Temperature responsive indicators for process control instruments

• US 7,528,737 B2
• Filed: 04/10/2006
• Issued: 05/05/2009
• 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
• Primary Examiner(s): Bugg; George A
• Assistant Examiner(s): LAI, ANNE VIET NGA
• Application Number:
  US11/401,074
• Publication Number:
  US 20070241916A1
• Time in Patent Office: 1,121 Days
• Field of Search: 340/533, 340/584, 340/679, 340/870.02, 340/870.01, 374142-143, 374/162, 345106-107, 737/53, 737/66, 732/042.5, 732/042.3, 732/042.7, 116/101, 116/216
• US Class Current: 340/870.01
• 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 for producing a sensor signal as a function of a process variable;

transmitter circuitry within the housing for producing a variable electrical output based on the sensor signal and communicating the variable electrical output over a process control loop; and

a temperature responsive indicator visible from an exterior of the housing, the indicator being visually responsive to a temperature change of the indicator induced by resistance heating of a conductive ink generated by the variable electrical output of the transmitter circuitry before being communicated over the control loop.

2. The process transmitter of claim 1 wherein the temperature responsive indicator includes a layer of thermochromic ink that displays a visual representation of a magnitude of the process variable.

3. The process transmitter of claim 1 wherein the temperature responsive indicator is located within the housing and is visible through an opening or a window in the housing.

4. The process transmitter of claim 1 wherein the visual responsiveness of the temperature responsive indicator indicates a magnitude of the process variable.

5. The process transmitter of claim 1 wherein the temperature responsive indicator includes 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.

6. The process transmitter of claim 1 wherein the transmitter circuitry and temperature responsive indicator are connected in series such that the variable electrical output is passed through the temperature responsive indicator before communication with the control loop.

7. An industrial process transmitter comprising:

a housing for connecting to an industrial process;

a sensor positioned within the housing and configured to interface with the industrial process to measure an industrial process parameter selected from the group consisting of pressure, temperature, level and flow of an industrial process fluid, and generate a variable sensor signal that is a function of the measured process parameter;

transmitter electronics positioned within the housing and connected to the sensor to condition and communicate the variable sensor signal over an external control loop as a loop current; and

a temperature responsive indicator visible from an exterior of the housing, the indicator comprising;

an electrically conductive layer configured to receive the loop current en route to the external control loop such that the electrically conductive layer undergoes a temperature change due to resistive heating; and

a temperature responsive layer positioned adjacent the electrically conductive layer for visually indicating a magnitude of the measured process parameter.

8. The industrial process transmitter of claim 7 wherein:

the electrically conductive layer comprises conductive ink; and

the temperature responsive layer comprises liquid crystal material.

9. The industrial process transmitter of claim 7 wherein:

the electrically conductive layer comprises conductive ink; and

the temperature responsive layer comprises thermochromic ink.

10. The industrial process transmitter of claim 7 wherein a surface area of the electrically conductive layer increases in a direction of current flow of the loop current such that the resistive heating of the electrically conductive layer decreases in the direction of current flow.

11. The industrial process transmitter of claim 7 wherein a current density of the loop current decreases in the direction of current flow across the electrically conductive layer such that the resistive heating of the electrically conductive layer decreases in the direction of current flow.

12. The industrial process transmitter of claim 11 wherein the temperature responsive layer is configured to visually change appearance when the electrically conductive layer exceeds a threshold current density.

13. The industrial process transmitter of claim 12 wherein the current density changes proportionally to a magnitude of the variable sensor signal.

14. The industrial process transmitter of claim 13 wherein the temperature responsive layer indicates the magnitude of the variable sensor signal at the threshold current density.

15. The industrial process transmitter of claim 7 wherein the electrically conductive layer is connected in series with the transmitter electronics and the control loop.