Multivariable transmitter

• US 5,495,769 A
• Filed: 05/22/1995
• Issued: 03/05/1996
• Est. Priority Date: 09/07/1993
• Status: Expired due to Term

• Current Assignee: Rosemount Incorporated (Emerson Electric Company)
• Original Assignee: Rosemount Incorporated (Emerson Electric Company)
• Inventors: Orth, Kelly M., Broden, David A., Voegele, Kevin D., Borgeson, Dale W., Lanctot, Jane B.
• Primary Examiner(s): Chilcot, Richard
• Assistant Examiner(s): PATEL, HARSHAD R
• Application Number:
  US08/445,469
• Time in Patent Office: 288 Days
• Field of Search: 73/861.02, 73/861.03, 73/861.52, 73/861.22, 73/861.24, 73/718
• US Class Current: 73/718
• CPC Class Codes: G08C 19/02 in which the signal transmitted is magnitude of current or voltage G08C19/36, G08C19/38 take precedence

Abstract

In this invention, a multivariable transmitter providing an output representative of mass flow has a dual microprocessor structure. The first microprocessor compensates digitized process variables and the second microprocessor computes the mass flow as well as arbitrating communications between the transmitter and a master. In a second embodiment of the present invention, a first microprocessor compensates digitized process variables, a second microprocessor computes an installation specific physical parameter such as mass flow and a third microprocessor arbitrates real-time communications between the transmitter and a master.

Claims

1. A two wire transmitter transmitting mass flow of a fluid, comprising:

a first pressure sensor for sensing a differential pressure of the fluid;

a second pressure sensor for sensing a line pressure of the fluid;

an input for receiving a temperature variable representative of process grade temperature;

a compensation microprocessor receiving the temperature variable and signals from the first and second pressure sensors and providing a compensated differential pressure output and a compensated line pressure output;

a mass flow microprocessor receiving the compensated differential pressure output and the compensated line pressure signal output and providing an output representative of mass flow; and

a communications microprocessor receiving the mass flow output for formatting the mass flow output and coupling to a two wire circuit which powers the transmitter.

2. The transmitter of claim 1 where the first pressure sensor is a capacitance based pressure sensor and the second pressure sensor is a strain gauge sensor.

3. The transmitter of claim 1 where the first and the second pressure sensors sense pressure by a change in capacitance.

4. A two wire transmitter for sensing process variables representative of a process, comprising:

a module housing comprising a first pressure sensor for providing a first process variable representative of a differential pressure, a second pressure sensor for providing a process variable representative of a relative pressure and means for receiving a third process variable representative of a process grade temperature, the module housing including a digitizer for digitizing the process variables, and a microprocessor for compensating the digitized process variables;

a temperature sensor in the transmitter compensating at least one of the sensed process variables; and

an electronics housing coupled to the module housing and to a two wire circuit over which the transmitter receives power, the electronics housing including microcomputer means calculating mass flow based upon differential pressure, relative pressure and process grade temperature of the process and for formatting and for coupling mass flow to the two wire circuit.

5. The transmitter of claim 4 where the temperature sensor for compensation is located in the sensor module.

6. The transmitter of claim 4 where the differential pressure sensor senses pressure as a function of a change in capacitance, and the line pressure sensor senses pressure as a function of a change in resistance.

7. The transmitter of claim 4 where the differential and the line pressure sensors sense pressure as a function of a change in capacitance.