Methods for regulating heaters and heaters

Abstract

The present invention relates to a method (8) for regulating a heater (1) having at least one heating element (4) comprising a temperature-dependent resistance (R). The heating element (4) exhibits a transition between NTC and PTC heating behavior at a transition temperature and a minimum resistance (R_MIN). Here, NTC heating behavior exists below the transition temperature, and PTC heating behavior exists above the transition temperature. According to the invention, the regulating unit (5) of the heater (1) determines the current heating behavior based on the time distribution of the resistance (R) during a check. Thereafter, the regulating unit (5) determines at least one input parameter of the heating element (4) based on the current heating behavior in a determination step (14). Thereafter, the regulating unit (5) regulates the heating element (4) via the input parameter in a regulating step (15). The invention also relates to a heater (1) having a regulating unit (5) for performing the method (8).

Description

Technical Field

[0001] This invention relates to a method for a heater having at least one heating element for a regulator, as described in the preamble of claim 1, said at least one heating element having a temperature-dependent resistance. The invention also relates to a heater having at least one heating element. Background Technology

[0002] Common electric heaters are known from the prior art. There, the heater includes at least one heating element having a temperature-dependent resistance (i.e., a so-called PTC thermistor). For example, EP 2 075 452 A2 discloses an electric heater having multiple PTC thermistors for heating fuel in a motor vehicle. EP 2 732 995 A1 discloses an electric heater having multiple PTC thermistors for heating air in a motor vehicle.

[0003] There, the heating element or PTC thermistor exhibits a positive temperature coefficient, or PTC heating behavior, between the transition temperature and the Curie temperature. Up to the transition temperature and from the Curie temperature onwards, the heating element or PTC thermistor exhibits a negative temperature coefficient, or NTC heating behavior. There, the heating element is regulated within a portion of the positive temperature coefficient range. During this process, the current temperature of the heating element or PTC thermistor is determined, and the heating element or PTC thermistor achieves the desired heating output by adjusting input parameters (e.g., current and voltage) to reach the desired temperature.

[0004] However, the current temperature of a heating element or PTC thermistor cannot be reliably determined solely from its resistance, as the same resistance value may exist at different temperatures. These temperature differences are attributed to both NTC and PTC heating behaviors, during which the behavior of the heating element or PTC thermistor deviates. The variation between PTC and NTC heating behaviors can occur uncontrollably due to changes in fluid flow rate or ambient temperature. To sense the heater temperature independently of resistance and to safely adjust the heater, a temperature sensor is typically installed within the heater. Disadvantageously, this increases the cost of the heater. Summary of the Invention

[0005] Therefore, the object of the present invention is to provide an improved or at least alternative method for regulating a heater having at least one heating element, and a suitably improved or at least alternative heater. In particular, the aforementioned disadvantages will be overcome by the method and the heater.

[0006] According to the invention, this objective is achieved by the subject matter of the independent claims. Advantageous embodiments are the subject matter of the dependent claims.

[0007] A method is provided for regulating a heater having at least one heating element, the at least one heating element having temperature-dependent resistance. At a transition temperature and a minimum resistance, the at least one heating element exhibits a transition between NTC heating behavior and PTC heating behavior. There, the at least one heating element exhibits NTC heating behavior below the transition temperature and PTC heating behavior above the transition temperature. According to the invention, a regulating unit of the heater determines the current heating behavior of the at least one heating element based on the time distribution of the resistance of the at least one heating element during a check. Based on the determined current heating behavior, the regulating unit determines at least one input parameter of the at least one heating element in a determination step. The at least one input parameter is preferably current and / or voltage. In the regulating step, the regulating unit now regulates the at least one heating element via the at least one input parameter.

[0008] During NTC heating behavior (NTC: Negative Temperature Coefficient), the at least one heating element has a negative temperature coefficient, and the resistance of the at least one heating element decreases as the temperature increases. During PTC heating behavior (PTC: Positive Temperature Coefficient), the at least one heating element has a positive temperature coefficient, and the resistance of the at least one heating element increases as the temperature increases. The heating element is a PTC thermistor, and more particularly, a ceramic PTC thermistor. In the adjustment step, the adjustment unit adjusts the at least one heating element by adjusting at least one parameter on the at least one heating element. Here, the at least one heating element of the heater is preferably adjusted via input parameters current and voltage. Preferably, a constant operating voltage and a variable average current are applied to the at least one heating element based on the duty cycle of the applied PWM signal (PWM: Pulse Width Modulation). Preferably, the duty cycle of the PWM signal is therefore determined in the determination step. Due to the change in the duty cycle of the PWM signal, the time for which current is applied to the at least one heating element changes. In other words, the percentage of the duty cycle of the applied PWM signal determines the percentage of time for which current is applied to the at least one heating element.

[0009] Unlike conventional adjustment methods, in the method according to the invention, the current heating behavior is determined based on the time distribution of resistance during the inspection period. Once the current heating behavior is determined, the current temperature can also be safely determined from the resistance. Advantageously, a temperature sensor, typically used to determine the current temperature of at least one heating element, is no longer needed. In this way, the cost of the heater can be advantageously reduced.

[0010] Advantageously, in this method, it is possible to specify that the regulating unit, during the regulating step, regulates the at least one heating element currently exhibiting PTC heating behavior to the desired heating output via the at least one input parameter. In other words, the desired heating output on the at least one heating element is specifically regulated during PTC heating behavior.

[0011] Advantageously, in this method, it can be specified that the regulating unit, during the regulating step, maximally regulates the at least one heating element currently exhibiting PTC heating behavior to its maximum output. Here, the maximum output is defined at a threshold resistance associated with a threshold temperature. The threshold resistance can advantageously be a balance between the maximum heating output and the optimal temperature. The threshold resistance depends on the behavior of the heating element and can be defined experimentally or theoretically. The threshold temperature associated with the threshold resistance is less than the Curie temperature of the at least one heating element and greater than the transition temperature of the at least one heating element. In other words, the temperature of the at least one heating element is always below the Curie temperature. Therefore, the at least one heating element in this method will never reach the Curie temperature, enabling overheat protection at temperatures below the Curie temperature. In this way, high-power heating elements can be used in the heater regardless of their Curie temperature.

[0012] Advantageously, in this method, it can be specified that the regulating unit verifies the status of the at least one heating element in a protection step after the check. When the temperature of the at least one heating element is higher than a threshold temperature and the temperature cannot be reduced in the regulating step, the regulating unit stops regulating and interrupts the energy supply to the heating element. In other words, when the temperature of the at least one heating element is higher than the threshold temperature and reducing the duty cycle of the PWM signal with reduced current does not lower the temperature, the regulating unit stops regulating and interrupts the energy supply to the heating element. In this way, as explained above, overheat protection in the at least one heating element can be achieved solely through this method. Therefore, high-power heating elements can be used in the heater regardless of their Curie temperature. Advantageously, the interruption of the energy supply can be restarted after a defined time interval (e.g., 30 seconds).

[0013] Advantageously, in this method, it can be specified that the regulating unit checks the time distribution of the resistance of the at least one heating element during the setup step in the inspection process. In this process, the regulating unit searches for a behavior that can be interpreted as a transition between NTC heating behavior and PTC heating behavior in the at least one heating element. When the searched behavior exists, the regulating unit determines the current heating behavior of the at least one heating element in the verification step. Thereafter, the regulating unit determines the at least one input parameter of the at least one heating element based on the current heating behavior in the determination step. However, when the searched behavior does not exist, no transition between NTC and PTC heating behavior occurs, and the heating element still has the same (i.e., previously detected) heating behavior. In this case, the regulating unit proceeds to the determination step and determines the at least one input parameter of the at least one heating element based on the same (i.e., previously detected) heating behavior.

[0014] When the at least one heating element changes from NTC heating behavior to PTC heating behavior or vice versa, the resistance of the at least one heating element drops to a minimum and then increases. The associated current change can be established by the regulating unit during the setup step. On the other hand, the resistance of the at least one heating element can also decrease and increase due to the surrounding environment—for example, through changes in fluid flow rate. Therefore, the resistance during PTC heating behavior increases during ambient heating of the at least one heating element and during NTC heating behavior when the at least one heating element is ambient cooling. To eliminate environmental errors, the regulating unit verifies the currently existing heating behavior in the verification step, thereby indirectly verifying whether the behavior determined during the setup step is actually a change.

[0015] Advantageously, in this method, it can be specified that the regulating unit measures the current on the at least one heating element within a predetermined time window during the setup step. Then, when the currently measured current value is higher than all previously measured current values, the regulating unit increments a counter while measuring the current. When the counter exceeds a predefined counter threshold, the regulating unit determines this as a behavior to be interpreted as a change.

[0016] To determine the current heating behavior or to ensure a transition at the at least one heating element, the regulating unit, during the verification step, can increase the duty cycle of the PWM signal of the initial current currently applied to the at least one heating element by a predefined value within a predetermined time interval, and sense the current change of the at least one heating element. Furthermore, during the verification step, the regulating unit can decrease the duty cycle of the PWM signal of the initial current currently applied to the at least one heating element by a predefined value within a predetermined time interval, and sense the current change of the at least one heating element. The increase and decrease of the duty cycle of the PWM signal of the initial current can advantageously be performed directly one after the other, where the order is not decisive. Preferably, the regulating unit increases and decreases the duty cycle of the PWM signal of the initial current by 10%, respectively. However, other values ​​are also conceivable.

[0017] Based on the resistance change calculated according to the sensed current of the at least one heating element, the adjustment unit can determine the current heating behavior during the verification step. In this process, when the duty cycle of the current PWM signal increases, the resistance calculated based on the sensed current increases; and when the duty cycle of the current PWM signal decreases, the resistance calculated based on the sensed current decreases. The adjustment unit determines the current heating behavior as PTC heating behavior during the verification step. Therefore, when the duty cycle of the current PWM signal increases, the resistance calculated based on the sensed current decreases; and when the duty cycle of the current PWM signal decreases, the resistance calculated based on the sensed current increases. However, when the resistance decreases during both the increase and decrease of the PWM current signal's duty cycle and increases during both the increase and decrease of the PWM current signal's duty cycle, the current heating behavior cannot be definitively determined.

[0018] When the regulating unit cannot determine the current heating behavior, the method allows for a repeat verification step. During this repeat verification step, the regulating unit increases and decreases the duty cycle of the PWM signal of the initial current currently applied to the at least one heating element by a predefined value within a predetermined time interval. This value is preferably higher than the predefined value during the previously performed verification step. Preferably, the regulating unit increases and decreases the duty cycle of the PWM signal of the initial current by 20%, respectively. However, other values ​​are also conceivable. Here, the increase and decrease of the duty cycle of the PWM signal of the initial current can also be performed directly one after another, where the order is not decisive.

[0019] Advantageously, in this method, it can be specified that the regulating unit determines the rise and fall of the resistance of at least one heating element by ramp determination during the verification step. Advantageously, the regulating unit can determine the minimum resistance of the at least one heating element during the verification step.

[0020] The present invention also relates to a heater having at least one heating element. Therein, the at least one heating element has a temperature-dependent resistance. The at least one heating element exhibits a transition between NTC heating behavior and PTC heating behavior at a transition temperature and a minimum resistance value. There, the at least one heating element exhibits NTC heating behavior below the transition temperature and PTC heating behavior above the transition temperature. Furthermore, the heater includes a regulating unit designed to perform the above-described method. Advantageously, the heater can be provided for use in battery electric vehicles.

[0021] Advantageously, the heater can be integrated into an electrical switching circuit, which then includes an energy source (e.g., a traction battery in a battery-powered motor vehicle) for supplying current and voltage to the heater and includes the heater itself. Advantageously, the heater's regulating unit can include a microcontroller and a switch for interrupting the switching circuit. There, the microcontroller can generate a square wave signal of variable width after the switch is opened and closed, thereby interrupting or resuming the switching circuit. In this way, the duty cycle of the PWM signal of the current flowing to the at least one heating element can be changed, and the at least one heating element can be regulated. Here, the heating element is a PTC thermistor, and in particular, a ceramic PTC thermistor. Furthermore, the microcontroller can read the current and / or voltage on the at least one heating element. This information can be used to regulate the at least one heating element to the desired output. Furthermore, this information can be used to calculate the resistance of the at least one heating element.

[0022] To avoid repetition, please refer to the explanation above.

[0023] Other important features and advantages of the invention will become apparent from the dependent claims, the accompanying drawings, and the description thereof.

[0024] It should be understood that, without departing from the scope of the invention, the features mentioned above and which will still be explained below can be used not only in the corresponding combinations described, but also in other combinations or individually. Attached Figure Description

[0025] Preferred embodiments of the invention are shown in the accompanying drawings, which are described in detail below, wherein the same reference numerals denote the same or similar or functionally identical components.

[0026] They are shown schematically respectively.

[0027] Figure 1 A view of a switching circuit with a heater according to the present invention is shown.

[0028] Figure 2The temperature-resistance behavior curves of a heating element with temperature-dependent resistance are shown.

[0029] Figure 3 A schematic diagram of a method for adjusting a heater according to the invention is shown;

[0030] Figure 4 A diagram illustrating the steps for establishing the method according to the present invention is shown;

[0031] Figure 5 A diagram illustrating the verification steps of the method according to the present invention is shown. Detailed Implementation

[0032] Figure 1 A view of a heater 1 and an energy source 2 according to the invention is shown, electrically interconnected as a switching circuit 3. Advantageously, the heater 1 can be provided for battery electric vehicles, and the energy source 2 is a traction battery for a car. Here, the heater 1 includes a heating element 4 having temperature-dependent resistance and an adjustment unit 5 having a switch 6 and a microcontroller 7. Here, the heating element 4 is a PTC thermistor, and in particular, a ceramic PTC thermistor. The microcontroller 7 generates a square wave signal (i.e., a variable-width PWM signal, i.e., a variable duty cycle after the switch 6 is closed and opened). In this way, the current on the heating element 4 is changed, and the heating element 4 is adjusted to the desired heating output. The voltage on the heating element 4 is not directly affected by the switch 6 and is constant. The microcontroller 7 can additionally read the current and / or voltage on the heating element 4. This information can be used to adjust the heating element 4 to the desired output and calculate the resistance R of the heating element 4.

[0033] Figure 2 The temperature-resistance behavior curve of heating element 4 is shown. Heating element 4 operates below the transition temperature. It exhibits NTC heating behavior and above the transition temperature It exhibits PTC heating behavior. Transition temperature This corresponds to the minimum resistance value R_MIN. Furthermore, a threshold temperature T_TH corresponding to the threshold resistance R_TH is defined. The threshold temperature T_TH is higher than the transition temperature. Furthermore, below the Curie temperature T_CURIE, at which threshold temperature, heating element 4 is physically destroyed.

[0034] Here, the adjustment unit 5 adjusts the heating element 4 to its maximum output at the threshold temperature T_TH and threshold resistance R_TH. In this way, overheat protection of the heating element 4 is achieved at the threshold temperature T_TH, rather than the Curie temperature T_CURIE. Therefore, the safe operating range I of the heating element 4 is below the threshold temperature T_TH and threshold resistance R_TH, and the unsafe operating range II is above the threshold temperature T_TH and threshold resistance R_TH.

[0035] Within the unsafe operating range II, an additional offset range II-A can be defined, within which the temperature and resistance of heating element 4 can be temporarily maintained without overheating heater 1. Conversely, the temperature and resistance of heating element 4 must not be within the remaining operating range II-B of the unsafe operating range II, as it is highly likely that overheating of heater 1 cannot be prevented. The unsafe operating range II is divided into operating ranges II-A and II-B at a limiting temperature T_G, which is calculated based on a threshold temperature T_TH with an offset. Therefore, the corresponding limiting resistance R_G is calculated based on the threshold resistance R_TH with an offset.

[0036] Figure 3 A schematic diagram of a method 8 for adjusting a heater 1 according to the invention is shown. There, method 8 begins with an initial step 9, in which, for example, the heater 1 is turned on. After the initial step 9, the adjustment unit 5 performs a check.

[0037] During the inspection, the adjustment unit 5 checks the time distribution of the resistance R of the heating element 4 in the setup step 12. Here, the resistance R is calculated based on the current and voltage measured on the heating element 4. There, the adjustment unit 5 determines the behavior that can be interpreted as the transition between NTC heating behavior and PTC heating behavior in the heating element 4. When the searched behavior exists, the adjustment unit 5 proceeds to the verification step 13, in which the adjustment unit 5 determines the current heating behavior of the heating element 4. In the subsequent determination step 14, the adjustment unit 5 determines at least one input parameter of the heating element 4 based on the current heating behavior. When the behavior searched by the adjustment unit 5 does not exist, the adjustment unit 5 proceeds directly to the determination step 14 after the setup step 12. The following is a summary of the process... Figure 4 and Figure 5 The determination step 14 and the verification step 13 will be explained in more detail.

[0038] In step 12, the adjustment unit 5 determines the behavior that can be interpreted as a transition between NTC heating behavior and PTC heating behavior. (Refer to...) Figure 2When heating element 4 changes from NTC heating behavior to PTC heating behavior or vice versa, the resistance R of heating element 4 drops to its minimum resistance value R_MIN and then rises from R_MIN. In step 12, the adjustment unit 5 can determine this behavior, thereby determining the transition between NTC and PTC heating behavior. The following is a description of... Figure 4 This will be explained in more detail.

[0039] Figure 4 The figure below shows the time distribution of the resistance R on the heating element 4, and the figure above shows the distribution of the counter Z, both based on the current values ​​measured on the heating element 4. There, the heating element 4 is initially heated and transitions from NTC heating behavior to PTC heating behavior. During this process, the resistance R decreases before the transition and increases again after the transition. Subsequently, the heating element 4 is cooled and transitions from PTC heating behavior to NTC heating behavior. During this process, the resistance R decreases before the transition and increases again after the transition. Here, the regulating unit 5 measures the current of the heating element 4 within a predetermined time window t_1 in step 12. While measuring the current, the regulating unit 5 increments the counter Z when the currently measured current value is higher than all previously measured current values. Referring to the figure above, when the counter Z exceeds the counter threshold Z_MAX, the regulating unit 5 establishes a transition-like behavior.

[0040] However, the resistance R of the at least one heating element 4 can also decrease and increase according to the surrounding environment, for example, through changes in fluid flow rate, and without any change. Therefore, the resistance R increases during ambient heating of the heating element 4 in PTC heating behavior and increases during ambient cooling of the heating element 4 in NTC heating behavior. To eliminate environmental errors, the adjustment unit 5 verifies the currently existing heating behavior in verification step 13. The following is a description of... Figure 5 This will be explained in more detail.

[0041] In the subsequent protection step 10, the adjustment unit 5 verifies the state of the heating element 4. When the heating element 4 overheats and the temperature cannot be reduced by decreasing the duty cycle of the PWM signal applying the current, the adjustment unit 5 stops the adjustment and interrupts the energy supply to the heating element 4 in the interruption step 11 within a defined time interval of, for example, 30 seconds. The heating behavior of the heating element 4 is also considered in the protection step 10. In particular, this prevents the heating element 4 from being shut down due to erroneous overheating detection during NTC heating. When the heating element 4 does not overheat under the current input parameters or when the temperature can be reduced normally, the adjustment unit 5 adjusts the heating element using the input parameters in the subsequent adjustment step 15. After adjustment step 15, the adjustment unit 5 proceeds again to the setup step 12.

[0042] Figure 5 The upper figure shows the time distribution of the duty cycle DC of the PWM signal used for the current on heating element 4. The lower figure shows the time distribution of the resistance R on heating element 4. The resistance R is calculated based on the current measured on heating element 4. When behavior similar to the transition is established during setup step 12, the current heating behavior is determined in verification step 13. Referring to the upper figure, the duty cycle DC of the PWM signal for the initial current I_0 on heating element 4 decreases and increases by 10% in time interval t_2, respectively. The duty cycle DC of the PWM signal for the initial current I_0 is the value currently applied to heating element 4 at the start of verification step 13. Referring to the lower figure, the resistance R of heating element 4 also changes with the change in the duty cycle DC of the PWM signal for the current I_0. The aforementioned change in resistance R is evaluated by the adjustment unit 5 through ramp determination.

[0043] When the resistance R decreases during the decrease of the duty cycle DC of the PWM signal for the initial current I_0 and increases during the increase of the duty cycle DC of the PWM signal for the initial current I_0, the adjustment unit 5 determines the current heating behavior as PTC heating behavior. This behavior corresponds to the current behavior on the heating element 4, whereby the current on the heating element 4 increases during the decrease of the duty cycle DC of the PWM signal for the initial current I_0 and decreases during the increase of the duty cycle DC of the PWM signal for the initial current I_0. When the resistance R increases during the decrease of the duty cycle DC of the PWM signal for the initial current I_0 and decreases during the increase of the duty cycle DC of the PWM signal for the initial current I_0, the adjustment unit determines the current heating behavior as NTC heating behavior. This behavior corresponds to the current behavior on the heating element 4, whereby the current on the heating element 4 decreases during the decrease of the duty cycle DC of the PWM signal for the initial current I_0 and increases during the increase of the duty cycle DC of the PWM signal for the initial current I_0. If it is not possible to definitively determine the heating behavior, the regulating unit can repeat the verification steps and decrease and increase the duty cycle DC of the PWM signal of the initial current I_0, for example, by increasing or decreasing it by 20% respectively.

[0044] exist Figure 5 In the circuit, the resistance R decreases as the duty cycle DC of the PWM signal for the initial current I_0 decreases, and increases as the duty cycle DC of the PWM signal for the initial current I_0 increases. Therefore, heating element 4 exhibits PTC heating behavior. (Refer to...) Figure 3 At this point, in step 14, at least one input parameter of the heating element 4 is determined based on the determined PTC heating behavior.

[0045] Method 8 enables safe regulation of the heater based on the resistance of heating element 4. In this way, costly temperature sensors are no longer needed, and the cost of the heater can be advantageously reduced.

Claims

1. A method (8) for regulating a heater (1) having at least one heating element (4), - in, The at least one heating element (4) has a temperature-dependent resistance (R). - Wherein, the at least one heating element (4) exhibits a transition between NTC heating behavior and PTC heating behavior at the transition temperature (T_Ü) and minimum resistance (R_MIN). - Wherein, the at least one heating element (4) exhibits the NTC heating behavior below the transition temperature (T_Ü) and the PTC heating behavior above the transition temperature (T_Ü). Its features are, - The regulating unit (5) of the heater (1) determines the current heating behavior of the at least one heating element (4) based on the time distribution of the resistance (R) of the at least one heating element (4) during inspection, and - The adjustment unit (5) determines at least one input parameter of the at least one heating element (4) based on the current heating behavior in the determination step (14), and - The adjustment unit (5) adjusts the at least one heating element (4) in the adjustment step (15) by means of the at least one input parameter.

2. The method according to claim 1, Its features are, In adjustment step (15), the adjustment unit (5) adjusts the at least one heating element (4) currently exhibiting PTC heating behavior to the desired heating output via the at least one input parameter.

3. The method according to claim 1 or 2, Its features are, - In adjustment step (15), the adjustment unit (5) adjusts at least one heating element (4) currently exhibiting PTC heating behavior to its maximum output, and - The maximum output is defined at the threshold resistance (R_TH) related to the threshold temperature (T_TH), and - The threshold temperature (T_TH) is less than the Curie temperature (T_CURIE) of the at least one heating element (4) and greater than the transition temperature (T_Ü) of the at least one heating element (4).

4. The method according to claim 1 or 2, Its features are, - After inspection, the adjustment unit (5) verifies the status of at least one heating element (4) in the protection step (10), and When the temperature (T) of the at least one heating element (4) is higher than the threshold temperature (T_TH) and the temperature (T) cannot be reduced to below the threshold temperature (T_TH) by the adjustment step (15), the adjustment unit (5) stops the adjustment of the at least one heating element (4) and interrupts the energy supply of the at least one heating element (4) within a defined time interval.

5. The method according to claim 1 or 2, Its features are, - During the inspection, the adjustment unit (5) checks the time distribution of the resistance (R) of the at least one heating element (4) in the setup step (12) and searches for behaviors that can be interpreted as the transition between NTC heating behavior and PTC heating behavior in the at least one heating element (4), and - When the searched behavior exists, the adjustment unit (5) determines the current heating behavior of the at least one heating element (4) in the verification step (13), and determines the at least one input parameter of the at least one heating element (4) based on the current heating behavior in the subsequent determination step (14), and - When the searched behavior does not exist, the adjustment unit (5) proceeds to the determination step (14) and determines the at least one input parameter of the at least one heating element (4).

6. The method according to claim 5, Its features are, - The regulating unit (5) measures the current on at least one heating element (4) within a predetermined time window (t_1) during the setup step (12), and - When the currently measured current value is higher than all previously measured current values, the adjustment unit (5) increments the counter (Z) during the current measurement, and - When the counter (Z) exceeds a predetermined counter threshold (Z_MAX), the adjustment unit (5) establishes behavior to be interpreted as a change.

7. The method according to claim 5, Its features are, - In the verification step (13), the adjustment unit (5) increases the duty cycle (DC) of the PWM signal of the initial current (I_0) currently applied to the at least one heating element (4) by a predefined value within a predetermined time interval (t_2), and senses the current change of the at least one heating element (4), and - In the verification step (13), the adjustment unit (5) reduces the duty cycle (DC) of the PWM signal of the initial current (I_0) currently applied to the at least one heating element (4) by a predefined value within a predetermined time interval (t_2), and senses the current change of the at least one heating element (4).

8. The method according to claim 7, Its features are, - When the resistance (R) calculated based on the sensed current increases as the duty cycle (DC) of the PWM signal of the initial current (I_0) increases, and when the resistance (R) calculated based on the sensed current decreases as the duty cycle (DC) of the PWM signal of the initial current (I_0) decreases, the adjustment unit (5) determines the current heating behavior as PTC heating behavior in the verification step (13), and - When the resistance (R) calculated based on the sensed current decreases as the duty cycle (DC) of the PWM signal of the initial current (I_0) increases, and the resistance (R) calculated based on the sensed current increases as the duty cycle (DC) of the PWM signal of the initial current (I_0) decreases, the adjustment unit (5) determines the current heating behavior as NTC heating behavior in the verification step (13).

9. The method according to claim 7, Its features are, - When the adjustment unit cannot determine the current heating behavior, the adjustment unit (5) repeats the verification step (13), and - The adjustment unit increases and decreases the duty cycle (DC) of the PWM signal of the initial current (I_0) currently applied to the at least one heating element (4) by a predefined value within a predetermined time interval (t_2) during the repeated verification step (13).

10. The method according to claim 5, Its features are, - The regulating unit (5) determines the increase and / or decrease of the resistance (R) of the at least one heating element (4) by ramp determination in the verification step (13), and / or - The adjustment unit (5) determines the minimum resistance (R_MIN) of the at least one heating element (4) in the verification step (13).

11. The method according to claim 1, Its features are, The at least one input parameter is current and / or voltage.

12. The method according to claim 9, Its features are, The predefined values ​​that the adjustment unit increases and decreases during the repeated verification step (13) are higher than the predefined values ​​in the previously executed verification step (13).

13. A heater (1) having at least one heating element (4), - in, The at least one heating element (4) has a temperature-dependent resistance (R). - Wherein, the at least one heating element (4) exhibits a transition between NTC heating behavior and PTC heating behavior at the transition temperature (T_Ü) and minimum resistance (R_MIN). - Wherein, the at least one heating element (4) exhibits the NTC heating behavior below the transition temperature (T_Ü) and the PTC heating behavior above the transition temperature (T_Ü). Its features are, The heater (1) includes an adjustment unit (5) designed to perform the method (8) according to any one of the preceding claims.

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