Temperature responsive indicators for process control instruments

• US 20070241916A1
• Filed: 04/10/2006
• Published: 10/18/2007
• Est. Priority Date: 04/10/2006
• Status: Active Grant

• Current Assignee: Rosemount Incorporated (Emerson Electric Company)
• Original Assignee: Rosemount Incorporated (Emerson Electric Company)
• Inventors: Hedtke, Robert
• Granted Patent: US 7,528,737 B2
• Time in Patent Office: Days
• US Class Current: 340/584
• CPC Class Codes: G01D 7/005 Indication of measured value by colour change
• CPC Class Codes: G01K 11/165 of organic liquid crystals
• CPC Class Codes: G01K 3/005 Circuits arrangements for indicating a predetermined temperature fire detection G08B17/00
• CPC Class Codes: G05B 23/027 Alarm generation, e.g. communication protocol; Forms of alarm

Abstract

A process transmitter includes a temperature responsive indicator to indicate an operating condition of the process transmitter. The operating condition may represent a level of a sensed process variable or an operating temperature of the process transmitter.

Claims

1. A process transmitter comprising:

a housing;

a sensor within the housing producing a sensor signal as a function of a process variable;

transmitter circuitry within the housing for producing an electrical output based on the sensor signal; and

a temperature responsive indicator visible from an exterior of the housing, the indicator being visually responsive to a temperature.

2. The process transmitter of claim 1 wherein the temperature is a temperature of the process transmitter housing.

3. The process transmitter of claim 2 wherein the temperature responsive indicator is located on an exterior of the housing.

4. The process transmitter of claim 2 wherein the temperature responsive indicator changes from an opaque color to a transparent color to reveal a printed message when a threshold temperature is reached.

5. The process transmitter of claim 4 wherein the temperature responsive indicator comprises a liquid crystal material layer.

6. The process transmitter of claim 2 wherein the temperature responsive indicator comprises a thermochromic ink layer.

7. The process transmitter of claim 2 wherein the temperature responsive indicator includes a temperature limit indicator.

8. The process transmitter of claim 1 wherein the temperature is a temperature of the indicator induced by the electrical output of the transmitter circuitry.

9. The process transmitter of claim 8 wherein the temperature responsive indicator displays a visual representation of a magnitude of the process variable.

10. The process transmitter of claim 8 wherein the temperature responsive indicator is located within the housing and is visible through an opening or a window in the housing.

11. A process transmitter for measuring a process variable, the process transmitter comprising:

transmitter circuitry for producing an electrical output representative of a sensed process variable; and

a temperature responsive indicator responsive to heat produced as a function of the electrical output in order to provide a visual indication representative of the process variable.

12. The process transmitter of claim 11 wherein the visual representation of the electrical output indicates a magnitude of the process variable.

13. The process transmitter of claim 11 wherein the temperature responsive indicator includes a layer of conductive ink having an increasing surface area from a first end to a second end, wherein the electrical output is passed from the first end to the second end causing resistance heating of the conductive ink layer.

14. The process transmitter of claim 13 wherein the temperature responsive indicator comprises a layer of thermochromic ink adjacent the layer of conductive ink, wherein the resistance heating of the conductive ink layer causes a visual change in the appearance of the thermochromic ink layer.

15. The process transmitter of claim 13 wherein the temperature responsive indicator comprises a layer of liquid crystal material adjacent the layer of conductive ink, wherein the resistance heating of the conductive ink layer causes a visual change in the appearance of the liquid crystal material layer.

16. A process transmitter for measuring a process variable, the process transmitter comprising:

a sensing element for sensing the process variable;

transmitter circuitry for producing an output based on the sensed process variable;

a housing containing the transmitter circuitry and sensing element; and

a temperature responsive indicator positioned on the housing and responsive to a temperature of the process transmitter housing.

17. The process transmitter of claim 16 wherein the temperature responsive indicator includes a layer of material that changes from an opaque color to a transparent color in response to a housing temperature in excess of a threshold temperature such that the transparent colored layer of material reveals a message.

18. The process transmitter of claim 17 wherein the layer of material comprises a layer of thermochromic ink.

19. The process transmitter of claim 17 wherein the layer of material comprises a layer of liquid crystal material.

20. The process transmitter of claim 16 wherein the temperature responsive indicator is affixed to an exterior of the housing.