WO1997043628A2

WO1997043628A2 - Sensor for determining the thermal conductivity and/or temperature of liquid, gaseous or viscous substances and process for driving the sensor

Info

Publication number: WO1997043628A2
Application number: PCT/PL1997/000007
Authority: WO
Inventors: Ryszard Maczan
Original assignee: Ryszard Maczan
Priority date: 1996-05-11
Filing date: 1997-05-12
Publication date: 1997-11-20
Also published as: WO1997043628A3; DE19780485D2; PL329848A1; DE19619133A1; AU2917897A

Abstract

A sensor is disclosed for determining the thermal conductivity and/or temperature of liquid, gaseous or viscous substances, for example engine oil. A process for driving the sensor is also disclosed. The sensor has a supporting body (1) and a measurement winding (7) of a type that reduces self-induction and inductivity. In order to create an appropriate sensor for determining the thermal conductivity and/or temperature of substances, the resistance wire (8) is uniformly arranged in an embedding space (9) provided for the measurement winding and having everywhere the same heat storage capacity, on a supporting body (1) of which each part has at the most the thermal capacity of a pair of adjacent resistance wire layers, so that the caloric medium temperature of the sensor may be sensed by means of the resistance wire (8). A predetermined cavity (10) for the substance to be examined is provided next to the sensor. The sensor is at first driven with a constant, low electric supply which is then changed to test the transmission behaviour of the sensor.

Description

Sensor for determining the thermal conductivity and / or the temperature of liquid, gaseous or semi-solid substances and method for exciting the sensor.

The invention relates to an electrical resistance sensor for determining the thermal conductivity of liquid, gaseous or semi-solid substances and / or their temperature according to the preamble of patent claim 1 and a method for introducing electrical auxiliary energy into the sensor (excitation of the sensor) according to the preamble of patent claim 12 .

Resting gases or liquids as well as gelatinous, slimy, pulpy, pasty, soft, more or less granular substances can be examined or analyzed due to their different thermal conductivity including the material temperature if either a binary mixture is present or if only one variable component is the thermal conductivity of the mixture significantly influenced. These substances are referred to below as the substances to be examined or in short as substances.

DE 3917935 C2 describes a device and a method for determining the thermal conductivity and concentration of liquid mixtures, in particular a gasoline / methanol mixture. According to the invention, a method and a device are specified for measuring a concentration in a mixture of first and second liquid components with different thermal conductivities. In the mixture, a film resistance is arranged with a temperature-dependent resistance value. A current is supplied to the thin film resistor to increase the resistance value. After a predetermined time, the current supplied to the internal resistor is limited to lower the resistance value. The rate of change of the resistance value of the thin film resistor is measured. The measured rate, which corresponds to the thermal conductivity of the mixture and therefore also the concentration of the first liquid component of the mixture, is converted into a value which is the concentration of this first Indicates liquid component of the mixture. The invention is based not only on the pure thermal conductivity of the substance, but the measurement result is also influenced by the change in the specific heat capacity and the density of the mixture. In this known device, a sensor is used, namely a typical thin-film resistor, in which - due to its construction - the carrier body and not the mixture to be examined predominantly influences the measured rate of change, and therefore the sensor can only detect the change in thermal diversity of the mixture via a low sensitivity feature.

It is known to determine the proportion of solid, liquid or gaseous substances in a mixture or layering of these substances with hooves of an electrical resistance wire, as described in DE 3122642 C2. The known method is characterized in that for the mixture or layering the The number n of the various substances is determined and the electrical resistance wire is embedded in the individual substances, and in each case predetermined n-1 different quantities of electrical energy are briefly within a few milliseconds up to a maximum of a few seconds up to a maximum below the evaporation or ignition temperature of the mixture or layering Substance with the lowest evaporation or ignition temperature is heated and calibration measurements of the feed times for the supply of the predetermined amounts of energy are carried out, and with one into the mixtures or layers to be examined embedded resistance wire of the same mechanical and electrical data and when feeding in the same predetermined amounts of energy as for the calibration measurements, the respective feed times are measured again and the individual substances of the mixture or stratification are determined from the values of these measurements and the calibration measurements. Although the known anaryysis method is based on the thermal conductivity of the substances, the actual parameter of the substance to be examined, the thermal conductivity, cannot be determined selectively from the measured variables of the measuring method, in this case from the feed times. Since the effects of influencing and disturbing effects such as the effects of the unstable temperature of the substance cannot be eliminated, the measuring method does not meet the higher requirements for accuracy DE 4135617 AI describes a device for determining a heat transfer value of substances for their assessment, the device having a measuring probe for converting the heat transfer value into an amplitude signal. The measuring probe consists of a housing made of heat-insulating material and of a displaceably mounted and lockable therein, elongated Tenroeraftiraufhehmer. In its non-functional control, the front measuring end of the temperature detector is located inside the housing, while in the measuring position it is just outside the housing in order to come into contact with the substance to be examined. For this purpose, in the measuring position, a temperature measurement is first carried out. Then, on the basis of mathematical relationships, including constant values of the measuring probe, the heat transfer value of the substance is calculated. This probe is preferably used when assessing the woman's cervical mucus. It has been found that with this known measuring probe it is not possible to achieve sufficient selectivity when converting the heat transfer value into an AmpUtudensignal, and therefore the application of the measuring probe to mixtures of substances with small changes in the homeopathic properties, i.e. the pure heat resistance, the density or the specific heat capacity, not possible.

For examining or analyzing gases, it is known to use thermal measuring devices (Dr. T. Pfeifer, Dr. P. Profos: Handbuch der industrial Messtechnik, R. Oldenburg Munich-Vienna, 6th edition 1994, pp. 913-923; LHengstenberg, B.Strum, O. Winkler: Measure, Control, Regein in Chemical Technology, Springer-Verlag Berlin, Heidelberg, New York, Third Edition, Volume U, pp. 94-112). Analysis devices for determining the gas content in a gas mixture, for example the CO∑ content, are of great importance. Carbon dioxide has a significantly lower heat resistance than the air and the CO2 content therefore has a significant influence on the heat capacity. The measurement of the thermal conductivity of a gas mixture takes place in zyifodeiform, theπnostatised measuring chambers in which heated platinum measuring wires are stretched out. The measuring wire assumes a higher temperature, the lower the heat resistance of the surrounding gas is. The resulting change in resistance of the measuring wire is evaluated. The use of this heat measuring device allows an accurate determination of the pure heat resistance of a gas mixture, but requires a sample and requires a lot great care bd the Temperature control of the measuring chambers and the elimination of external temperature effects and keeping the measuring current constant and thus a relatively large amount of equipment.

Bd liquid lubricants, such as lubricating oils, especially motor oils, there is a risk of aging and / or contamination of the substances with the disadvantage that these lubricants become unusable after a long period of use and must be replaced. In practice, the lubricant is mainly exchanged according to fixed operating times. Since the quality of the oil used varies depending on the degree of use, machine condition, type of oil, degree of refining and others according to fixed operating times, the optimal operating time of the oil can usually not be set universally. Accurate but relatively expensive and time-consuming laboratory tests of the lubricants in question are known, e.g. according to DIN 51551 (the coke residue as a measure of the aging condition of an oil). Known simpler methods use e.g. the dielectric constant (US Pat. No. 4733556) or the electrical impedance (impedance) of the oil (US Pat. No. 5200027), but it is difficult to correlate these parameters of the oil concerned with its lubrication quality in any case and therefore they can Do not ensure the required selectivity when differentiating between a new and a used oil under all operating conditions.

Electrical resistance sensors are known which are provided for determining the temperature of substances. Since the dynamic parameters of such a sensor are variable, these sensors with delays can only be approximately described in terms of their transmission behavior, and therefore their exact dynamic correction, which eliminates the dynamic errors and thus ensures an increased accuracy of the temperature measurement, is practically impossible.

The invention has for its object to provide a heat-sensitive, suitable for determining the thermal capacity and / or the temperature of liquid, gaseous or semi-solid substances, and to stimulate it so that a determination of the thermal capacity and / or the temperature from its output signal of the substance becomes possible, and that the heat-specific and electromagnetic interference effects, which overlay the actual measured variable when they occur, predominate in their effect can be eliminated. This makes it possible to precisely determine the temperature and / or the temperature of substances in order to determine a change in the state of the substance or the properties or concentrations of the substances, and the sensor is also simply constructed and in place, without sampling and Sample preparation, ie without sampling errors, is easy to use

The following are to be understood as heat-specific interference effects: a. the unstable temperature of the substance. b. the movement of the substance or its gas or liquid substance and the measurement of the thermal conductivity

Electromagnetic interference effects are understood to mean the following: a. electromagnetic interference from the environment b. the electrical interference voltages sdtens of the electrical excitation signal.

The object is achieved according to the invention by the features of claims 1 and 12. Preferred embodiments of the invention are specified in the subclaims.

The invention is therefore based on the idea of an interference-free investigation of the transmission behavior of a sensor proposed by the invention, which is heat-sensitive thanks to its design and behaves practically in its transmission behavior like a linear measuring element of the 1st order for the principle-related determination of the thermal conductivity and / or the temperature of the resting material directly touching it, in order to be able to get information from the output signal of the sensor about how intensively the certain electrical power accumulating in its measuring winding is transferred to the material with a changing thermal conductivity, causing the influence of the influences the result of the investigation has a negligible influence.

For a better understanding of the context of the present invention, it should be explained: a. The thermal conductivity to be measured is to be understood as the thermal conductivity of the substance, which relates to the specific thermal capacity and the density of the substance The pure thermal conductivity of the substance is calculated from the thermal conductivity to be measured according to the formula

K- ^ c (1) calculated, where K is the pure thermal conductivity, b the thermal conductivity to be measured, Ω the density and C the specific heat capacity of the substance. The thermal conductivity to be measured is briefly referred to as the thermal conductivity b. Such a heat-sensitive, linear sensor of the 1st order is to be understood as a sensor whose output quantity, the electrical resistance of the measuring winding, the heat energy stored in the sensor, which corresponds to the caloric mean temperature, is proportional, ie its heat sensitivity is constant, and also its transmission behavior can be completely described by first order differential equation. c. Under the most interference-free investigation of the

Such a sensor is understood to be an experimental determination of the functional dynamic relationship between a specific output signal, the electrical excitation signal of the sensor, as the cause and its output signal, the change in resistance of the measuring winding, as an effect, whereby the output signal is influenced by an influencing variable, the thermal conductivity of the substance , being affected. The interference effects are suppressed by the investigative and design measures d. The principle-related determination of the Wänneldt ability and / or the temperature means that the basis for such a determination is the first law of thermodynamics (energy balance for the sensor) and Fourier's basic law of heat conduction (kinetic approach for the substance to be investigated), and that it is secondly to determine the caloric mean temperature of the sensor.

The sensor can be used to selectively determine the thermal conductivity and / or the temperature of the substance, the effects of which are largely eliminated from the heat-specific and electromagnetic interference effects which can occur during the determination. This makes it possible to make reliable statements about the finest changes in the state of matter or properties or concentrations of liquid, gaseous or semi-solid substances. The solution according to the invention can be used universally and can be carried out under practical conditions with a relatively small amount of equipment. The relevant examinations can be carried out on the spot in such a way that sampling is not necessary. This also eliminates those measurement errors which result from sampling and sample preparation. The sensor is also used to measure the current material temperature, which is either taken as the reference temperature for the thermal conductivity or, after the elimination of static and dynamic errors, can be used as a measured variable or an influencing variable in various fields of measurement and control technology.

The sensor is used quasi-continuously with a suitable evaluation circuit to monitor the condition of various substances. An economically particularly important field of application is the monitoring of a lubricating oil, in particular the motor oil of a motor vehicle. It has been found through ongoing oil sampling that some specific physical and chemical properties of a lubricating oil change as it is used (Lubrication Engineering, August 1994, pp. 605-611). Due to the inherent aging processes in the lubricating oil, e.g. due to the oxidation taking place in the oil and the mechanical chopping of the oil molecules, or through the penetration of dirt particles into the oil, oxidation, polymerisation and other foreign products are formed which have significantly shorter molecular chains in their internal structure and thus have poorer lubricating properties than the new oil itself. One speaks of an increased external degree of freedom of the molecules, which results in a permanent weakening of the force effect among the molecules, i.e. a deterioration in the viscosity of the oil, since the intermolecular forces significantly mean the pure thermal conductivity, the specific heat capacity and the density of liquids influence (VDI-Wärmeatlas, 7th edition 1994, p. Da 33), the "proportion" affects the thermal conductivity of the oil to be measured noticeably. Therefore a change in thermal conductivity can be corrected with the lubricating quality of the oil and it is possible by its exact determination It is also known that once an oil has exceeded a certain level of aging, the further aging progresses very quickly, which makes the oil unusable quickly. It can then be read on a measuring device that the condition engine oil deteriorates rapidly, so the oil should be changed soon. In a special embodiment of the sensor, the following construction principles were preferably used, reference being made to the explanations in the special description part and in the patent claims by reference numerals

The size and shape of the free space 10 are to be determined in this way so that the substance to be examined fills the free space 10 and therefore comes into direct contact with the sensor without any contact heat resistance, and that no movement occurs during the first process step the one to be examined, ie warming material can take place. Since the semi-solid substances can practically not flow, the free space 10 should only be predetermined in such a way that it is free of other substances, provided that the subject matter of the invention is used for determining the thermal conductivity of thin-bodied or gaseous substances, i.e. If an undesirable, corrosive heat transfer to the material is nevertheless possible, a predetermined cavity should be provided around the sensor, inside which the discoloration suppresses the natural convection of the fabric and strongly inhibits possible movements. The cavity (free space 10) should then depend on the footing behavior of the substance and taking into account the strength, frequency and duration of the excitation signal, which will become clear.

The linearity of the sensor can be improved in that the length dimensions of the sensor do not differ much. Further design-related changes in the sensor from a linear measuring element of the first order can be reduced by the fact that the materials of the sensor components (carrier body 1, content of the embedding space 9, insulation of the resistance wire and the resistance wire 8 itself) have almost the same temperature capability, i.e. that the temperature compensation in these components runs quickly

The detection of the caloric mean temperature of the sensor by the resistance wire 8 can be better ensured if it fills the sensor as completely as possible and if no temperature differences can occur on the cross section of this resistance wire. Therefore, a very thin resistance wire is to be used to form the measuring winding 7, with any metal or metal oxide strand underneath the resistance wire Understanding is, for example, copper, platinum, Ni-Cr or silver coating, thin strip or a strip-shaped layer resistor laid on a fine substrate

The effects of the electromagnetic interference effects can be reduced in that the measuring winding 7 is arranged in a two-wire manner on a carrier body and the half-windings formed in this way are arranged electrically opposite a Wheatstone bridge, with the starting connection points of the half-windings being on the same bridge diagonal.

A very advantageous electrical independence of the output signal Uy from fluctuations in the supply voltage Uo can be achieved by dividing the amplitude signal U1 by the voltage voltage signal Uo with the aid of a multiplier 28 arranged in the negative feedback branch of the amplifier circuit 27.

Thanks to an easy-to-implement and relatively lightly evaluable, smudge-shaped late signal signal for the sensor, the heat-specific interference effects can also be suppressed by calculation and therefore the immunity to interference of the measurement, in conjunction with the structural features of claims 1 to 11, is considerably increased.

The structure of the sensor and the excitation method is explained in more detail below using two exemplary embodiments and a method example in conjunction with the attached drawings.

It shows:

1 shows a partial cross section of a sensor in execution play S 1,

2 shows an overview sketch of a sensor in exemplary embodiment S2, specifically with a mechanical device surrounding it, FIG. 3 shows an amplifier-free measuring circuit, such as is used, for example, for determining the absolute thermal conductivity,

4 shows an amplifier-free measuring circuit, such as is used, for example, for determining the relative thermal capacity, FIG. 5 shows a linear feed and measuring device and an evaluation device, 6 shows an example of the excitation signals of the sensor,

7 shows an example of the current temperature distribution in the sensor and in the material, Fig. 8 test results of the sensor S2 in connection with an engine oil

ArnfWirungsbeispiel SI

The present example represents a basic form of the sensor and describes an embodiment of the invention which alone enables the determination of the thermal conductivity and / or the temperature of substances which themselves cannot flow.

The exemplary embodiment SI shown in FIG. 1 has a carrier body, generally designated 1, which has the shape of a very small, coil-shaped component. The component consists of a thin, inner metal rod 2 with two thin metal walls 3a and 3b and a metal cylinder 4 The metal rod 2 has a diameter of approximately 0.4mm and the metal walls 3a, 3b and the wall of the cylinder 4 are approximately 0.2mm thick. The thickness of any section of the support body 1 is approximately the thickness of an adjoining the section of the resistance wire 8 gldch, so that the temperatures in the sensor are influenced very little by the heat capacities of the support body 1. The sensor must not be equipped with any other protective fitting. The carrier body is equipped with a holder 5, which is provided for fastening the sensor in a measuring insert 6.

To the carrier body 1, a measuring winding 7 is arranged, which is formed from a double resistance wire 8 and consists of two identical, parallel, mutually insulated copper wires. Each wire of this double resistance wire 8 has a diameter of approximately 0.1 mm and an insulation thickness of 5 μm. The double resistance wire 8 is arranged spatially and tightly in the embedding space 9 and impregnated with a metal-based, very good temperature-insulating protective lacquer, so that there is a typical gold-like winding coil, which can be seen in FIG. Since the measuring winding 7 in the sensor consists of a double resistance wire with golden wires, there are two half-windings 7a and 7b in the sensor, each with a starting connection point Ila, 11b and with an end connection point 12a, 12b. These points are with inner lead wires 13 of the measuring insert 6 connected, which in turn are connected to its terminals. It itself is similar to a measuring set for resistance thermometers according to DIN 43762 and consists of a flexible jacket tube 13a with four inner lines 13, a flange and a base with the connecting terminals.

Example S2

The present example creates another embodiment on the basis of the exemplary embodiment SI, which enables the determination of the heat conductivity and / or the temperature of liquid and gaseous substances and can be used, for example, for the investigation of the aging stage of a liquid mixture

The exemplary embodiment S2 shown in FIG. 2 consists of a basic form of the sensor SI from FIG. 1, which is generally 14, and a mechanical device, which surrounds it and is generally 15. This mechanical device

15 is designed in the form of a cylinder 17 and creates an incompletely closed space around the sensor 14, in this case an annular-gap-shaped chamber

16 (cavity). It is fully open from above to allow the sensor to get inside. The lower end wall 18 has inflow openings 20 which allow part of the liquid or gaseous material to flow into the chamber 16 and to flow out of it very slowly. This ensures that there is material of the golden state in the cavity and in the space behind it. As can also be seen from FIG. 2, the sensor 14 is arranged at a short distance (approx. 5 mm) from the cylinder 17. In this way, there is no sufficiently large flow space around the sensor for the natural convection of the heated material and thus its movement there is strongly suppressed. The cavity 16 is, however, large enough to accommodate all the heat that flows in the direction of the negative temperature gradient in the material of the 2nd procedural step is transferred. The provision of the mechanical device 15 also has the advantage that no disturbing external currents can act on the sensor, ie the partially open chamber 16 represents a calming space for the substance. 3 shows an amplifier-less measuring circuit, generally designated 21a, for converting changes in resistance of the double resistance wire 8 into an amplitude signal U1. It is used to measure the absolute thermal capacity and is designed in the form of a Wheatstone bridge. The half-windings 7a and 7b, which have arisen due to the twisted-wire winding formation, are, in terms of aesthetics, arranged as the same bridge resistances opposite a Wheatstone bridge, with the starting junctions Ila, 11b of Haibwickhmgcn 7a and 7b are located on the same diagonal of the Wheatstone bridge as can be seen from FIG. 3, and the other bridge resistors 22 are similar, non-adjustable resistors with a small temperature coefficient and are also similar to the Wheatstone bridge 3 electrically arranged and mechanically attached to the terminals in the base. The ohmic value of each fixed bridge resistor 22 is predetermined in such a way that it is equal to the ohmic resistance of a half-winding 7a, 7b in the reference temperature for the thermal conductivity of the substance, ie the Wheatstone Bridge is located during the excitation of the sensor in an optimal, almost balanced state.

If the two half-windings 7a and 7b of the twisted-wire winding configuration according to FIG. 3 are arranged to form a Wheatstone bridge, then the current flows in them in the opposite direction and thus generates largely compensating magnetic fields. In this way, the electromagnetic interferences from the environment cancel each other out in the two half-windings and the electrical interference voltages generated during the excitation by self-induction in the measuring winding 7 are greatly reduced. Bd the heating of the sensor by approx. 5 K, i.e. in the heating range during the excitation, the output signal Ul resulting from the bridge circuit is practically proportional to the change in resistance of a half-winding 7a, 7b, which can be explained electrically without further explanation

The two other bridge resistors 22 can also consist of half-windings 7c and 7d of another sensor constructed according to the invention, but which is in a known laminate. The half-windings 7c and 7d of this sensor are, in addition to the half-windings 7a and 7b, in the measuring circuit 21b in In the form of a Wheatstone bridge according to FIG. 4, the initial connection points 11c, 11d of half-windings 7c and 7d are arranged on the same Diagonals of the Wheatstone Bridge are located. Such a measuring circuit contains two identical sensors, one of which is immersed in the substance to be examined, the other in the composite material at the same temperature. In contrast to the measuring circuit 21a described above, this amplifying measuring circuit 21b is used to carry out a relative measurement of the thermal conductivity between the substance to be examined and a known comparative substance. This solution alone does not enable the material temperature to be measured, but limits the linearity errors which occur, for example, in the measuring circuit 21a.

A common housing 23 is shown schematically in FIG. 5, in which a linear feed and measuring device 24 and an evaluation circuit 25 as well as an electrical energy source 26 are provided. The linear feed and measuring device 24 contains an amplifier circuit 27 which is arranged in a series circuit with the amplifier-less measuring circuit 21a or 21b and with the evaluation circuit 25 and amplifies the amplitude signal U1 emerging from the measuring circuit. The linear feed and measuring device 24 inputs its output signal Uy into the evaluation circuit 25. The amplifier circuit 27 has an analog multiplier 28 which is arranged in its negative feedback and which is provided for multiplying the output signal Uy by the supply voltage signal Uo the amplifier-less measuring circuit 21a or 21b and the amplifier circuit 27 becomes constant.

5 further shows that a supply circuit 29 is provided in the linear supply and measuring device 24, which is constructed in the form of a controlled supply voltage source for the amplifier-less measuring circuit 21a or 21b. The linear supply and measuring device 24 also has an adjusting element 30 , which is controlled by the evaluation circuit 25 and on the other hand controls the feed circuit 29. The setting member 30 is constructed as a programmable function generator and is provided for generating a behavior test signal which is explained below. The evaluation circuit 25 has a conversion circuit 31, which is responsible for the analog-digital conversion of the signals Uy and Uo and for the output and reception of binary control signals for the setting element 30 Microcomputer 32 equipped, which is provided for the execution of measurement algorithms, for the sensor-specific Meßsignah / erarbdrung and for the evaluation of the signals Uy and Uo, as well as for the computational determination of the measured or the pure heat ability and / or the temperature of the substance to be examined is

Excitation process

The sensor SI or S2 is electrically excited in one or more measuring processes, in conjunction with the measuring circuit 21a or 21b, the spdse and measuring device 24 and the evaluation circuit 25, each in two process steps, in such a way that from the output signal of the Sensor the determination of the temperature and the thermal conductivity of the material coming into contact with the sensor is possible.

The excitation process may be illustrated using a practical example. Should e.g. the lubricating oil of an engine are examined, the sensor is held in the oil through the oil dipstick of the engine, as in the exemplary embodiment S2, the mechanical device 15 being found inside the engine. The amplifier-less measuring circuit 21a is used to convert the changes in resistance of the measuring winding into an amplitude signal The measurement of the absolute thermal capacity should take place in relation to the operating temperature of the oil, in the almost balanced state of the Wheatstone bridge.

The aim of the first process step is to determine the oil temperature and to determine the thermal stability state of the oil and the sensor. Therefore, similar to a resistance thermometer, it is excited with an electrical supply signal, which enables the conversion from the change in resistance into a voltage signal and only introduces a small amount of electromagnetic power into the current-carrying measuring winding. Thus, the amplifier-less measuring circuit 21a is supplied with a supply voltage Uo (so-called initial value). , at a height of 200 mV. The amplitude signal U1 resulting from the measuring circuit 21a is passed on to the microcomputer 32 after a corresponding amplification in the amplifier circuit 27 (output signal Uy) and after conversion into a digital signal in the conversion circuit 31. The signal is the change in resistance of the half-winding 7a and 7b proportional and corresponds to the Change in the caloric mean temperature of the sensor. The microprocessor 32 incorporates the sensor-specific measurement signal processing for resistance thermometers, for example the correction of exemplary scatter of zero point and slope and of non-linearities. The first process step can extend over any length of time. The second process step can be carried out at a central point of your choice, but if it is established that the measured temperature no longer changes, ie the temperature of the sensor is stable and the temperature of the oil.

The aim of the second process step is the experimental coupling of the energy balance of the sensor and the heat insulation of the substance in the form of a first-order differential glazing, which describes the transmission behavior of the sensor.This differential glazing, main glazing for the sensor, defines the relationship between the change in its average calorific temperature and the electrical excitation signal, taking into account the constant width of the sensor and the thermal conductivity of the substance. The experimental coupling of the energy balance and the thermal insulation provides an output signal Uy, which, together with the electrical excitation signal, enables the solution of the main glazing to be determined. This makes it possible to determine the thermal conductivity of the substance.

By exciting the sensor according to the invention, an electrothermal power is generated in its current-carrying measuring winding which causes the temperature of the sensor to change. Due to the temperature difference between the sensor and the fabric, the heat is transferred in the direction of the negative temperature gradient in the fabric. The difference between the heat flow in and out is stored in the sensor, which is good

where F is the electrical power supplied to the sensor, F _{a0 is} the heat flux absorbed by the sensor and Fs is the heat flow stored in the sensor.

Good for heat storage F _s

F __ _/ - »dV _s dt (3) where Cs is the heat storage capacity and Vg is the calorific temperature of the sensor. In purely arithmetical terms, V _{9 means} the over-temperature compared to the reference temperature of the substance determined in the first process step.

For the transfer of heat from the sensor to the Fab && fabric

Here K is the pure thermal capacity, V the temperature of the substance, S the surface and R the radius of one

Sensors.

Inserting gaps 3 and 4 into the gasket 2 is the main seal for the sensor

F "-K" S * (g) _ι _ _R -rC. * 3 ^! , (5)

The equation 5 represents a first order differential equation which, with the following well-founded assumption that the caloric mean temperature of the sensor is equal to its surface temperature, can be represented in a detachable form, as will become clear.

If the sensor designed according to the invention borders on a resting substance with the thermal conductivity to be determined and is decisive for a transfer behavior test, then the transfer of heat from the sensor to the substance and then also the thermal conductivity of the substance from the main structure 5 can be based on the values of the measuring caloric mean temperature can be determined. To enable this determination, it is necessary to excite the sensor either with a changing but not recurring or with a periodically changing electrical power.

The non-recurring excitation signals that are decisive for a transmission quality test include typical test functions that are simple to implement, such as the pulse, jump and ramp function. The change in the mean temperature to be measured represents a process, at the end of which there is a new one sets stationary temperature distribution in the substance The evaluation of the measurement results can be carried out in the manner which is explained in the already mentioned DE 4135617 AI

The periodic excitation signals that are decisive for a transmission behavior test include, for example, the smusty course of the stimulating electrical equipment with a constant amplitude and with a constant frequency or the periodic signal in the form of rectangular feed energy pulses with a constant amplitude and in a pseudo-random sequence with a short cycle time. In addition to these excitation signals, the change in the mean caloric temperature contains a temporary and a periodic component, with only the periodic component determining the transmission behavior test. The periodic part only begins after the end of a temporary process, which arrives at the start of the vibrations of the electrical power supply and is reflected in a non-periodic temperature distribution in the sensor and in the substance to be examined. The temporary process in the substance to be examined ends earlier, the smaller the distance from the sensor and the greater the temperature ability of the substance. The course of the mean temperature to be measured can therefore only be properly evaluated after a setting time. Otherwise, a systematic measurement error occurs, which can falsify the measurement results. However, the duration of the second process step should generally be limited in order to be able to avoid the heating of the material outside the free space 10.

Since the heat transfer to the material resulting from the sinusoidal excitation can be determined relatively poorly and the thermal processes inside the sensor and in the material to be examined are easily recognizable, this easily realizable form of the signal for the electrical supply of the sensor is to be preferred for excitation. Thus, when examining the engine oil, at a selectable point in time and after establishing the stated thermal stability state, the amplifier-less measuring circuit 21a is excited with a sinusoidal supply voltage uo = Uo sin (ωot-ε) (6), whereupon the amplitude, CDQ the frequency of the supply voltage and £ mean the initial phase shift bd of the time measurement. The supply voltage of the amplifier-less measuring circuit 21a has an amplitude of 10V and a Frequency of 1 Hz. Electromagnetic heat flow is then generated in the measuring winding

Fzu = Fo [l-cos 2 (ωot-ε) l (7) of the two components, one constant and one periodic, contains (Fig. 6).

The constant component is responsible for the temporary portion in the course of the average calorific temperature and is together for the two current-carrying half-windings

where RQ means the resistance of a half winding in the initial temperature (reference temperature). The change in the constant component sdd the change in the sensor temperature by approximately 5 K is not more than 0.01%, and must not be taken into account in the evaluation. The periodic component is liable for the periodic portion in the course of the caloric mean temperature of the sensor and is

Fo cos2 (ωot-ε).

Their frequency CO is, compared to the frequency of the supply voltage COQ, twice as high (2 Hz).

Corresponding to the sinusoidal change in the electrothermal heat flow that arises in the current-carrying measuring winding, the heat detection is initiated in the sensor and in the oil to be examined. Since not as much heat is withdrawn from the sensor as is being supplied at that moment, the thermal energy stored in the sensor, and thus also its temperature, changes - also in a smoky manner. The heat flow is supplied to the entire sensor, which has a certain heat capacity, at lightning speed.As the sensor largely consists of a resistance wire and a heat-sealable metal sheath and only has a small, metallic support body, its internal heat resistance is also very low and therefore occur slight temperature differences. The temperature of the sensor depends only on the Zdt, but not on the spatial coordinates, ie the caloric mean temperature to be measured is practically the same as its surface temperature. The intensity of the heat transfer to the oil, ie the local absorption of the oil temperature on the surface of the sensor is not constant in the course of the second step of the driver. It can be based on the theory of temperature periods ("Conduction of Heat in Sohds" by HS Carslaw, Oxford University Press , 1959, pp. 64-70) and the resulting distribution of the instantaneous temperature in the sensor and in the oil (Fig. 7), whereby the oil must not move during the second process step, because it can be expected that if the oil on its edge (here sensor surface) is heated sinusoidally, - after a setting time - both the temperatures on the surface of the sensor and inside the oil will show a similar progression The temperature of the signal of 2 Hz causes the temperature wave in the oil pr can actually penetrate to the depth of a few millimeters, ie only to a partial thickness of the free space 10. Experiments have shown that the oil does not heat up outside the free space 10 during this time of about 5-6 seconds and that the sensor is momentarily heated by about 5 K in the time room. Due to the relatively low temperatures, there will still be no significant natural convection of the oil inside the mechanical device 15. The effective internal color in the oil is particularly large in this case not only because the distance from the sensor to the cylinder is relatively small and large shear stresses have to be overcome, but also because of the transient thermal and hydrodynamic processes in the gap chamber 16 , a constantly changing acceleration of the oil particles takes place. Therefore, in addition to the shear stresses, the inertia of the oil has to be overcome.

Since the temperatures on the surface of the sensor V * in the oil change with the speed

spread, this vibration is at depth Δx

Δx = J2κω Δt (10) for the temperature value f ω

_V k + ι _{= V} k _e - 2JC Δx

(11) sunk. The local mapping of the oil temperature on the surface of the sensor can then be done for the hourly sampling interval Δt from the formula

are calculated, the index K being assigned to a measured value at the sampling point

has been recorded, and K means the temperature difference of the oil to be examined. The main glow 5 for the sensor in the form of a differential glow for the discrete values of the caloric mean temperature of the sensor

V _g can then be in the form

F ^ & S * _Δt7Ä + C ₈ * - s- d3), and after the deformation it reads

The animal-physical characteristics of the oil: the pure thermal conductivity K, the density P and the specific thermal capacity C are summarized in this equation as the thermal conductivity D to be measured. The numerical calculation of the thermal capacity is possible from the equation 14 for each sampling period Δt. It is

The values F and V * necessary for the calculation can, due to the

Supply voltage signal Uo and the output signal Uy, in which microcomputers 32 are determined and the other required values are available from the beginning.

The determination procedure presented above enables the determination of the

Heat capacity Dk ^m each individual Zduntervaü Δt of the decisive process during the 2nd process step. From the individual values Dk wύti an average value D to limit random errors is calculated b = £ ∑bk. (16) The rest of the random error can be determined in its overall value by means of expensive functions and by statistical parameters, such as, for example, the average error and the mean square error. Therefore, the detection process has good reliability.

The test results of the sensor S2 in connection with an engine oil are shown in Fig. 8, whereby the calibration factor of the sensor has been estimated. On the basis of an existing comparison table with the values of the absolute heat capacity for the oil to be examined, it can now be determined whether the tested oil has changed its stock so that it is even more usable. In special cases, the pure thermal conductivity K of the oil, based on the equation 1, can be calculated in the microcomputer 32 from the values of the thermal conductivity D to be measured, for predetermined values of the specific thermal capacity and the density of the oil.

The thermal conductivity can also be determined from the amplitude values of the signals Fzu and V _s in connection with the main equation for the sensor. This solution offers, in particular, the possibility of determining the relative thermal conductivity of a substance in a simpler manner with the aid of the measuring circuit 21b, and can be used for operational substance analysis. However, it has a lower accuracy and reliability, which in turn is due to the relatively small number of available

Amplitude values of the signals F come out to u * ^{10 *} V s.

The invention is also suitable for use in the ground to determine the current moisture content so that timely moistening measures can be used and to keep the moisture fluctuations within the narrowest possible limits. The sensor can also be used to examine mucus, especially cervical mucus, whose changes in condition during the course of a woman's cycle or in the course of a woman's disease are determined for medical reasons. The invention is also suitable for the investigation of various gas (vapor) mixtures, for example in connection with a gasoline / alcohol / fuel mixture, or for determining the degree of saturation or for determining the boiling state of a mixture. Finally, it is also pointed out that the sensor can be used advantageously for permanent, statically and dynamically corrected temperature measurement. Thus, with the aid of the evaluation circuit 25, the static and, with the inclusion of equation 14, the dynamic correction of the temperature measurement, in particular bd the periodic temperature measurement, can be carried out. An example of this is temperature control (on-off control) using thermostats.

Claims

claims

1.Sensor for the determination of the thermal conductivity and / or the temperature of liquid, gaseous or semi-solid substances, consisting of a carrier body and a measuring winding arranged therefor of a type of winding which reduces self-induction and inductance, the measuring winding consisting of an electrically insulated metallic resistance wire with a There is a temperature-dependent resistance value and is connected via an amplifier-free measuring circuit provided for converting changes in resistance of the resistance wire into an amplitude signal, to a linear supply and measuring device interacting with an evaluation circuit, characterized in that the resistance wire (8) is used in a suitable manner for the measuring winding provided, at all points having the same heat storage capacity, an embedding space (9) on a support body (1), each section of which at most adjusts the heat capacity of a few to the section zenden resistance wire layers, is arranged such that the caloric mean temperature of the sensor can be detected with the resistance wire (8), and, from the delimitation of the sensor, a predetermined free space (10) is provided for the substance to be examined.

2. Sensor according to claim 1 for low-viscosity or gaseous substances, characterized gekennzdchnet that the predetermined, the sensor comprising free space (10) in the form of at least one cavity with the help of a mechanical device (15) arranged around it.

3. Sensor according to claim 2, characterized gekennzdchnet that the mechanical device (15) consists of a thin-walled open cylinder (17) with a perforated end wall (18)

4. Sensor according to claim 1 or 2, characterized gekennzdchnet in that it is designed in the form of a coil and its height is approximately gldch its diameter

5. Sensor according to claim 1 or 2, characterized gekennzdchnet in that the Temperaturidtfunktionkdt of all components of the sensor is similar to the Tempcraturldtfahigkdt of the resistance wire (8)

6. Sensor according to claim 1 or 2, characterized gekennzdchnet in that the resistance wire (8) is a double resistance wire, and that each wire of the double resistance wire forms a half-winding of the measuring winding, each with a start and end connection point

7. Sensor according to claim 6, characterized gekennzdchnet that the wires of the double resistance wire are gldche, very thin copper wires with a fine insulating coating.

8. amplifier-free measuring circuit (21a) for the sensor according to claim 6 or 7 for determining the absolute thermal conductivity, consisting of a Wheatstone bridge, gekennzdchnet that zwd opposing bridge resistors forming the measuring winding (7) each from the half-windings (7a, 7b) of the measuring winding (7), and that the other bridge resistors (22) are identical fixed resistors.

9. amplifier-less measuring circuit (21b) for the sensor according to claim 6 or 7 for determining the relative Wäπneldtfahigkdt consisting of a Wheatstone bridge, thereby gekennzdchnet that zwd opposite, the measuring winding (7) of the sensor immersed in the substance to be examined forming bridge resistances each consist of the half-windings (7a, 7b) of the measuring winding (7) of the sensor, and that the other bridge resistors forming the measuring winding (7) of the other sensor immersed in a known composite material each consist of the half-windings (7c, 7d) of the measuring winding (7) of the sensor.

10. amplifier-less measuring circuit according to claim 8 or 9, characterized gekennzdchnet that each bdden the starting connection points of the half-windings (7a, 7b; 7c, 7d) on the same diagonal of the Wheatstone bridge are arranged electrically opposite.

11. Linear feeding and measuring device for the sensor according to at least one of claims 1 to 7, consisting of a feed circuit (29) for electrically feeding the unamplified measuring circuit (21a; 21b) and an amplifier device (27) for amplifying the unamplified measuring circuit (21a; 21b) arriving 5 amplitude signal Ul, characterized gekennzdchnet that an analog multiplier (28) for the multiplication of the output signal Uy of the amplifier circuit (27) with the output signal Uo of the Spündeschaltung (29) is arranged in the negative feedback branch of the amplifier circuit (27)

10. A method for exciting a sensor according to at least one of claims 1 to 7, characterized by the following method steps:

1) that the electrical supply of the amplifier-less measuring circuit is kept constant, wobd the constant amplitude of the electrical supply signal (initial value) is predetermined such that the

15 in the current-carrying measuring winding (7) resulting electro-thermal power has a low value.

2) that the electric power supply of the amplifier-type measuring circuit is changed significantly for a transmission behavior test, the amplitude of the hectare feed signal and its time course being predetermined in such a way that the sensor, during this process step, due to the electro-electromagnetic power arising in its current-carrying measuring winding (7) is heated to a maximum below the temperature which can cause a noticeable natural convection of the gas or liquid substance of the substance to be examined located in the free space 10 and that no heating of the material outside the predetermined free space 10 takes place during this step. can take place.

13. The method according to claim 12 step 2, characterized in that the electrical supply of the amplifier-measuring circuit takes place in the form of a periodic feed signal, which causes a 0 sinusoidal change in the current-carrying measuring winding (7) of the sensor resulting electrothermal power