Method of measuring temperature and apparatus for effecting the method

In a method and apparatus for measuring temperature by using a state change of a working fluid, a temperature measurement is executed in a manner such that the working fluid is initially supplied at a constant mass flow rate into a flow channel having a throttle portion at a temperature-sensitive portion. Upon the measurement of a pressure difference between opposite ends of the throttle portion, the temperature can be determined through a calculation using the measured pressure difference. The temperature measuring apparatus includes a source of a working fluid and a probe. The probe includes an external cylinder closed at one of its ends and an internal cylinder which is accommodated in the external cylinder and has a capillary tube at its forward end. The apparatus further includes a supply tube for introducing the working fluid from the source into either the internal cylinder or the external cylinder, and a pressure control device. A mass flow control device is further disposed in series with the supply tube to control the mass flow rate. A differential pressure gauge for detecting a pressure drop across the capillary tube and a temperature determining device for determining the temperature in accordance with a signal output from the differential pressure gauge is included in the temperature measuring apparatus.

BACKGROUND OF THE INVENTION 
The present invention generally relates to a method of measuring 
temperature and an apparatus employed for accomplishing this method, and 
more particularly, to a method and 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 stage 
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, such thermometers are 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 a 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 the 
working fluid at a constant pressure through a pressure control device 40. 
The pressure drop .DELTA.P across the capillary tube 42 within the probe 
41 which arises in correspondance with the temperature of an atmosphere to 
be measured is detected as a pressure difference .DELTA.Pc 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 .DELTA.Pc by a fluidic element 44, the pressure 
difference is detected as an electric signal by a pressure transducer 45. 
Such a system is substantially similar in construction to a kind of 
electric circuit called a 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 state change of the working 
fluid caused by an environmental temperature causes the fluctuation with 
respect to the pressure drop at each of the aforementioned valves 46, 47 
and 43. Since this fact is, in appearance, regarded as a fluctuation of 
the pressure drop .DELTA.P at the capillary tube 42 within the probe 41, 
i.e. a change in temperature detected by tne probe 41, the temperature 
measuring apparatus of this kind has a disadvantage because it can be 
subjected to the influence of 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 in 
it causing the working fluid to spill out or the atmosphere to enter the 
probe 41, the signal outputted from the pressure transducer 45 will 
continuously output a signal that does not correctly correspond to the 
temperature being measured. 
The damage of the probe in the fluidic resistance type temperature 
measuring apparatus is substantially equivalent to burnout with respect to 
the thermocouple. However, although no signal is outputted in the case of 
burnout, the 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 its measurement, for example, by the 
fluidic resistance type temperature measuring apparatus, the temperature 
will be 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 the 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 between them. Such construction, 
however, undesirably produces some new problems different from the 
aforementioned ones. 
A first problem is that since the environmental temperatures are different 
for each of 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 these valves being located at the 
upstream side of each probe, the points to be measured in temperature 
undergo influences by the environmental temperatures which differ from 
each other. In other words, there occur measurement errors because of the 
temperature difference from one location to another measurement location 
making it impossible to correct the measurement errors. 
A second problem is that it is impossible to supply the working fluid to 
each probe at a constant pressure. More specifically, the source S of the 
working fluid and the pressure control device 40 are commonly used, and 
therefore, since the pipings for supplying the working fluid to each probe 
41 is inevitably long, a pressure fluctuation is produced in the working 
fluid while in the pipings because of the influence of the environmental 
temperature. As a result, this phenomenon causes a large measurement error 
in temperature. 
As shown in FIG. 3, it is possible to supply the working fluid to each 
probe at the constant pressure, by restricting the pressure fluctuation 
occurring in the pipings being restricted. This restriction is 
accomplished by using additional correcting pressure control devices 40a 
for provided immediately before each temperature sensor unit. However, 
since the pressure fluctuation on the primary side of each pressure 
control device 40a is large, the pressure cannot be fully controlled. 
Accordingly, not only the measurement error in temperature becomes 
undesirably large, but also a plurality of the pressure control devices 
for correction use are inevitably needed. The number of these extra 
pressure control devices needed corresponds to the number of points used 
to measure temperature. These additional devices cause the temperature 
measuring apparatus to be manufactured at an undesirably increased cost, 
thereby causing the third problem. 
A fourth problem is that since the multi-temperature measuring apparatus as 
shown in FIG. 2 or 3 has a plurality of the temperature sensor units that 
are juxtaposely connected with each other at the downstream side of the 
source S of the working fluid, it is necessary to supply the working fluid 
at a constant pressure to each unit, thereby causing the consumption of 
the working fluid to undesirably increase proportionately to the increased 
number of the points used for measuring. 
SUMMARY OF THE INVENTION 
Accordingly, the present invention has been developed to substantially 
eliminate the above described disadvantages inherent in the prior art 
method and apparatus for measuring temperature, and has for its essential 
objective to provide an improved method and apparatus for measuring 
temperature which is capable of measuring high temperatures without any 
influence upon a working fluid caused by the environmental temperature or 
the temperature of the working fluid. 
Another important objective of the present invention is to provide the 
temperature measuring apparatus of the above described type which is 
capable of preventing a measurement error by detecting if a temperature 
sensor is damaged. 
A further objective of the present invention is to provide the temperature 
measuring apparatus of the above described type which is capable of 
sequentially measuring high temperatures, with excellent accuracy, at a 
plurality of locations, while utilizing the working fluid effectively. 
In accomplishing these and other objectives, according to one preferred 
embodiment of the present invention, there is provided a method of 
measuring temperature through a change of state of a fluid. This method 
includes the steps of supplying a working fluid at a constant mass flow 
rate into a flow channel, defining a throttle portion in the flow channel 
at a temperature-sensitive portion, measuring a pressure difference 
between opposite ends of the throttle portion, and calculating the 
temperature from the measured pressure difference. 
In another embodiment of the present invention, there is provided a fluidic 
resistance type temperature measuring apparatus including a source of a 
working fluid; a probe having an external cylinder closed at one of its 
ends, and an internal cylinder which is accommodated in the external 
cylinder, and a capillary tube at the internal cylinder's forward end; a 
supply tube of the working fluid for introducing the working fluid from 
the source into either the internal cylinder or the external cylinder; a 
pressure control device and a mass flow control device disposed in series 
with the supply tube; a differential pressure gauge for detecting a 
pressure drop across the capillary tube, and a temperature calculating 
means for operating the temperature on the basis of a signal sent from the 
differential pressure gauge. 
In a further embodiment of the present invention, a fluidic resistance type 
temperature measuring apparatus includes a source of a working fluid; a 
plurality of probe connected in series with each other; each probe having 
an external cylinder closed at one of its ends, and an internal cylinder 
which is accommodated in the external cylinder, and a capillary tube at 
the internal cylinder's forward end; a supply tube of the working fluid 
connected to a first probe to introduce the working fluid from the source 
into the first probe; a pressure control device and a mass flow control 
device disposed in series with of the supply tube; a plurality of 
differential pressure gauges, each gauge corresponding to each probe to 
detect a pressure drop across the capillary tube; and a temperature 
operating means for calculating the temperatures on the basis of signals 
sent from each respective differential pressure gauges.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
Referring now to the drawings, there is shown in FIG. 4, a temperature 
measuring apparatus according to a first embodiment of the present 
invention, which is provided with a probe 1 or a temperature sensor as a 
temperature-sensitive portion; a source S of a working fluid for supplying 
the working fluid to 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 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 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 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 
is detected by the mass flowmeter 10-1 to be compared with a predetermined 
value in th valve-opening regulator 10-2. The regulator 10-2, then 
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 through pressure detecting tubes 11a and 11b 
respectively to detect a pressure drop .DELTA.P 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. 
The temperature operator 12 is 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 .DELTA.P by 
the differential pressure gauge 11, as will be described in detail below. 
A method for measuring the temperature will be explained below with the use 
of the temperaure 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 the working fluid. The working fluid 
supplied from the source S is reduced in pressure down to a predetermined 
value by the reducing valve 8 and the pressure control device 9. The gas 
is then supplied to the first channel 3, i.e. the internal cylinder 4 
within the probe 1 at a constant rate of mass flow Q caused by the mass 
flow control device 10. 
The working fluid supplied to 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 .DELTA.P arises at the portion of the 
capillary tube 2. The pressure drop is calculated in the below equation by 
having 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 .mu.(T) and the density .rho.(T) of the working fluid at the 
same temperature. 
##EQU1## 
More specifically, the following Hagen-Poiseuille equation is established 
with respect to a volumetric flow rate Qv flowing within the capillary 
tube 2. 
##EQU2## 
In addition, the following equation (3) is established between the 
volumetric flow rate Qv and the mass flow rate Q. 
EQU Q=.rho.(T).multidot.Qv (3) 
Accordingly, the equation (1) can be obtained. 
Besides, when the kinematic viscosity of the working fluid is represented 
by .nu.(T), 
EQU .nu.(T)=.mu.(T)/.rho.(T). (4) 
the equation (1) is derived as follows. 
##EQU3## 
Consequently, when a fluid such as Ar gas or the like which change in state 
is known by temperature is employed as the working fluid, and since 
.nu.(T) is known and the mass flow rate Q is constant, .DELTA.P is 
represented as a function of temperature T, thus resulting in that the 
temperature T can be calculated through detection of .DELTA.P 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 on the 
kinematic viscosity .nu.(T) is generally extremely large as compared with 
a change in the inner diameter or the length of the capillary tube caused 
by a thermal expansion. Accordingly, there is practically little problem 
in considering from the equation (5) that .DELTA.P is substantially 
dependent upon .nu.(T). 
It is 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 .DELTA.P and 
the temperature is graphically shown in FIG. 6 in the case where the 
liquid is employed as the working fluid or in FIG. 7 in the case where the 
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.times.10.sup.-6 /.degree.C. and the inner diameter d and the length l 
are, respectively, 0.76 m and 13 mm at a temperature of 0.degree. C. as 
shown in FIG. 9 with Ar gas being employed as the working fluid. Since the 
pressure drop .DELTA.P 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, the heat 
transfer within the probe 1 does not correspond to the flow, and the 
temperature difference between the fluid and the atmosphere within the 
furnace becomes large, thus causing an incorrect temperature of the 
atmosphere to be indicated. Accordingly, since the flow of the working 
fluid would be inevitably restricted at its upper limit which largely 
depends upon the construction, configuration and dimensions of the probe 
1, these limits 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 to the second channel 5 formed between the internal cylinder 4 
and the external cylinder 6 of the probe 1 and is then fed 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 .DELTA.P 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 above. 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 its response characteristic. 
Accordingly, when there exists a rapid change of the temperature within 
the furnace, it is 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 also being coupled with the differential pressure gauge 11. The 
differentiation circuit 16 differentiates a signal representing the 
pressure drop .DELTA.P sent from the differential pressure gauge 11 with 
respect to time to calculate a fluctuating rate of the pressure drop 
.DELTA.P. Upon comparing the fluctuating rate with a predetermined 
reference fluctuating rate using a comparative operation processing 
circuit 17a, if the pressure drop .DELTA.P has an abnormal fluctuating 
rate, an abnormal signal is emitted from the comparative operation 
processing circuit 17a to cause warning means 18 to emit the warning. 
An operating principle of the probe damage detecting means 15a will be 
explained below, by way of example, with reference to the temperature 
measuring apparatus of FIG. 11. 
Consideration will be given with respect to a case where the external 
cylinder 6 of the probe 1 has been damaged from the 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 
.DELTA.P detected by the differential pressure gauge 11 instantaneously 
increases simultaneously with the damage to the probe 1, the fluctuating 
rate d.DELTA.P/dt will become 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 .DELTA.P12 
produced through the capillary tube 2 of the probe 1 is detected with a 
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 are influenced greatly 
by the 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 making it 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 
.alpha. and the wall thickness w of the probe 1 are known. 
EQU t2=w/16.alpha. (6) 
Accordingly, the fluctuating rate .DELTA.P12/dt of the aforementioned 
pressure drop .DELTA.P12 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 .DELTA.P1 and .DELTA.P2. 
##EQU4## 
The equation (7) means that the fluctuating rate 
##EQU5## 
of the pressure drop detected by the differential pressure gauge 11 does 
not exceed at least 
##EQU6## 
unless the probe 1 has been damaged. 
On the other hand, when .DELTA.Pmax and .DELTA.Pmin respectively represents 
the pressure drop corresponding to the upper temperature limit Tmax and 
the lower temperature limit Tmin within the temperature measuring range of 
the temperature measuring apparatus of the fluidic resistance type, the 
fluctuating rate 
##EQU7## 
of the pressure drop detected by the temperature measuring apparatus can 
be expressed as follows: 
##EQU8## 
The predetermined reference fluctuating rate is represented by 
##EQU9## 
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 
##EQU10## 
of the detected pressure drop may be obtained. Upon comparing 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. 
##EQU11## 
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. 
An explanation will be made below in the case where the pressure PO within 
the furnace is lower than the pressure P1 within the probe 1. 
When the external cylinder 6 of the probe 1 has been damaged as described 
above, a part of the working fluid having entered the probe 1 flows into 
the furnace. As a result, the pressure drop .DELTA.P detected by the 
differential pressure gauge 11 rapidly decreases simultaneously with the 
damage of the probe 1 and the fluctuating rate 
##EQU12## 
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 
##EQU13## 
of the detected pressure drop may be obtained. Upon comparing the 
fluctuating rate 
##EQU14## 
with the predetermined reference fluctuating rate 
##EQU15## 
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. 
##EQU16## 
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 .DELTA.P 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 operating 
temperature may be calculated instead of the detected pressure drop 
.DELTA.P. Upon comparing the calculated fluctuating rate of the operating 
temperature with a reference fluctuating rate in the comparative operation 
processing circuit 17a, the damage of the probe 1 can be readily detected. 
It is also 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, it 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 
above-mentioned mass flowmeter 10-1 of the mass flow control device 10. 
The damage of the probe 1 is detected by comparing, in the comparative 
operation processing circuit 17b, the mass flow of the working fluid on 
the supply side and the mass flow 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 undamaged, both flow signals coincide with each other. On the 
contrary, when the probe 1 has been damaged, they inevitably disagree with 
each other. Accordingly, when the discrepancy has been detected in the 
comparative operation processing circuit 17b, the abnormal signal is 
emitted 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 detecting the change of the 
fluctuating rate of the pressure drop .DELTA.P or the temperature and a 
second probe damage detecting portion for detecting the damage of the 
probe 1 by detecting 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 close on the 
occasion when the probe 1 is damaged. 
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. 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 on the basis of 
the method of measuring temperature according to the present invention. 
The multi-temperature measuring apparatus of FIG. 15 is provided with five 
probe comprising a first, a second, a third, a fourth and a fifth probe 
1-1, 1-2, 1-3, 1-4 and 1-5, as the temperature-sensitive sensors, where 
the 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. The supply port 4a of the working fluid of the first probe 1-1 
is coupled to a supply tube or piping 7 for supplying the working fluid to 
the first probe 1-1 and the discharge port 6a of the working fluid of the 
fifth probe 1-5 is open to the atmosphere. In the above-mentioned 
arrangement, the working fluid is caused to flow at the constant mass flow 
rate from the source S of the workig 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 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 of these probes, respectively through the pressure 
detecting tubes 11a and 11b to directly detect the pressure drop .DELTA.P 
across the capillary tube 2 within each 1. The pressure signals sent from 
the differential pressure gauges 11-1, 11-2, 11-3, 11-4 and 11-5 are 
applied to the temperature operating means 12. 
The operation of temperature measurement using the apparatus having the 
above described construction will be explained below. 
The working fluid, for example, Ar gas or the like, is initially supplied 
from the source S of the working fluid. The working fluid supplied is not 
only reduced in pressure 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 to 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. It passes then 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 .DELTA.P1 arises at the capillary 
tube 2, upon detection of the pressure drop .DELTA.P1 by the differential 
pressure gauge 11-1, the temperature T1 of the atmosphere at the 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 to the second probe 1-2 from the supply 
port 4a and passes through the capillary tube 2 within the second probe 
1-2 to be discharged from the discharge port 6a. The capillary tube 2 
within the probe 1-2 produces the pressure drop .DELTA.P2, and the 
temperature T2 of the atmosphere at a location where the second probe 1-2 
is provided through calculation using the detected pressure drop 
.DELTA.P2, in the same way as described for 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 of the present invention, since the pressure drop 
.DELTA.P across the capillary tube 2 depends upon only the temperature of 
the working fluid at the time when the working fluid passes through it, 
the pressure drop .DELTA.P never undergoes any influence from the 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 can 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 providing 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 damage 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 noted that the multi-temperature measuring apparatus shown in FIG. 16 
may be further provided with the probe damage detecting means 15a, 15b, 
15c, or 15d for detecting the damage of any of the probes 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 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, it may be open to the atmosphere in the 
case where the fluctuation of the atmospheric pressure including that 
caused by any noise is negligibly small or extremely slow in fluctuating 
rate. 
It is further 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 accumulating the working fluid to be discharged, as 
shown in FIG. 18. In either of these two cases in contrast with the 
aforementioned case, even if 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 FIG. 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 above description, according to the method of the 
present invention, the working fluid is supplied at a constant mass flow 
rate into a flow channel which defines 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 calculations using the measured pressure 
difference. 
Furthermore, according to the temperature measuring apparatus of the 
present invention employed for utilizing the above-mentioned method, there 
are provided a source of a working fluid; a probe having an external 
cylinder closed at one of its 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 into either the internal cylinder or the 
external cylinder; a pressure control device and a mass flow control 
device disposed in series with the supply piping; a differential pressure 
gauge for detecting a pressure drop across the capillary tube, and a 
temperature calculating means for operating the temperature on the basis 
of a signal sent from the differential pressure gauge. 
Consequently, by making use of the method and apparatus of the present 
invention, it is possible to achieve the temperature measurement with high 
reliability even at the high temperature in a range of 1500.degree. to 
3000.degree. C., without any influence from the environmental temperature 
or the temperature of the working fluid, notwithstanding the apparatus is 
simple in construction. 
When a probe damage detecting means for detecting the damage of the probe 
is additionally provided, allowing the damage to the probe to be readily 
detected, an erroneous measurement can be advantageously prevented. 
In addition, the present invention provides a fluidic resistance type 
temperature measuring apparatus including a source of supply of a working 
fluid, a plurality of probes connected in series with each other and each 
probe having an external cylinder closed at its one end and an internal 
cylinder which is accommodated in the external cylinder and havng a 
capillary tube at its forward end; a supply piping of the working fluid 
connected to a first probe to introduce the working fluid from the source 
to the first probe; a pressure control device and a mass flow control 
device disposed in series with the supply tube, a plurality of 
differential pressure gauges, each gauge corresponding to each probe to 
detect a pressure drop across the capillary tube; and a temperature 
operating means for calculating the temperatures on the basis of signals 
sent from the respective differential pressure gauges. 
As a result, since the working fluid supplied to each probe flows at a 
constant mass flow rate at all times, sequential temperature measurements 
can be executed with excellent accuaracy at a plurality of locations which 
are high in temperature, with the working fluid being effectively 
utilized. 
Although the present invention has been fully described by way of examples 
with reference to the accompanying drawings, it is to be noted here that 
various changes and modifications will be apparent to those skilled in the 
art. Therefore, unless such changes and modifications depart from the 
scope of the present invention, they should be construed as being included 
therein.