Portable field maintenance tool with resistor network for intrinsically safe operation

Patent metadata

Field	Value
Publication number	US-10764083-B2
Application number	US-201715454725-A
Country	US
Kind code	B2
Filing date	Mar 9, 2017
Priority date	Jul 25, 2016
Publication date	Sep 1, 2020
Grant date	Sep 1, 2020

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 communication interface that is disposed through the housing, the communication interface including an internal portion accessible within the housing and a set of terminals accessible outside the housing, the set of terminals electrically connectable to a field device external to the housing by way of a wired link configured to carry a composite signal including: (i) a communication signal transmitted to or from the field device, and (ii) a power signal transmitted to the field device for powering the field device;
(C) a communication circuit disposed within the housing and electrically connected to the internal portion of the communication interface, the communication circuit configured to encode or decode the communication signal; and
(D) a power supply disposed within the housing and electrically connected to the internal portion of the communication interface and to the communication circuit, the power supply configured to provide, in an intrinsically safe manner, loop power for the field device by transmitting the power signal of the composite signal;
wherein providing the loop power for the field device in an intrinsically safe manner comprises transmitting the power signal of the composite signal such that no voltage of the composite signal exceeds 29 volts;
wherein the communication circuit includes a resistor network having a resistance within a range to cause a voltage drop, at the set of terminals, associated with the composite signal, the voltage drop being: (i) above a minimum voltage threshold associated with reading the composite signal, and (ii) below a maximum voltage threshold.

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 communication circuit includes a DC current controller and a digital frequency modulation (FM) modem, and wherein the composite signal includes:
(i) an analog DC signal that includes the power signal and that varies in amplitude to convey information; and
(ii) a digital FM communication signal superimposed on the analog DC signal.

4. The portable field maintenance tool of claim 1 , wherein the minimum voltage threshold is a minimum peak-to-peak voltage associated with reading the communication signal.

5. The portable field maintenance tool of claim 1 , wherein the maximum voltage threshold is below a voltage sufficient to generate a spark at the set of terminals.

6. The portable field maintenance tool of claim 1 , wherein the power supply is configured to transmit the power signal at a voltage that is at or below the maximum voltage threshold.

7. The portable field maintenance tool of claim 6 , wherein the maximum voltage threshold is a value between 10 V and 30 V.

8. The portable field maintenance tool of claim 7 , wherein the maximum voltage threshold is a value between 21 V and 24 V.

9. The portable field maintenance tool of claim 1 , wherein the minimum voltage threshold is a value between 50 mV peak-to-peak and 500 mV peak-to-peak.

10. The portable field maintenance tool of claim 1 , wherein the minimum voltage threshold is a value of 120 mV peak-to-peak.

11. The portable field maintenance tool of claim 1 , wherein the resistor network includes one or more resistors exceeding 2 mm in length and exceeding 2 mm in width so that the one or more resistors have sufficient surface area to protect against a temperature spike above a temperature threshold.

12. The portable field maintenance tool of claim 1 , wherein the range is 75 Ohms to 750 ohms.

13. The portable field maintenance tool of claim 1 , wherein the resistor network includes a plurality of resistors.

14. The portable field maintenance tool of claim 13 , wherein the plurality of resistors are arranged such that the resistor network maintains the resistance within the range when any one of the plurality of resistors fails.

15. The portable field maintenance tool of claim 13 , wherein the resistor network includes a plurality of switches, each of the plurality of switches in series with a one of the plurality of resistors and actuatable to: (i) remove the one of the plurality of resistors from the resistor network, or (ii) add the one of the plurality of resistors to the resistor network.

16. The portable field maintenance tool of claim 15 , wherein each of the plurality of switches is a solid state relay.

17. The portable field maintenance tool of claim 15 , wherein a resistance of each of the plurality of resistors is selected so that each of the plurality of switches is actuatable to adjust the resistance of the resistor network to a value within a range of 75 ohms and 750 ohms.

18. The portable field maintenance tool of claim 1 , wherein the resistor network includes a first resistor sub-network arranged in parallel with a second resistor sub-network.

19. The portable field maintenance tool of claim 18 , wherein the resistor network further includes a third resistor sub-network arranged in parallel with the first resistor sub-network and the second resistor sub-network.

20. The portable field maintenance tool of claim 19 , wherein:
the first resistor sub-network has a resistance between 200 ohms and 300 ohms;
the second resistor sub-network has a resistance between 400 ohms and 600 ohms; and
the third resistor sub-network has a resistance between 700 ohms and 800 ohms.

21. The portable field maintenance tool of claim 1 , further comprising a fuse electrically connected to the communication interface, the fuse configured to limit a current at the communication interface to below a current threshold.

22. The portable field maintenance tool of claim 21 , wherein the current threshold is a value between 10 mA and 150 mA.

23. The portable field maintenance tool of claim 21 , wherein the current threshold is 50 mA.

24. The portable field maintenance tool of claim 1 , wherein the set of terminals includes: (i) a positive terminal connectable to a first wire of the wired link, and (ii) a negative terminal connectable to a second wire of the wired link.

25. The portable field maintenance tool of claim 1 , wherein the wired link is connected to the field device via a second wired link connected to the field device.

26. A method of communicating with a transmitter field device, the method comprising:
communicatively connecting, via a wired link, a set of terminals of a portable field maintenance tool to a transmitter field device external to the portable field maintenance tool;
supplying power from the portable field maintenance tool, via the wired link, to the transmitter field device to power the transmitter field device in an intrinsically safe manner such that no voltage on the wired link exceeds 29 volts;
receiving by the portable field maintenance tool, via the wired link, a communication signal superimposed on the supplied power; and
limiting a voltage drop at the set of terminals, associated with the communication signal and the supplied power, to between a minimum voltage threshold and a maximum voltage threshold by:
(i) limiting the supplied power so that the voltage drop does not exceed the maximum voltage threshold; and
(ii) activating or deactivating one or more resistors of a resistor network disposed within the portable

Assignees

• Fisher Rosemount Systems Inc

Inventors

• Benson Roger
• Dalal Mehul Rajeshbhai
• Ferguson Anthony
• Toepke Todd M

Classifications

• H04L2012/4026

  Bus for use in automation systems · CPC title

• G05B19/4186 Primary

  by protocol, e.g. MAP, TOP · CPC title

• G05B2219/31129

  Universal interface for different fieldbus protocols · CPC title

• H04B1/3827

  Portable transceivers · CPC title

• H04L12/40039 Primary

  Details regarding the setting of the power status of a node according to activity on the bus · CPC title