectional view of another device in accordance with the invention, and Figure 7 is a schematic longitudinal sectional elevation of an arrangement employing a plurality of devices as- shovn in Fig β. As sho..*n in Figs 1 and 2, a haet exchanger ccmprises a duct 1 forming part of a supply main for carrying a flow of hot fluid and a receiver duct 2 above the duct 1 for carrying a flow of cooler fluid forming part of a consumer system such as a domestic heating circuit. The intended directions of flow of the hot and cooler fluids are indicated in Figure 1 by the respective arrows E and C. Heat can be transferred between fluids in the ducts 1 and 2 via a plurality of mutually independent thermosiphons 3» As seen in Fig 2, the thermosiphons are arranged in rows extending trans¬ versely across the ducts, and as seen in Fig 1 there are a plurality of such rows disposed at successive locations longitu- dinally of the duct. Each thennosiphon is in the foim of a hermetically sealed cylindrical vessel containing a liquid in contact with its vapour (not shown) - water being a particularly suitable liquid where the ducts 1 and 2 are to carry water. The lower part 5 o the wall of each thermosiphon protrudes into and across the supply duct 1, and this area of the vessel wall constitutes a first heat transfer area which serves as an evauoratcr area. The upper part of the wall of each thei-≥osiphon protrudes into and across the receiver duct 2, and this area of the vessel wall constitutes a second heat" transfer are which serves as a condenser area * ■ 5 In use of such a heat exchanger, hot and cooler water flow in countexcurrent through the respective ducts 1 and 2 as indicated by the arrows H and C. Water sealed within each thermosiphon vessel 3 boils within the evaporator area 5 as a result of heat transferred front the water in the duct 1. Vapour thus created •JO rises up within the vessel 5 an condenses within the cooler condenser area of the vessel wall, giving up its latent heat of vapourisation which is transferred through the wall to the cooler fluid in the duct 2. The condensate runs back under gravity down the sides of the vessel 5 into the evaporator area 5 where it can 5 boil again. This is a conventional operation of a thercosiphon, in which it ' acts as a highly efficient thermal conductor. In order to provide a measure of the quantity of thercal energy transferred, each thermosiphon is provided with means (not shown) for measuring the quantity of condensate returned to the 0 evaporator. In practice this will most readily be achieved by providing separate flow paths for vapour and condensate. The volume of condensate descending to the evaporator is exactly related to the quantity of heat transferred froa the duct 1 to the duct 2 by the equationS- Q = VLD where Q is the quantity of heat transferred D is the density of the liquid in the vessel 3 I is the latent heat of vapourisation of the liquid in the vessel 3 0 V is the volume of condensate descending Thus, if the product LD can be assumed constant, the volume of condensate is in direct proportion to the quantity of heat transferred, and measuring that volume is a si__ple and effective way of deteitiining the quantity of heat trans erred. A most suitable fluid for use in the thercosiphon vessel 3 is water, for which the value of LD vari-es slightly with temperature. The temperature of the water in the vessel 3 is always between the temperature of the hot fluid and that of the cooler fluid. Typically in use in a district heating scheme it might vary from 80 to 100 C, and in that range the product LD varies by 5&. If an average value were used, the maximum error from this cause would thus be only ± 1J&. Thus, by measuring only the quantity of liquid condensate flowing down through each vessel 3 during a given period, and summing the values for each vessel, an indication of the heat transferred is readily obtainable. In order to obtain good heat transfer, an array of heat transfer elements, as for example in Figures 1 and 2, is desirable. the provision of separate flowmeter for each of such a large number of separate thermosiphons, and means to sumaate their readings, is inconvenient and expensive. In Figure there is shown a heat exchange device comprising a single thermosiphon 30 having a plurality of distinctcondenser areas in the form of cylindrical tubular elements 3^. and a plurality of distinct evaporator areas in the fora of cylindrical tubular elements 35. The evaporator areas 35 are arranged transversely across a supply duct 1 for hot water so that the hot water can flow between them for good heat transfer, and the condenser areas jk are similarly arranged transversely across a receiver duct 2 for cooler water. The lower ends of the evaporators are connected to a common sump *Vl, and the lower ends of the condensers are connected to a common sump hO * The sumps 0 and *Vl are interconnected through a single dovncoEier or liquid passage **2, so that all condensate from the condenser areas 3^ drains through the sump kQ, via the liquid passage *+2, to the sump .-1. The upper ends of the evaporators are connected by a common header space 3, and the upper ends of the condensers are connected by a common header space 44, the spaces -3 and 44 being connected by a single vapour passage 5. The condensers defined by the condenser areas 34, the evaporators defined by the evaporator areas 35, the sumps 40 and 4 * 1, the header spaces 43 and 44 and the passages 2, 45 collectively define a hermetically sealed vessel constituting the single theππosiphon 30. A liquid flowrate meter 46 is located in the downcoruer 42 to measure the fluid flow therethrough. The meter 46 is of a kind hich produces a pulsed electrical output, each pulse representing a quantum of volume of the flow therethrough. The pulsed output is transmitted via an electrical connection 47 to a counting and display device 46, which counts the number of . electrical pulses received, and displays the total on a scale calibrated in units of thermal energy consumed. It is intended that the thermosiphon 30 should replace a transverse row of thermosiphons 3 such as those shown in Fig 2, so that only a single flowmeter is needed instead of one for each theπsosiphon 3« In the heat exchanger shown in Figs 1 and 2, there are eight transverse tows of the thermosiphons 3« Such an array will typically give temperature profiles as shown in Fig 3 for counter- current flow where t fa is the temperature of the hot liquid in duct 1, t is the temperature of the cold liquid in duct 2, and c x represents distance in the longitudinal direction of flow in the duct 1. Similar profiles will be obtained when each transverse row °f thermosiphons 3 is replaced by a single thermosiphon 3°. Each thermosiphon 3 must have its own fiow eter 46, but if the flowmeters are each calibrated to produce electrical pulses representing the same volume of liquid, connections h ~ can feed the outpits of all flowmeters 46 to a common counting and display device 48. Although a plurality of flowmeters are required, a single counting and display device is sufficient. For a pure countereurrent heat exchanger transferring the maximum quantity of heat, an infinite number of thermosiphons 30 would be required theoretically. However, considerable cost saving with very little loss of performance can be obtained by providing only three thermosiphons 3 of comparable surface area. In many systems, satisfactory performance may be achieved with only two such thermosiphons-30, with thus only two flowmeters required. It might be thought that further savings could be achieved by having a plurality of thermosiphons 30 modified to have a single liquid do ncoaer 42 common to then all. Only a single flowmeter would then be required for the entire device. This approach would not give very satisfactory results because as illustrated in Figure 5* the temperature of the liquid within the linked vessels 30 would assume the same value ts in each vessel 30. The temperature t of the hot liquid could not fall below t and the temperature t of the cooler liquid could-not rise above t , no c s matter how many thermosiphons 30 v.ere used. Thus, although only a single flowmeter would be required, the heat transfer would be inefficient as compared with the true countereurrent arrangement described with reference to Figures 1 to 4. It will be apparent that the thermosiphon through which heat is conveyed from source to sink need not consist of tubular elements constituting the evaporator and/or condenser areas, nor need any such elements be vertically orientated. As a further example, Figure 6 illustrates an embodiment of the invention in which a shell boiler arrangement is used for both evaporator and condenser. Alternatively, a plate boiler or other suitable heat exchange device might be used. As shown in Figure 6, a device for the transfer of heat from a supply fluid flowing in a supplymain 51 to a consumer fluid flowing in a receiver duct 52 forcing part of a consumer system comprises a boiler 53 and a condenser 5 each of shell and tube designo The boiler 53 comprises a hot water box 55 having a flanged * inlet connection into an upstream am of the supply main 51 and a second hot water box ^ having a flanged outlet connection into a downstream arm of the supply main 1• 3_αe boxes 55 and 5^ are connected together by a pltirality of tubes 57, so that within the boiler 53 the supply main duct is split into a plurality of distinct supply dust portions constituted by the tubes 57. The condenser 54 comprises a receiver water box & having a flanged inlet connection into an upstream arm of the receiver duct 52, and a second receiver water box 59 having a flanged outlet connection into a downstream arm of the receiver duct 52. The boxes δ and 59 are connected together by a plurality of tubes 60, so that within the condenser 54 the receiver duct 52 is split into a plurality of distinct receiver duct portions constituted by the tubes βθ» Eeat can be transferred from the boiler 53 to the condenser 5k by means of a theπnosiphon comprising a boiler shell 61, a condenser shell 62, a vapour passage 63 and a liquid downcomer 6*+, the elements 6 * 1, 62, 63 and 6k together constituting a hermetically sealed vessel containing a liquid and its vapour. The boiler shell 61 is bounded in part by walls of the boxes 55. 56 and the tubes 57 pass through the shell 6l, Hot liquid (water) constituting a heat source flowing through the supply duct 51 can thus transfer heat to the thermosiphon fluid through those bounding walls of the boxes 55 * . 56, and the walls of the tubes 57, which walls thus constitute evaporator areas of the thermosiphon. The condenser shell 62 is bounded in part by the walls of the boxes 58, 59 and the tubes 60 pass through the shell 62. Cooler liquid constituting a heat sink flowing through the receiver duct 52 can thus receive heat from the thermosiphon fluid through those bounding walls of the boxes 8 and 59, and the walls of the tubes 6θ, which walls thus constitute condenser areas of the thermosiphon. • During the heat transfer process, liquid boils in the boiler shell 61, rises up the vapour passage 63, condenses in the condenser shell 62, and returns under gravity through the dov comer 6k to the boiler shell 6 * 1. This cycle is continuously performed by the thermosiphon fluid during the heat transfer process. In order to provide a measure of the quantity of heat transferred, a flowmeter 65 is included in the downcomer 6 , which provides a pulsed output via an electrical connection 66 to a counting and display device 67» The operation is the same as that of the flowmeter k6 and counting and display device k& 9 In order to provide for more efficient heat exchange, a plurality of separate thermosiphons each for example as shown in Fig 6 and each comprising a boiler 53 and a condenser 5*+, can be provided as illustrated in Figure 7. In use the hot fluid constituting the heat source flows in the duct 6 * 1 in the direction of the arrow H, and the cooler fluid constituting the heat sink flows in counterflσw thereto in the duct 62, in the direction of the arrow C. The temperature distribution along the ducts 61 and 62 will- be substantially as shown in Figure 3, ie substantially as for a true countercurrent heat exchanger. Although three thermosiphons as shown in Fig 7 will often provide the best compromise between performance and economy, arrangements with " either two or four or more thermosiphons are possible. It should be noted that a separate flowmeter 65 is required for each thermosiphon, although it can be arranged that the outputs of all flowmeters are summed and displayed in a single counting and display device. This can be done readily where the flovaeters 65 provide a pulsed ' output, each pulse representing the same unit of volume. It will be apparent to those skilled in the art that the present invention provides many advantages in the supply of metered quantities of thermal energy. Conventional heat meters have to measure not only volume, but also two temperatures, and a complicated integration of the product of the several variables must be performed. Their accuracy is usually limited by the accuracy with which the difference between the two temperatures can be measured, when the difference is small. The present invention provides a system in which no temperature measurement or complicated calculation is required. Furthermore, the flowmeter required in the conventional heat meter has to cope with the hot dirty working fluid in the main or the domestic system. In the present invention, the liquid which is metered is the relatively small quantity recirculated continuously within the thermosiphon vessel. This liquid can be of a high degree of purity so that the adverse effect on the flowmeter is avoided, irrespective of the quality of the fluid in the main or domestic circuit. Heat metering devices according to the present invention also have the effect of isolating the main from the consumer's circuit. This can be important where the main is at high pressure. OMPI

Claims: CLAIMS 1. A device for the transfer and metering of the total quantity of thermal energy transferred between a supply main and a consumer system, said device being characterised by at least one thermosiphon (30) comprising a hermetically sealed vessel containing a liquid in contact with its vapour and having a first heat transfer area (35) of the vessel wall adapted to make thermal contact with a supply fluid which can flow in the supply main, a second heat trasnfer area (3k) of the vessel wall adapted to make thermal contact with a consumer fluid which can flow in the consumer system, a vapour passage (k5) through which the vapour can flow between the first and second heat transfer areas, a liquid passage (k2) through which a return flow of liquid condensate can occur between the first and second heat transfer areas, and means (k6) for measuring the quantity of the liquid which flows through the liquid passage. 2. A device according to claim 1 characterised by a supply duct (1) for connection into the supply main and a receiver duct (2) for connection into the consumer ' system, said first heat transfer area (35) being located adjacent the supply duct (1) and said second heat transfer area (3*+) being located adjacent the receiver duct (2). 3. A device as claimed in claim 2 characterised in that the said first heat transfer area (35) of the vessel wall constitutes an evaporator area in which the liquid within the sealed vessel (30) can be evaporated, and the said second heat transfer area (3k) of the vessel wall constitutes a condenser area in which vapour within the sealed vessel can be condensed. P 4. A device as claimed in claim 3 characterised in that the said at least one thermosiphon (30) has a plurality of separate evaporator areas (35) and a plurality of separate condenser areas (34), the evaporator areas being connected to the condenser areas by a common liquid passage (42), the separate evaporator areas (35) of each thermosiphon (30) being arranged to extend transversely with respect to the direction of flow in the supply duct (1), and the separate condenser areas (34) of each thermosiphon 30) ^ being arranged to extend transversely v;ith - respect to the direction of flow in the receiver duct (2). 5. A device as claimed in claim 4 characterised in that the said separate evaporator areas (35) are connected to the said separate condenser areas (34) by a common vapour passage (42). 6. A device as claimed in claim 3 characterised in that the supply duct is split into a plurality of distinct supply duct portions (57) which pass through the sealed vessel, each supply duct portion being defined at least in part by a wall which seals the interior of the said supply duct portion from the interior of the sealed vessel and constitutes a part of the evaporator area. 7« A device as claimed in claim 3 or claim 6 characterised in that the receiver duct is split into a plurality of distinct receiver duct portions (60) which pass through the sealed vessel, each receiver duct portion being defined at least in part by a wall which seals the interior of the portion from the interior of the sealed vessel and constitutes a part of the condenser area. 8. A device as claimed in any one of claims 3 to 7 characterised in that it comprises two or more mutually independent thermo¬ siphons (53, 54, 63, 64) having the evaporator areas of independent thermosiphons arranged successively along the intended direction of flow in the supply main (6D and the condenser areas of independent thermosiphons arranged successively along the intended direction of flow in the consumer system (62). 9. A device as claimed in any one preceding claim characterised in that the means for measuring the quantity of liquid which flows through the liquid passage comprises, in each liquid passage, a flowrate meter (k6. 65) of a kind which produces a pulsed electrical output, each pulse representing a quantum of volume of the flow therethrough. 10. A device as claimed in claim 9 characterised in that the pulsed output of the or each liquid flowmeter (65) is trans¬ mitted to a counting device (48) which counts the number of electrical pulses received. 11. A device as claimed in claim 10 characterised in that the counting device (48) is capable of a display representing the total number of electrical pulses on a scale calibrated in units of theraal energy consumed. 12. A device according to claim 1 and substantially as hereinbefore described. 13« A device substantially as hereinbefore described with reference to Figures 1 and 2, Figure 4, Figure 6 or Figure 7 of the accompanying drawings. lk Any novel and inventive featvire or combination of features disclosed herein. OMPI

Inventors: EMERSON WALTER HUGH
Applicants: SECRETARY INDUSTRY BRIT
Application year: 1982
Main classification: G01K17
IPC codes: G01K17