DE102009024937A1 - Method and arrangement for determining liquid parameters - Google Patents

Abstract

The invention relates to an arrangement and a method for the determination of liquid parameters, such as the mobility μ and the concentration of the dominant ion species, the electrical conductivity σ, the transit time T and the pH. The arrangement consists of a measuring chamber M for receiving the liquid S to be measured, with a measuring cell M arranged in the measuring chamber having at least two electrodes E and Emit arranged at the same distance d from each other, the conductive surfaces A and A and a temperature sensor T, an electrical module connected to the measuring cell M, which has a switch S and has means to measure the electrical current I = I passed through the measuring cell, the measuring chamber M, the voltage source U, the switch S, the temperature sensor T, the means for measuring the electric current I via interfaces with an evaluation unit with a computer program and a display for recording and storing all acquired data and for calculating and displaying the parameters of the liquid are connected. The invention has the advantage that with the method and the arrangement consisting of only one device and one probe, several parameters of liquids can be determined at the same time, irrespective of whether they are thin or viscous and dirty or dirty.

Description

The invention relates to a method and an arrangement for determining parameters of liquids, such as the electrical conductivity σ, the drift mobility μ _d and concentration n _{d of} a dominant type of ion, the transit time T _r and the pH and their use.

The measurement of the electrical conductivity σ, its ionic transport parameters μ _d and n _d , the transit time Tr and the pH value of liquids is for the industry and economy, for example for the production and monitoring of food and lubricants and their quality, for the control of processes, for the research and development and in the medical technology of great importance. The method and arrangement therefore have a wide range of applications. The method and arrangement therefore have a wide range of applications.

To In the prior art, one uses several, different Probes and devices to B. the desired parameters σ and to determine pH value.

In general, a distinction is made here between laboratory, process and field measurement technology. In these measurement techniques, the σ and / or pH parameters are determined at a constant temperature T _c and each with two different probes and devices, since their modes of operation and designs differ quite significantly.

The Measurement of the electrical conductivity of liquids has been known for about 130 years. Today's commercial conductivity meters work with different AC voltages and frequencies. Due to the optimal design of the measuring cells, z. B. the Selection of materials for the measuring cell and the electrodes (Stainless steel or platinum), the choice of cell constant, the Voltages and frequencies; can be the unwanted Minimize polarization.

The commercial conductivity meter systems consist mostly of the measuring cell or measuring probe and the measuring device. Today's measuring cells are based on the Kohlrausch measuring cell, the are measuring cells with two electrodes. These are mostly made of coal, platinum-plated or stainless steel. Also are four-electrode measuring cells known, which have numerous advantages. These are z. B. the bypass the polarization effects and the constancy of the cell constants. With Help of electrodeless cells, d. H. the inductive conductivity measurement the unwanted polarization effects can be avoided. These systems are mostly at high conductivities applied.

Of the Term pH was first introduced by Paul Lauritz Sörensen Proposed in 1909; in Comptes-Rendus of the Travaux du Laboratoire de Carlsberg 8me Volume 1re Livraison, Copenhague, 1909. In the past 100 years, this method has become a recognized pH measurement technology with multiple applications in industry, chemistry, biology and developed in medical technology.

The Commercial pH meter systems are mostly made up the combined electrode - d. H. as pH and reference electrode in one, with additionally integrated temperature sensor - and the meter.

The basic principle of pH measurement consists in an indirect measurement of the H ⁺ ion concentration of a liquid, because H ⁺ ions migrate into the electrode through the diaphragm of the pH electrode in the acidic medium or migrate out with a basic liquid. Since the pH electrode (usually a glass electrode) has an internal buffer with constant pH, there is a charge difference between the environment inside and outside the pH electrode. The (combined) pH electrode is more complicated than the conductivity cells due to its function, ie because of the diaphragm for the required ion exchange. As a result, they are also more sensitive to: mechanical, chemical and electrical loads.

The Today's σ and pH measurement technology is from the industry Special devices have been technically advanced. The Evaluation of the measurement results is largely automated and PC-based.

One Disadvantage of the prior art, however, is that in liquids, with only a small proportion of water, d. H. about <5%, only relative pH values determined can be. This applies in particular to high-resistance liquids, z. B. biodiesel or lubricating oils.

Furthermore, the commercial measuring systems, in particular pH probes against soiling the liquid, high mechanical loads or spontaneous temperature changes or high temperatures (membrane) are known to be very sensitive. Also, the installation and maintenance of pH probes for process measurement are problematic and technically complex.

in addition comes that determination of each parameter of a liquid requires a special probe and a special device. Apparatus and methods for the simultaneous measurement of relevant Parameters of liquids are unknown.

The invention is therefore based on the object to provide a method and an arrangement for determining parameters of liquids, with which both the electrical conductivity σ, the drift mobility μ _d and the carrier concentration n _d a dominant ion species, the transit time T _r and the pH Value can be determined. And from thin and viscous as well as polluted and almost anhydrous liquids.

According to the invention the object is achieved by a method, which is characterized in that at a constant temperature and a constant total voltage U _c , at a measuring chamber M _k with a measuring cell M _z with the liquid to be tested S _x and at least two at the same distance d arranged electrode surfaces A ₁ and A ₂ with known means the measuring cell voltage U _z determined and in a defined cycle time t _i the measuring current I _{mi is} determined and then the electric field strength E _zi after e zi = U zi / d Eq. 1 where U _{zi is} the cell voltage at time t _i and d is the distance of the electrode surfaces A ₁ and A ₂ ,
is determined and thereafter as a fluid parameter
the mobility of the dominant ions μ _di according to the equation μ di = d / (t i · e zi ) Eq. 2 where t _{i is} the clock time from i = 1 to n,
is determined and / or as another fluid parameter
the electrical conductivity σ _i according to the equation σ zi = (I Wed. / A m ) / (U zi / d) Eq. 3 where A _{m is} the mean electrode area A _m = (A ₁ + A ₂ ) / 2,
e is the elementary charge and I _{mi is} the measurement current at time t _i ,
is determined and / or as a fluid parameter
the dominant ion concentration n _di according to the equation n di = σ i / (S · μ di ) Eq. 4 where i = 1 to n,
is determined and / or as another fluid parameter
the transit time T _{r is determined} as the intersection of the functions n _di (t _i ) and μ _di (t _i )
and / or as a further fluid parameter
the pH value according to the equation pH ≈-Ig (In σ I / (6.0021 x 10 23 ) Eq. 5 in which In _d I the dominant ion concentration is dimensionless and is to be inserted in cm ^-3 and is related to t = 0 or t = T _r and the quantity (6.001 × 10 ²³ ) is the avogadro constant,
is determined.

According to a preferred embodiment of the invention, the measuring current is in digital by means of a series connected with the measuring cell M _z ammeter A, or instead with a digital current-voltage converter or an external sensing resistor R _m and connected in parallel therewith digital voltmeter (DV), or instead, with Help of an oscilloscope or recorder or voltage converter, wherein when using the external measuring resistor whose size R _m << R _zi , the mean internal resistance of the measuring cell M _z .

A further embodiment of the inventive method, the voltage dropping at the measuring resistor _Rm voltage U _mi with a high impedance digital voltmeter in the defined cycle time t _i to be measured and so for t _i and U _mi, where i = 1 to n pairs resulting measured values to capture and store and the cell voltage U _zi according to the equation U zi = U c - U Wed. Eq. 6 to determine and from this the measuring current I _mi according to the equation I Wed. = U Wed. / R m Eq. 7 wherein R _m is variably selectable from about 0.1 Ω to 10 ⁹ Ω,
to determine.

According to further embodiments of the invention, the constant voltage U _{c is} periodic, alternating, ie as + U _c and -U _c equal or different duration .DELTA.t with and without short circuit of the measuring cell during a dead time (in which U _c = 0) or without dead times is applied and provided by a pole turner and the voltage U _{c is applied} as a constant alternating voltage with a constant or variable frequency.

Further embodiments of the method according to the invention provide that time-variable voltages or voltage pulses with the amplitude ± U _c and arbitrary pulse shapes and frequencies are applied and that constant or freely selectable values are used as the intervals Δt of the cycle times t _i .

According to the invention the object is further achieved by an arrangement for carrying out the method according to the invention, consisting of a measuring chamber M _k for receiving the liquid to be measured S _x , with a arranged in the measuring chamber M _k measuring cell M _z with at least two at the same distance d from each other arranged electrodes E ₁ and E ₂ with the conductive surfaces A ₁ and A ₂ and a temperature sensor T _s , an electrical module connected to the measuring cell M _z , which supplies the measuring cell M _z with an electrical voltage U _c , a switch S and Means has to measure the guided through the measuring cell M _z electrical current I _m = I _z , wherein the voltage source U _c , the temperature sensor T _s , the means for measuring the electrical current Im via interfaces with an evaluation unit with a computer program and a Display for the acquisition and storage of all collected data as well as for the calculation and display of the parameters of the Liquid are connected.

A particularly preferred embodiment of the arrangement provides for the measurement of the current Im an ammeter, a measuring resistor R _{m to use} a for detecting the voltage drop across the measuring resistor R _m , connected digital voltmeter DV, an oscilloscope, a current voltage converter or a recorder.

According to further embodiments of the arrangement according to the invention, the surfaces A ₁ and A _{2 of} the electrodes E ₁ and E ₂ are flat or curved and preferably designed as plates of the same or different geometric shape, as a half-cylinder or as a cylinder and the size of the electrode surfaces A ₁ = A ₂ or A _{1 are} not equal to A ₂ and are all isolated except for the mutually positioned electrode surfaces A ₁ and A ₂ all other surfaces of the electrodes E ₁ and E ₂ .

Finally, further embodiments provide that the measuring chamber M _k can be heated or cooled directly or indirectly and that the electronic module is equipped with software for calculating, storing and displaying the liquid parameters.

According to the invention the arrangement for controlling and monitoring the parameters of liquids, preferably in internal combustion or electric motors and / or in technological processes and / or in hydraulic systems and / or in medical technology and / or in wind turbines and / or used in supply lines and as immersion measuring cell, immersion probe, Measuring cell with a constant volume, as a flow measuring cell or flow probe.

It is an outstanding advantage of the invention that with the provided method and the present invention consisting of only one device and a probe arrangement simultaneously several parameters of liquids can be determined regardless of whether they are thin or viscous and polluted or almost anhydrous.

With the help of the invention is a simple and timely monitoring of the real state of liquids in technological processes and, for example, in engines possible by the detection of several state-typical parameters to z. B. changes depending on the duration of operation, the influence of temperature and pressure or other factors to capture. For this purpose, it is advantageous that several parameters, such as σ, μ _d , n _d , T _r and the pH can be detected simultaneously with a simple probe and a device; which is not possible according to the state of the art.

in the Below, the invention with reference to drawings closer be explained. Show it:

1a an arrangement for measuring the electric current in liquids with a pico-ammeter;

1b an arrangement for measuring the electric current in liquids with a measuring resistor R _m ;

2a a sample container with plate electrodes in section;

2 B a perspective view of the plate electrodes of the sample container according to 2a ;

3 a thermally and electrically isolated measuring chamber in section;

4a a coaxially formed measuring cell in section

4b the top view of the measuring cell according to 4a ;

5 the schematic representation of a complex device concept for measuring different liquid parameters;

6 the graphical representation of the temporal dependence of the measuring voltage, the distilled water, U _m (t);

7 the graph of the dependence of the drift mobility μ _d and the concentration of drifting ions n _d of the time t, of distilled water;

8th the graphical representation of the temporal dependence of the measuring voltage of the biodiesel, U _m (t);

9 the graphical representation of the dependence of the drift mobility μ _d and the concentration of the drifting ions n _d of the time t, of biodiesel;

10 the graphical representation of the time dependence of the measuring voltage, U _m (t), of the oil 04/2;

11 the graphical representation of the dependence of the drift mobility μ _d and the concentration of the drifting ions n _d of the time t, the oil 04/2;

12 the graphical representation of the dependence of the drift mobility μ _d of different, but constant temperatures T _cj , of the oil 04/2;

13 the graphical representation of the dependence of the drift mobility μ _d and the concentration of the drifting ions n _d of the time t, from waste oil 04/2;

14 the graphical representation of the temporal dependence of the measuring voltage, U _m (t), of glycerol;

15 the graphical representation of the dependence of the drift mobility μ _d and the concentration of drifting ions n _d of the time t, glycerol;

16 the graphical representation of the temporal dependence of the measuring voltage, U _m (t), of petroleum;

17 the graph of the dependence of the drift mobility μ _d and the concentration of the drifting ions n _d from the time t, from kerosene;

18 Tabular summary of measurement results of different liquids and the indication of their typical parameters;

First, with the 1 to 5 Arrangements are described which consist of individual devices, modules or elements, with which the required parameters can be determined, which are required to determine the conductivity and its associated parameters and the pH.

1a shows a simple arrangement with an insulated measuring chamber (M _k ) in which the internal temperature of the measuring liquid (T _c ) with a temperature sensor (T _s ) can be measured. (Simplifies, because in this case the measuring cell dips into the liquid and unwanted side currents, eg from the back of the electrode, are neglected.)

In the measuring chamber M _k , the measuring cell M _{z is} arranged, which is simplified by a plate capacitor. Here are two identical and flat stainless steel plates with the electrode surfaces A _1.2 - parallel and at a distance d - arranged directly to each other. In between there is air (or possibly a vacuum) in the empty state or the liquid S _x from which the parameters are to be measured. The arrangement further includes a voltage source with a constant adjustable DC electrical voltage U _c , a digital pA ammeter and a switch S. Instead of an amperemeter z. B. also a current-voltage converter can be used.

The 1b shows in excerpts 1a a measuring resistor R _m , which replaces the ammeter. In this case, the voltage drop at R _{m is} measured with the digital voltmeter DV and from this the measuring current Im is determined. Instead of a DV, a digital voltage-current converter can be used or replaced by an oscilloscope or by a recorder. The voltage source, the switch, the temperature sensor, the pA ammeter or R _m and the DV or the other device variants are connected via their interfaces S _s to a PC, which detects, stores and displays the measured parameters or data.

The measuring chamber M _k according to 1a , can be optimally realized by a sample container, similar to the known Küvettengeometrie, as in the 2a and 2 B is shown. The measuring cell M _z is here formed by the fact that the electrodes A are attached to the two large inner surfaces of the container B, the z. B. may consist of Teflon or glass. In this way, one also obtains a defined internal volume of the measuring cell V _z = A _1,2 · d, which can also be minimized in this way. In this type of measuring cell, a liquid volume is filled; they are called volume measuring cells. In contrast to the immersion measuring cells, which are simply immersed in the liquid. If the surfaces of the electrodes A are connected at its rear side with the large wall surfaces of the container B by a screw thread and the electrical contacts are guided as lines L to the outside, at the same time eliminating the insulating spacers, which help otherwise realize the constant distance d of the measuring cell. Different electrode spacings d are realized in such sample containers by differently thick electrodes or cuvettes, whereby the cuvette geometry and thus the surfaces of the electrodes A remain the same. The symbols 1 and 2 in the 2a , are intended to indicate different levels of liquid; z. B. in cold or heat. With this measuring cell variant (see 2 B ) In addition, all surfaces except the opposite electrode surfaces A ₁ and A ₂ could be formed isolated. On the other hand, the electrodes are bright polished surfaces (BF). In this illustration, the isolated surfaces visible in this view are also marked with (IF). The two electrodes can also be arched as a semicylinder and thus the measuring cup can be cylindrical. In the completed plan view, ie cylindrical body with the electrodes, one would see a circle showing in the middle a curved double slit, between which the liquid is located. These two variants of measuring cells are also suitable as flow cells, if hose nozzles for inflow and outflow are still provided. A transparent sample container made of thermoglass, similar to a cuvette, would at the same time enable the electrical insulation and the rapid heating or cooling of the liquid to be measured in a temperature-controlled bath.

3 shows the outer measuring chamber M _kä with the outer and inner insulation I _SO or I _SOi and a cover D ₂ in more detail than in 1 described. The inner measuring chamber M _ki , z. B. realized by a good cold or heat-conducting container, which is filled with a liquid S _x . A measuring cell M _{z is} immersed in the liquid S _x to be examined. In this measuring cell, all other surfaces except for the active electrode surfaces are formed in isolation. In this view, two spacers, here as ge dashed lines between the electrodes of the measuring cell M _z arranged. With the two temperature sensors T _s , the temperatures in the vicinity of the electrodes and those of the bath are measured. The space between the outer wall of the container B, for example a Schott beaker or a Thermoglasküvette, the inner insulation I _ISOi and the lid D ₂ is filled with the liquid S _u , which generates the generated cold or heat from the cold-heat Zone (KW zone) to the vessel B forwards. The KW zone is z. B. realized by a copper coil through which a medium to be cooled or to be heated flows. With the second temperature sensor, the bath temperature T _{bath is} monitored and / or regulated. The KW zone can be z. B. also be realized as a heating and / or as a Peltier element. With the electrical lines L, the electrical voltage U _{z is passed} to the measuring cell M _z and the current detected by the measuring cell I _z . For the cover opening D _{3 is} provided. He can also serve to compensate for overpressure.

The 4a and 4b show as another example, another measuring cell variant M _z , which can be used as immersion measuring cells or as a measuring cell with a defined volume. It consists of two coaxial stainless steel cylinders which dive into or through the liquid. The 4a shows the vertical section through the cylinders. The distance between the inner surface of the first, large cylinder and the outer surface of the inner, smaller cylinder is d. Since the electrode surfaces differ in this arrangement, the outer cylindrical surface of the inner cylinder (Z _i ) is: A ₁ <A ₂ , the inner cylindrical surface of the outer cylinder (Z _a ).

The 4b shows the top view of the coaxial measuring cell M _z . This variant can also be realized only by two half cylinders, which are behind each other and in the gap with the distance d, the liquid S _{x is} introduced. For simplicity, the insulating mounting elements for symmetrical cohesion, the inflow and outflow of a moving medium, the shielding and lining of the arrangement and the electrical lines have been omitted here. Likewise, the holders of immersion measuring cells or the bodies which, by mounting the electrodes, result in the defined volume of the volume measuring cells.

In 5 schematically a complex device concept for determining the liquid parameters is shown. The device concept comprises one or two separate measuring chambers M _K , which may be, for example, an integrated cooling and heatable arrangement, each with a measuring cell M _z . With the other electronic components, the required voltages are provided and measured. At least one measuring resistor R _m is used to measure the cell current, the voltage drop of which is measured very precisely and digitally. Advantageously, a plurality of freely selectable measuring resistors, wherein R _m << should be as R _z . In this way, the relatively expensive pA meter can be saved.

About the single interfaces are all required parameters, such. B. U _c , I _z or U _mi , T _cj , t _i (measurement time), etc. digitally detected and the constant quantities, such. As date, time, S _x , R _m , etc. entered. By means of an electronic control module or microprocessor Md, the constant and variable parameters can be stored, programmed, queried, calculated and. be controlled specifically.

At the end, the calculation and the display of the desired quantities take place automatically: electrical conductivity σ and / or μ _d , n _d , T _r and the pH value.

When PC could also serve a laptop loaded with a CD which is a software for the required commands and contains calculations.

The further description of the 6 to 18 is made in the individual embodiments.

To The description of the device arrangement will be described below scientific contexts on which the functions refer to the arrangement and the method for the determination of parameters supported by liquids, shown and explained.

at experimental and theoretical investigations on numerous High and low ohmic liquids have been found that They are in a relatively large and individual voltage range fulfill the Ohm's Law of Electricity. This makes them very similar to the electrolytic solutions.

In Liquids becomes the electrical conductivity not by electrons but by ions (ionic conduction). This is superficial but not electrolytic Processes, but the ionic conduction in homogeneous and molecular Substances, eg. As water, biodiesel, motor oil, waste oil, Glycerol and petroleum, d. H. pure and undiluted. Used Motor oil (waste oil) is a targeted exception.

U_c

die konstante Gesamtspannung;

U_z

die Zellenspannung;

U_m

die Messspannung.

In the following, known equations are used:
In the figures 1a and 1b two electrical arrangements are shown. In this case, the external, electrical source supplies the series connection with a constant voltage U _c , which consists of the measuring cell M _z and the pico-ammeter (FIG. 1a ) or z. B. from the measuring cell M _z and the measuring resistor R _m ( 1b ) consists. Therefore the equation applies: U c = U z + U m Eq. 6 in which mean:

U _c

the constant total voltage;

U _z

the cell voltage;

U _m

the measuring voltage.

When the switch (in 1a ) S _{e, a is} closed, then an electric current flows, that is the measuring current I _m . For him: I _m = U _c / R _z , if the low-impedance ammeter is in series. Or if according to 1b the measuring resistor is in series: I m = U m / R m , Eq. 7

E_z

die elektrische Feldstärke in der Messzelle E_z;

U_z

die Zellenspannung

d

Abstand der Elektroden.

The electric field strength in the measuring cell E _z , is determined by the cell voltage U _z and the distance of the electrodes d. The following applies: e z = U z / d, Eq. 1 in which mean:

E _z

the electric field strength in the measuring cell E _z ;

U _z

the cell voltage

d

Distance of the electrodes.

T_r

Transitzeit, gleich Laufzeit der driftenden Ionen zwischen den Elekltroden;

μ_d

die Beweglichkeit der dominierenden Ionen in oder gegen die Richtung des elektrischen Feldes;

d

Abstand der Elektroden;

E_z

die elektrische Feldstärke in der Messzelle.

Now, based on solid-state physics, the concept of the transit time T _{r is} adopted. Here, it is the transit time T _r , the drifting ions between the two electrode surfaces A ₁ and A ₂ , which may be the same or different (see, for example, FIG. 2 B and 4a and 4b ). By definition, then: T r = d / (μ d · e z ) Eq. 8th and after transformation: μ d = d / (T r · e z ), Eq. 2 in which mean:

T _r

Transit time, equal to the duration of the drifting ions between the electrodes;

μ _d

the mobility of the dominant ions in or against the direction of the electric field;

d

Distance of the electrodes;

E _z

the electric field strength in the measuring cell.

J_z

die Stromdichte des Zellenstromes I_z, durch die Elektrodenfläche A;

U_z

die Zellenspannung, in der Messzelle;

E_z

die elektrische Feldstärke in der Messzelle;

d/A

die Zellenkonstante der Messzelle, mit dem

d

Abstand der Elektroden und der

A

Elektrodenfläche, oder den Elektrodenflächen.

The electrical conductivity in the measuring cell σ _z is: σ za = J z / e z = (I z / U z ) · (D / A) Eq. 9a in which mean:

J _z

the current density of the cell current I _z , through the electrode surface A;

U _z

the cell voltage, in the measuring cell;

E _z

the electric field strength in the measuring cell;

there

the cell constant of the measuring cell, with the

d

Distance between the electrodes and the

A

Electrode surface, or the electrode surfaces.

n_d

die dominierende Ionenkonzentration und:

σ_z

die elektrische Leitfähigkeit in der Messzelle;

e

die Elementarladung;

μ_d

die dominierende Ionenbeweglichkeit.

And for σ _zb , for _example , another relation is known, which is given by Eq. 9a is identical: σ eg = e · n d · μ d , Eq. 9b when transforming the equation: n d = σ z / (S · μ d ) and, Eq. 4 in which mean:

n _d

the dominant ion concentration and:

σ _z

the electrical conductivity in the measuring cell;

e

the elementary charge;

μ _d

the dominant ion mobility.

The pH can be found in the well-known Sörenson term: pH ≈-Ig [(cH + ) / (Mol · I -1 )], Eq. 10 Here, cH ⁺ stands for the H ⁺ ion concentration per liter.

The denominator in parenthesis of Eq. 10 "mol", can be substituted with the help of the Avogadro constant 6.0221 · 10 ²³ . And if even the usual unit, the dominant ion concentration cm ^-3 , is also used in liters, one obtains from n _d = In _d I · cm ^-3 → In _d I / 10 ³ cm ³ . After forming, from Eq. 10: pH ≈-Ig [In d I / (6.0221 x 10 23 )], Eq. 5

To The logarithmation is known to give the sought pH.

If σ and the pH value are to be measured in a flow, the influence of the flow velocity on the internal drift velocity v _d or on μ _d must be taken into account.

in the The invention is based on exemplary embodiments be explained in more detail.

Began becomes with the embodiment 1 (water) and after The embodiments refer to the following liquids: Biodiesel, oil, waste oil, glycerol and petroleum.

Embodiment 1 (Distilled Water, dw 01)

For measurement, a modified arrangement according to 1a and 1b used. For the pico-ammeter, a measuring resistor of 100 Ω (or less) is used, and then the voltage dropping thereon is measured with a high-impedance digital voltmeter (DV, eg of the type: Digitek DT80000, company: Elektronik Literatur Verlag (ELV)) which is connected to the PC via the RS-232 interface. The switch S _{e, a} in 1 is replaced by a pole turner, which allows alternating operation of the measuring cell with +/- U _z and the intermediate short-circuit (for this purpose a self-propelled unit "Viskosi" was used). The voltage source used was a static power supply with the performance data: 96 V / 0.6 A.

The Temperature variation and stabilization was done using a see-through thermostat CT 52 and a flow cooler CK 300, the Schott company AG secured. In the water bath of the thermostat hung a stainless steel cup with lid, which was filled with Slikonöl and in the beaker stood with the probe. The silicone oil served to exchange the temperature between the water bath and the interior of the beaker, for storage during short-term temperature fluctuations (and to extend the possible creepage distance from the water bath to the measuring substance).

through an integrated temperature sensor with glass cladding (eg TFX 430, the company ebro) became additional and ongoing the temperature of the Dw 01. and thus the liquid layer inside the measuring cell and in the beaker in two places behind the comma measured exactly.

The measuring chamber (in this example a beaker) was filled with about 125 ml of distilled (pure) water filled (Dw 01). In it, the (cleaned and dust-free) probe was immersed, which is designed here as a plate capacitor. Unfortunately, the areas facing away from the electrodes were not yet isolated. It is still advantageous if the container, as in the 2a and 3 shown (see D ₂ ), tightly covered to prevent dust, evaporation or interaction with the ambient air of the liquid.

The other versions relate to the 6 , with the graphical representation of the data from the measurement: U _m (t) _211-K 2. It shows the time curve of the measuring voltage Um and relates to the y-axis. At an external DC voltage (U _c ) of 4 V, the measuring voltage U _m (t) dropped on a measuring resistor of 100 Ω, which lay in series with the measuring cell. And as x-axis time is plotted; Here, a measurement was carried out in 1 second (sampling interval 10).

Based on 6 and the following ones 7 Let us now show how to determine the transit time T _r from the course of U _m (t) according to this method:
The 6 first shows the typical U _m (t) run of distilled water at this DC voltage and temperature. Now on the x-axis of 6 50 adjacent times selected (starting with i = 1, 2, 3 s, etc.). An Excel spreadsheet was used to measure U _m (t) _211-K2. It was digitally recorded by the PC during the measurement and contains two columns, the time of the measurement and the amount of the measurement voltage.

With the help of U _mi and (equation 6). and then easily determine U _zi , because U _{c is} known and constant. Similarly, I can _zi = I _m by the knowledge of R _m and U _mi according to Eq. 7 determine.

Then with the help of Eq. 1, 2, 6 and 7 E _zi and μ _di (t) are determined as a function of t _i for i = (1, 2, 3, ... to 50) s. From the variables U _zi , I _zi and the cell constants for A _1,2 and d (see above) can be calculated according to Eq. (9a and 4) σ _i and n _i can be easily calculated because μ _di (t _i ) was previously calculated with Eq. 2 has already been determined. This is done by a programmed Excel spreadsheet that performs the equations. In the end, a table extract can be created from this, which again contains t _i , and μ _i and n _i and is suitable for a diagram formation. For this purpose, the two sizes μ (t _i) and n (t _i) as functions of time (t _i, at the same time x-axis) PC-supported in a x, y-diagram applied. The overlapping of the two functions μ _di (t) and n _di (t) in one diagram produces a defined intersection point. It has been found that at the temperature T _ci and U _zi or R _{m it} corresponds to the transit time T _r . This quantity will be used as a reference for the parameters: μ _d , n _d , σ and pH. See z. B. 7 , The exponential decay curve shows μ _d (t _i ) and the linearly increasing function n _d (t _i ). It was determined in the measurement (211-K2) the corresponding time of the intersection of both functions at 20.67 ° C, it was T _r = 35.05 s. Here, the applied total voltage U _{c was set} to 4.00 V.

At the end of this embodiment, it will be shown how σ and the pH value can be determined with the new method. To obtain σ two ways are shown. In the first way in the Eq. 9a, the parameters U _z and I _z at T _r and d and A used. But in order to use U _z , first U _m (T _r ) from the diagram, according to 6 be determined. This gives: U _m (T _r ) = 547.36 mV. By changing the Eq. 6, U _z = 3.4526 V, as the cell voltage at time T _r . With the help of Eq. 7, I _z = I _{m is} determined. This gives 5.4736 μA. And now these parameters can be converted into Eqs. 9a are used and gives for the measurement (211-K2): 5.17 μS / cm. In this and the other examples of Dw 01, the plate spacing was d = 0.083 cm and the electrode area, each A _1.2 = 25.46 cm ² .

In the second way, the parameters μ _d and n _d determined by the new method are calculated from the 7 read and in Eq. 9b used. And so there is an easy way to calculate σ, since at T _r both numerical values (μ _d and n _d ) differ only by their units and in the μ _d , n _d diagram after 7 are readable.

The results are: μ _d = 5.66 x 10 ^-5 cm ² / Vs and n _d = 5.66 x 10 ^{+ 17} cm ^-3 . This gives with Eq. 9b: σ (T r ) = 1.6022 · (Iμ d I or In d I) 2 · (10 (-19 + x + y) ) * S / cm, where x corresponds to the 10 'exponent of μ _d and y corresponds to the 10' exponent of n _d .

Thus: σ (T _r ) = 1.6022 x (5.66) ² x 10 ^-7 S / cm = 5.132 μS / cm. (The small deviation of both σ values is attributed to the two-fold, manual removal of the parameters from the diagrams and the intermediate calculations). A first relative pH can already be found by the fact that on the x-axis of the Time t = 0 searched and at this point n _d (t = 0) is read. For t = 0, n _d = 0.21 × 10 ¹⁷ cm ^-3 . With the help of Eq. 5 is obtained: pH = 7.46. On the other hand, if one evaluates n _d (T _r ), one obtains: 5.66 × 10 ¹⁷ cm ^-3 ; and from this pH = 6.03.

• 1. Hanna Instruments, Typ HI 120 mit der Elektrode: HI 1053, bei 20,2°C pH = 6,134.
• 2. WTW, Typ pH 91, mit der Sonde Bioblock (90431), bei 21,3°C pH = 6,14.

Comparative measurements on fresh (deionized) water (eg Dw 01) gave the following pH measurement results with the devices mentioned here:

• 1. Hanna Instruments, type HI 120 with the electrode: HI 1053, at 20.2 ° C pH = 6.134.
• 2. WTW, type pH 91, with the Bioblock probe (90431), at 21.3 ° C. pH = 6.14.

(The small deviation of the pH measurements between the method with Standard equipment (see 1. and 2.) and the new process, is also attributed to that in this Experiment the electrodes on the side surfaces and at the Back not isolated and therefore not optimal.)

The necessary calculations were first carried out with a scientific calculator (type: hp 33s) and then on the PC - by extension and programming of the U _mi -t _i Excel tables above. The time period for the evaluation of a measurement can be shortened even further with the aid of suitable software and / or a microprocessor. So that the results are available immediately at the end of a measurement (eg after a few seconds or minutes).

The Accuracy of the method can be increased even more that z. B. a high-quality digital table multimeter (eg from Fluke 8845A) is used in a s 100 or recorded more measured values and allowed the data transfer to the PC.

Now the following important additions to the procedure have to be made concerning the polarity of the voltage:
At the beginning, a constant DC voltage was assumed, without paying attention to the sign of the voltage. But with constant current direction, known polarization effects generally form, which have a disruptive effect on the measurement. However, since a precise time constant T _{r is} required, it has been found that it is advantageous when working with alternating direct voltages. Ie. The measurement is started with a constant, positive or negative DC voltage. A few seconds or minutes after the duration of the measurement, the measuring cell is short-circuited to neutralize the inner polarization field again. At the beginning of a new measurement, the short circuit is canceled again and then further worked with the same voltage amount, but with the opposite sign and so on. At the end, the mean value is calculated from the measured values.

By the application of a Polwender with temporary short circuit make reproducible measurements, because in this way the problem the polarization is reduced. The pole turner (eg a switcher or relays; at the same time a short-circuiter) can of course be replaced by a special rectangular generator, in particular variable amplitudes, long pulses and the intermediate short circuit of the Can supply measuring cell.

In the 18 These and other measurement results, including other liquids, are listed.

Exemplary embodiment 2 (biodiesel, Bd 06 (commercial fuel))

The measuring arrangement and the sampling took place as already explained in the exemplary embodiment 1. Again, a constant temperature (T _cj ) in the beaker is assumed.

The diagram according to 8th , shows the typical course of the measuring voltage U _m (t) _229-K20 of the biodiesel 06 at 30.02 ° C. The measuring resistor was 100 kΩ. This was explained in detail as in the embodiment 1 (Dw 01), according to the new method, the 9 won. To determine the transit time T _r is the attention to the 9 , the μ _d / n _d diagram of Um (t) _229-K20 ( 8th ). Obtained from this diagram at 30.02 ° C z. For example, T _r = 18.65 s, μ _d (T _r ) = 4.9731 x 10 ^-5 cm ² / Vs, and n _d (T _r ) = 4.9731 x 10 ^{+ 13} cm ^-3 .

Now we want to show how the new method can be used to determine σ and the pH value. To obtain σ (from the measurement: 229-K20), Eqs. 9b uses the parameters μ _d and n _d , which are derived from the 9 can be read at T _r . The parameters μ _d (T _r ) and n _d (T _r ) and Eq. 9b: σ (T _r ) = 0.396 x 10 ^-9 S / cm.

Then in the 9 , n _d at (t = 0) and n _d (t = T _r ) read. With the help of Eq. 5 and the onset of the respective In _d I, one obtains: pH = 10.78 or 10.08 at T _r . Further exemplary parameters for biodiesel 06 include the 18 ,

Embodiment 3 (Oil. 02/4 (commercial motor oil, type: 10 W-40)

The sampling, the determination of the transit time and the μ _d and n _d parameters were carried out analogously, as set forth in the exemplary embodiments 1 to 2.

In the 10 the course of U _m (t) _241-K19 from oil 02/4 at 34.84 ° C is shown. In this measurement, the total voltage was -12.00 V and the measuring resistor was 100 kΩ. In the 11 again μ _d and n _{d are shown} as a function of time. In this case, a measurement was carried out every 5 seconds. The results at 34.84 ° C are: T _r = 36.29 s, the corresponding transport parameters can be seen from the diagram 11 read off. They are: μ _d = 1.6774 x 10 ^-5 cm ² / Vs and n _d = 1.6774 x 10 ⁺ 14 cm ^-3 .

In the 12 is of this lubricating oil still μ _d = f (T _cj ) shown. One recognizes well the typical, exponentially increasing mobility with increasing temperature.

Similar to biodiesel, the following parameters were determined by oil 04/2: μ _d , n _d , σ, T _r and the pH value. These parameters are in the table, according to 18 listed.

Embodiment 5 (automotive waste oil, in the fresh state, the oil. 02 was)

The sampling, the determination of the transit time and the μ _d and n _d parameters were carried out, as already detailed in the embodiments 1 to 4.

This Used oil was a commercial one in the freshness state Engine oil, type: 10W-40.

It was created after 20,000 km mileage of a small delivery truck. The following table compares typical parameters of fresh oil and used oil. Table 1 Parameter comparison of fresh and used oil 04/2 (after 20,000 km) Measurement Lb 03/237-K9 LB 05/96-K3 T (° C) 11.88 11.84 T (K) 285.03 284.99 U _c (V) 12:00 12:00 U _z (V) 11.95 11.98 T _r (s) 66.28 30.53 μ _d (T _r ) (10 ^-6 cm ² / Vs) 9.13 20.96 n _d (T _r ) (10 ^{+ 12} cm ^-3 91.3 20.96 sigma (10 ^-9 S / cm) 0133 0.0704 pH (T _r ) 9.82 10:46 n _opt 1:48 1.69 The refractive index (n ₀ ) is used here only for comparison.

In the 13 has been recovered and prepared by this method for waste oil μ _d and n _d at 25.01 ° C. Their and other parameters are in the 18 listed.

Embodiment 6 (viscous Glycerol (Glycerol 02, PH. EUR. 5.0)

The sampling, the determination of the transit time and the μ _d and n _d parameters were carried out as already detailed in the embodiments 1 to 5.

The glycerol (see eg. Merck Catalog, from 2005-2007, page 461 ) has the structural formula C ₃ H ₈ O ₃ . Furthermore, the following parameters are known: the condensation point at 16.85 and the melting point at 18 ° C. And it has a relatively high density of 1.26 g / cm ³ at 20 ° C.

The 14 shows the course of the measuring voltage as a function of time. And the 15 shows μ _d and n _d at the same temperature as in 14 , ie 20.08 ° C and U _c = +5.00 V. Analogously to the embodiments 1 to 5 is to be pointed finally to parameters of glycerol 02, which in the 18 are listed, for. B. on the pH of glycerol 02.

Embodiment 6 (Petroleum for analysis, Fa. Merck)

The preparation and performance of the measurement were again as described above. In the 16 U _m (t) is shown. The temperature was 19.97 ° C, the voltage U = -30.00 V and R _m was 1 MΩ. And the 17 shows μ _d and n _d at the same temperature and voltage as in 16 ,

Other parameters of petroleum contains the 18 ,

With the invention it is for example possible to derive the change of the oil in engines depending on the change of objective factors and not - as is often still the case - from empirical values. So are currently accidents. on internal combustion engines and wind turbines, in which gearboxes were destroyed, although the measured viscosity values of the oils used were still in the "operating range". The detectable with the aid of the invention changes the parameters σ, μ _d , n _d and T _r , but especially the pH value as a function of the operating time and the operating temperatures makes it possible to objectify the need for oil change and to avoid long-term damage.

With Help of software belonging to the probe and the device and that captures the presented relationships the desired liquid parameters in the shortest time Time can be determined and displayed automatically.

REFERENCE NUMBERS

• A ₁ , A ₂

  electrode surfaces

  A _m

  average electrode area, from A ₁ , A ₂

  mA

  Current unit, milliamps

  pA

  Pico Ammeter

  B

  container or vessel, e.g. B. glass cup or a rectangular cuvette

  BF

  Blank polished and conductive electrode surfaces

  cm

  Length unit, also as area or volume unit, z. B. cm ² or cm ³

  cH ⁺

  Hydrogen ion concentration

  d

  electrode distance

  e

  elementary charge

  DV

  Digital voltmeter

  D ₁

  Insulating spacers between the electrodes, equal to d

  D ₂

  Cover of the measuring chamber

  D ₃

  Opening for Bushings, z. B. for electrical cables or for ventilation or pressure equalization

  e

  Electric field strength, generally

  E _c

  constant, electric field strength

  E _z

  electric field strength in the measuring cell

  E _zi

  electric field strength in the measuring cell, at time t, during the digital Measurement

  E ₁

  Electrode 1, with the area A ₁

  f

  general function symbol

  Eq. x

  Equation with the Number x

  IF

  Isolated surfaces, from the active and conductive electrode surfaces, mostly vertical (as side edges) or facing away in parallel (Back surfaces, the electrodes)

  I _m

  Measuring current, general

  I _mi

  Measuring current, at the time t, during the digital measurement

  I _z

  Electrical current, through the measuring cell, also cell current

  I _{like that}

  Thermal and electrical isolated measuring chamber

  I _soi

  Inner wall of the insulated measuring chamber

  J

  Current density, general

  J _z

  Current density, in the cell

  K

  Kelvin

  KW

  Refrigerated Heating elements for temperature control of the ambient bath

  L

  electrical conductor or wires

  I

  liter symbol

  Ig

  Decadal logarithm

  M _d

  module

  M _K

  measuring chamber

  M _z

  Measuring cell, in general, or designed as a dip-cell

  mol

  Unit of substance quantity

  n _d

  Concentration of dominant and drifting ions, generally in cm ^-3

  In _d i

  Amount or numerical value of this concentration, the unit, z. B. 10 ⁺¹³ cm ^-3 , stands separately as a factor

  n _opt

  Optical refractive index

  PC

  personal computer

  pH

  symbol for the pH parameter

  R _m

  variable measuring resistor, z. B. 10 Ω or 100 kΩ

  R _z

  Ohmic resistance the measuring cell

  S _{e, a}

  Switch, on / off and / or Polwender, which reverses the measuring cell

  S

  Siemens, unit of electrical conductivity

  S _s

  Interface to PC or notebook

  S _u

  Ambient bath, to temperature compensation

  S _x

  Measuring liquid, general or liquid substance

  t

  general time parameter

  t _i

  Time parameters, eg. For example, i = 5 means the time t _i = 25 s when a measurement was made every 5 seconds

  T _b

  Impulse width of the rectangular pulse (eg +/- U _c )

  T _bad

  Bath temperature in one measuring chamber

  T _c

  constant temperature, generally constant temperature values, eg. B. with the index j = 3, z. B. T ₃ = 15 ° C

  T _r

  Transit time, medium Transit time of S between the electrodes A at a distance d

  T _s

  temperature sensor

  U _c

  adjustable, constant Voltage source, at the same time total voltage

  U _m

  measuring voltage

  U _m (t)

  the time-dependent measuring voltage

  U _mi

  Measuring voltage, at time t _i , during the digital measurement

  U _z

  attached to the measuring cell tension

  U _zi

  voltage applied to the measuring cell, at time t _i , during the digital measurement

  V _d

  drift velocity the ions, z. B. in a flow

  V _z

  Volume of the measuring cell

  Z _a

  outer stainless steel cylinder

  Z _i

  inner stainless steel cylinder

  μ _d

  Drift mobility, a dominant ionic species

  uA

  Unit of electrical Electricity, microampere

  σ

  Electric conductivity, generally

  σ _z

  Electric conductivity, in the measuring cell

  Ω

  Unit of resistance, also kΩ (kilo ohms) or MΩ (10 ⁶ ohms)

QUOTES INCLUDE IN THE DESCRIPTION

This list The documents listed by the applicant have been automated generated and is solely for better information recorded by the reader. The list is not part of the German Patent or utility model application. The DPMA takes over no liability for any errors or omissions.

Cited non-patent literature

• - Merck Catalog, from 2005-2007, page 461 [0109]

Claims (15)

Method for determining liquid parameters, such as the mobility μ _d and the concentration n _{d of} the dominant ion species, the electrical conductivity σ, the transit time T _r and the pH, characterized in that at a constant temperature T _cj and a constant total voltage U _c , the measuring cell voltage U _zi detected at a measuring chamber M _k with a measuring cell M _z with the liquid to be tested S _x and at least two parallel spaced d from each other electrode surfaces A ₁ and A ₂ , which are directly opposite by means known per se and in a defined cycle time t _i the measuring current I _{mi is} determined and then the electric field strength E _zi after e zi = U zi / d Eq. 1 where U _{zi is} the cell voltage at time t _i and d is the distance of the electrode surfaces A ₁ and A ₂ , and then as a fluid parameter the mobility of the dominant ions μ _di according to the relationship μ di = d / (t i · e zi ) Eq. 2 wherein t _{i is} the cycle time of i = 1 to n, is determined and / or as another liquid parameter, the electrical conductivity σ _i according to the relationship σ zi = (I Wed. / A m ) / (U zi / d) Eq. 3 where A _{m is} the mean electrode area A _m = (A ₁ + A ₂ ) / 2, e is the elementary charge and I _{mi is} the measurement current at time t _i , and / or the liquid ion parameter is the dominant ion concentration n _di according to the relationship n di = σ zi / (S · μ di ) Eq. 4 wherein i = 1 to n, is determined and / or as a further liquid parameter, the transit time T _r as the intersection of the functions μ _di (t _i ) and n _di (t _i ) is determined and / or as another liquid parameter of the pH after the relationship pH ≈-Ig (In d I / (6.0021 x 10 23 ) Eq. 5 where In _d I the dominant ion concentration is dimensionless and is to be inserted in cm ^-3 and is related to t = 0 or t = T _r and the magnitude (6.001 x 10 ²³ ) is the avogadro constant. A method according to claim 1, characterized in that the measuring current Im by means of a digital amperemeter connected in series with the measuring cell M _z (DA) or instead with a digital current-voltage converter or an external measuring resistor R _m and parallel thereto digital voltmeter (DV) or Instead, it is determined with the aid of an oscilloscope or recorder or voltage transformer, wherein when using the external measuring resistor whose size R _m << R _zi , the average internal resistance of the measuring cell M _z . Method according to Claim 2, characterized in that the voltage U _mi dropping across the measuring resistor R _{m is} measured with a high-impedance digital voltmeter in the defined cycle time t _i and which thus results in pairs for t _i and U _mi , with i = 1 to n Measurements are recorded and stored and the cell voltage U _zi according to the relationship U zi = U c - U Wed. Eq. 6 is determined and the measuring current I _mi after the relationship I Wed. = U Wed. / R m Eq. 7 wherein R _{m is} approximately variable from about 0.1 Ω to 10 ⁹ Ω, is determined. Method according to one of claims 1 to 3, characterized in that the constant voltage U _c periodically, alternately, ie as + U _c and -U _c same or different duration .DELTA.t with and without shorting the measuring cell during a dead time (in which U _c = 0) or without dead times, applied and provided by a pole turner. Method according to one of claims 1 to 4, characterized in that the voltage U _{c is applied} as a constant alternating voltage with a constant or variable frequency. Method according to one of claims 1 to 5, characterized in that time-variable voltages or voltage pulses with the amplitude ± U _c and arbitrary pulse shapes and frequencies are applied. Method according to one of Claims 1 to 6, characterized in that constant or freely selectable values are used as the intervals Δt of the cycle times t _i . Arrangement for determining fluid parameters by the process according to claims 1 to 7 consisting of: - a measuring chamber M _k for receiving the liquid to be measured S _x, arranged with a _k arranged in the measuring chamber M cell M _z of at least two at the same distance d from each other, Electrodes E ₁ and E ₂ with the conductive surfaces A ₁ and A ₂ and a temperature sensor T _s , - connected to the measuring cell M _z electrical module that supplies the measuring cell M _z with an electrical voltage U _c , a switch S _{a, e} and having means for measuring the conducted through the measuring cell M _z electrical current I _m = I _z , wherein - the measuring chamber M _k , the voltage source U _c , the switch S _{a, e} , the temperature sensor T _s , the means for measuring the electric current Im interfaced with an evaluation unit with a computer program and a display for the acquisition and storage of all acquired data and for calculation and display the parameters of the liquid are connected. Arrangement according to claim 8, characterized in that for measuring the current Im a sensitive ammeter, a measuring resistor R _m , a for detecting the voltage drop across the measuring resistor R _m , connected digital voltmeter DV, an oscilloscope, a voltage current transformer or a recorder are provided. Arrangement according to claim 8 or 9, characterized in that the surfaces A ₁ and A _{2 of} the electrodes E ₁ and E ₂ are planar or curved and are preferably formed as plates of the same or different geometric shape, as a half-cylinder or as a cylinder and the size of the electrode surfaces A ₁ = A ₂ or A _{1 is} not A ₂ . Arrangement according to one of claims 8 to 10, characterized in that all but the mutually positioned conductive electrode surfaces A ₁ and A ₂ all other surfaces of the electrodes E ₁ and E _{2 are formed} insulated. Arrangement according to one of claims 8 to 11, characterized in that the measuring chamber M _k can be heated or cooled directly or indirectly. Arrangement according to one of claims 8 to 12, characterized in that the electronic module with a Software for calculation, storage and display of fluid parameters Is provided. Use of the arrangement according to the Claims 8 to 13 for the purpose of determination, control and monitoring the parameter of liquids, preferably in incineration or electric motors and / or in technological processes and / or in hydraulic systems and / or in medical technology and / or in wind turbines and / or in supply lines and / or in laboratory and field measurement technology. Use of the arrangement according to the Claims 8 to 13 for control and monitoring the parameter of liquids as immersion measuring cell, immersion probe, Measuring cell with a defined volume, as a flow measuring cell or flow probe.