METHOD AND DEVICE FOR DETERMINING THE ABSOLUTE TEMPERATURE OF A MEASURING BODY

Abstract: A method for determining the absolute temperature TA of a measuring body (2) at the time t comprises using a reference body (1) whose thermal capacity c is known and which is arranged such that the heat transmission coefficient p between the reference body (1) and the measuring body (2) is known or can be determined. The method also comprises measuring the temperature difference (TA-TR) between said measuring body (2) and said reference body (1), and calculating the absolute temperature TA of said measuring body according to formula (I), in which <SIGN> is the absolute temperature of the measuring body at the time 0, V(t) is a physical parameter mathematically related to the measured temperature difference (TA-TR) and g is a function indicating the mathematical relation between V(t) and (TA-TR). A device for carrying the method into effect comprises means (3) for determining the temperature difference (TA-TR) and means (9) for calculating the absolute temperature TA of the measuring body at the time t according to the above formula.

Description: METHOD AND DEVICE FOR DETERMINING THE ABSOLUTE TEMPERATURE OF A MEASURING BODY «tT The present invention relates to a method for de- termining the absolute temperature T Δ of a measuring body at the time t by means of a reference body whose thermal capacity c is known when the heat transmission 5 coefficient p between said reference body and said measuring body is known. The invention also comprises a device for carrying the method into effect. In some technical applications, there is a need for measuring, with extremely high resolution, the tem- 10 perature over a wide range. One example are scanning calorimeters for studying, for example, the thermal capacity of chemical, physical and biological systems as a function of the temperature in order to gain increased insight in the properties of the system 15 and to be able to describe these properties thermo- dynamically. In calorimetric measurements and other measure¬ ments where high-precision measurement and control of temperatures are essential, use is made today of, 20 for example, platinum resistance thermometers whose resolution over a temperature range of about 150° is approximately 10 °, or quartz thermometers with a resolution of about 10 °. However, for various reasons, these thermometers are not entirely satis- 25 factory. For example, the resolution of the platinum resistance thermometer is not sufficiently high for measurements in connection with biological systems. ? Although a high resolution is per se obtainable with this thermometer, the dynamic range will then be small. Sr 30 Actually, the resolution of the quartz thermometer is sufficient, but it uses a quartz crystal whose frequency is dependent on temperature, and in order to obtain a resolution as high as 10 °, the frequency 2 must be counted for about 100 sec, which is entirely unacceptable for many types of measurement since one cannot then measure more rapid fluctuations. It therefore is the object of this invention 5 to provide a novel method and a novel device for ab¬ solute temperature measurement with high resolution over a wide range. This object is achieved by means of a method which is of the type mentioned by way of introduction 10 and which is characterised in that the temperature difference T - between the measuring body and the reference body is measured, and that the absolute temperature T of the measuring body at the time t is calculated as n t 15 T A = A + [ J " V(t) • dt + £ ( Vtt ) " V ( 0 ) ) ] _p_ ... ( 1 ) 0 p c«g wherein T A is the absolute temperature of the measuring body at the time 0, V(t) is a physical parameter mathe¬ matically related to the measured temperature difference 20 T.-T- and g is a function indicating the mathematical relation between V(t) and T -T . The method according to the invention can be carried into effect by means of a device which is characterised by means for determining the temperature 25 difference T -T between the measuring body and the reference body, and means for calculating the absolute temperature T of said measuring body at the time t according to the formula Ω t 30 T = T" + [/ V(t) • dt + c (V(t) - V(0})] p , 0 p c-g in which the parameters have the meaning indicated above. The method and the device described above make 35 it possible to measure the temperature with a resolu- —6 tion of at least about 10 ° over a range from at least about -40°C to at least about 120°C. In other words, the present invention gives a higher resolution over an essentially wider range than is possible with * prior art devices. A further advantage of the inven- ^ 5 tion is that it is extremely well suited ' for use with calorimeters. A number of non-restrictive embodiments of the present invention will now be described with reference to the accompanying drawings. Fig. 1 is a schematic 10 view illustrating a device according to the invention for absolute temperature measurement. Fig. 2 illustrates the application of the present invention to a calori¬ meter. The device shown in Fig. 1 for measuring the 15 absolute temperature T of a measuring body 2 com¬ prises a reference body 1 which may consist of, for example, gold, silver, copper, aluminium or some other material whose thermal capacity c is known and in which no phase transition occurs within the temperature 20 range for which the device is intended. The reference body must be arranged such that the heat transmission coefficient p between the reference body 1 and the measuring body 2 is known or can be determined. Such determination is effected by means of a technique 25 well known to a person skilled in the art. The device further comprises a means 3 for de¬ termining the temperature difference (T A Λ -T_Jx) between the measuring body 2 and the reference body 1. The means 3 may comprise, for example, one or more etal- 30 lie thermocouples, semi-conductor thermocouples (Peltier modules) or thermistors coupled to a resistance bridge, * ^ or platinum or copper resistance thermometers. The measuring means 3 has a first input 4 connected with "^ the reference body 1, a second input 5 connected with 35 the measuring body 2, and an output 6 coupled to an amplifier 7. The amplifier output is in turn coupled to the input of an analog-to-digital converter 8 hav- ing a resolution of 12-14 bits and having its outputs connected to the inputs of a calculating means 9 which preferably is a microprocessor. The calculating means 9 comprises means 10 for calculating the absolute tem- perature T ft of the measuring body at the time t accord¬ ing to the above formula 1. In the embodiment illustrat¬ ed, the calculating means 9 also comprise means 11 for correcting the thermal inertia of the measuring means 3 according to formula dT T A (corr) = T A + τ p x - ...(2) in which τ is a time constant. Finally, the calculat- ing means 9 comprise means 12 for selecting either the absolute temperature T as calculated by the means 10, or the T value as corrected by the means 11. The means 10-12 preferably are in software form. Final¬ ly, the output of the calculating means 9 is connected to a display unit 13 for displaying the absolute tem¬ perature. Before the function of the device illustrated in Fig. 1 is described, the above-mentioned formula 1 for calculating the absolute temperature will be derived. For the output signal of the measuring means 3 V = g x (T A -T R ) ...(3) in which V is a physical parameter mathematically related to the temperature difference between the measuring body 2 and the reference body 1, g is a function indicating the mathematical relation between V and the temperature difference T -T , T, is the temperature of the measuring body, and T n is the tem- perature of the reference body. Derivation of formula 3 in respect of time gives dV dT A d R, , , dT R d A 1 dV dt = g (~ dt ~ " dt> <=> " dt = " dt " g * dt ••• (4) Inserting 3 and 4 in the following formula derived from the first main theorem of thermodynamics, 5 in which c is the thermal capacity of the reference body 1 and p is the heat transmission coefficient between the reference body 1 and the measuring body 2, gives 10 Integration of this expression gives the absolute temperature T of the measuring body at the time t as n t T Δ = T Λ + Cf v <t ) • dt + c (V ( t ) - V ( 0))] _p_ Ά Ά 0 p c-g 15 It should also be pointed out in this connection ' that the thermal capacity c, the heat transmission . coefficient p, and the function g are temperature dependent, which, as will be described below, must be duly considered upon measurement. 20 The function of the device illustrated in Fig. 1 will now be described. If the temperature dependence of the thermal capacity c, the heat transmission coeffi¬ cient p, and the function g are not known, this must first be determined before the device can be used 25 for measuring purposes. This is done by a reference measurement for a number of temperatures, for example 3-4 temperatures, and a subsequent polynomial adapta¬ tion. The temperature dependence need be determined but once since the above-mentioned parameters are 30 material constants, which means that their temperature dependence does not vary. Furthermore, the temperature T, of the measuring body 2 at the time 0 must be determined, which can be done by means of an absolute temperature gauge, or by calibration against, for example, an ice-water reference. Then the temperature T & of the measuring body at an optional time t can be determined as follows: 5 The temperature difference between the measuring body 2 and the reference body 1 is determined by means of the measuring means 3 which supplies an output signal V mathematically related to the temperature difference, for example proportional thereto. The l ' JX output signal V is amplified in the amplifier 7 and analog-to-digital converted in the analog-to-digital converter 8. After that, the microprocessor 9 calculates the absolute temperature T Λ of the measuring body 2 by means of formula 1. If very rapid sequences are 15 to be recorded, the calculated absolute temperature is corrected by means of formula 2. However, this entails a certain delay before the measuring result is obtained, for which reason this technique is un¬ suitable when the result is to be used for control 20 purposes. Finally, one chooses that of the two tempe¬ rature values which is to be displayed in the character display unit 13 of the selector unit 12. To ensure that the measuring result is not affected by interference signals, recalibration is preferably 25. carried out at regular intervals. Fig. 2 illustrates the application of the inven¬ tion to a twin calorimeter 20. The calorimeter com¬ prises two sample holders 21, 22 for, respectively, a measuring sample and a reference sample, an alumi- 30 nium block 23 surrounded by heating means 24, and a surrounding block 25 with controlled temperature. By means of this calorimeter, it is possible to deter¬ mine, for example, the thermal capacity of a measuring sample by supplying the same amount of heat to the 35 two samples via the heating means 24 and measuring the temperature difference between the measuring sample and the reference sample. The temperature difference is a measure of the difference in thermal capacity between the samples, and if the thermal capacity of the reference sample is known, the thermal output of the measuring sample can thus be determined. For measuring the temperature difference, the calorime¬ ter comprises in known manner Peltier elements 26, an amplifier 27 for the measuring sample signal, an amplifier 28 for the reference sample signal, and a differential amplifier 29. The output signal from the differential amplifier 29 indicates the tempera¬ ture difference between the measuring sample and the reference sample and thus constitutes the calorimetric signal. For measurements of the type here concerned, it is desired to control the temperature within the aluminium block 23 very carefully, and therefore it is also important that the temperature therein can be measured with high resolution. For this measurement, use is preferably made of the method according to the invention since one can utilise the output signal already available from the reference sample amplifier 28. This signal which represents the temperature dif¬ ference between the reference sample which corresponds to the reference body in the device shown in Fig. 1, and the aluminium block 23 which corresponds to the measuring body in the said Figure, is supplied via an amplifier 30 and a multiplexer 31 to an analog-to- digital converter 32 and on to the microprocessor 33 in which the absolute temperature of the aluminium block 23 is calculated by means of the above-mentioned formula 1. The microprocessor 33 then supplies a tem¬ perature control signal dependent on the temperature thus determined to a digital-to-analog converter 34 and on to the heating means 24. For the sake of com- pleteness, it should be mentioned that the device also comprises a conventional measuring probe 35 and a conventional temperature measuring device 36 whose output signal is supplied to the microprocessor 33 for purposes of calibration. Even though the method and the device according to the present invention have been described in connec- tion with a calorimeter, this must not be interpreted to mean that the invention is limited to this applica¬ tion. The principles of the invention are also applic¬ able to, for example, temperature measurement on sur¬ faces, or in gases or liquids. Furthermore, the inven- tion is not limited to the embodiment described above, and many modifications are possible within the scope of the appended claims.

Claims: CLAIMS 1. A method for determining the absolute tempera¬ ture T of a measuring body (2) at the time t by means of a reference body (1) whose thermal capacity c is known when the heat transmission coefficient p between said reference body (1) and said measuring body (2) is known, c h a r a c t e r i s e d in that the temperature difference (T A-TK D ) between the measuring body (2) and the reference body (1) is measured, and that the absolute temperature T of the measuring body at the time t is calculated as t T " A = - T*A° ++ 1[ " / V(t) • dt + C (V(t) - V(0))] _p_ 0 p c-g wherein T is the absolute temperature of the measuring body at the time 0, V(t) is a physical parameter mathe¬ matically related to the measured temperature difference (T -T ) and g is a function indicating the mathematical relation between V(t) and (T -T ). 2. A method as claimed in claim 1, c h a r a c - t e r i s e d in that g is a proportionality constant. 3. A device for determining the absolute tempera¬ ture T of a measuring body (2) at the time t by means of a reference body (1) whose thermal capacity c is known when the heat transmission coefficient p between said reference body (1) and said measuring body (2) is known, c h a r a c t e r i s e d by means (3) for determining the temperature difference (T -T„) between the reference body and the measuring body, and means (9) for calculating the absolute te pera- ture Ά of said measuring body at the time t according to the formula n t T Δ = T Δ + C/ v(t) • d + c ( V ( t ) - V ( 0 ) ) ] p , Ά Ά 0 p c-g wherein T Δ is the absolute temperature of the measuring body at the time 0, V(t) is a physical parameter mathe¬ matically related to the measured temperature diffe¬ rence (T -T ) and g is a function indicating the mathe¬ matical relation between V(t) and (T -T ). 4. A device as claimed in claim 3, c h a r a c ¬ t e r i s e d by analog-to-digital converting means (8) coupled between said means (3) for determining the temperature difference and said means (9) for cal¬ culating the absolute temperature. 5. A device as claimed in claim 3 or 4, c h a ¬ r a c t e r i s e d in that said means (9) for calcu¬ lating the absolute temperature T comprise means (11) for correcting the thermal inertia of said means (3) ffoorr ddeetteerrmmiinniinngg tthhee itemperature difference (T -T..,) according to formula dT T A (corr) = T A + τ p x -^

Inventors: SUURKUUSK JAAK, SUURKUUSK, JAAK
Applicants: SUURKUUSK JAAK, SUURKUUSK, JAAK
Application year: 1987
Main classification: G01K7
IPC codes: G01K7, G01K17