Elevator cord health monitoring

1. A method of fault detection of a belt or rope comprising:

interconnecting a plurality of cords of the belt or rope, the cords including a plurality of wires, to form a bridge circuit, at least two legs of the bridge circuit comprising separate and distinct cords of the plurality of cords;

subjecting the bridge circuit to an excitation voltage;

outputting a signal voltage from the bridge circuit, the bridge circuit structure suppressing environmental noise to increase signal to noise ratio of the signal voltage; and

monitoring the signal voltage to detect a fault condition of the rope,

wherein each leg of the bridge circuit is configured as an LCR circuit allowing for measurement of complex impedance of the legs of the bridge circuit.

2. The method of claim 1 , wherein the output voltage is proportional to an impedance difference between cords of the plurality of cords.

3. The method of claim 2 , wherein the output voltage is indicative of an impedance difference between laterally inner cords of the belt and laterally outer cords of the belt.

4. The method of claim 1 , wherein at least one leg of the bridge circuit comprises a fixed resistor.

5. The method of claim 4 , wherein two legs of the bridge circuit each comprise at least one cord and two legs of the bridge circuit each comprise a fixed resistor.

6. The method of claim 1 , further comprising comparing the signal voltage to the excitation voltage in magnitude and phase to detect the fault condition of the rope.

7. The method of claim 1 , further comprising:

comparing a profile of a measured electrical impedance to a baseline electrical impedance profile; and

determining a fault condition of the belt or rope via the comparison.

8. The method of claim 1 , wherein each leg of the bridge circuit comprises at least one cord of the belt or rope.

9. The method of claim 8 , wherein each leg of the bridge circuit comprises two or more cords of the belt or rope.

10. The method of claim 1 , wherein fault conditions include wire breakage, fretting and/or birdcaging.

11. The method of claim 1 , wherein the electrical impedance is measured substantially continuously.

12. The method of claim 1 , further comprising switching the interconnection of the plurality of cords via a switching mechanism operably connected to the plurality of cords.

13. The method of claim 1 , wherein the excitation voltage is supplied from an AC voltage source.

14. An elevator system comprising:

an elevator car;

one or more sheaves;

a belt or rope comprising a plurality of wires arranged into a plurality of cords for supporting and/or driving the elevator car routed across the one or more sheaves and operably connected to the elevator car, the plurality of cords interconnected to form a bridge circuit, at least two legs of the bridge circuit comprising separate and distinct cords of the plurality of cords;

wherein each leg of the bridge circuit is configured as an LCR circuit allowing for measurement of complex impedance of the legs of the bridge circuit.

15. The elevator system of claim 14 , wherein each leg of the bridge circuit comprises at least one cord of the belt or rope.

16. The elevator system of claim 15 , wherein each leg of the bridge circuit comprises two or more cords of the belt or rope.

17. The elevator system of claim 14 , wherein at least one leg of the bridge circuit comprises a fixed resistor.

18. The elevator system of claim 17 , wherein two legs of the bridge circuit each comprise at least one cord and two legs of the bridge circuit each comprise a fixed resistor.

19. The elevator system of claim 14 , further comprising a switching element operably connected to the plurality of cords to change an interconnection configuration of the plurality of cords.

20. The elevator system of claim 14 , further comprising an AC voltage source operably connected to the belt or rope.

21. The elevator system of claim 14 , wherein the belt or rope is a coated belt or rope.