APPARATUS FOR MEASURING TEMPERATURE

Abstract: A method and apparatus for measuring temperature by making use of a state change of a working fluid. The temperature measurement is executed in a manner that the working fluid is initially supplied at a constant mass flow rate into a flow channel thereof defining a throttle portion at a temperature-sensitive portion and upon measurement of a pressure difference between opposite ends of the throttle portion, the temperature can be recognized through calculation of the measured pressure difference. The temperature measuring apparatus includes a source of supply of a working fluid, a probe having an external cylinder closed at its one end and an internal cylinder which is accommodated in the external cylinder and has a capillary tube at its forward end, a supply tube of the working fluid for introducing the working fluid from the source thereof into either the internal cylinder or the external cylinder, a pressure control device and a mass flow control device disposed in series in the course of the supply tube, a differential pressure gauge for detecting a pressure drop across the capillary tube, and a temperature operating device for operating the temperature on the basis of a signal sent from the differential pressure gauge.

Description: The present invention relates to an apparatus for measuring temperature, for example, the temperature within a furnace, the temperature of a molten material such as a molten iron or the like by making use of a state change resulting from a temperature change of a fluid. Conventionally, a thermocouple, a resistance thermometer or the like has been widely employed for measurement of a high temperature within a boiler, a furnace or the like. However, since these kinds of thermometers are, in principle, restricted in material of a temperature-sensitive portion exposed to the high temperature, it has been difficult to take any countermeasure against oxidization or other causes shortening the life of the thermometer and accordingly, either of such thermometers is generally improper to be used for a long time. Accordingly, there has been developed a temperature measuring apparatus of fluidic resistance type or a fluidic pyrometer which offers an advantage such that a material of a probe i.e., a temperature sensor forming a temperature-sensitive portion can be freely selected in view of its life without any restriction by a measuring principle. As for the principle of the fluidic resistance type temperature measuring apparatus, the temperature is detected through a change of pressure drop of a gas at the time when it passes through a throttle portion such as a capillary tube, by making use of a temperature dependence of the viscosity coefficient of the gas. Fig. 1 illustrates a fundamental construction of the temperature measuring apparatus of the above described type in which a working fluid such as Ar gas or the like is initially supplied from a source S′ of supply of the working fluid at a constant pressure through a pressure control device 40. The pressure drop ΔP across the capillary tube 42 within the probe 41 which arises correspondingly to the temperature of an atmosphere to be measured is detected as a pressure difference ΔPc between the pressure on the secondary side of a trim valve 43 and the pressure on the secondary side of the capillary tube 42. Thereafter, upon amplification of the pressure difference ΔPc by a fluidic element 44, it is detected as an electric signal by a pressure transducer 45. Such system is substantially similar in construction to a kind of electric circuit called Wheatstone bridge and, a slight fluctuation of the pressure drop at a sensitivity set valve 46, an amplifier supply valve 47 or the trim valve 43 exerts a large influence upon the pressure signal from the fluidic element 44. Accordingly, a change of state of the working fluid caused by an environmental temperature change results in fluctuation with respect to the pressure drop at each of the aforementioned valves 46, 47 and 43 and since this fact is, in appearance, regarded as the fluctuation of the pressure drop ΔP at the capillary tube 42 within the probe 41 i.e., a change in temperature detected by the probe 41, the temperature measuring apparatus of this kind has the disadvantage that it is liable to be subjected to the influence by the environmental temperature. In addition, in the aforementioned fluidic resistance type temperature measuring apparatus, when the probe 41 as the temperature-sensitive sensor is damaged, for example, it is cracked or a hole is accidentally made therein, so that the working fluid spills out or the atmosphere enters the probe 41, the signal outputted from the pressure transducer 45 is continuously outputted therefrom in a state where it does not correctly correspond to the temperature to be measured. The damage of the probe in the fluidic resistance type temperature measuring apparatus is substantially equivalent to a burnout of a thermocouple. However, although no signal is outputted in case of a burnout of the thermocouple, a wrong signal is continuously outputted in the fluidic resistance type temperature measuring apparatus. It is, therefore, difficult to detect the damage of the probe 41 and, in the case where the temperature is controlled through measurement thereof, for example, by the fluidic resistance type temperature measuring apparatus, the temperature is controlled undesirably to a value different from the predetermined one. This is another shortcoming of the fluidic resistance type temperature measuring apparatus. On the other hand, in the case where the temperature within the furnace is controlled, the temperature measurement is generally executed simultaneously at a plurality of locations within the furnace. Accordingly, when the aforementioned fluidic resistance type temperature sensor is employed in a multi-temperature measuring apparatus, it is considered, as shown in Fig. 2, that plural sets of the fluidic resistance type temperature sensors are connectively juxtaposed with each other, with the source S of supply of the working fluid and the pressure control device 40 being commonly used therein. Such construction, however, undesirably produces some new problems different from the aforementioned ones. A first problem is that since the environmental temperatures are different from each other at the locations or points where the amplifier supply valves 47, sensitivity set valves 46 and trim valves 43 generating the reference pressure drop are provided, all of which valves are located at the upstream side of each probe, the points to be measured in temperature undergo the influences by the environmental temperatures different from each other. In other words, there occur measurement errors of temperature different from each other at the points to be measured and this fact results in that it is, in fact, impossible to correct the measurement errors. A second problem is that it is impossible to supply the working fluid to each probe at the constant pressure. More specifically, the source S of supply of the working fluid and the pressure control device 40 are used commonly and therefore, since the pipings for supplying the working fluid towards each probe 41 therethrough inevitably become long, a pressure fluctuation is produced in the working fluid in the course of the pipings under the influence of the environmental temperature. As a result, this phenomenon causes the large measurement error in temperature. As shown in Fig. 3, it is possible to supply the working fluid towards each probe at the constant pressure, with the pressure fluctuation in the course of the pipings being restricted by pressure control devices 40a for correction use additionally provided immediately before each temperature sensor unit. However, since the pressure fluctuation on the primary side of each pressure control device 40a for correction use is large, the pressure can not be fully controlled thereby. Accordingly, not only the measurement error in temperature undesirably becomes large, but also a plurality of the pressure control devices for correction use are inevitably needed by the number corresponding to that of the points to be measured in temperature and the additional provision of some devices causes the temperature measuring apparatus to be manufactured undesirably at increased cost. This problem is the third one. A fourth problem is that in the multi-temperature measuring apparatus as shown in Fig. 2 or 3, since a plurality of the temperature sensor units are connectively juxtaposed with each other at the downstream side of the source S of supply of the working fluid, it is necessary to supply the working fluid at the constant pressure towards each unit, thus resulting in that the consumption of the working fluid is undesirably increased proportionately to the increased number of the points to be measured. Another device for measuring temperature and fugacity is known from the patent application US-A-4 264 423 comprising a solid electrolyte sensor, a passageway for a reference fluid in said sensor, said passageway including a capillary restriction, a first metallic conductor lead on the outside of the sensor, a second metallic conductor lead on the inside of the sensor in said passageway and opposite said first lead, and pressure drop means to measure the pressure drop of the reference fluid when flowing through said capillary, whereby pressure drop measurement permits determination of temperature of a material. The problem of such construction is that it is not capable of indicating a damage on condition of pressure drop and respectively the calculated and indicated temperature is not the real temperature of the material. SUMMARY OF THE INVENTION Accordingly, the present invention has been developed with a view to substantially eliminating the above described disadvantages inherent in the prior art apparatus for measuring temperature, and has for its essential object to provide an improved apparatus for measuring temperature, which is capable of measuring high temperatures without any influence upon a working fluid by the environmental temperature or the temperature of the working fluid. Another important object of the present invention is to provide the temperature measuring apparatus of the above described type which is capable of preventing a measurement error through detection of a damage of a temperature sensor. In accomplishing these and other objects, according to the embodiment of the present invention, there is provided a fluidic resistance type temperature measuring apparatus as defined in claim 1, including a source of supply of a working fluid, a temperature-sensing means having an external cylinder closed at its one end and an internal cylinder which is accommodated in the external cylinder and has a capillary tube at its forward end, a supply tube of the working fluid for introducing the working fluid from the source thereof into either the internal cylinder or the external cylinder, a pressure control device and a mass flow control device disposed in series in the course of the supply tube, a differential pressure gauge for detecting a pressure drop across the capillary tube, and a temperature operating means for calculating the temperature on the basis of a signal sent from the differential pressure gauge as well as damage detecting means for detecting damage of said temperature-sensing means. BRIEF DESCRIPTION OF THE DRAWINGS These and other objects and features of the present invention will become apparent from the following description taken in conjunction with the preferred embodiments thereof with reference to the accompanying drawings, throughout which like parts are designated by like reference numerals, and in which: Fig. 1 is a diagrammatic view of a conventional fluidic pyrometer (already referred to); Fig. 2 is a schematic view of one example of a multi-temperature measuring apparatus employing therein the fluidic pyrometer of Fig. 1 (already referred to); Fig. 3 is a view similar to Fig. 2, which particularly shows another example thereof (already referred to); Fig. 4 is a schematic view of a fluidic resistance type temperature measuring apparatus according to the present invention; Fig. 5 is a schematic view of a mass flow control device employed in the temperature measuring apparatus of Fig. 4; Fig. 6 is a graph showing a relation between a pressure drop across a capillary tube disposed within a temperature sensor employed in the temperature measuring apparatus of Fig. 4 and a temperature of the working fluid in the case where a liquid is employed as a working fluid; Fig. 7 is a graph similar to that of Fig. 6 in the case where a gas is employed as the working fluid; Fig. 8 is a graph similar to that of Fig. 7 in the case where Ar gas is employed as the working fluid, with a mass flow thereof being caused to be a parameter; Fig. 9 is a fragmentary sectional view of a probe employed as a temperature sensor, which provides the graph of Fig. 8; Fig. 10 is a view similar to Fig. 4 Fig. 11 is a schematic view of the fluidic resistance type temperature measuring apparatus of the present invention having a probe damage detecting means; Fig. 12 is a view similar to Fig. 11, which particularly shows another example of the probe damage detecting means; Fig. 13 is a view similar to Fig. 11, which particularly shows still another example of the probe damage detecting means; Fig. 14 is a view similar to Fig. 11, which particularly shows a further example of the probe damage detecting means; Fig. 15 is a schematic view of a multi-temperature detecting apparatus; Fig. 16 is a view similar to Fig. 15, which particularly relates to a modification thereof; Fig. 17 is a view similar to Fig. 4, which is further provided with a silencer as a fluidic resistance means at the downstream side of the working fluid; and Fig. 18 is a view similar to Fig. 17, which is provided with an accumulator in place of the silencer at the downstream side of the working fluid. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT Referring now to the drawings, there is shown in Fig. 4, a temperature measuring apparatus according to the present invention, which is provided with a probe 1 or a temperature sensor as a temperature-sensitive portion, a source S of supply of a working fluid for supplying the working fluid towards the probe 1, and the like. The probe 1 is composed of an internal cylinder 4 having, at its forward end, a capillary tube 2 which assumes a form of a throttle portion and an external cylinder 6 having one closed end. The probe 1 is set, for example, across a furnace wall F as shown in Fig. 4, to measure a temperature within the furnace. The source S of supply of the working fluid is connected with the internal cylinder 4 through a reducing valve 8, a pressure control device 9, a mass flow control device 10 and pipings 7 so that the highly pressurized working fluid may be supplied from the source S thereof into the internal cylinder 4 sequentially through the reducing valve 8, the pressure control device 9 and the mass flow control device 10. A first flow channel 3 of the working fluid is defined within the internal cylinder 4 and a second flow channel 5 thereof is formed between the internal cylinder 4 and the external cylinder 6. As shown in Fig. 5, the mass flow control device 10 includes a mass flowmeter 10-1, a valve-opening regulator 10-2 and a valve 10-3 so that the mass flow of the working fluid sequentially supplied from the source S thereof is detected by the mass flowmeter 10-1 to be compared with a predetermined value thereof in the valve-opening regulator 10-2 and thereafter, the regulator 10-2 controls the opening of the valve 10-3 in accordance with the comparison result in order to keep the mass flow rate constant. There is also provided a differential pressure gauge 11 connected with an inlet portion of the internal cylinder 4 and an outlet portion of the external cylinder 6 respectively through pressure detecting tubes 11a and 11b to detect a pressure drop ΔP across the capillary tube 2 within the probe 1. The differential pressure gauge 11 is further coupled to a temperature operator 12 for calculating the temperature in accordance with an output signal from the differential pressure gauge 11, with the temperature operator 12 being also coupled to a temperature indicator 13 for indicating the temperature. The temperature within the furnace is measured through detection of the aforementioned pressure drop ΔP by the differential pressure gauge 11, as will be described in detail hereinbelow. In the next place, a method of measuring temperature will be explained hereinafter with the use of the temperature measuring apparatus having the above described construction. A highly pressurized working fluid such as Ar gas or the like is initially supplied from the source S of supply of the working fluid. The working fluid supplied from the source S thereof is reduced in pressure down to a predetermined value by the reducing valve 8 and the pressure control device 9 and is then supplied into the first channel 3 i.e., the internal cylinder 4 within the probe 1 at a constant rate Q of the mass flow effected by the mass flow control device 10. The working fluid supplied into the probe 1 at the constant mass flow rate Q is discharged to the atmosphere from a discharge port 6a of the external cylinder 6 through the capillary tube 2 of the internal cylinder 4. At this moment, the pressure drop ΔP arises at the portion of the capillary tube 2 and is calculated as follows with the use of the temperature T within the probe 1, the inner diameter d and the length ℓ of the capillary tube 2 at the temperature T, and the viscosity coefficient µ(T) and the density ρ(T) of the working fluid at the same temperature. More specifically, the following Hagen-Poiseuille equation is established with respect to a volumetric flow rate Qv flowing within the capillary tube 2. In addition, the following equation (3) is established between the volumetric flow rate Qv and the mass flow rate Q. Q = ρ(T)·Qv (3) Accordingly, the equation (1) can be obtained. Besides, when the kinematic viscosity of the working fluid is represented by ν(T), ν(T) = µ(T)/ρ(T). (4) Therefore, the equation (1) is derived as follows. Consequently, when a fluid such as Ar gas or the like which is known by its temperature dependent state change is employed as the working fluid, since ν(T) is known and the mass flow rate Q is constant, ΔP is represented as a function of temperature T, thus resulting in that the temperature T can be made known through detection of ΔP i.e., the differential pressure between a pressure P1 within the first channel 3 and another pressure P2 at the discharge port 6a of the working fluid by the differential pressure gauge 11. The temperature dependence of the kinematic viscosity ν(T) is generally extremely large as compared with the change of the inner diameter or the length of the capillary tube caused by thermal expansion thereof. Accordingly, there is practically little problem in considering from the equation (5) that ΔP is substantially dependent upon ν(T). It is to be noted that although the working fluid may be either a gas or a liquid, the gas is superior to the liquid in resolving power with respect to temperature, since the former is generally highly dependent upon the temperature as compared with the latter. As a rule, the kinematic viscosity of the liquid decreases, as the temperature rises and on the contrary, the kinematic viscosity of the gas increases, as the temperature rises. Accordingly, the relation between the pressure drop ΔP and the temperature is graphically shown in Fig. 6 in the case where a liquid is employed as the working fluid or in Fig. 7 in the case where a gas is employed as the working fluid. Fig. 8 graphically shows one example of the latter in which the mass flow rate Q of the working fluid is made a parameter on condition that the capillary tube 2 within the probe 1 is made up of tungsten having a thermal expansion coefficient of 20 x 10⁻⁶/°C and the inner diameter d and the length ℓ thereof are respectively 0.76 mm and 13 mm at a temperature of 0 °C, as shown in Fig. 9, with Ar gas being employed as the working fluid. Since the pressure drop ΔP becomes more highly dependent upon the temperature, as the mass flow rate Q increases, it appears that the temperature measuring apparatus is improved both in temperature resolving power and in accuracy. However, when the flow exceeds an appropriate amount thereof, the heat transfer within the probe 1 can not follow the flow and the temperature difference between the fluid and the atmosphere within the furnace becomes large, thus resulting in that the temperature of the atmosphere can not be correctly indicated. Accordingly, since the flow of the working fluid would be inevitably restricted up to its upper limit which largely depends upon the construction, configuration and dimensions of the probe 1, those of the probe 1 are required to be determined experimentally. Fig. 10 shows the temperature measuring apparatus according to a second embodiment of the present invention, in which the working fluid is supplied into the second channel 5 formed between the internal cylinder 4 and the external cylinder 6 of the probe 1 and is then led into the first channel 3 within the internal cylinder 4 through the capillary tube 2 to be discharged from the probe 1. The pressure drop ΔP across the capillary tube 2 which is an output of the temperature measuring apparatus of the fluidic resistance type, is determined by the temperature of the working fluid in the capillary tube 2, as described hereinabove. In view of only this fact, if the inside of the probe 1 decreases in thermal resistance, the temperature measurement is feasible, as long as the measurement is performed with respect to a steady temperature or a gradual change of the temperature, in the case where the working fluid is caused to flow from the internal cylinder 4 towards the external cylinder 6, as shown in Fig. 4, as well as in the case shown in Fig. 10. In the case shown in Fig. 4, however, since there exists the second channel 5 i.e., the discharge channel of the working fluid between the first channel 3 and the external cylinder 6 of the probe 1, the temperature measuring apparatus of this kind decreases in response characteristic. Accordingly, when there exists a rapid change of the temperature within the furnace, it is to be desired that the working fluid is caused to flow as shown in Fig. 10. In Fig. 11, the temperature measuring apparatus of the fluidic resistance type is further provided with a probe damage detecting means 15a which includes a differentiation circuit 16, a comparative operation processing circuit 17a and a warning means 18, all of which are sequentially connected with one another in this order, with the differentiation circuit 16 being also coupled with the differential pressure gauge 11. The differentiation circuit 16 differentiates a signal of the pressure drop ΔP sent from the differential pressure gauge 11 with respect to time, to calculate a fluctuating rate of the pressure drop ΔP and thereafter, upon comparison of the fluctuating rate with a predetermined reference fluctuating rate by the comparative operation processing circuit 17a, if the pressure drop ΔP is abnormal in its fluctuating rate, an "abnormal" signal is emitted from the comparative operation processing circuit 17a to effect the warning means 18 to emit the warning. Subsequently, an operating principle of the probe damage detecting means 15a will be explained hereinbelow by way of example with reference to the temperature measuring apparatus of Fig. 11. A consideration will be given with respect to a case where the external cylinder 6 of the probe 1 has been damaged on condition that the pressure within the furnace is higher than the pressure within the probe 1. Since the pressure P0 within the furnace is higher than the pressure P1 within the probe 1, a part of the gas which forms the atmosphere within the furnace flows into the probe 1 and pass through the capillary tube 2, together with the working fluid As a result, since the pressure drop ΔP detected by the differential pressure gauge 11 instantaneously increases simultaneously with the damage of the probe 1, the fluctuating rate thereof in this event is greater than the fluctuating rate corresponding to the fluctuation of the temperature within the furnace. More specifically, supposing that the temperature within the furnace fluctuates instantaneously from T1 to T2, the pressure drop ΔP12 produced through the capillary tube 2 of the probe 1 is detected with time lag represented by a time t1 required for the external surface of the external cylinder 6 of the probe 1 to turn from T1 to T2 in temperature, a time t2 required for the internal surface of the external cylinder 6 to become T2 in temperature and a time t3 required for the working fluid to become T2 in temperature. The time lags t1 and t3 undergo great influences respectively by components, pressure, flow condition or the like of the atmosphere and by the pressure, flow condition or the like of the working fluid and accordingly, it is actually difficult to forecast or recognize these time lags t1 and t3. On the contrary, the time lag t2 can be substantially estimated by the following equation, since a thermal transfer coefficient α and the wall thickness w of the probe 1 are known. t2 = w/16α (6) Accordingly, the fluctuating rate of the aforementioned pressure drop ΔP12 can be expressed by the following equation (7), when the pressure drops corresponding to the temperatures T1 and T2 within the furnace are represented respectively by ΔP1 and ΔP2. The equation (7) means that the fluctuating rate of the pressure drop detected by the differential pressure gauge 11 does not exceed at least unless the probe 1 has been damaged. On the other hand, when ΔPmax and ΔPmin respectively represents the pressure drops corresponding to the upper temperature limit Tmax and the lower temperature limit Tmin within the measuring range of temperature detectable by the temperature measuring apparatus of the fluidic resistance type, the fluctuating rate of the pressure drop detected by the temperature measuring apparatus can be expressed as follows. Hereupon, the predetermined reference fluctuating rate is represented by in accordance with the aforementioned equation (8) and the output signal from the differential pressure gauge 11 is differentiated with respect to time by the differentiation circuit 16 so that the fluctuating rate of the detected pressure drop may be obtained. Thereafter, upon comparison of the fluctuating rate of the detected pressure drop with the predetermined reference fluctuating rate in the comparative operation processing circuit 17a, when the former is greater than the latter i.e., it is judged that the probe 1 has been damaged and the "abnormal" signal is emitted to cause the warning means to emit the warning. Conversely, an explanation will be made hereinafter in the case where the pressure P0 within the furnace is lower than the pressure P1 within the probe 1. At the same time when the external cylinder 6 of the probe 1 has been damaged, a part of the working fluid having entered the probe 1 flows out therefrom into the furnace. As a result, the pressure drop ΔP detected by the differential pressure gauge 11 rapidly decreases simultaneously with the damage of the probe 1 and the fluctuating rate of the detected pressure drop in this event is greater than the predetermined reference fluctuating rate as described so far. In the same manner as described above, the output signal from the differential pressure gauge 11 is differentiated with respect to time by the differentiation circuit 16 so that the fluctuating rate of the detected pressure drop may be obtained and thereafter, upon comparison of the fluctuating rate with the predetermined reference fluctuating rate in the comparative operation processing circuit 17a, if the former is greater than the latter, it is judged that the probe 1 has been damaged and the "abnormal" signal is emitted to cause the warning means 18 to emit the warning. Accordingly, in the case where the following equation is established, the warning is emitted from the warning means 18. It is to be noted that although the differentiation circuit 16 is coupled to the differential pressure gauge 11 in the temperature measuring apparatus of Fig. 11, the probe damage detecting means 15b may be provided with the differentiation circuit 16 coupled to the temperature operator 12, as shown in Fig. 12. Also, in this case, after the detected pressure drop ΔP has been converted into temperature by the temperature operating means 12, the temperature signal is inputted into the differentiation circuit 16 so that a fluctuating rate of the operated temperature may be calculated instead of that of the detected pressure drop ΔP. Thereafter, upon comparison of the calculated fluctuating rate of the calculated temperature with a reference fluctuating rate thereof in the comparative operation processing circuit 17a, the damage of the probe 1 can be readily detected. It is also to be noted that the predetermined reference fluctuating rate is not limited by that described so far on the basis of the measuring apparatus of the present invention, but the fluctuating rate of the pressure drop, temperature or the like corresponding to, for example, a heat curve of a material to be treated may be appropriately selected as the reference fluctuating rate. Moreover, as shown in Fig. 13, the measuring apparatus may be modified such that the probe damage detecting means 15c is provided with a mass flowmeter 20 for detecting the mass flow of the working fluid on the discharge side of the working fluid of the probe 1 and the comparative operation processing circuit 17b coupled to both of the mass flowmeter 20 and the aforementioned mass flowmeter 10-1 of the mass flow control device 10, and the damage of the probe 1 is detected through comparison, in the comparative operation processing circuit 17b, between the mass flows of the working fluid on the supply side and on the discharge side of the working fluid of the probe 1 i.e., the flow signal from the mass flow control device 10 and that from the mass flowmeter 20. In other words, when the probe 1 is functioning as intended, both flow signals are coincident with each other and on the contrary, when the probe 1 has been damaged, they are inevitably discrepant from each other. Accordingly, when the discrepancy has been detected in the comparative operation processing circuit 17b, the "abnormal" signal is emitted therefrom to cause the warning means 18 to emit the warning. In addition, the apparatus may be further modified such that the probe damage detecting means comprises a first probe damage detecting portion for detecting the damage of the probe 1 by the change of the fluctuating rate of the pressure drop ΔP or the temperature and a second probe damage detecting portion for detecting the damage of the probe 1 by the discrepancy between the mass flows. There is shown in Fig. 14, one example of the probe damage detecting means 15d having the first probe damage detecting portion i.e., the probe damage detecting means 15a and the second probe damage detecting portion i.e., the probe damage detecting means 15c, wherein a couple of solenoid valves 21 and 22 are disposed respectively on the supply side and on the discharge side of the working fluid of the probe 1 so as to be closed on the occasion of the damage of the probe 1. It should be noted that although either of the probe damage detecting means 15a, 15b, 15c and 15d described so far is employed in the temperature measuring apparatus having the probe 1 in which the working fluid flows from the external cylinder 6 towards the inside of the internal cylinder 4, the working fluid may be caused to flow, within the probe 1, from the inside of the internal cylinder 4 towards the external cylinder 6, as shown in Fig. 4 and also in this case, the damage of the probe 1 can be detected by either the "abnormal" pressure or the "abnormal" mass flow rate in the same manner as described above. Fig. 15 illustrates a multi-temperature measuring apparatus. The multi-temperature measuring apparatus of Fig. 15 is provided with five probes comprising a first, a second, a third , a fourth and a fifth proves 1-1, 1-2, 1-3, 1-4 and 1-5 as the temperature-sensitive sensors, which probes are connected with one another in series. More specifically, each probe 1-1, 1-2, 1-3 or 1-4 exclusive of the fifth probe 1-5 is connected, at its discharge port 6a of the working fluid which is the outlet portion of the external cylinder 6 of the probe 1-1, 1-2, 1-3 or 1-4, with the supply port 4a of the working fluid of the adjacent probe 1-2, 1-3, 1-4 or 1-5 which port is the inlet portion of the internal cylinder 4 thereof, with the supply port 4a of the working fluid of the first probe 1-1 being coupled to a supply tube or piping 7 for supplying the working fluid therethrough into the first probe 1-1 and the discharge port 6a of the working fluid of the fifth probe 1-5 being open to the atmosphere. By the aforementioned arrangement, the working fluid is caused to flow at the constant mass flow rate from the source S of supply of the working fluid towards the internal cylinder 4 of the first probe 1-1 sequentially through the reducing valve 8, the pressure control device 9, the mass flow control device 10 and the supply piping 7 of the working fluid. Each one differential pressure gauge 11-1, 11-2, 11-3, 11-4 or 11-5 is coupled to the supply port 4a of the working fluid of the corresponding probe 1-1, 1-2, 1-3, 1-4 or 1-5 and to the discharge port 6a thereof respectively through the pressure detecting tubes 11a and 11b to directly detect the pressure drop ΔP across the capillary tube 2 within each probe 1, with the pressure signals sent from the differential pressure gauges 11-1, 11-2, 11-3, 11-4 and 11-5 being applied to the temperature operating means 12. The temperature measurement by the apparatus having the above described construction will be explained hereinafter. The working fluid, for example, Ar gas or the like is initially supplied from the source S of supply of the working fluid. The working fluid supplied is not only reduced in pressure down to the predetermined value through the reducing valve 8 but also simultaneously controlled so as to be held at the constant pressure through the pressure control device 9. In this state, the working fluid is further supplied towards the supply port 4a of the working fluid of the first probe 1-1 at the constant mass flow rate Q through the mass flow control device 10 and thereafter, it passes through the capillary tube 2 to be discharged from the discharge port 6a of the working fluid of the first probe 1-1. In this event, since the pressure drop ΔP1 arises at the capillary tube 2, upon detection of the pressure drop ΔP1 by the differential pressure gauge 11-1, the temperature T1 of the atmosphere at a location where the first probe 1-1 is provided is calculated by the temperature operating means 12 in accordance with the detected result. The working fluid discharged from the discharge port 6a of the working fluid of the first probe 1-1 is then supplied into the second probe 1-2 from the supply port 4a thereof and passes through the capillary tube 2 within the second probe 1-2 to be discharged from the discharge port 6a thereof. Also in this event, the capillary tube 2 within the probe 1-2 produces the pressure drop ΔP2 and the temperature T2 of the atmosphere at a location where the second probe 1-2 is provided is detected through operation of the pressure drop ΔP2, in the same way as in case of the first probe 1-1. Henceforth, the temperature measurement through detection of the pressure drop at the capillary tube is repeated until the working fluid has passed through the capillary tube 2-5 of the last probe i.e., the fifth probe 1-5 in the arrangement shown in Fig. 15. The working fluid passed through each probe 1-1, 1-2, 1-3, 1-4 or 1-5 one by one is finally discharged to the atmosphere from the discharge port 6a of the fifth probe 1-5. As described so far, according to the construction of the multi-temperature measuring apparatus, since the pressure drop ΔP across the capillary tube 2 depends only upon the temperature of the working fluid at the time when the working fluid passes therethrough, the pressure drop ΔP never undergoes any influence by a progress of the temperature or pressure of the working fluid before it enters any one probe, the material, quality of the material or configuration of the probe, the environmental temperature around the material, the atmospheric pressure or the like. In other words, even if the working fluid has passed through a plurality of probes previously, this fact never exerts any influence upon the pressure drop of the working fluid at the time when it passes through the next probe. Accordingly, not only the correct temperature measurement can be executed, but also a plurality of the temperature measurements corresponding to the number of the probes can be sequentially executed by provision of the needed number of the probes at the locations required for the measurements. In Fig. 16, there are additionally provided five three-way valves 23, five on-off valves 24-1, 24-2, 24-3, 24-4 and 24-5 and five by-pass valves 25-1, 25-2, 25-3 25-4 and 25-5 including necessary pipings in the multi-temperature measuring apparatus shown in Fig. 15. Even when only the second probe 1-2 has been damaged or intentionally out of use, for example, the temperature measurement can be continued without any influence upon the other probes 1-1, 1-3, 1-4 and 1-5. It is to be noted that the multi-temperature measuring apparatus shown in Fig. 16 may be further provided with the aforegoing probe damage detecting means 15a, 15b, 15c or 15d for detecting the damage of any probe 1-1, 1-2, 1-3, 1-4 or 1-5. In this case, when the damage of any probe has been detected, the above described on-off valve, the by-pass valve and the three-way valve corresponding to the probe subjected to the damage are operated by the signal sent from the comparative operation processing circuit 17a or 17b. It is also to be noted that in either of the embodiments described so far, the pressure detecting tube 11b on the low pressure side is connected to the differential pressure gauge 11 and might be open to the atmosphere in case of the fluctuation of the atmospheric pressure including that caused by any noise being negligibly small or extremely slow in fluctuating rate. It is further to be noted that there may be provided a resistance means 30 such as a silencer producing a large flow resistance, as shown in Fig. 17, or an accumulator 31 for once accumulating therein the working fluid to be discharged, as shown in Fig. 18. In either of these two cases in contrast with the aforementioned case, even when the atmospheric pressure violently fluctuates, a hunting phenomenon hardly takes place with respect to the output from the measuring apparatus. As for the hunting, not only it can be physically restricted in a manner as shown in rig. 17 or 18, but also it may be electrically eliminated in a manner that the electric signal picked up from the differential pressure gauge 11 is caused to pass through a filter circuit. As clearly shown in the description made so far, the working fluid is supplied at a constant mass flow rate into a flow channel defining a throttle portion at a temperature-sensitive portion thereof and upon measurement of a pressure difference between opposite ends of the throttle portion, the temperature can be recognized through calculation of the measured pressure difference. Furthermore, according to the temperature measuring apparatus of the present invention, there are provided a source of supply of a working fluid, a temperature-sensitive means having an external cylinder closed at its one end and an internal cylinder which is accommodated in the external cylinder and has a capillary tube at its forward end, a supply piping of the working fluid for introducing the working fluid from the source thereof into either the internal cylinder or the external cylinder, a pressure control device and a mass flow control device disposed in series in the course of the supply piping, a differential pressure gauge for detecting a pressure drop across the capillary tube, and a temperature operating means for operating the temperature on the basis of a signal sent from the differential pressure gauge as well as damage detecting means for detecting damage of the temperature-sensitive means. Consequently, by making use of the apparatus of the invention, it is possible to achieve the temperature measurement with high reliability even at a high temperature in a range from 1500 to 3000 °C, without any influence by the environmental temperature or the temperature of the working fluid, notwithstanding the apparatus is simple in construction. Besides, as a probe damage detecting means for detecting the damage of the probe is additionally provided, since the damage of the probe can be readily detected, an erroneous measurement can be advantageously prevented.

Claims: A fluidic resistance type temperature measuring apparatus comprising a source (S) of supply of a working fluid; a temperature-sensitive means (1) having an external cylinder (6) closed at its one end and an internal cylinder (4) accommodated in said external cylinder (6) and having a capillary tube (2) at one end thereof; a supply tube (7) of said working fluid for introducing said working fluid from said source (S) into one of said external cylinder (6) and said internal cylinder (4); a pressure control means (9) disposed in the course of said supply tube (7); a mass flow control means (10) disposed in the course of said supply tube (7) in series with said pressure control means (9); a differential pressure gauge (11) for detecting a pressure drop across said capillary tube (2); an operating means (12) for calculating the temperature on the basis of a signal sent from said differential pressure gauge (11); characterized by a damage detecting means (15a; 15b; 15d) for detecting damage of said temperature-sensitive means (1), said damage detecting means (15a; 15b; 15d) comprising means (16) for calculating a fluctuating rate of an output signal from said differential pressure gauge (11) and means (17a) for judging whether or not said temperature-sensitive means (1) is functioning as intended by comparing the calculated fluctuating rate with a predetermined reference fluctuating rate.

Inventors: HIGETA, KAZUYA, MURAKAMI, KOJI, TOUCHI, HACHIRO
Applicants: CHUGAI RO CO., LTD.
Application year: 1987
Main classification: G01K11
IPC codes: G01K1, G01K11