WO1999040451A1

WO1999040451A1 - Measuring and electrochromic display system for electrically measured variables

Info

Publication number: WO1999040451A1
Application number: PCT/EP1999/000410
Authority: WO
Inventors: Dietrich Haarer; Stephan Schmidt; Christian Paulus
Original assignee: Bayer Aktiengesellschaft
Priority date: 1998-02-04
Filing date: 1999-01-22
Publication date: 1999-08-12
Also published as: EP1053481A1; DE19804332A1; JP2002502983A; TW434408B; AU2621099A; DE19804332C2

Abstract

The present invention relates to a measuring and electrochromic display system for electrically measured variables, wherein said system comprises an electrochromic substance located between two electrodes having their base surface determined by a short and a long axes. One of said electrodes is transparent and one electrode has a finite surface resistance. The signal is measured by modifying the voltage difference between the two electrodes along the long axis.

Description

Electrochromic measuring and display device for electrical measurands

The invention relates to an analog measuring and display instrument for electrical measured variables, which an electrochromic medium (ECM) simultaneously for measurement and

The measured variable is used.

Two types of instruments are used to display and measure electrical parameters. In the first type, the measurement of the electrical quantity is attributed to the measurement of a current. The display is mechanical. The galvanometer is a typical measuring device with mechanical display. In the galvanometer, a current-carrying coil is deflected by the Lorentz force in the field of a permanent magnet. A pointer firmly connected to the coil moves over the measuring scale in accordance with the current strength in the coil. Such electro-mechanical measuring and display instruments are complex to build and not very robust. With their mechanics, they are also subject to constant wear.

Newer measuring instruments measure the electrical measured quantities electronically via an operational amplifier. The output voltage of the operational amplifier is processed via an analog / digital converter for display in a, mostly liquid-crystalline, display. In these newer measuring instruments, the measuring unit and the display unit are separated from one another. This makes the construction complex.

The object of the invention is to design a measuring device which on the one hand works wear-free and on the other hand is simply constructed by coupling the measuring and display function.

An electrochrome cell (EC cell) consists of two electrodes between which the ECM is located. When a sufficiently high voltage is applied to the electrodes, a current flows between the electrodes and the ECM changes color. This is the electrochromic effect (ECE). The current-voltage characteristic of an EC cell 2

is S-shaped (Fig. 1). Below a certain voltage, the switching voltage (U _sch ), no current flows in the EC cell and there is no ECE. Above the switching voltage there is an increase in the current due to the increasing charge transfer from the electrode to the ECM and the ECE starts. When the saturation voltage (U _Satt ) is reached, the current changes to a saturation current

(I _Satt ) above, which remains constant even with a further voltage increase. At U _Satt , the EC cell reaches its maximum color depth.

The invention is based on the idea of combining the switching behavior of the ECM with a voltage drop along at least one electrode surface in such a way that the location of the EC cell at which U _{Sch is} exceeded and the ECM changes color can be read as a measure of the voltage applied can.

The present invention accordingly relates to an analog measuring and display device for electrical measured variables, which consists of an EC cell which contains an ECM between two electrodes, at least one of the electrodes being at least partially transparent and at least one of the electrodes being finite Has surface resistance. The base area of the electrodes is described by a short and a long axis. The base area is preferably rectangular. The base area can also be horseshoe-shaped. The short and long axes describe the aspect ratio on a horseshoe-shaped surface. Electrodes with a finite sheet resistance preferably have a resistance of 10 to 200,000 ohms between the sides corresponding to the short axis.

One pole of the measurement signal is applied to a side of the electrode corresponding to the short axis with finite sheet resistance. The other pole is either applied to the other side of the electrode with finite sheet resistance corresponding to the short axis or to one side of the other electrode corresponding to the short axis. If both poles of the measurement signal are applied to the electrode with finite surface resistance, then this electrode becomes electrically conductive on one side corresponding to the short axis with one of the short ones 3

Axis corresponding side of the other electrode connected. If both poles of the measurement signal are applied to the sides of different electrodes corresponding to the short axis, the electrodes can either be insulated from one another or be electrically conductively connected on their sides corresponding to the short axis. Electrically conductive connections between the electrodes can also contain, for example, fixed or variable resistors or non-linear components.

Both electrodes can have the same or different sheet resistances. One of the electrodes can in particular have a metallic conductivity.

Further electrical components, such as fixed and / or variable resistors or diodes, can be inserted into the connection or connections between the poles of the measurement signal and the electrode with the finite sheet resistance. Components that are used to connect the electrodes can be separate components. Components, in particular the resistors, can also be implemented as integrated structures in the conductive coatings or as conductive spacers between the two electrode surfaces. This connection of the electrodes with additional electrical components can serve to determine the measuring range.

The signal is measured via the change in the voltage difference between the two electrodes in the direction of the long axis resulting from the finite surface resistance of at least one electrode.

Electrochromic media (ECMs). which can be used in the EC cell are described, for example, in US Pat. No. 3,451,741, EP-A 240,226, WO 94/23333, WO 97/30134 and WO 97/30135. Electrochromic liquids preferred according to the invention are described in German patent applications 19 605 441, 19 621 865 and 19 631 729. The preferred ECMs offer 4

a strong electrochromic absorption change in the visible and have a high reversibility.

The electrochromic medium can be a liquid, a gel or a solid. Liquids and gels are preferred.

They contain one or more electrochromic substances, optionally at least one solvent, optionally at least one UV absorber, optionally at least one salt to increase the conductivity and optionally at least one thickener.

Suitable electrochromic substances are pairs of redox substances, one of which can be reduced and the other can be oxidized. Both are particularly colorless or only slightly colored. After a voltage is applied to the EC cell, one substance is reduced, the other is oxidized, at least one becoming colored. After the voltage is switched off, the two original redox substances re-form and the EC cell decolors.

RED ₁ + OX _{2 4} ► OX ₁ + RED ₂ (colorless) (colored)

(Low energy pair) (high energy pair)

Suitable pairs of redox substances, of which the reducible substance at least two chemically reversible reduction waves in the cyclic voltammogram and the oxidizable substance correspondingly at least two chemically reversible

Oxidation waves are known from US Pat. No. 4,902,108. Such redox systems are known from WO 97/30134 in which RED, and OX ₂ or OX, and RED _{2 are} covalently bonded to one another via a bridge B. Such substances are also suitable. Also suitable are those redox systems in which the reversible transition between RED and OX or vice versa with the release or

Closing a σ bond is connected. Such substances are, for example, from 5

WO 97/30135 known. Metal salts or metal complexes of metals which exist in at least two oxidation states are also suitable for the purposes of the invention. The two oxidation levels advantageously differ by one oxidation level. Also suitable are oligomers and polymers which contain at least one of the redox systems mentioned, but also pairs of such redox systems as defined above. Mixtures of the substances just described are also suitable, provided that these mixtures contain at least one reducible and at least one oxidizable redox system. Suitable solvents, salts, UV absorbers and thickeners are known.

The switching voltages of such electrochromic liquids are usually in the range between 0.2 and 3 volts, in particular 0.3 to 1.5 volts.

The ECM can be self-extinguishing. The cell decolours again by recombining the ions of the ECM as soon as the applied voltage drops below U _Sc . If self-extinguishing ECMs are used, measuring and display devices with high

Contrast of the display and long service life possible.

If the ECM is not self-extinguishing, a counter potential must be applied in order to undo the electrochromic effect. If a non-self-extinguishing ECM is used, the display remains after the measurement until a counter potential is applied until it is deleted.

If the ECM is a liquid or a gel with low viscosity, then the electrodes are expediently applied to a stable, solid or flexible material (substrate). At least one substrate then consists of a translucent material, for example glass or plastic, such as polycarbonate or polymethyl methacrylate (PMMA). This substrate is on the side in contact with the ECM with an electrically conductive, translucent layer, for example indium tin oxide (ITO), a conductive polymer, for example polyethylene dioxythiophene (PEDT), or any other conductive, translucent layer 6

Mistake. Such electrically conductive and translucent layers can have a specific surface resistance of 1 to 10,000 ohms per square.

The second electrode can be configured identically to the first electrode. However, it can also consist of a metal plate or of an electrically conductive layer applied to a substrate, this layer having reflective properties. In this case, the substrate does not have to have translucent properties. However, the reflective property can also be achieved by coating the translucent substrate on the side not facing the ECM with a reflective substance, e.g. a metal.

If the ECM is a solid, for example an electrochromic polymer, then only one electrode has to consist of a stable substrate. In this case, the other electrode can only consist of a conductive layer, for example a conductive polymer film or a metallic vapor deposition layer. One of the two electrodes must be translucent.

A better display function is achieved if numbers, symbols or letters are made visible in the display field, especially those relating to the

Obtain scaling of the measured value. This can be achieved by appropriate structuring of one or both electrodes or by printing on the substrate surface if the electrically conductive coating is transparent, or by printing on the electrically conductive coating itself.

The electrochromic cell can also be divided into different compartments, preferably it is divided in sections in the direction of the longer axis. This subdivision increases the characteristic curve of the display and thus increases the measuring accuracy, since the possibility of diffusion of the charge carriers in the longitudinal direction of the cell is limited. An even sharper resolution is achieved by modulating the conductivity of the electrode with finite surface resistance 7

along its longitudinal axis if the conductivity changes exactly at the boundaries between the compartments.

The measuring and display device according to the invention is simple in construction. It can be implemented in almost any geometric shape and combines measurement and display functions. The measuring and display device according to the invention can be used for the measurement of direct voltages or pulsed direct voltages, such as are obtained after rectification of alternating voltages. The measuring range is preferably in the range between the switching voltage U _sch and 3 times the saturation voltage U _Satt . Should voltages be measured that are outside of this

Of the measuring range, they must be adapted to this measuring range, if necessary by external conversion. The measurement and display range is expediently adapted by means of calibration and series resistors.

"The device is therefore suitable for displaying battery voltages, mains voltages, if necessary after rectification, and for displaying any measurement variables after conversion into a voltage signal.

The invention is explained in more detail below with the aid of the attached figures and the examples:

1 shows the current-voltage characteristic measured on an electrochromic cell.

Fig. 2 shows a first embodiment of the measuring and display device according to the invention.

Fig. 3 shows a second embodiment of the measuring and display device according to the invention. 8th

Fig. 4 shows a third embodiment of the measuring and display device according to the invention.

5 shows a combination of structuring of the electrically conductive layer and printed symbols, as can be used in a battery tester.

6 shows an electrode of the EC cell with a constricted electrode geometry.

1 shows a typical characteristic curve of an electrochromic liquid located between two electrodes. When the voltage U rises, no current initially flows until the switching voltage U _{sch is reached} . The current rises at U _sch . At U _Salt the saturation current I _{Satt is} reached. Above U _Satt , the current remains constant even when the voltage continues to rise.

9

example 1

Fig. 2 shows a measuring and display device according to the invention, which has two transparent plates made of polycarbonate 1, 2, which are provided on their inward side with an ITO layer 3, 4. The two plates together with the surrounding, electrically insulating frame 5 form a cell 6 within which the ECM is located. The cell e.g. a ratio of the length of the side which corresponds to the long axis (in the direction of the cross-sectional drawing shown) to the length of the side which corresponds to the short axis (perpendicular to the plane of the drawing) of 3: 1. The resistance of the ITO layers in the longitudinal direction of the cell is each

300 ohms. The narrow sides of the ITO layers led out of the cell have metallic contacts 7 and 8, to which a voltage source 10 is connected via a series resistor 9. The series resistor is selected as a function of the internal resistance and the voltage of the voltage source 10 so that the voltage between the electrodes 3 and 4 in the vicinity of the center of the longitudinal extent of the cell (arrow 11) corresponds to the switching voltage U _Sch . On the left of the arrow the voltage is higher than the switching voltage due to the ohmic resistance of the ITO layers, on the right of the arrow 1 1 lower. Accordingly, the cell appears saturated in color up to arrow 11 (dotted area), and colorless to the right of arrow 11. The measuring range of the measuring device is between 80 and 125% of the choice of the

Series resistor 9 set as 50% color saturation probable measured value.

Example 2

In the alternative embodiment of the invention according to FIG. 3, the one transparent glass plate 101 is provided with an ITO layer 103, the resistance of which in the longitudinal direction of the cell is, for example, 500 ohms. In the example, the other plate 102 has a metallic coating 104 with negligible electrical resistance. In principle, this can also be any conductive

Be coating, with only the conductivity being better than that of 103 10

should. One short side of the electrode is short-circuited (1 12). The cell 106 is formed by the coated plates 101 and 102 and the circumferential, electrically insulating frame 105.

The one to be measured between the electrical contacts 107 and 108

Voltage drops along ITO layer 103. In the area in which the voltage against the metallic counter-electrode 104 exceeds the switching voltage of the ECM of, for example, 0.8 volts, the saturation current I _Satt flows between the electrodes 103 and 104, so that this part of the cell is saturated with color (dotted area in the Drawing). The most probable measured value is by means of

Series resistor 109 calibrated approximately for the center of the cell (arrow 1 1 1), the measuring range is between 50% and 170% of this most probable measured value if the measuring range is limited to a range of 20% to 70%) of the longitudinal extent of the cell.

Example 3

In the alternative embodiment of the invention according to FIG. 4, one transparent plate 201 is provided with an ITO layer 203, the resistance of which in the longitudinal direction of the cell is, for example, 200 ohms. The other plate 202 has a metallic coating 204 with negligible electrical resistance. The coated plates are connected to one another on the narrow sides in an electrically conductive manner via the spacers 205 and 206, which have finite conductivity. The resistance through this connection is 400 ohms each.

The narrow sides of the ITO layers led out of the cell have metallic contacts 207 and 208 to which a voltage source 209 is connected. The plate 202 with the metallic coating 204 is connected to only one of the metallic contacts. Otherwise, the cell 210 is formed by the coated plates 201 and 202 and the electrically insulating walls on the long sides. An external series resistor can be omitted. 11

The applied voltage drops along 205 and 206 and the electrode 201. In this example, the falling voltages behave as 2: 1: 2 (400/200/400 Ohm). If an accumulator, for example a standard mignon cell with a voltage of typically 1.5 volts, is connected directly to the contacts, the potential along the coating of the transparent plate is 0.9 to 0.6 volts. The potential for the plate with the metallic coating is a uniform 0 volts. With a switching voltage of the electrochromic medium of e.g. The entire cell is saturated with 0.6 volts. If the accumulator is discharged, the accumulator voltage is typically 1.0 volt. The potential along the coating of the transparent plate is then only 0.6 to 0.4 volts and the cell remains colorless.

Example 4

Special measuring and display functions can be structured by structuring the

Realize electrodes. 6 shows an electrode geometry constricted in the central area. The constriction results in a local increase in the resistance of the electrode and leads to a scale expansion. Such a display can be used to particularly stretch the deviation from a most probable measured value (setpoint). The same effect can be achieved by changing the resistance of the ITO layer, a local increase in the resistance of the ITO layer causing a scale stretch and a local decrease in the resistance of the ITO layer causing scale compression.

Example 5

Symbols can be applied to the cell for the display function. These symbols will be printed next to the actual display, but they can also be applied directly on both sides of a transparent electrode or on the inner side of a reflective electrode. Depending on the color of the symbols and the place where the symbols are applied, the symbols are 12

always visible or, when the cell is stained, less or no longer visible. As a rule, symbols printed on the electrodes are more visible in the de-energized (uncolored) state than in the current-carrying (colored) state.

Symbols can also be made visible through the fine structuring of the electrically conductive layers. It is possible to remove the layer in the form of a symbol (negative) or to form a symbol from the conductive layer (positive). In the first case, the place where the conductive layer is missing does not color and a bright (uncolored) symbol appears. In the de-energized state there is none

See icon. In the second case, only the area with the symbol stains, while the rest of the cell remains unstained.

The structuring of the electrically conductive layers can be combined with printed symbols.

Fig. 5 shows a measuring and display device according to the invention, which can be used for example for testing batteries. To simplify matters, only the states BAD and GOOD appear in this example. The inscription BAD (3) is printed on the lower and in this case reflective, electrically conductive layer and is always visible in the de-energized state. This also classifies batteries that, due to their state of charge, provide no or only a voltage below the switching voltage of the electrochromic medium. If the voltage is sufficiently high, the area in which the lettering is located changes color and the lettering BAD disappears when the color of the lettering corresponds to that of the electrochromic medium. If the applied voltage of the battery is above the value determined by the geometry and the electrical properties of the cell, the rear area of the cell and the lettering GOOD (2), which has been removed from the electrically conductive layer (1), also become colored visible as bright lettering.

Claims

13 Patent claims

1. Measuring and display device for electrical measured quantities consisting of an electrochromic medium between two electrodes, the base of which is described by a short and a long axis, at least one of the

Electrodes is at least partially transparent, and at least one electrode has a finite sheet resistance, and one pole of the measurement signal on one side of the electrode with finite sheet resistance corresponding to the short axis and the other pole on a further side corresponding to the short axis of one of the two electrodes is applied and the measurement of the signal takes place via the change in the voltage difference between the two electrodes in the direction of the long axis.

2. Measuring and display device for electrical measured variables according to claim 1, characterized in that the poles of the measuring signal are connected to one side of the two electrodes corresponding to the short axis and the electrodes are only electrically conductively connected by the electrochromic medium.

3. Measuring and display device for electrical measured quantities according to claim 1, characterized in that the poles of the measurement signal are connected to one side of the two electrodes corresponding to the short axis and the electrodes are electrically conductively connected to one side corresponding to the short axis.

Measuring and display device for electrical measured quantities according to claim 1, characterized in that the poles of the measurement signal are connected to the two sides of the electrode corresponding to the short axis with finite surface resistance, and the two electrodes are electrically conductively connected to one side corresponding to the short axis become. 14

5. Measuring and display device for electrical measured quantities according to one of claims 1 to 4, characterized in that the electrodes have different surface resistances.

6. Measuring and display device for electrical measured variables according to one of claims 1 to 5, characterized in that one of the electrodes has metallic conductivity.

7. Measuring and display device for electrical measured variables according to one of claims 1 to 6, characterized in that the measuring range is determined by additional electrical components in the connection between the electrode with the finite sheet resistance and the pole of the measurement signal.

8. Measuring and display device for electrical measured variables according to claim 7, characterized in that the measuring range with variable and / or fixed

Resistance is set.

9. Measuring and display device for electrical measured variables according to one of claims 1 to 8, characterized in that the one electrode is connected at least at one point by a variable and / or fixed resistor to the second electrode.

10. Measuring and display device for electrical measured variables according to one of claims 1 to 9, characterized in that an electrode is connected to the second electrode by a non-linear electrical component.

1 1. Measuring and display device for electrical measured quantities according to one of claims 1 to 10, characterized in that at least one electrode is structured. 15

12. Measuring and display device for electrical measured variables according to claim 1 1, characterized in that the structuring of the at least one electrode contains symbols for scaling the measured value.

13. Measuring and display device for electrical measured variables according to one of claims 1 to 12, characterized in that at least one substrate surface has symbols for scaling the measured value.

14. Measuring and display device for electrical measured variables according to one of claims 1 to 13, characterized in that at least one substrate surface is mirrored.

15. Measuring and display device for electrical measured variables according to one of claims 1 to 14, characterized in that the electrochromic medium is divided into different compartments.

16. Measuring and display device for electrical measured variables according to one of claims 1 to 15, characterized in that the electrochromic medium is a solution, a gel or a solid.

17. Measuring and display device for electrical measured quantities according to one of claims 1 to 16, characterized in that the electrochromic medium contains at least one pair of redox substances, one of which can be reduced and the other is oxidizable, at least one being colored.

18. Electrochromic measuring and display device for electrical measured variables according to claim 17, characterized in that

a) the reducible substance at least two chemically reversible

Reduction waves in the cyclic voltammogram and the 16

oxidizable substance correspondingly have at least two chemically reversible oxidation waves, or

b) the reducible substance and the oxidizable substance are covalently bonded to one another via a bridge B, or

c) selected as the reducible and / or oxidizable substance are those in which the reversible transition between the oxidizable form and the reducible form is associated with the loosening or closing of a σ bond, or

d) the reducible substance and the oxidizable substance are metal salts or metal complexes of those metals which exist in at least two oxidation states, or

e) the reducible and / or oxidizable substance are oligomers and polymers which contain at least one of the redox systems mentioned, but also pairs of such redox systems as defined under a) to d), or

Mixtures of the substances described in a) to e) are used as the reducible and / or oxidizable substance, provided that these mixtures contain at least one reducible and at least one oxidizable redox system.