Spur Isolation in a Fieldbus Network

Abstract

A method for providing galvanic isolation between an input or trunk interface (30) and multiple outputs or spur interfaces (38) for connecting field devices (14) to a trunk (20) of a two-wire (44a, 44b) process control network (10) includes connecting multiple sets of multiple spur interfaces to respective isolating elements (34). Each isolating element (34) connects a respective set of outputs or spur interfaces (38) to the trunk interface (30) and galvanically isolates (40, 42) the respective set of spur interfaces (38) from the trunk interface (30). Field devices (14) attached to different sets of spur interfaces are also galvanically isolated from one another.

Claims

1. A device coupler capable of connecting a plurality of field devices to a network trunk of a two-wire fieldbus network of the type that transmits data signals and power over the two wires, the device coupler comprising: a trunk interface for connecting the device coupler to a network trunk and two or more spur isolation sets connected to the trunk interface in parallel with one another; and each spur isolation set comprising: an isolating element connected to the trunk interface and a set of two or more spur interfaces connected to the isolating element, the spur interfaces being connected in parallel with one another to the isolating element, the isolating element connecting the trunk interface and the spur interfaces together and galvanically isolating the trunk interface from the spur interfaces.

2. The device coupler of claim 1 wherein in each spur isolation set: the isolating element comprises a respective transformer, the transformer comprising a first transformer winding connected to the trunk interface and a second transformer winding connected to the set of spur interfaces.

3. The device coupler of claim 2 wherein the first transformer windings of the spur isolation sets are connected to the trunk interface in parallel with one another.

4. The device coupler of claim 2 wherein the two or more spur interfaces of each spur isolation set are connected to the second transformer winding of the spur isolation set in parallel with one another.

5. The device coupler of claim 2 wherein the second transformer windings of the spur isolation sets are not connected to one another.

6. The device coupler of claim 1 wherein the two or more spur isolation sets comprises a first spur isolation set and a second isolation set; and the plurality of spur interfaces of the first spur isolation set is galvanically isolated from the plurality of spur interfaces of the second spur isolation set by at least the isolating elements of the first and second spur isolation sets.

7. The device coupler of claim 6 wherein the isolating element of each of the two or more spur isolation sets is a transformer whereby the plurality of spur interfaces of the first spur isolation set is galvanically isolated from the plurality of spur interfaces of the second spur isolation set by at least the transformers of the first and second spur isolation sets.

8. The device coupler of claim 1 wherein the device coupler is connected to the network trunk, a field device is attached to one of the spur interfaces of the device coupler, and the field device is located in a hazardous area.

9. The device coupler of claim 1 wherein the device coupler is connected to the network trunk and the device coupler is located in a hazardous area.

10. The device coupler of claim 1 wherein the device coupler is connected to the network trunk and a power supply is connected to the network trunk.

11. The device coupler of claim 10 wherein a field device is connected to one of the spur interfaces of the device coupler and the power supply supplies power to the field device.

12. The field device coupler of claim 1 wherein the device coupler comprises a terminating impedance being adapted to terminate an end of the network trunk.

13. A method of connecting a plurality of outputs to an input for transmission between input and outputs, the input being adapted for connection to a network trunk of a two-wire fieldbus network that transmits data signals and power for field devices over the two wires, the outputs being adapted for connection of field devices, the method comprising the step of: dividing all of the plurality of outputs into two or more sets of outputs, each output being in one and only one set of the two or more sets of outputs, each set of outputs including two or more outputs; connecting two or more isolation elements in parallel with one another to the input and connecting the isolation elements to the sets of outputs, each set of outputs being connected in parallel with one and only one isolation element, the one isolation element connecting the set of outputs to the input and galvanically isolating the set of outputs and the input; whereby each set of outputs are galvanically isolated from the network trunk and from the other sets of outputs when the input is connected to the network trunk.

14. The method of claim 13 wherein the step of connecting isolation elements comprises the step of connecting a respective transformer between the input and each set of outputs.

15. The method of claim 14 wherein the step of connecting a respective transformer comprises the step of connecting a first winding of the transformer to the input and connecting the set of outputs associated with the transformer in parallel with a second winding of the transformer.

16. The method of claim 15 wherein after connecting the isolating elements to the input and outputs, each set of outputs is galvanically isolated from each other set of outputs by at least two of the transformers.

17. The method of claim 13 comprising the step of connecting a field device to one of the outputs, the field device being located in a hazardous area.

18. A two-wire process control network that transmits data signals and power over the network comprising: a trunk comprising two wires, the two wires transmitting the data signals and the power; a trunk interface connected to the trunk; two or more sets of spur interfaces connected to the trunk interface, each set of spur interfaces comprising two or more spur interfaces, each spur interface in one and only one set of spur interfaces; and each set of spur interfaces connected to a respective isolating element, each isolating element connected to the trunk interface and galvanically isolating the trunk interface from the set of spur interfaces connected to the respective isolating element.

19. The network of claim 18 wherein the two or more sets of spur interfaces comprises a first set of spur interfaces and a second set of spur interfaces, a first field device connected to one spur interface of the first set of spur interfaces and a second field device connected to one spur interface of the second set of spur interfaces.

20. The network of claim 18 comprising a field device attached to one spur interface, the field device being located in a hazardous area.

21. The network of claim 18 wherein the spur interfaces are located in a hazardous area.

Description

BRIEF SUMMARY OF THE DRAWINGS

[0032] FIG. 1 illustrates a two-wire process control network that includes an embodiment of the disclosed device coupler connecting field devices to the network trunk; and

[0033] FIGS. 2-4 illustrate prior art device couplers.

DETAILED DESCRIPTION

[0034] FIG. 1 illustrates a two-wire process control network that transmits process control signals between a control processor 12 and field devices 14, three field devices 14a, 14b, 14c being shown. The illustrated network 10 is a Foundation Fieldbus H1 network that includes a conventional fieldbus power supply 16 and a power conditioner 18 connected to an end of a network trunk 20. Terminating impedances 22 are located at both ends of the network trunk 20.

[0035] The control processor 12 is connected to the network trunk 20 to receive and transmit data signals transmitted along the trunk 20. The field devices 14a, 14b, 14c are connected to a device coupler 24 that in turn is connected to the network trunk 20. The field devices 14a, 14b, 14c receive and transmit data signals along the network trunk 20 through the device coupler 24 and also receive power transmitted from the power supply 16 through the network trunk 20 and through the device coupler 24.

[0036] The field devices 14 may be process controllers, measurement devices and the like as is known in the fieldbus art. The illustrated field devices 14a, 14b, 14c are located in a hazardous area 26. The device coupler 24 is located in an area 28. The area 28 may be the same as the hazardous area 26 or may be a different hazardous or non-hazardous area than the area 26.

[0037] The network trunk 20 is shown in FIG. 1 extending directly between the control processor 12 and the device coupler 24. There may, however, be other device couplers or field devices (not shown) connected to the network trunk 20 between the control processor 12 and the device coupler 24 or connected to the network trunk 20 downstream from the device coupler 24.

[0038] The network topology shown in FIG. 1 is a conventional trunk and spur topology; other conventional fieldbuses topologies are known and the device coupler 24 can be used in the other topologies to connect fieldbus devices to fieldbus segments.

[0039] The device coupler 24 includes an input trunk interface 30 that connects the device coupler 24 to a network trunk or fieldbus segment and multiple spur isolation sets 32 connected in parallel with the trunk interface 30 that connect the field devices to the device coupler 24. Each spur isolation set 32 includes an isolating element 34 and a set 36 of two or more outputs or spur interfaces 38 that connect the field devices to the device coupler 24. Each spur interface 38 is a member of only one spur interface set 36.

[0040] Within a spur isolation set 32, the isolating element 34 is connected to the trunk interface 30 and the spur interfaces 38 are connected in parallel with the isolating element 14. The isolating element 34 connects the trunk interface 30 with each spur interface 38 of the spur interface set 36 and galvanically isolates the trunk interface 30 from each spur interface 30 of the spur interface 36.

[0041] The illustrated device coupler 24 has two spur isolation sets 32. One spur isolation set 32 includes a spur interface set 36 that contains the four spur interfaces 38 labeled “SPUR INTERFACE 1” through “SPUR INTERFACE 4” in FIG. 1. The other spur isolation set 32 includes a spur interface set 36 that contains the four spur interfaces 38 labeled “SPUR INTERFACE 5” through “SPUR INTERFACE 8” in FIG. 1. It should be understood that other embodiments of the device coupler 24 could include additional spur isolation sets 32, or that a spur interface set 36 could contain 2, 3, 4, or more than 5 spur interfaces 38.

[0042] Each isolating element 34 in the illustrated embodiment is a transformer having a primary winding 40 and a secondary winding 42. The primary winding 40 is connected to the trunk interface 30. The spur interfaces 38 of the spur interface set 36 associated with the isolating element 34 are connected in parallel with the secondary winding 42. The secondary windings 42 are not connected to one another.

[0043] The device coupler 24 is shown in FIG. 1 being connected to the network trunk 20 by a set or pair of terminals 44a, 44b that are connected to respective wires 46a, 46a of the network trunk 20.

[0044] FIG. 1 illustrates one field device 14a connected to the spur interface 38 labeled “SPUR INTERFACE 1”, a second field device 14b connected to the spur interface 38 labeled “SPUR INTERFACE 2”, and a third field device 14b connected to the spur interface 38 labeled “SPUR INTERFACE 5”. That is, the field devices 14a, 14b are connected to one spur interface 36 and the other field device 14b is connected to the other spur interface set 36. Each field device 14 is connected to its respective spur interface 36 by a two-wire spur 48 for transmission of data signal and power between the field device 14 and the device coupler 24.

[0045] As is evident in FIG. 1, each field device 14 is galvanically isolated from the trunk interface 30 by the isolating element 34 of the spur isolation set to which the field device 14 is attached. A field device attached to one spur isolation set 32 is galvanically isolated from a field device attached to another spur isolation set 32 by both isolating elements 34 because any current flow between a pair of spur isolation sets 32 must flow through both isolating elements 34 of the two spur isolation sets 32.

[0046] In FIG. 1, the field devices 14a, 14b are galvanically isolated from the trunk interface 30 and the field device 14c is galvanically isolated from the field devices 14a, 14b by both transformers 34. If the spur 48 connected to the field device 14c is noisy, the noise will not couple onto the spurs 48 connected to the field devices 14a, 14b. If it known that a field device 14c generates noise, the spur isolation set 32 may be dedicated solely for connection of the field device 14c.

[0047] The device coupler 24 also includes a terminating impedance 50 that is selectably connectable to the trunk interface 30. If the device coupler 24 is placed at the end of the network trunk 20, the device coupler impedance 50 can be manually or automatically connected to the trunk interface 30 in conventional manner to terminate an end of the network trunk 20.

[0048] While this disclosure includes one or more illustrative embodiments described in detail, it is understood that the one or more embodiments are each capable of modification and that the scope of this disclosure is not limited to the precise details set forth herein but include such modifications that would be obvious to a person of ordinary skill in the relevant art, as well as such changes and alterations that fall within the purview of the following claims.