Barrier device

• US 5,710,552 A
• Filed: 06/06/1995
• Issued: 01/20/1998
• Est. Priority Date: 09/30/1994
• Status: Expired due to Term

• Current Assignee: Rosemount Incorporated (Emerson Electric Company)
• Original Assignee: Rosemount Incorporated (Emerson Electric Company)
• Inventors: McCoy, Steven J., Edwards, Grant B., Templin, James E., Schumacher, Mark S., Kielb, John A., Longsdorf, Randy J., Palan, Donald F.
• Primary Examiner(s): Hofsass, Jeffery
• Assistant Examiner(s): MANNAVA, ASHOK K
• Application Number:
  US08/472,695
• Time in Patent Office: 959 Days
• Field of Search: 340/870.3, 340/87.39, 340/870.16, 340/870.17, 340/870.21, 340/660, 340/661, 340/662, 340/664, 361/18, 361/54, 361/57, 361/58, 73/4 R, 73/753, 73/866.5
• US Class Current: 340/870.21
• CPC Class Codes: G01D 3/08 with provision for safeguarding the apparatus, e.g. against abnormal operation, against breakdown
• CPC Class Codes: G01F 23/284 Electromagnetic waves
• CPC Class Codes: H02H 9/008 Intrinsically safe circuits

Abstract

A barrier device threadably mounts to a cabling aperture on a field mounted transmitter. The field mounted transmitter receives and transmits signals, and is wholly powered by a current loop circuit. The barrier device has a conductive housing with at least a first and a second aperture and a pair of conductors passing through the first aperture of the barrier device, for connecting to a terminal block in the transmitter. A pair of signal terminals, preferably as ring tongue lug, is mounted in the second aperture of the barrier device. The signal terminals are connectable to a handheld communicator, which is used to calibrate, monitor and test the transmitter. A barrier circuit is mounted in the housing and is electrically connected between the signal terminals and the conductors. Signals from the communicator access the terminal block through the barrier circuit, and the barrier circuit limits the power available at the signal terminals. One embodiment of the barrier device has a third aperture directly across from the first aperture. The first aperture threadably connects to the transmitter, so that cabling from the transmitter can pass through a passageway formed between the first and third apertures. Another embodiment has a stub shaped housing, with one end of stub being the first aperture, and the other end being the second aperture. The first aperture threads to the cabling aperture on the transmitter, and the barrier circuit is potted in the stub shaped housing.

Claims

1. A barrier device for mounting in the field, comprising:

a housing with a first aperture and an open passageway extending from the first aperture to a second aperture to carry cabling to a transmitter through the first aperture;

a pair of conductors, separate from the cabling, passing through the first aperture for connecting for to a terminal block in a transmitter;

a pair of signal terminals mounted to the housing and accessible from the field, the signal terminals connectable to a handheld communicator in the field; and

a barrier circuit mounted in the housing and electrically connected between the signal terminals and the conductors, where the barrier circuit allows frequency encoded signals from the communicator to access the terminal block and limits the power available at the signal terminals.

2. The barrier device of claim 1 where the housing has an extended portion, and where the signal terminals are disposed on the extended portion and the barrier circuit is mounted in the extended portion.

3. The barrier device of claim 2 where the barrier circuit is potted in the extended portion.

4. The barrier device of claim 3 where the extended portion has an inner surface, the inner surface having grooves disposed thereon.

5. The barrier device of claim 1 where a threaded cap is threadably joined to the extended portion so as to seal the signal terminals from the atmosphere.

6. The barrier device of claim 5 where the cap is removably attached to the housing by a chain.

7. The barrier device of claim 1 where the housing has a ground connection for electrically grounding the housing.

8. The barrier device of claim 1 where the barrier circuit further comprises a current limiting resistor having a first end common to one of the signal terminals.

9. The barrier device of claim 8 further comprising a zener diode, the zener diode connected between the other of the signal terminals and the second end of the current limiting resistor.

10. The barrier device of claim 8 further comprising two zener diodes each having an anode and a cathode, the anode of both zeners connected together, the cathode of one of the zeners connected to the second end of the current limiting resistor and the cathode of the other zener connected to the other of the signal terminals.

11. The barrier device of claim 10 where three sets of two zener diodes are connected between the other of the signal terminals and the second end of the current limiting resistor.

12. A field mounted measurement transmitter powered by and communicating over a current loop, the measurement transmitter comprising:

a housing;

an A/D converter for converting a sensed process variable into a digitized process signal;

a microprocessor for compensating the digitized process signal;

an output circuit having a pair of process terminals within the transmitter for coupling the compensated digitized process signal to the current loop;

a barrier circuit disposed in the housing electrically connected to the process terminals; and

a pair of signal terminals mounted to the housing and accessible from the field, the signal terminals connectable to a communicator for receiving frequency encoded signals therefrom, the signal terminals electrically connected to the barrier circuit, where the barrier circuit limits the amount of power available at the signal terminals.

13. A field mountable measurement transmitter for sensing a level of a fluid in a tank and providing power to and communicating with a temperature sensor sensing a temperature of the fluid in the tank, the measurement transmitter comprising:

a housing;

a measurement circuit for measuring the level of the fluid;

a first output circuit for powering the temperature sensor and receiving a sensor signal representative of the temperature of the fluid;

a microprocessor coupled to the measurement circuit for receiving a first signal representative of the level of the fluid and coupled to the output circuit for receiving the sensor signal, where the microprocessor calculates a value of a selected parameter of the fluid as a function of a value of the first signal and a value of the sensor signal;

a second output circuit coupled to the microprocessor for transmitting all output signal representative of the value of the selected parameter; and

a barrier device comprising;

a second housing with a first and a second aperture;

a pair of conductors passing through the first aperture, for connecting to the first output circuit;

a pair of signal terminals mounted in the second aperture and accessible from the field, the signal terminals connectable to a handheld communicator in the field;

pair of signal lines extending out the second aperture and electrically connected to the temperature sensor; and

a barrier circuit mounted in the second housing and electrically connected between the signal terminals and the conductors, and electrically connected between the pair of signal lines and the conductors, where the barrier circuit allows frequency encoded signals from the communicator to access the output circuit and limits the power available at the signal terminals and through the pair of signal lines.

14. A field mountable transmitter in a process control loop, comprising:

a sensor for sensing a process variable;

a transmitter housing having a first threaded aperture and a second threaded aperture joinable to conduit;

a conduit joined to the first threaded aperture for carrying conductors of the process control loop;

an input circuit disposed in the transmitter housing for receiving an input signal indicative of the process variable;

an output circuit disposed in the transmitter housing having process terminals electrically connected to the conductors of the process control loop for communicating information to a remote location and for receiving power; and

a barrier device comprising;

a housing joined to the second threaded aperture;

a pair of signal terminals mounted to the housing and accessible from the field, the signal terminals being connectable to a handheld communicator in the field; and

a barrier circuit mounted in the housing and electrically connected between the signal terminals and the process terminals, where the barrier circuit allows frequency encoded signals from the communicator to access the terminal block and limits the power available at the signal terminals.

15. The transmitter of claim 14 wherein the housing of the barrier device includes a passageway for carrying conductors of the process loop to the transmitter.

16. The transmitter of claim 14 where the housing of the barrier device is stub shaped and one end of stub is joined the second aperture, and wherein the signal terminals are disposed at the other end.

17. The transmitter of claim 16 where the barrier circuit is potted in the housing.

18. The transmitter of claim 16 where the housing has a ground connection for electrically grounding the housing.

19. A field mountable transmitter in a process control loop, comprising:

a sensor for sensing a process variable;

a transmitter housing having a first threaded aperture joinable to conduit, and a second threaded aperture;

a conduit joined to the first threaded aperture for carrying conductors of the process control loop from a remote location;

an input circuit disposed in the transmitter housing for receiving an input signal indicative of the process variable;

an output circuit disposed in the transmitter housing having process terminals accessible through the second threaded aperture, the process terminals electrically connected to the conductors of the process control loop for communicating information to the remote location and for receiving power; and

a cover joined to the second threaded aperture;

a pair of signal terminals mounted to the cover and being accessible from the field with the cover joined to the second threaded aperture, the signal terminals being connectable to a handheld communicator in the field; and

a barrier circuit electrically connected between the signal terminals and the process terminals, where the barrier circuit allows frequency encoded signals from the communicator to access the process terminals and limits the power available at the signal terminals.

20. The transmitter of claim 19 wherein the barrier circuit is mounted to the cover.