Portable field maintenance tool with a bus for powering and communicating with a field device

Patent metadata

Field	Value
Publication number	US-10505585-B2
Application number	US-201715454744-A
Country	US
Kind code	B2
Filing date	Mar 9, 2017
Priority date	Jul 25, 2016
Publication date	Dec 10, 2019
Grant date	Dec 10, 2019

Abstract

A portable field maintenance tool may perform one or more tasks, such as communicating with a field device, powering a field device, diagnosing a field device, or diagnosing a communication link in a plant environment to which a field device is connected. The portable field maintenance tool may interact with field devices configured according to a number of different communication protocols, such as the HART protocol and the Fieldbus protocol. The portable field maintenance tool may be energy limited and fault tolerant, and may operate in compliance with Intrinsic Safety standards, enabling use of the portable field maintenance tool in hazardous areas.

First claim

What is claimed is:

1. A portable field maintenance tool comprising:
(A) a housing;
(B) a power supply disposed within the housing;
(C) a communication circuit disposed within the housing;
(D) a communication bus disposed within the housing and electrically connected to the power supply and the communication circuit; and
(E) a communication interface disposed through the housing, the communication interface including: (i) an internal portion electrically connected to the communication bus, and (ii) a set of terminals electrically connectable to a field device external to the housing via a wired link to thereby electrically connect the field device to the communication bus so that a composite signal carried by the wired link includes:
(a) a power signal to supply power, from the power supply disposed within the housing, to the field device external to the housing via the communication bus and the wired link; and
(b) a digital amplitude modulated (AM) communication signal transmitted via the communication bus and the wired link between the communication circuit and the field device.

2. The portable field maintenance tool of claim 1 , wherein the communication circuit and the power supply are each configured for intrinsically safe operation.

3. The portable field maintenance tool of claim 1 , wherein the set of terminals includes a first terminal and a second terminal connectable to the field device via the wired link.

4. The portable field maintenance tool of claim 3 , wherein the set of terminals further includes a third terminal that is electrically connected to the power supply, wherein:
(i) placing a shunt between the third terminal and a one of the first terminal and the second terminal causes the power supply to supply the power to the communication bus and the wired link; and
(ii) removing the shunt creates an open circuit between the third terminal and the one of the first terminal and the second terminal to thereby prevent the power supply from supplying the power to the communication bus.

5. The portable field maintenance tool of claim 1 , wherein the communication bus includes one or more terminators providing load impedance for the communication circuit.

6. The portable field maintenance tool of claim 5 , further including one or more switches electrically connected to the one or more terminators.

7. The portable field maintenance tool of claim 1 , wherein the power signal on the wired link has a current in a range of 34 mA and 40 mA, and wherein the digital AM communication signal on the wired link is biased on top of the power signal and has a current modulated at a peak-to-peak amplitude, the peak-to-peak amplitude being any value in a range of 14 mA to 21 mA.

8. The portable field maintenance tool of claim 1 , wherein the communication circuit includes a DC current controller configured to draw from the communication bus a current in a range of 10 mA to 12 mA.

9. The portable field maintenance tool of claim 1 , further comprising a fuse that is electrically connected to the communication interface and that limits a current at the communication interface to below a current threshold.

10. The portable field maintenance tool of claim 9 , wherein the current threshold is a value between 25 mA and 75 mA.

11. The portable field maintenance tool of claim 1 , wherein the power supply is limited to a maximum output to limit a voltage across the set of terminals to below a maximum voltage threshold.

12. The portable field maintenance tool of claim 11 , wherein the maximum output of the power supply is a maximum current, the maximum current being a value between 34 mA and 40 Ma.

13. The portable field maintenance tool of claim 11 , wherein the maximum voltage threshold is 17.5 V.

14. The portable field maintenance tool of claim 1 , wherein the power supply is configured to:
ramp the power signal over a time period when the power signal is initially supplied to the field device via the communication bus to limit current on the communication bus to a maximum current threshold.

15. The portable field maintenance tool of claim 14 , wherein the maximum current threshold is 300 mA.

16. A method of communicating with a field device, the method comprising:
communicatively connecting a field device, disposed external to a housing of a portable field maintenance tool, to a communication bus disposed within the housing of the portable field maintenance tool by way of a communication interface of the portable field maintenance tool; and
transmitting by the portable field maintenance tool, via the communication bus, a composite signal including: (i) a power signal to power the field device, and (ii) a digital amplitude modulated (AM) communication signal to communicate with the field device.

17. The method of claim 16 , further comprising:
placing a shunt between a third terminal of the communication interface and a one of the first terminal and the second terminal to electrically connect a power supply disposed within the housing to the communication bus.

18. The method of claim 16 , further comprising:
activating one or more terminators of the communication bus to provide load impedance for interpreting the digital AM communication signal.

19. The method of claim 16 , wherein the power signal has a value in a range of 10 mA and 20 mA, and wherein the digital AM communication signal is current modulated at a peak-to-peak amplitude, the peak-to-peak amplitude being any value in a range of 14 mA to 21 mA peak-to-peak.

20. The method of claim 16 , further including drawing from the communication bus, by the communication circuit, a current modulated at a peak-to-peak amplitude, the peak-to-peak amplitude being any value in a range of 14mA to 21 mA peak-to-peak.

21. The method of claim 16 , further including limiting a voltage of the composite signal at the communication interface to a maximum value, the maximum value being any value in a range of 9 V to 18 V.

22. The method of claim 16 , further including deactivating a power supply of the portable field maintenance tool when the composite signal exceeds a maximum electrical threshold.

23. The method of claim 22 , wherein the maximum electrical threshold is a current threshold having any value in a range of 45 mA to 55 mA.

24. The method of claim 22 , wherein the maximum electrical threshold is a power threshold having any value in a range of 1 W to 1.5 W.

25. The method of claim 16 , further including deactivating a power supply of the portable field maintenance tool when the composite signal drops below a minimum electrical threshold.

26. The method of claim 25 , wherein the minimum electrical threshold is a voltage threshold having any value between 5 V and 9 V.

27. A portable field maintenance tool comprising:
(A) a communication circuit;
(B) a power supply;
(C) a housing that houses the communication circuit and the power supply;
(D) a first set of terminals electrically connected to the communication circuit and isolated from the power supply, the first set of terminals electrically connectable to a field device external to the housing to transmit to the field device a communication signal from the communication circuit without transmitting a power signal from the power supply; and
(E) a second set of terminals electrically connected to the communication circuit and electrically connected to the power supply, the

Assignees

• Fisher Rosemount Systems Inc

Inventors

• Benson Roger
• Ferguson Anthony D
• Dalal Mehul Rajeshbhai
• Gorivale Sameer Parshuram

Classifications

• G05B2219/31088

  Network communication between supervisor and cell, machine group · CPC title

• H04L2012/2843

  Mains power line · CPC title

• H04L12/40045

  Details regarding the feeding of energy to the node from the bus · CPC title

• H04B3/548 Primary

  the power on the line being DC (arrangements for feeding power H04L12/10; extracting feeding power from signals H04L25/02) · CPC title

• H04B1/3827

  Portable transceivers · CPC title