Embedded temperature sensor for a windshield heater

Abstract

sensor protective disc having a protective disc heater, wherein the protective disc heater has a measuring circuit and a thin-film layer, wherein the thin-film layer has an elongated contact electrode, and a heating current flows from the elongated contact electrode through the thin-film layer to another contact electrode, and a temperature measuring current of the measuring circuit flows through the elongated contact electrode, so that the elongated contact electrode also acts as a temperature-dependent measuring resistor, or a temperature measuring current of the measuring circuit flows from the elongated contact electrode through the thin-film layer to the other contact electrode, so that the thin-film layer also acts as a temperature-dependent measuring resistor.

Description

[0001] The invention relates to the heating of a front screen of a sensor, which is also designed as a protective screen. Such a sensor protective screen is typically used to protect the optics and electronics of optical sensors. For example, in optical scanners or light barriers, a protective screen or protective cover that is transparent in the measuring wavelength range of the sensor is provided to protect the sensor from environmental influences. Due to changes in the ambient conditions to which the sensor is exposed during operation, for example due to changes in the ambient temperature or changes in humidity, the protective screen or protective cover can fog up, or condensation can form inside the sensor. Fogging of the sensor protective screen changes the optical transparency of the protective screen and thus influences the function of the sensor.Condensation inside the sensor can cause lasting damage to the sensor's electrical components.

[0002] In order to ensure the faultless function of an optical sensor with a sensor protective screen even under changing ambient conditions, a heater is typically integrated on the protective screen or the protective cover of such a sensor.

[0003] In order to determine the heating output of a protective screen heater that is adapted to changing ambient conditions and thus enable control of the heater, a temperature measurement of the screen is necessary. Temperature sensors are used for this purpose, which are positioned close to each other inside the optical sensor. Alternatively, temperature sensor structures embedded in the sensor screen can be used.

[0004] Such spatially resolved temperature measurements are typically performed using temperature sensors, which serve as temperature probes and are available in various technical designs. Examples include thermocouples, PTC (positive temperature coefficient) resistors or NTC (negative temperature coefficient) resistors, resistance thermometers, semiconductor-based temperature sensors, or temperature sensors implemented as integrated circuits.

[0005] For a temperature sensor to accurately measure the temperature of a medium, such as air, water, or a protective screen, a thermal coupling must exist between the temperature sensor and the medium. Depending on the quality of the coupling, a more accurate and / or more dynamic measurement of the temperature of the medium is achieved. The thermal coupling for measuring the temperature of a protective screen can be achieved, for example, through direct contact between the protective screen and the temperature sensor, by positioning the temperature sensor on the protective screen, for example, by gluing it, or by convection of the air between the temperature sensor and the protective screen.

[0006] Temperature measurement using radiation transmission is also possible. For example, the infrared component of the thermal radiation emitted by the protective screen, depending on the temperature, is detected by a temperature sensor designed as a radiation detector, and the measured radiation intensity is used to calculate the temperature of the protective screen.

[0007] Integrated temperature sensors, i.e., those implemented in the protective screen, may not reliably detect the temperature to be measured, depending on their installation position, due to insufficient thermal coupling. Non-contact measurement methods, such as the method described using a radiation detector, are comparatively expensive and complex, requiring significant calibration effort to achieve high measurement accuracy.

[0008] Furthermore, when using a thermocouple as a temperature sensor, for example, the actual temperature can only be calculated if the measurement is made against a known reference temperature, which increases the electrical circuitry of the measuring circuit for determining the temperature.

[0009] For example, application DE 10 2019 115 962 A1 describes a pressure sensor in which the temperature of the medium is also determined in addition to the pressure of the medium. The problem is described here that coupling to a temperature sensor often leads to poor temperature measurement accuracy. As a solution, the document proposes using a contact pin, which is electrically connected to one of the electrodes and the evaluation circuit of a capacitive pressure measuring cell, as a heat conductor and then thermally coupling this contact pin to a temperature-dependent resistance element so that the contact pin transfers the heat transferred to it to the temperature sensor with particularly low loss. A platinum temperature sensor in a standardized SMD design is proposed as the temperature sensor.This allows the thermal coupling and thus the accuracy of the measurement to be improved, however the measurement is carried out locally by the contact pin and the installation of the contact pin in the pressure measuring cell requires thermal shielding of the contact pin so that the heat is essentially completely transported to the temperature sensor, which in turn is associated with higher construction effort and costs.

[0010] It is therefore an object of the invention to overcome the aforementioned disadvantages of the prior art and to provide a sensor protective screen with a protective screen heater, which has a high degree of accuracy, can be implemented cost-effectively and can be produced with little effort, as well as a method for measuring the temperature of a sensor protective screen with a protective screen heater.

[0011] The object is achieved by the sensor protection screen according to claim 1, as well as the method according to claim 13. Further embodiments are the subject of the dependent claims.

[0012] The sensor protective screen according to the invention with a protective screen heater has a measuring circuit and a, in particular optically transparent, thin-film layer, wherein an elongated contact electrode is arranged on the thin-film layer, and a heating current I_H flows from the elongated contact electrode through the thin-film layer to a further contact electrode on the thin-film layer, and a temperature measuring current I_T of the measuring circuit flows through the elongated contact electrode, so that the elongated contact electrode also acts as a temperature-dependent measuring resistor, or a temperature measuring current I_T of the measuring circuit flows from the elongated contact electrode through the thin-film layer to the further contact electrode, so that the thin-film layer also acts as a temperature-dependent measuring resistor.

[0013] An optically transparent thin film layer is a thin layer of a material that is applied to the surface of a protective screen. This can be a true thin film or foil, or for example, a layer made of so-called carbon nanotubes. In general, a thin film layer has a significantly smaller thickness compared to the size of the surface of the protective screen on which it is located. This layer can be made of various materials, including metals, semiconductors, dielectrics, or organic compounds. The thickness of the thin film layer can vary depending on the application, but typically ranges from a few nanometers to a few micrometers. The thin film layer can be applied to the protective screen using physical or chemical deposition processes such as vapor deposition, sputtering, chemical vapor deposition, or spin coating.Controlling the thickness and composition of the thin film layer allows specific properties such as electrical conductivity, light transmittance, and scratch resistance to be specifically influenced. In this case, the electrical resistance of the layer can be adjusted by the thickness and material of the layer so that the layer heats up when an electrical heating current I_H is passed through the layer. For this purpose, the thin film layer has at least two contact electrodes to which electrical conductors, for example electrical wires such as metal wires, copper wires, aluminum wires, gold wires, or platinum wires for coupling in the heating current I_H are applied, for example by a soldering process or by welding. The external contact of the electrodes is realized, for example, by contact springs, which establish contact with the electrode only through contact force.The heating current then flows from one contact electrode to the other through the thin-film layer. The electrical power of the heating current heats the thin-film layer due to its electrical resistance.

[0014] In this context, contact electrodes are understood to mean, in particular, thin-film electrodes, which are applied to the thin-film layer using the methods described above. However, screen printing methods, for example, can also be used to print contact electrodes onto the thin-film layer using a screen-printing paste. A contact electrode is electrically conductive, so that an electrical conductor attached to the contact electrode, for example a metal wire, couples current, in particular the heating current I_H, into the contact electrode and from the contact electrode into the thin-film layer, so that a current flows between the contact electrodes through the thin-film layer.

[0015] In the present case, an elongated contact electrode is understood to mean, in particular, a rectangular electrode, i.e., in particular, an electrode in the shape of an elongated conductor and having a first and second end, such that a current, in particular a temperature measurement current I_T, can flow from the first to the second end of the elongated electrode when the electrode is electrically contacted by an electrical conductor at the first end and at the second end. The contact electrode can have contact points configured for electrical contacting by a conductor at the first and / or second end.

[0016] The temperature of the thin-film layer and thus the temperature of the protective screen heater is controlled by the heating current I_H. The control is based on determining the temperature of the thin-film layer. For this purpose, the protective screen heater comprises a measuring circuit that provides a temperature measuring current I_T. The temperature measuring current flows either through the thin-film layer or, alternatively and preferably, through the elongated contact electrode. The ohmic resistance is fundamentally temperature-dependent; thus, the ohmic resistance of the thin-film layer or the ohmic resistance of the elongated contact electrode changes depending on the temperature. This means that the thin-film layer, in addition to its function as a heating layer, can also be used as a temperature sensor or as a temperature-dependent measuring resistor. In the preferred alternative, the elongated contact electrode, in addition to its function as an electrode, is also used as a temperature sensor or as a temperature-dependent measuring resistor.To measure resistance, i.e., temperature, which is essentially proportional to the change in resistance, a temperature-compensated constant current is applied to the elongated contact electrode or to the thin-film layer. A change in the heating current changes the temperature and thus the resistance of the thin-film layer. If the thin-film layer is also used directly as a temperature-dependent measuring resistor, i.e., as a temperature sensor, the change in resistance of the thin-film layer results in a temperature-induced voltage drop in the measuring circuit. The measuring circuit includes a measuring amplifier that increases the voltage drop to a specific voltage level. This voltage is recorded by an analog-to-digital (A / D) converter in the measuring circuit and digitized for further processing.

[0017] If, alternatively and preferably, the elongated contact electrode is also used directly as a temperature-dependent measuring resistor, i.e., as a temperature sensor, the temperature-dependent ohmic resistance change of the elongated contact electrode results from the change in the temperature of the thin-film layer, since the temperature change is directly transferred to the temperature of the contact electrodes. This results in a temperature-induced voltage drop in the circuit of the measuring circuit. The measuring amplifier of the measuring circuit increases the voltage drop to a certain voltage level, and the analog-to-digital (A / D) converter of the measuring circuit records the voltage level and digitizes it for further processing. Theoretically, both electrodes could also be used for temperature measurement, although this would require somewhat more electronic circuitry.

[0018] A particularly advantageous feature is that the electrical coupling of the contact electrodes on the thin-film layer also ensures particularly good thermal coupling, eliminating the need for specific components required for heat conduction or modifications to the structure of the protective screen itself. Furthermore, the particularly good thermal coupling also ensures particularly high temperature measurement accuracy. Another advantage is that no additional temperature sensor, such as a PT resistance sensor, is required as an additional component. This allows the protective screen heating to be implemented in a sensor protective screen particularly cost-effectively and without complex modifications.

[0019] In a particularly preferred embodiment of the sensor protection screen, the additional contact electrode is also designed as an elongated contact electrode. This has the advantage that, for example, a temperature measuring current I_T can be conducted through both elongated contact electrodes, thus allowing the temperature to be determined more accurately by averaging.

[0020] In a particularly preferred embodiment of the sensor protective screen, the two elongated contact electrodes are arranged opposite each other, in particular parallel to each other, on the thin-film layer. This arrangement has the advantage that the heating current I_H heats the thin-film layer symmetrically, thus resulting in higher temperature measurement accuracy, since the temperature distribution is evenly distributed, or homogeneous, over a wide area of ​​the thin-film layer.

[0021] In a particularly preferred embodiment of the sensor protective screen, the elongated contact electrode is formed along a long side edge of the thin-film layer, in particular along the entire long side edge of the thin-film layer. In the present case, a long side edge of the thin-film layer is understood to mean the longer side of the geometric surface on which the thin-film layer is formed. If, for example, the thin-film layer is rectangular, the long side edge corresponds to the longer side surface of the rectangle. This has the advantage that the heating current I_H is coupled into the thin-film layer over a long region of the latter, thus creating a more homogeneous electric field distribution because the heating current runs undisturbed over a long region of the field distribution, i.e., it spreads throughout the thin-film layer.This means that the temperature is distributed more homogeneously within the thin film layer and thus the temperature measurement represents the actual temperature more accurately.

[0022] In a particularly preferred embodiment of the sensor protection disk, the temperature measuring current I_T flows through the entire elongated contact electrode. This means that the entire length of the elongated contact electrode also acts as a resistance-dependent temperature sensor, making the measurement more accurate, particularly when the elongated electrode runs along the longest side edge of the thin-film layer. This means that in such a case, the elongated contact electrode comprises, for example, a first end with a first contact point for contacting an electrical line of the measuring circuit and a second end at which a further contact point is provided for contacting another electrical line of the measuring circuit.

[0023] In a preferred embodiment of the sensor protection screen, the thin-film layer comprises or is formed as an indium tin oxide (ITO) layer. Other materials are conceivable and known from the literature, such as antimony tin oxide (ATO).

[0024] In a particularly preferred embodiment of the sensor protective screen, the elongated contact electrode is designed as a thin-film electrode and, in particular, has or is designed as a gold-nickel layer. Other materials such as platinum, tungsten, aluminum, and the like that can be electrically connected to the heating layer are possible.

[0025] The design of the particularly elongated contact electrode as a thin-film layer electrode has the advantage that the layer can be applied to the thin-film layer in an electrically conductive manner using conventional thin-film technologies, which ensures particularly good thermal conductivity and the heat of the thin-film layer is transferred to the particularly elongated contact electrode with particularly low loss.

[0026] In a particularly preferred embodiment of the sensor protective screen, the measuring circuit has a temperature-compensated constant current source which provides the temperature measuring current I_T.

[0027] In a preferred embodiment of the sensor protection disc, the elongated contact electrode comprises an electrical resistance in the range of 1 to 10 Ω and the thin film layer comprises an electrical resistance in the range of 20 to 200 Ω.

[0028] The electrical resistance of the thin-film layer and / or the elongated contact electrode in a thin-film layer electrode design can advantageously be adjusted, in particular continuously, via the thickness of the thin-film layer. This allows a large difference between the electrical resistance of the elongated contact electrode and the thin-film layer to be achieved, thereby advantageously reducing the influence on the heating and temperature measurement resulting from the heating of the contact electrodes by the current flow, I_H or I_T.

[0029] In a preferred embodiment of the sensor protective screen, the measuring circuit has at least one switch, so that while the temperature measuring current I_T is flowing, the heating current I_H can be interrupted, i.e., the heating current I_H is not flowing. This has the advantage that the heating current does not influence the temperature measurement. In a particularly advantageous embodiment, the protective screen heater has one switch each for a heating current circuit of the heating current I_H and one for a temperature measuring current circuit of the temperature measuring current I_T, so that the currents cannot influence each other.

[0030] In a preferred embodiment of the sensor protective screen, the measuring circuit has an amplifier that converts the temperature measuring current I_T into a proportional voltage and an analog-to-digital converter that converts the proportional voltage into a digital signal.

[0031] In a further preferred embodiment of the sensor protection screen, the measuring circuit uses the heating current I_H as the temperature measuring current I_T or provides the heating current I_H. This embodiment offers the advantage that the complexity of the electrical circuits, in particular the measuring circuit, can be simplified and components can be saved cost-effectively.

[0032] The invention further relates to a method for determining the temperature of a sensor protective screen, in particular comprising a protective screen heater, comprising the following steps: - Providing a heating current I_H and a measuring circuit that generates a temperature measuring current I_T; - Providing a particularly optically transparent thin film layer on the sensor protective screen; - Providing an elongated contact electrode and another contact electrode as electrical connections of the thin film layer; - connecting the elongated contact electrode and the further contact electrode to an electrical circuit such that the heating current I_H flows from the elongated contact electrode through the thin film layer to the further contact electrode; - Connecting the elongated contact electrode and the further contact electrode to a circuit of the measuring circuit such that the temperature measuring current I_T flows from the elongated contact electrode through the thin-film layer to the further contact electrode and the thin-film layer also acts as a temperature-dependent measuring resistor; Alternatively, and particularly preferably, the elongated contact electrode is connected to a circuit of the measuring circuit such that the temperature measuring current I_T flows through the elongated contact electrode and the elongated contact electrode also acts as a temperature-dependent measuring resistor.

[0033] In a preferred variant of the method for determining the temperature of a sensor protective screen with a protective screen heater, the method additionally comprises the following step that the elongated contact electrode and the further contact electrode are applied as elongated thin-film layer electrodes, in particular on opposite long side edges of the thin-film layer.

[0034] In a further preferred variant of the method for determining the temperature of a sensor protective screen with a protective screen heater, the method further comprises the following step of connecting at least one of the electrical thin-film layer electrodes to the circuit of the measuring circuit, so that the temperature measuring current I_T flows, in particular completely, through the thin-film layer electrode and the thin-film layer electrode also acts as a temperature-dependent measuring resistor.

[0035] Further preferred embodiments of the sensor protective screen according to the invention and of the method for measuring the temperature of a sensor protective screen with a protective screen heater will become apparent from the following description of the exemplary embodiments in conjunction with the figures and their description. Identical components are essentially identified by identical reference numerals unless otherwise stated or apparent from the context. Fig. 1 shows a schematic representation of the sensor protective screen with a protective screen heater; Fig. 2 shows a sectional view A of the Fig. 1 shown illustration of the sensor protection screen.

[0036] In Fig. 1 shows an embodiment of the sensor protective screen 1 with a protective screen heater, wherein the protective screen heater has a measuring circuit 2. In the Fig. In the embodiment shown in Figure 1, the thin-film layer 3 is shown rectangularly on the sensor protective screen as a thickly hatched area. Within this sharpened area of ​​the thin-film layer 3, a rectangular, elongated contact electrode 4 is shown, which is connected to the measuring circuit 2 by electrical conductors 15. The electrical conductors 15 are, for example, soldered or welded onto contact points 13 of the elongated contact electrode 4. The contact points 13 are located at the respective ends of the rectangularly shown contact electrode 4, so that the temperature measuring current I_T flows through the entire elongated contact electrode 4, starting from the switch 8, to a reference potential, which can be the ground 14 or something other than the system ground. The exemplary current direction of the temperature measuring current I_T is shown in Fig. 1 is indicated by an arrow. The measuring circuit 2 further comprises the amplifier 9 and the A / D converter 10, which are Fig. 1 are symbolically represented outside the sensor's protective screen. The switch 8 of the measuring circuit 2 can be used to separate the temperature measurement current from the constant current source 7, i.e., to interrupt the current flow I_T. This prevents the currents I_T and I_H from influencing each other. Another similar switch 8 is also located in the heating current I_H circuit, so that I_H can also be separated from the current source 12, thus preventing it from influencing the temperature measurement.

[0037] Opposite the elongated contact electrode 4, the electrode 5 is also located on the long side edge 6 of the thin film layer 3, which is arranged in the Fig. 1, is also rectangular in shape as an elongated contact electrode. The two contact electrodes are arranged opposite each other and parallel to each other on the respective long side edges 6 of the thin-film layer 3, so that a homogeneous electric field can spread over large parts of the thin-film layer to heat the thin-film layer. There are no electrodes along the short side edge 11 of the thin-film layer 3. The direction of the heating current I_H in the thin-film layer is indicated by the arrow marked I_H. In the embodiment shown in Fig. In the embodiment shown in Figure 1, the temperature is measured by the propagation of the temperature measurement current I_T in the elongated contact electrode 4, i.e., the elongated contact electrode serves as a temperature-dependent resistor. Since the contact electrodes 4, 5 are applied to the thin-film layer 3 in an electrically conductive manner, the thermal conduction or heat transfer from the thin-film layer to the contact electrodes 4, 5 is also very good, which is why the temperature measurement is very accurate.

[0038] In Fig. 2 is a sectional view A of the Fig. 1. The direction of the heating current I_H is indicated by the arrow labeled I_H. The propagation of the temperature measuring current I_T is represented by the circled cross labeled I_T. The contact electrode 4 has an electrical conductor 15 on its contact point 13, through which the connection to the measuring circuit 2 is established. In the contact area between the contact point 13 and the conductor 15, an oval thickening is shown, which is intended to indicate soldering or welding material for contacting the conductor 15 on the contact electrode 4. The contact electrode 5 is according to the Fig. 1 is shown without a conductor 15, since only one contact point 13 of the contact electrode 5 is connected to the power source 12 with a conductor 15. List of reference symbols 1 sensor protective screen 2 measuring circuit 3 Thin film layer 4 Elongated contact electrode 5 Contact electrode 6 Long side margin 7 Constant current source 8 switches 9 amplifiers 10 analog-to-digital converters 11 Short margin 12 Power source 13 contact points 14 Grounding 15 Electrical conductor QUOTES CONTAINED IN THE DESCRIPTION

[0000] This list of documents submitted by the applicant was generated automatically and is included solely for the convenience of the reader. This list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions. Cited patent literature

[0000] DE 10 2019 115 962 A1

[0009]

Claims

[1] Sensor protective screen (1) with a protective screen heater, comprising a measuring circuit (2) and a particularly optically transparent thin-film layer (3), wherein an elongated contact electrode (4) is arranged on the thin-film layer (3), and a heating current (I_H) flows from the elongated contact electrode (4) through the thin-film layer (3) to a further contact electrode (5) on the thin-film layer (3), and a temperature measuring current (I_T) of the measuring circuit (2) flows through the elongated contact electrode (4), so that the elongated contact electrode (4) also acts as a temperature-dependent measuring resistor, or a temperature measuring current (I_T) of the measuring circuit (2) flows from the elongated contact electrode (4) through the thin-film layer (3) to the further contact electrode (5), so that the thin-film layer (3) also acts as a temperature-dependent measuring resistor. [2] Sensor protection screen according to claim 1, characterized bythat the further contact electrode (5) is also designed as an elongated contact electrode (4). [3] Sensor protection screen according to claim 2, characterized by that the two elongated contact electrodes (4) are arranged opposite each other on the thin film layer (3). [4] Sensor protection screen according to one of the preceding claims, characterized by that the elongated contact electrode (4) is formed along a long side edge (6) of the thin film layer (3), in particular along the entire long side edge (6) of the thin film layer (3). [5] Sensor protection screen according to one of the preceding claims, characterized by that the temperature measuring current (I_T) flows through the entire elongated contact electrode (4). [6] Sensor protection screen according to one of the preceding claims, characterized by that the thin film layer (3) comprises an indium tin oxide layer (ITO layer). [7] Sensor protection screen according to one of the preceding claims, characterized by that the elongated contact electrode (4) is designed as a thin-film layer electrode and in particular has a gold-nickel layer. [8] Sensor protection screen according to one of the preceding claims, characterized by that the measuring circuit (2) has a temperature-compensated constant current source (7) which provides the temperature measuring current (I_T). [9] Sensor protection screen according to one of the preceding claims, characterized by that the elongated contact electrode (4) has an electrical resistance in the range of 1 to 10 Ω and the thin film layer (2) has an electrical resistance in the range of 20 to 200 Ω. [10] Sensor protection screen according to one of the preceding claims, wherein the measuring circuit (2) has at least one switch (8) so that while the temperature measuring current (I_T) is flowing, the heating current (I_H) can be interrupted. [11] Sensor protection screen according to one of the preceding claims, wherein the measuring circuit (2) comprises an amplifier (9) which converts the temperature measuring current (I_T) into a proportional voltage and an analog-digital converter (10) which converts the proportional voltage into a digital signal. [12] Sensor protection screen according to one of the preceding claims, characterized by that the measuring circuit (2) also uses the heating current (I_H) as the temperature measuring current (I_T). [13] Method for determining the temperature of a sensor protective screen (1), comprising a protective screen heater, comprising the following steps: - Providing a heating current (I_H) and a measuring circuit (2) which generates a temperature measuring current (I_T); - Providing a particularly optically transparent thin film layer (3) on the sensor protective screen (1); - providing an elongated contact electrode (4) and a further contact electrode (5) as electrical connections of the thin film layer (3); - connecting the elongated contact electrode (4) and the further contact electrode (5) to a circuit so that the heating current (I_H) flows from the elongated contact electrode (4) through the thin film layer (3) to the further contact electrode (5); - Connecting the elongated contact electrode (4) and the further contact electrode (5) to a circuit of the measuring circuit (2) such that the temperature measuring current (I_T) flows from the elongated contact electrode (4) through the thin-film layer (3) to the further contact electrode (5) and the thin-film layer (3) also acts as a temperature-dependent measuring resistor; or connecting the elongated contact electrode (4) to a circuit of the measuring circuit (2) such that the temperature measuring current (I_T) flows through the elongated contact electrode (4) and the elongated contact electrode (4) also acts as a temperature-dependent measuring resistor. [14] Method for determining the temperature of a sensor protective screen (1) comprising a protective screen heater, according to claim 13, further comprising the following step: - applying the elongated contact electrode (4) and the further contact electrode (5) as elongated thin-film layer electrodes on the thin-film layer (3), in particular on opposite long side edges (6) of the thin-film layer (3). [15] Method for determining the temperature of a sensor protective screen (1), comprising a protective screen heater according to claim 14, further comprising the following step: - Connecting at least one of the electrical thin-film electrodes to the circuit of the measuring circuit (2) so that the temperature measuring current (I_T) flows completely through the thin-film electrode and the thin-film electrode also acts as a temperature-dependent measuring resistor.

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