Control device for an electric surface heating and surface heating

Abstract

The invention relates to a control device for an electric surface heating system, wherein a current difference between two connection arrangements is determined and used to detect a fault condition. The invention further relates to a surface heating system with such a control device.

Description

[0001] The invention relates to a control device for an electric surface heating system and a surface heating system with such a control device.

[0002] Surface heating systems are often used to heat living spaces or the interior of units such as mobile homes, caravans, boats, or other mobile or stationary facilities. In the electrical version of such surface heating systems, current is typically passed through one or more electrical conductors. These electrical conductors are laid in a flat element, which is then heated using the principle of resistance heating. A surface thus heats up and thus heats, for example, a room.

[0003] It has been found that such surface heating systems can fail if they are improperly handled after installation. For example, a motorhome owner might drive a screw into a surface to secure another element, such as a coat rack. This could damage an electrical conductor in the surface heating system.

[0004] It is therefore an object of the invention to provide a control device for an electric surface heating system that, compared to known designs, is designed alternatively or, for example, is better configured to respond to fault conditions. It is further an object of the invention to provide a surface heating system that includes such a control device. This is achieved according to the invention by a control device and a surface heating system according to the respective main claims. Advantageous embodiments are claimed in the respective subclaims.

[0005] The invention relates to a control device for an electric surface heating system. The control device has a first connection arrangement and a second connection arrangement. An electrical conductor of the surface heating system can be connected between the first connection arrangement and the second connection arrangement. The first connection arrangement and the second connection arrangement are designed to apply an electrical current to the electrical conductor of the surface heating system. The control device has a current difference measuring device configured to measure a current difference between the first connection arrangement and the second connection arrangement. The control device has an evaluation device configured to detect an error condition based on the current difference exceeding a current difference threshold value.

[0006] Using such a control device, not only can the supply of electrical current to an electrical conductor of a surface heating system be ensured, but it can also automatically detect the presence of a fault. In particular, it has been shown that such a fault becomes noticeable when there is a difference in current strength between the first connection arrangement and the second connection arrangement. If, for example, a screw is driven into a surface heating system and inadvertently contacts an electrical conductor of the surface heating system, a fault current can occur at the contact point between the screw and the surface heating system. Such a fault current then leads to the current occurring at the first connection arrangement being different from the current occurring at the second connection arrangement.Some of the current is thus lost along the way and is dissipated, for example, via the screw and other elements. The control device described here thus reliably protects against further damage that could occur due to unintentional current flow, such as fire or material damage. Damage caused by another object, particularly a conductive foreign body, is also possible instead of a screw being driven in; in this case, the protective mechanism described here also applies.

[0007] The control device can in particular be designed as an electronic, analogue, or combined electronic and analogue device. For example, it can contain a microprocessor or a microcontroller that can perform the monitoring and / or control tasks described herein. For example, the control device can contain processor means and memory means, wherein the memory means contains program code, the execution of which causes the processor means to behave in the manner described herein. In particular, the memory means can be non-volatile memory means. Alternatively, however, a purely analogue design of the control device is also possible, for example. A surface heating system is understood to mean, in particular, an element that serves to heat a surface.For example, the surface could be the surface of a piece of furniture or the wall of a unit such as a caravan, motorhome, boat, or stationary building. Typically, it is used to heat an interior space, but it can also be used to heat an exterior space.

[0008] In particular, the control device can be designed to operate in the low-voltage range. This can mean, in particular, that the voltage applied to the surface heating system is a maximum of 36 V. Accordingly, a power supply of the control device can be designed to receive such a voltage or to step down a received mains voltage, which may be higher.

[0009] The first connection arrangement can, in particular, have one or more first connections, and the second connection arrangement can, in particular, have one or more second connections. The electrical conductor of the surface heating system can be connected to these connections. This allows it to be supplied with current. To apply the electrical current, a voltage source or a current source can, for example, be contained in the control device or connected to the control device. For example, such a voltage source or current source can be connected to a power supply such as a public grid, an in-house network, or the on-board network of a mobile unit.

[0010] The current difference measuring device measures the current difference between the two terminal arrangements. If a terminal arrangement has only one terminal, the current flowing through this terminal typically corresponds to the total current of the terminal arrangement. If the terminal arrangement has multiple terminals, a total current is typically formed across these terminals, which is then measured by the current difference measuring device. The decisive factor for detecting a fault is typically not the absolute value of a current, but rather the difference between the two terminal arrangements. Such a difference typically provides an indication of a fault condition.

[0011] According to one embodiment, the current difference threshold can be zero, so that a fault condition is detected at any measurable current difference. However, the current difference threshold can also have a positive absolute value, so that certain current differences are tolerated, which, for example, may also occur during typical operation, even if no fault condition exists.

[0012] It should be understood that when comparing the current difference and the current difference threshold, the absolute value is fundamentally important. That is, it would be equivalent for a positive current difference to exceed a positive current difference threshold and for a negative current difference to fall below a negative current difference threshold. Corresponding implementations are considered equivalent.

[0013] The evaluation device can be electronic or analog, for example. Please refer to the relevant explanations above.

[0014] In particular, the control device can be configured to switch off or reduce the current at the first terminal arrangement and / or the second terminal arrangement in response to the detection of a fault condition. This allows immediate response to a detected fault condition. By switching off or reducing the current, the risk of a fire or other escalation of the fault can be prevented.

[0015] In particular, the control device can be configured to issue an alarm in response to the detection of a fault condition. Such an alarm can be issued, for example, visually, acoustically, and / or by issuing an electronic signal to another unit. This can immediately warn an operator that a fault condition exists. For example, this can prompt the operator to unscrew a screw screwed into the underfloor heating system or to arrange for an inspection by a specialist.

[0016] According to one embodiment, the first connection arrangement has only a first connection. According to one embodiment, the second connection arrangement has only a second connection. Typically, the entire current at the first connection arrangement or at the second connection arrangement is output via the respective connection. From such a connection, the current can be conducted, for example, via a respective connecting cable to the electrical conductor of the surface heating. The electrical conductor then typically has a resistance suitable for generating heat due to the flowing electrical current. For a wire of a certain diameter and length, the resistance [ohms], together with the voltage, determines the heating. A connection is typically understood to be a socket, a plug, or other contact for attaching a connector or for soldering, clamping, or otherwise securing a connecting cable.

[0017] According to one embodiment, the first connection arrangement has a plurality of first connections. According to one embodiment, the second connection arrangement has a plurality of second connections. This allows the current at the respective connection arrangement to be distributed among a plurality of connections. The current-carrying capacity of a respective connection or a respective connecting line to the electrical conductor can thus be selected to be lower. Furthermore, a certain degree of redundancy can be achieved, so that, for example, functionality is still possible if a connection or connecting line fails.

[0018] According to one embodiment, the control device is configured to apply the current in a timed manner. This allows the desired power output of a surface heating system to be set in a suitable manner. A timed application of a current can, in particular, mean that the current or voltage is on for certain periods of time and then off for certain periods of time. Such periods can, in particular, alternate. During a period in which the current or voltage is on, the current or voltage can typically be applied unchanged. Subsequently, the current or voltage is switched off for a certain period of time.

[0019] In particular, the control device can be configured to measure a temperature. The control device can be configured, in particular, to apply current only when the temperature falls below a temperature threshold. This can, for example, provide for the control device to only provide heating for the surface heating when the temperature is low. If, for example, a room is already warm enough and the temperature therefore does not fall below the temperature threshold, heating can be omitted. This can save energy.

[0020] According to one embodiment, the current difference measuring device comprises a first current measuring device and a second current measuring device. The first current measuring device is particularly designed to measure a first current at the first connection arrangement, and the second current measuring device is particularly designed to measure a second current at the second connection arrangement. The current difference measuring device is particularly configured to calculate the current difference based on the first current and the second current. As a result, the currents can initially be measured separately, with a current difference subsequently being calculated. In particular, a difference between the two currents can be calculated. Alternatively, a direct measurement of a current difference is also possible.

[0021] In particular, the control device can be configured to limit the current, the first current, and / or the second current to a maximum value. This allows for additional safety, for example, preventing fires caused by excessive currents. For example, the current to be limited can refer to the maximum current present during the on-phases of a clocking operation. Alternatively, the current to be limited can also refer to the average or effective current during a clocking operation or to a constant current.

[0022] The invention further relates to a surface heating system. The surface heating system has an electrical conductor. The surface heating system has a control device, in particular a control device as described herein. With regard to the control device, all embodiments described herein can be used. The electrical conductor is connected to the first connection arrangement and the second connection arrangement of the control device. By means of such a surface heating system, the advantages already described above can be achieved. In particular, safety can be increased.

[0023] The electrical conductor can be designed, in particular, as an electrically conductive wire, especially a single-phase one. It can be laid, for example, straight, flat, in serpentine lines, or in any other form within the surface heating system or a flat element.

[0024] According to one embodiment, the first connection arrangement has a plurality of first connections and / or the second connection arrangement has a plurality of second connections. The electrical conductor can, in particular, be connected to a plurality of first connections or to a plurality of second connections. This allows the total current flowing through the electrical conductor to be distributed among a plurality of connections, thereby reducing the respective required current-carrying capacity.

[0025] According to one embodiment, the surface heating has a first contact, at which the electrical conductor is connected to a plurality of first connecting lines to the first connections. According to one embodiment, the surface heating has a second contact, at which the electrical conductor is connected to a plurality of second connecting lines to the second connections. Such embodiments can in particular also be used independently of the other embodiments described herein and can be regarded as a separate aspect of the invention. The first contact and / or the second contact can, for example, be designed as a plug or socket for a plug. They can, for example, be arranged in a flat element which is to be heated and in which the electrical conductor is laid.

[0026] The electrical conductor can have only one electrical connection, in particular between the first contact and the second contact. Parallel current conduction can be dispensed with. This increases the current strength in the electrical conductor. The resistance can be specified, in particular, in ohms per unit area. A flat electrical conductor, which in particular has a predetermined electrical resistance to generate a heating effect, can be contacted by low-resistance electrodes. These can, in particular, be arranged on both sides and ensure even current distribution. They typically require only one contact each, which is then typically connected to the control device.

[0027] In particular, the first connecting leads can be detachable from the electrical conductor at the first contact. In particular, the second connecting leads can be detachable from the electrical conductor at the second contact. This allows for improved modularity and usability. For example, a flat element with the two contacts can be installed, and the connecting leads can then be connected. This is generally also possible if only a first connection and / or only a second connection is used.

[0028] According to an alternative embodiment, the surface heating system can have one or more additional electrical conductors connected in parallel with the electrical conductor. This makes it possible, for example, to supply multiple electrical conductors, which may be installed in a single flat element, with just one first connection and / or just one second connection.

[0029] According to one embodiment, in the event of polarity reversal, i.e., an error in connecting the control device to a power source, a differential current can be induced in components of the control device, whereby the circuit already implemented in the control device, described above, detects a current difference and reacts accordingly. This allows for automatic polarity reversal protection to be implemented.

[0030] A surface heating system can, for example, be designed as a radiant panel. Such surface heating systems can be used, for example, in the interior design of buildings, mobile homes, ships, or similar vehicles. In particular, these can be land vehicles, watercraft, or aircraft.

[0031] Such surface heating systems typically operate at low voltage, particularly in the extra-low voltage range. Such heaters can typically be pressed or laminated into substrate materials. Heating surfaces typically feature a less conductive material to achieve the required performance. Such "lost" power is typically converted into heat as evenly as possible across the surface to avoid hot spots. The production of such electrically homogeneous surfaces is typically well-known.

[0032] An externally visible decorative side of such a heat radiator panel can be formed, for example, by a wood veneer, but it is also possible to use printed paper, which is protected from abrasion and moisture by an outer layer of melamine resin, similar to a kitchen worktop. The actual heating surface can, for example, be as thin as paper, contain carbon fibers, and / or be provided with thin electrical conductors, for example in the form of copper strips or in the form of a sprayed-on copper material, e.g. with a very thin layer. Contacting can be problematic, for example, if you want to achieve corresponding power or heat. For this purpose, the contacts can be arranged in parallel, for example, so that the same currents are always achieved within the direct connection line between the electrodes.Since the voltage is constant and the material can be considered homogeneous, shorter distances between the electrodes will heat up more than longer distances.

[0033] For example, if you assume a low voltage of 36 VDC and want to heat an area with approximately 700 W, this typically requires currents of approximately 20 A flowing through a contact. The power supply and transitions to the electrodes must be designed accordingly. Such a contact can, for example, be implemented as multiple contacts, so that the total current can be distributed across the number of contacts. This is a separate aspect of the invention.

[0034] Surface heating elements, such as veneers, are typically not recognizable as such due to their use. Therefore, there is a risk of accidental damage. It's not the operating voltage that's dangerous—this is typically comparable to an electric train—but rather the high current generated by the desired heating. The less visible the electrical conductors are from the outside of a finished panel, the more difficult it can be to ensure reliable, large-area electrical contact between these conductors.

[0035] In the event of accidental contact due to damage, for example, due to a screw, nail, or similar element being inserted into the surface element without knowledge of the risk, a faulty condition can occur. Faulty contacts can therefore occur during the installation of a radiant panel, for example, as a furniture front in a factory that manufactures the interior of a mobile home. Another fault can occur later during the use of the mobile home or the radiant panel by the end customer, for example, if they drive thumbtacks, screws, or nails into the furniture surface and damage the heating layer of the laminate.

[0036] Parasitic currents in such locations would lead to excessive heating and fires. Even small currents can cause damage through galvanic effects, even in completely different locations, since the current path is unpredictable.

[0037] Monitoring the current is therefore a challenge, as it determines the power output. This is especially true at the contacts to the electrodes, as this is where the current is concentrated and transfers from the connecting wire to the electrode embedded in the material. If the contact resistance increases here, for example, due to a poor contact, the current in the supply line decreases, but the increased voltage drop at the contact causes the power loss at the contact itself to rise sharply, and the area can become overheated.

[0038] What is therefore proposed here is a heating control system that, in addition to temperature control, includes differential current measurement. This is based in particular on the consideration that the outgoing and returning current are identical without a malfunction. Anything else means that there is a fault in the system and current is taking an uncontrolled path. In the event of a fault, the control system can, for example, cause the heating to be turned down. Alternatively or additionally, an alarm can be triggered. The differential current measurement will typically always result in the value "zero" if there is no fault. Similar to what is known from residual current circuit breakers, small tolerances can also be taken into account in the control system, meaning that slight differences in current strength can be tolerated if necessary.

[0039] For example, a maximum current can be set to ensure that the surface only reaches a certain maximum temperature, such as a maximum temperature of 60 °C. This current can depend, in particular, on the heating material (surface resistance), the electrode spacing on the heating material, the length of the electrodes or the heating medium, and the ambient temperature. Ideally, the maximum current is determined empirically, for example, by measuring in perfect condition and at a controlled ambient temperature. If the material parameters are known and a room temperature of 20 °C can be assumed, for example, the heating module could also control the temperature itself.

[0040] In particular, the control can also enable overcurrent measurement.

[0041] A target temperature can be set, for example, using a pulse generator or a similar method. It can be set quasi-continuously between 0% and 100%. The current occurring during an active phase typically always corresponds to the maximum current. The output power can be set, for example, using a pulse-pause ratio (PVR) of a control voltage. This allows the heater temperature to be controlled. Due to the relatively large heat capacity, the frequency of the PVR can be relatively low, for example, 10 Hz or less, particularly because the heat capacity, with its integrating effect, cannot map temperature jumps. Furthermore, acoustic side effects are excluded due to the low frequency.

[0042] For example, additional protective measures can be provided that are relevant in the event that the proposed heating control system is connected directly to a battery without a backup fuse, for example, contrary to the installation instructions. For example, in the event of a fault, a short circuit, such as the failure of a semiconductor in the circuit and a missing or overly large backup fuse, can prevent higher than the permissible maximum currents from flowing for an extended period. A direct battery circuit in a motor vehicle is typically limited only by the internal resistance of the battery, which is typically on the order of magnitude of a starting current.

[0043] If the supply voltage is reversed, higher currents can also flow through the heating module. Electrical components such as protective diodes are typically not a sensible solution in this case. Connected in series, they are typically required to have the same current-carrying capacity as the rest of the circuit and would therefore heat up considerably, representing avoidable power loss. Connected in parallel with the input voltage, they are intended to trigger the power supply or backup fuse by briefly overloading the external circuit. This, too, only works if everything is connected correctly. Reverse polarity protection can be provided, for example, by a specially designed relay circuit that safely interrupts the power supply in the event of an overcurrent or even prevents the power supply from being switched on in the event of reverse polarity. It is often overlooked that high direct currents generate arcs when interrupted.These are preferably extinguished or mechanically interrupted by means of a separating blade or similar. Since losses always occur in the components with high switched currents, an internal temperature monitor can also be integrated. This ensures safe shutdown in the event of overheating and prevents restart before a lower temperature threshold is reached. A temperature check of the module or control device can also be carried out before the heater is switched on. Vehicles or interiors can heat up considerably on their own and without being in operation, for example due to sunlight. This also applies to a heating module or control device when switched off. Therefore, the internal temperature threshold can advantageously be checked before the heater is switched on.

[0044] The heating control or control device can be operated, for example, via one or more buttons or via a wireless interface. In addition, status information such as output power, set currents, faults, etc. can be communicated wirelessly, thus simplifying operation for the operator.

[0045] The invention will now be described with reference to the drawing, which shows: Fig. 1: a surface heating system.

[0046] Fig. 1 shows a surface heating system 10 according to an embodiment of the invention.

[0047] The surface heating system 10 comprises a flat element 20. This can, for example, be a panel installed in a piece of furniture. An electrical conductor 30 is provided in the flat element 20. This is typically installed in such a way that it is not visible from the outside. In this case, the electrical conductor 30 is flat, but it could also be designed as a wire, for example, that is installed in the flat element 20.

[0048] The planar element 20 has a first contact 40 and a second contact 50. The electrical conductor 30 is connected to the first contact 40 and the second contact 50, so that any current between the two contacts 40, 50 flows through the electrical conductor 30. Parallel current paths are not provided, thus a single-phase wiring arrangement is realized.

[0049] The surface heating system 10 further comprises a control device 100. The control device 100 comprises a first connection arrangement 110 with, in this case, three first connections 112 and a second connection arrangement 120 with, in this case, three second connections 122. The first connections 112 are connected to the first contact 40 via first connection lines 45. The second connections 122 are connected to the second contact 50 via second connection lines 55. The connection lines 45, 55 are removable at the contacts 40, 50, so that the flat element 20 can be transported and installed independently of the control device 100.

[0050] The control device 100 further comprises a power supply unit 130. This is connected to the terminals 112, 122 via a first current measuring device 115 and a second current measuring device 125. The first current measuring device 115 measures the total current flowing through the first terminals 112. The second current measuring device 125 measures the total current flowing through the second terminals 122. Generally, the current flows between the first terminals 112 and the second terminals 122 through the first connecting lines 45, the first contact 40, the electrical conductor 30, the second contact 50, and the second connecting lines 55. Unless a malfunction occurs, the respective current measured by the two current measuring devices 115, 125 should be identical. To monitor the currents, the two current measuring devices 115, 125 are connected to an evaluation device 140.This receives the measured current values ​​or a current difference determined from them. If the difference between the measured current values ​​is below a current difference threshold, normal operation continues. If the difference is above the current difference threshold, the flowing current is reduced or, if the difference is too high, switched off completely. An alarm can also be issued, for example, an audible, visual, or electronically transmitted alarm via communication means. This can significantly increase overall safety.

[0051] The two current measuring devices 115, 125 together form a current difference measuring device 150, which, together with the evaluation device 140, performs a monitoring function and significantly increases operational safety. For example, if a fault current were to occur due to a screw driven into the electrical conductor 30, this would lead to a higher current difference, and the system would react accordingly. Depending on the design, the evaluation device 140 can be considered a component of the current difference measuring device 150 or separate from it. It also performs tasks such as detecting and further processing a fault condition. List of reference symbols 10 Surface heating 20 flat element 30 electrical conductors 40 first contact 45 first connecting cables 50 second contact 55 second connecting cables 100 control device 110 first connection arrangement 112 first connections 115 first current measuring device 120 second connection arrangement 122 second connections 125 second current measuring device 130 Power supply unit 140 Evaluation device 150 Current difference measuring device

Claims

[1] Control device (100) for an electric surface heating system (10), the control device (100) comprising: - a first connection arrangement (110) and a second connection arrangement (120), wherein an electrical conductor (30) of the surface heating (10) can be connected between the first connection arrangement (110) and the second connection arrangement (120), and wherein the first connection arrangement (110) and the second connection arrangement (120) are designed to apply an electrical current to the electrical conductor (30) of the surface heating (10), - a current difference measuring device (150) which is configured to measure a current difference between the first connection arrangement (110) and the second connection arrangement (120), and - an evaluation device (140) which is configured to detect an error condition based on the current difference exceeding a current difference threshold value. [2] Control device (100) according to claim 1, - wherein the control device (100) is configured to switch off or reduce the current at the first terminal arrangement (110) and / or at the second terminal arrangement (120) in response to the detection of a fault condition. [3] Control device (100) according to one of the preceding claims, - wherein the control device (100) is configured to issue an alarm in response to detecting a fault condition. [4] Control device (100) according to one of the preceding claims, - wherein the first connection arrangement (110) has only a first connection (112), and / or - wherein the second connection arrangement (120) has only a second connection (122). [5] Control device (100) according to one of the preceding claims, - wherein the first connection arrangement (110) has a plurality of first connections (112), and / or - wherein the second connection arrangement (120) has a plurality of second connections (122). [6] Control device (100) according to one of the preceding claims, - wherein the control device (100) is configured to apply the current in a clocked manner. [7] Control device (100) according to one of the preceding claims, - wherein the control device (100) is configured to measure a temperature, and - wherein the control device (100) is configured to apply the current only when the temperature falls below a temperature threshold. [8] Control device (100) according to one of the preceding claims, - wherein the current difference measuring device (150) comprises a first current measuring device (115) and a second current measuring device (125), - wherein the first current measuring device (115) measures a first current at the first terminal arrangement (110) and the second current measuring device (125) measures a second current at the second terminal arrangement (120), and - wherein the current difference measuring device (150) is configured to calculate the current difference based on the first current and the second current. [9] Control device (100) according to one of the preceding claims, - wherein the control device (100) is configured to limit the current, the first current and / or the second current to a maximum value. [10] Surface heating (10), comprising - an electrical conductor (30), and - a control device (100) according to one of the preceding claims, - wherein the electrical conductor (30) is connected to the first connection arrangement (110) and the second connection arrangement (120) of the control device (100). [11] Surface heating (10) according to one of claims 9 or 10, - wherein the first connection arrangement (110) has a plurality of first connections and / or the second connection arrangement (120) has a plurality of second connections, and - wherein the electrical conductor (30) is connected to a plurality of first terminals (112) or to a plurality of second terminals (122). [12] Surface heating (10) according to claim 11, - wherein the surface heating (10) has a first contact (40) to which the electrical conductor (30) is connected to a plurality of first connecting lines (45) to the first terminals (112), and / or - wherein the surface heating (10) has a second contact (50) to which the electrical conductor (30) is connected to a plurality of second connecting lines (55) to the second terminals (122). [13] Surface heating (10) according to claim 12, - wherein the electrical conductor (30) has only one electrical connection between the first contact (40) and the second contact (50). [14] Surface heating (10) according to one of claims 12 or 13, - wherein the first connecting lines (45) at the first contact (40) are detachable from the electrical conductor (30), and / or - wherein the second connecting lines (55) at the second contact (50) are detachable from the electrical conductor (30).

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