OPERATING METHOD FOR AN ELECTRIC HEATER

Abstract

An operating method for an electric heater having at least one control unit with at least one temperature sensor measuring a reference temperature, and at least one heating element having a positive temperature coefficient mode above a critical temperature and a negative temperature coefficient mode below the critical temperature, may include heating a fluid passing the electric heater to an outlet temperature by the at least one heating element, and operating the electric heater in one of a normal mode or a protection mode. In the normal mode, the at least one heating element may be supplied with at least one of a direct current and a direct voltage. In the protection mode, electrical power supplied to the at least one heating element may be regulated by pulse width modulation. The electric heater may be operated in the normal mode if the reference temperature is less than or equal to the critical temperature, and in the protection mode if the reference temperature is greater than the critical temperature.

Claims

1. An operating method for an electric heater having at least one control unit with at least one temperature sensor measuring a reference temperature, and at least one heating element having a positive temperature coefficient mode above a critical temperature and a negative temperature coefficient mode below the critical temperature, the operating method comprising: heating a fluid passing the electric heater to an outlet temperature by the at least one heating element; and operating the electric heater in one of a normal mode, in which the at least one heating element is supplied with at least one of a direct current and a direct voltage, or a protection mode, in which electrical power supplied to the at least one heating element is regulated by pulse width modulation; wherein the electric heater is operated in the normal mode if the reference temperature is less than or equal to the critical temperature; and wherein the electric heater is operated in the protection mode if the reference temperature is greater than the critical temperature.

2. The operating method according to claim 1, wherein: the critical temperature is stored in the control unit; the control unit compares the reference temperature with the critical temperature; the control unit triggers the normal mode if the reference temperature is less than or equal to the critical temperature; and the control unit triggers the protection mode if the reference temperature is greater than the critical temperature.

3. The operating method according to claim 1, wherein the control unit determines an electrical resistance of the at least one heating element while the electric heater is being operated in the protection mode.

4. The operating method according to claim 3, wherein: the control unit compares the electrical resistance of the at least one heating element with a maximal electrical resistance value; and if the electrical resistance is greater than the maximal electrical resistance value, the electrical power supplied to the at least one heating element is reduced by the pulse width modulation.

5. The operating method according to claim 4, wherein the comparison of the electrical resistance of the heating element with the maximal electrical resistance value is performed continuously.

6. The operating method according to claim 3, wherein the control unit determines the outlet temperature of the fluid via the electrical resistance of the at least one heating element.

7. The operating method according to claim 6, wherein: at least one of a reference table and a transfer function is stored in the control unit; for a given electrical resistance of the at least one heating element, the at least one of a reference table and a transfer function provides a corresponding outlet temperature of the fluid; and the control unit determines the outlet temperature of the fluid via the at least one of a reference table and a transfer function.

8. The operating method according to claim 6, wherein: the control unit compares the outlet temperature with a maximal temperature value; and if the outlet temperature is greater than the maximal temperature value, the electrical power supplied to the at least one heating element is reduced by the pulse width modulation.

9. The operating method according to claim 8, wherein the comparison of the outlet temperature with a maximal temperature value is performed continuously.

10. An electric heater comprising: at least one control unit with at least on temperature sensor measuring a reference temperature; and at least one heating element having a positive temperature coefficient mode above a critical temperature and a negative temperature coefficient mode below the critical temperature wherein the control unit is at least one of formed, configured, and programmed to: operate the electric heater in a normal mode, in which the at least one heating element is supplied with at least one of a direct current and a direct voltage, if the reference temperature is less than or equal to the critical temperature; and operate the electric heater in a protection mode, in which electrical power supplied to the at least one heating element is regulated by pulse width modulation, if the reference temperature is greater than the critical temperature.

11. The electric heater according to claim 10, wherein the electric heater comprises at least one switching element.

12. The electric heater according to claim 11, wherein the switching element is controlled by the control unit.

13. The electric heater according to claim 11, wherein the switching element is electrically conductively connected with the at least one heating element and with at least one power source connection.

14. The electric heater according to claim 12, wherein the switching element is electrically conductively connected with the at least one heating element and with at least one power source connection.

15. The operating method according to claim 2, wherein the control unit determines the electrical resistance of the at least one heating element while the electric heater is being operated in the protection mode.

16. The operating method according to claim 15, wherein: the control unit compares the electrical resistance of the at least one heating element with a maximal electrical resistance value; and if the electrical resistance is greater than the maximal electrical resistance value, the electrical power supplied to the at least one heating element is reduced by the pulse width modulation.

17. The operating method according to claim 16, wherein the comparison of the electrical resistance of the heating element with the maximal electrical resistance value is performed continuously.

18. An operating method for an electric heater having at least one control unit with at least one temperature sensor measuring a reference temperature, and at least one heating element having a positive temperature coefficient mode above a critical temperature and a negative temperature coefficient mode below the critical temperature, the operating method comprising: heating a fluid passing the electric heater to an outlet temperature by the at least one heating element; comparing, by the control unit, the reference temperature with the critical temperature, which is stored in the control unit; operating the electric heater in a normal mode, in which the at least one heating element is supplied with at least one of a direct current and a direct voltage, if the reference temperature is less than or equal to the critical temperature; operating the electric heater in a protection mode, in which electrical power supplied to the at least one heating element is regulated by pulse width modulation, if the reference temperature is greater than the critical temperature; and determining an electrical resistance of the at least one heating element while the electric heater is being operated in the protection mode.

19. The operating method according to claim 18, wherein: the control unit compares the electrical resistance of the at least one heating element with a maximal electrical resistance value; and if the electrical resistance is greater than the maximal electrical resistance value, the electrical power supplied to the at least one heating element is reduced by the pulse width modulation.

20. The operating method according to claim 18, wherein the control unit determines the outlet temperature of the fluid via the electrical resistance of the at least one heating element.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0033] In the drawings, in each case schematically,

[0034] FIG. 1 shows a diagram of a first embodiment of the inventive method,

[0035] FIG. 2 shows a diagram of a second embodiment of the inventive method.

DETAILED DESCRIPTION

[0036] In block 1 in FIG. 1 a reference temperature is measured by a control unit with at least one temperature sensor. An electric heater is operated in the normal mode if the reference temperature is less than or equal to a critical temperature of a heating element. The electric heater is operated in the protection mode if the reference temperature is greater than the critical temperature. The diagram in FIG. 1 describes the protection mode.

[0037] In block 2, the electric voltage across the heating element is measured by the control unit and/or by a first sensor arrangement. In block 3, the electrical current flowing through a heating element is measured by the control unit and/or by a second sensor arrangement. In block 4, the control unit determines the electrical resistance of the heating element by Ohm's law. In block 5, the control unit compares the electrical resistance of the heating element with a maximal electrical resistance value. In block 6, the electrical power supplied to the heating element is reduced by pulse width modulation if the electrical resistance is greater than the maximal electrical resistance value. In block 7, as a result of the pulse width modulation, the output temperature of the electrical heater is controlled and/or regulated.

[0038] The diagram in FIG. 2 describes the protection mode of the electrical heater. In contrast to FIG. 1, in block 5a the control unit determines the outlet temperature of the fluid of the electrical heater by means of the reference table and/or transfer function and compares the outlet temperature with a maximal temperature value. In block 6a, the electrical power supplied to the heating element is reduced by pulse width modulation if the outlet temperature is greater than the maximal temperature value.