Process control instrument with multiple functions

• US 6,452,493 B1
• Filed: 01/19/2000
• Issued: 09/17/2002
• Est. Priority Date: 01/19/2000
• Status: Expired due to Fees

• Current Assignee: SOR Inc.
• Original Assignee: SOR Inc.
• Inventors: Kumarakulasingam, Prabhaharan, Womack, Arthur David Jr., Ma, Xiqing, Donnelly, John M., Bartrum, Mark Stephen
• Primary Examiner(s): POPE, DARYL C
• Application Number:
  US09/487,019
• Time in Patent Office: 972 Days
• Field of Search: 340/506, 340/507, 340/508, 340/514, 340/531, 340/533, 340/538, 340/310.01
• US Class Current: 340/533
• CPC Class Codes: G05B 9/02 electric
• CPC Class Codes: G08C 19/02 in which the signal transmitted is magnitude of current or voltage G08C19/36, G08C19/38 take precedence

Abstract

A process control instruments includes a sensor for sensing a process variable in a processing environment, and a switch, a gauge, and a transmitter. The sensor, switch, gauge, and transmitter, a controller to which each of the stated and related components are connected, are powered via a two-wire power loop. In particular, the two-wired power loop also comprises the transmitter, such that the controller, upon receiving information indicative of the level of a variable being sensed by the sensor, modulates the amplitude of the current on the two-wire loop to a level corresponding to the level of the processed variables sensed. Each of the switch, gauge, and transmitter are independently scalable. In the preferred embodiment of the invention, a pair of switches in the form of relays are provided, and a logic circuit operates to power the components of the invention, with the exception of the relays, when the process variable being sensed with within a selected range. When, however, the process variable being sensed dips below the lower threshold(s) or rises above an upper threshold(s), the logic circuit operates to provide power to the components of the invention through a relay corresponding to the threshold reached.

Claims

1. A device comprising:

a sensor for sensing a condition in an environment;

a switch, wherein said switch is switched when said condition being sensed reaches a selected threshold;

a two-wire loop power supply, wherein the two-wire loop power supply powers said sensor and said switch and comprises a transmitter for transmitting information indicative of that which is sensed by said sensor; and

a controller, connected to said sensor, and powered by said two-wire loop power-supply, wherein said controller receives from said sensor, data indicative of that which is sensed at said sensor and controls an electrical current on said two-wire power supply loop to correspond with said received data.

2. The device as set forth in claim 1, wherein said controller in response to an increase in that which is sensed by said sensor correspondingly increases said electrical current and, in response to a decrease in that which is sensed by said sensor, correspondingly decreases said electrical current.

3. The device as set forth in claim 1, wherein said electrical current, when corresponding to a sensed condition, is generally within the range of 4-20 milliamps.

4. The device as set forth in claim 1, said device further comprising

a gauge for displaying a readout indicative of that which is sensed by said sensor.

5. The device as set forth in claim 1, said device further comprising:

a gauge for displaying a readout indicative of that which is sensed by said sensor, wherein each of said switch and said gauge are powered by said two-wire loop power supply.

6. The device as set forth in claim 5, wherein said switch, said transmitter, and said gauge are independently scalable.

7. The device as set forth in claim 1, wherein said controller processes said received data and causes said transmitter to transmit information indicative thereof within approximately 35 milliseconds.

8. The device as set forth in claim 1, wherein said controller processes said received data and causes said switches to switch within approximately 35 milliseconds.

9. The device as set forth in claim 7, wherein said controller is a microprocessor.

10. The device as set forth in claim 9, wherein said controller is a reduced instruction set microprocessor.

11. A device for sensing a condition in a process, said device comprising:

a switch;

a gauge;

a transmitter, wherein each of said switch, said gauge, and said transmitter is powered by a common two-wire power supply loop, and wherein said transmitter comprises said two-wire power loop;

a sensor; and

a controller, wherein said sensor senses a condition in an environment in which said sensor is placed, and wherein said controller receives, from said sensor, data indicative of a sensed condition and controls an electrical current on said two-wire loop so that said electrical current corresponds to said sensed condition, thereby transmitting information regarding said sensed condition.

12. The device as set forth in claim 11, wherein said sensor, said gauge, and said controller consume less than 4 milliamps of electrical current, and wherein said electrical current on said loop corresponding to a sensed condition is generally within the range of 4-20 milliamps.

13. The device as set forth in claim 11, wherein said switch, said gauge, and said transmitter are independently scalable.

14. The device as set forth in claim 11, wherein said sensor is a pressure sensor.

15. The device as set forth in claim 14, wherein said pressure sensor is selected from the group consisting of a Wheatstone bridge strain gauge, a resonant wire sensor, a variable capacitance sensor, and a variable reluctance sensor.

16. The device as set forth in claim 11, wherein said sensor is a temperature sensor.

17. The device as set forth in claim 11, wherein said sensor is selected from the group consisting of a temperature sensor, a volumetric flow sensor, a level sensor, a differential pressure or differential temperature sensor.

18. The device as set forth in claim 11, wherein said sensor is selected from the group consisting of a thermocouple, an RTD sensor, a sensor comprising thermistors, an ultrasonic sensor, and a positive displacement sensor, a hydrostatic pressure sensor, a radio frequency capacitance sensor, and a radio frequency impedance sensor, a microwave radar sensor, and magnetostrictive sensor.

19. A device comprising:

a controller;

a sensor for sensing a variable in a process and for transmitting data indicative thereof to said controller;

a power supply having a two-wire loop for powering said controller and said sensor;

a relay, wherein said relay is activated when said variable sensed by said sensor reaches a selected threshold; and

a logic circuit, wherein said logic circuit operates to provide power from said power supply to said controller and said sensor, but not to said relay, when said variable being sensed has not reached said selected threshold, and wherein said logic circuit operates to provide power to said controller and said sensor through said relay when said variable being sensed reaches said selected threshold.

20. The device as set forth in claim 19, further comprising a housing for housing said controller, said relay, and said logic circuit, wherein said housing has an exterior dimension comprising no greater than approximately 32 cubic inches.