Safety circuit, a safety circuit operation method and an electrically operated motor comprising a safety circuit

1. A safety circuit for temperature tripping with redundancy, the safety circuit comprising:

a first temperature evaluation module comprising a first input arranged to receive a first input signal derived from a temperature by means of a temperature-dependent element; the first temperature evaluation module being arranged to evaluate said first input signal and determine a first temperature state as one of at least two states, whereof at least one state is a trip state; the first temperature evaluation module further comprising a first output arranged to provide a first output signal corresponding to said determined first temperature state;

a second temperature evaluation module comprising a second input arranged to receive a second input signal derived from said temperature by means of said temperature-dependent element, the second input signal being different from said first input signal; the second temperature evaluation module being arranged to evaluate said second input signal and determine a second temperature state as one of at least two states, whereof at least one state is a trip state; the second temperature evaluation module further comprising a second output arranged to provide a second output signal corresponding to said determined second temperature state; and

a tripping monitoring unit connected to said first and second outputs and being arranged to establish a tripping command signal when at least one of said first and second output signals changes to said trip state.

2. The safety circuit according to claim 1 , wherein said first input and said second input are connected to different terminals of said temperature-dependent element.

3. The safety circuit according to claim 1 , wherein said temperature-dependent element comprises at least one thermistor.

4. The safety circuit according to claim 1 , wherein said temperature-dependent element comprises two terminals, and by series-coupling between two resistors forms a voltage divider with two taps for providing said different first and second input signals.

5. The safety circuit according to claim 1 , wherein said first temperature evaluation module is arranged to perform said determining said first temperature state based on a first reference value, and said second temperature evaluation module is arranged to perform said determining said second temperature state based on a second reference value different from said first reference value.

6. The safety circuit according to claim 5 , wherein said first and second temperature evaluation modules comprise different reference sources ( 26 , 36 ) to establish said different first and second reference values ( 25 , 35 ), respectively.

7. The safety circuit according claim 1 , wherein said tripping monitoring unit is arranged to establish said tripping command signal by forcing a trip signal output with a voltage level denoting “high” to change to a voltage level denoting “low”.

8. The safety circuit according to claim 1 , wherein the safety circuit comprises or is communicatively coupled to an electrically operated switch, controlled in response to said tripping command signal; and wherein said temperature-dependent element is located in an electrically powered load and wherein said electrically operated switch is arranged to disconnect said electrically powered load in response to said tripping command signal.

9. The safety circuit according to claim 1 , wherein the safety circuit comprises two or more first and second inputs arranged to receive two or more first and second input signals, respectively, derived from two or more respective temperatures by means of two or more respective temperature-dependent elements so that each pair of a first and second input signal relates to the same of said two or more temperatures and is connected to different terminals of the same of said two or more temperature-dependent elements; the first and second input signal of each pair being different.

10. A safety circuit operation method for temperature tripping with redundancy, the safety circuit operation method comprising the steps of:

providing a first input signal derived from a temperature by means of a temperature-dependent element;

processing the first input signal by a first temperature evaluation module, the processing comprising determining a first temperature state as one of at least two states, whereof at least one state is a trip state, and providing a first output signal corresponding to said determined first temperature state;

providing a second input signal derived from said temperature by means of said temperature-dependent element, the second input signal being different from said first input signal;

processing the second input signal by a second temperature evaluation module, the processing comprising determining a second temperature state as one of at least two states, whereof at least one state is a trip state, and providing a second output signal corresponding to said determined second temperature state;

establishing a tripping command signal when at least one of said first and second output signals changes to said trip state.

11. The safety circuit operation method according to claim 10 , wherein said first input signal and said second input signal are connected to different terminals of said temperature-dependent element.

12. The safety circuit operation method according to claim 10 , wherein said temperature-dependent element comprises at least one thermistor.

13. The safety circuit operation method according to claim 10 , wherein said temperature-dependent element comprises two terminals, and by series-coupling between two resistors forms a voltage divider with two taps for said providing said different first and second input signals.

14. The safety circuit operation method according to claim 10 , wherein said processing by said first temperature evaluation module uses a first reference value to determine said first temperature state, and said processing by said second temperature evaluation module uses a second reference value different from said first reference value to determine said second temperature state.

15. The safety circuit operation method according to claim 10 , wherein said step of establishing said tripping command signal comprises forcing a trip signal output with a voltage level denoting “high” to change to a voltage level denoting “low”.

16. The safety circuit operation method according to claim 1 , wherein the method further comprises a step of operating an electrically operated switch on the basis of said tripping command signal; and wherein said temperature-dependent element is located in an electrically powered load, and wherein said method comprises a step of disconnecting said electrically powered load in response to said tripping command signal by means of said electrically operated switch.

17. The safety circuit operation method according to claim 10 , wherein the method further comprises providing two or more first and second input signals derived from two or more respective temperatures by means of two or more respective temperature-dependent elements so that each pair of a first and second input signal relates to the same of said two or more temperatures and is connected to different terminals of the same of said two or more temperature-dependent elements; the first and second input signal of each pair being different.

18. The safety circuit operation method according to claim 17 , wherein the method comprises

processing said two or more first input signals by said first temperature evaluation module, the processing comprises determining said first temperature state as said trip state when at least one of said two or more first input signals evaluates to said trip state; and

processing said two or more second input signals by said second temperature evaluation module, the processing comprises determining said second temperature state as said trip state when at least one of said two or more second input signals evaluates to said trip state.

19. An electrically powered motor comprising a safety circuit for temperature tripping with redundancy;

the safety circuit with redundancy comprising:

a first temperature evaluation module comprising a first input arranged to receive a first input signal derived from a temperature by means of a temperature-dependent element; the first temperature evaluation module being arranged to evaluate said first input signal and determine a first temperature state as one of at least two states, whereof at least one state is a trip state; the first temperature evaluation module further comprising a first output arranged to provide a first output signal corresponding to said determined first temperature state;

a second temperature evaluation module comprising a second input arranged to receive a second input signal derived from said temperature by means of said temperature-dependent element, the second input signal being different from said first input signal; the second temperature evaluation module being arranged to evaluate said second input signal and determine a second temperature state as one of at least two states, whereof at least one state is a trip state; the second temperature evaluation module further comprising a second output arranged to provide a second output signal corresponding to said determined second temperature state; and

a tripping monitoring unit connected to said first and second outputs and being arranged to establish a tripping command signal when at least one of said first and second output signals changes to said trip state; and

said electrically powered motor further comprising at least one temperature-dependent element of which one terminal is connected to said first input of said safety circuit and another terminal is connected to said second input of said safety circuit.

20. The electrically powered motor according to claim 19 comprising an electrically operated switch arranged to disconnect said motor from one or more supply phases in response to said tripping command signal of said safety circuit.