System and method for monitoring relay contacts

1. A system for monitoring at least one relay contact, the system comprising:

an emitter adapted for electrical communication with a first side of a first relay contact and for electrical communication with a first side of a second relay contact, the emitter configured to emit a monitoring signal;

a first receiver adapted for electrical communication with a second side of the first relay contact and configured to detect the monitoring signal emitted by the emitter;

a second receiver adapted for electrical communication with a second side of the second relay contact and configured to detect the monitoring signal emitted by the emitter; and

a controller adapted for electrical communication with the emitter and the first and second receivers, the controller configured to determine an open or a closed state of the first relay contact and to determine an open or a closed state of the second relay contact;

wherein the controller controls the emitter to emit the monitoring signal comprising a first component and a second component different than the first component, the controller determines a closed state of the first relay contact if the first receiver detects the first component, the controller determines an open state of the first relay contact if the first receiver fails to detect the first component, the controller determines a closed state of the second relay contact if the second receiver detects the second component, and the controller determines an open state of the second relay contact if the second receiver fails to detect the second component.

2. The system of claim 1 wherein the controller controls the emitter to emit the monitoring signal around a rail voltage of the first relay contact after a relay coil is driven in order to open the first relay contact or prior to closing the first relay contact.

3. The system of claim 1 wherein the first component has a first amplitude, the second component has a second amplitude different than the first amplitude, the first receiver is configured to detect the first component, and the second receiver is configured to detect the second component.

4. The system of claim 1 wherein the first component has a first frequency, the second component has a second frequency different than the first frequency, the first receiver is configured to detect the first component, and the second receiver is configured to detect the second component.

5. The system of claim 1 wherein the first component has a first digital identifier, the second component has a second digital identifier different than the first digital identifier, the first receiver is configured to detect the first component, and the second receiver is configured to detect the second component.

6. A system for monitoring a first relay contact and a second relay contact, each of the first and second relay contacts having a first side and a second side, the system comprising:

an emitter adapted for electrical communication with the first side of each of the first and second relay contacts and configured to monitoring signal;

a receiver adapted for electrical communication with the second side of each of the first and second relay contacts and configured to detect the monitoring signal emitted by the emitter; and

a controller adapted for electrical communication with the emitter and the receiver, the controller configured to determine an open or a closed state of each of the first and second relay contacts;

wherein the controller controls the emitter to emit the monitoring having a first component and a second component different than the first component, the controller determines a closed state of the first relay contact and an open state of the second relay contact if the receiver detects only the second component of the monitoring signal, the controller determines a closed state of the second relay contact if the receiver detects the first component of the monitoring signal, and the controller determines an open state of both the first relay contact and the second relay contact if the receiver fails to detect both the first and second components of the monitoring signal.

7. The system of claim 6 wherein the first component of the monitoring signal has a frequency that is substantially attenuated by a battery and/or a DC-link impedance, and the second component of the monitoring signal has a frequency that is non-substantially attenuated by a battery and a DC-link impedance.

8. The system of claim 7 wherein the first component is a lower frequency signal, L(f), the second component is a higher frequency signal, H(f), and the frequency of the monitoring signal emitted by the emitter, S(f), is defined by the equation S(f)=L(f)+H(f).

9. The system of claim 8 wherein a signal detected by the receiver, R(f), is defined by the equation R(f)=K 2 *L(f)+K 2 *H(f)+K 1 * H(f), where K i =0 if a relay has an open state and K i =1 if a relay has a closed state, for i=1, 2.

10. A method for monitoring at least one relay contact, the method comprising:

emitting a monitoring signal comprising a first component and a second component different than the first component;

determining a closed state of a first relay contact if a first receiver detects the first component; and

determining an open state of the first relay contact if the first receiver fails to detect the first component;

determining a closed state of a second relay contact if a second receiver detects the second component, and

determining an open state of the second relay contact if the second receiver fails to detect the second component.

11. The method of claim 10 wherein the first component has a first frequency, the second component has a second frequency different than the first frequency, the first receiver is configured to detect the first component, and the second receiver is configured to detect the second component.

12. The method of claim 10 wherein the first component has a first amplitude, the second component has a second amplitude different than the first amplitude, the first receiver is configured to detect the first component, and the second receiver is configured to detect the second component.

13. The method of claim 10 wherein the monitoring signal is emitted around a rail voltage of the first relay contact after a relay coil is driven to open the first relay contact or prior to closing the first relay contact.

14. The method of claim 10 wherein the first component has a first digital identifier, the second component has a second digital identifier different than the first digital identifier, the first receiver is configured to detect the first component, and the second receiver is configured to detect the second component.

15. A method for monitoring a first relay contact and a second relay contact, the method comprising:

emitting a monitoring signal having a first component and a second component different than the first component;

determining a closed state of the first relay contact and an open state of the second relay contact if a receiver detects only the second component of the monitoring signal;

determining a closed state of the second relay contact if the receiver detects the first component of the monitoring signal; and

determining an open state of both the first relay contact and the second relay contact if the receiver fails to detect both the first and second components of the monitoring signal.

16. The method of claim 15 wherein the first component is a lower frequency signal, L(f), that is substantially attenuated by a battery and/or a DC-link impedance, the second component is a higher frequency signal, H(f), that is non-substantially attenuated by a battery and a DC-link impedance, and the frequency of the emitted monitoring signal, S(f), is defined by the equation S(f)=L(f)+H(f), and a signal detected by the receiver, R(f), is defined by the equation R(f)=K 2 *L(f)+K 2 *H(f)+K 1 * H(f), where K i =0 if a relay has an open state and K i =1 if a relay has a closed state, for i=1, 2.