Process transmitter isolation compensation

Patent metadata

Field	Value
Publication number	US-11226242-B2
Application number	US-201916423548-A
Country	US
Kind code	B2
Filing date	May 28, 2019
Priority date	Jan 25, 2016
Publication date	Jan 18, 2022
Grant date	Jan 18, 2022

Abstract

An industrial process temperature transmitter for measuring a temperature of a process medium includes a temperature sensing unit, a compensation circuit, an output circuit and a housing. The temperature sensing unit includes a process temperature sensor and a secondary temperature sensor. A temperature signal that is indicative of the temperature of the process medium is produced based on a process temperature signal output from the process temperature sensor and a secondary temperature signal output from the secondary temperature sensor. The compensation circuit compensates the temperature signal for a response time of the temperature measurement to a change in the temperature of the process medium, and outputs a compensated temperature signal. The output circuit produces a temperature output as a function of the compensated temperature signal. The housing is attached to an exterior of the process vessel and contains the secondary temperature sensor.

First claim

What is claimed is:

1. An industrial process temperature transmitter for measuring a temperature of a process medium contained in a process vessel, the transmitter comprising:
a temperature sensing unit including:
a process temperature sensor separated from the process medium by an isolation wall; and
a secondary temperature sensor configured to produce a secondary temperature signal based on a sensed temperature;
wherein the temperature sensing unit configured to produce a temperature signal that is indicative of the temperature of the process medium based on a process temperature signal output from the process temperature sensor and the secondary temperature signal during a temperature measurement;

a compensation circuit configured to provide a dynamic compensation to the temperature signal for a response time of the temperature measurement to a change in the temperature of the process medium and a rate of change of the temperature measurement, and output a compensated temperature signal;
an output circuit configured to produce a temperature output as a function of the compensated temperature signal; and
a housing attached to an exterior of the process vessel and containing the secondary temperature sensor.

2. The transmitter according to claim 1 , wherein:
the response time of the temperature measurement is dependent on at least one property of the isolation wall selected from the group consisting of a mass of the isolation wall, a thermal conductivity of the isolation wall, and a thickness of the isolation wall; and
the compensation circuit compensates the temperature signal and outputs the compensated temperature signal based on the at least one property of the isolation wall.

3. The transmitter according to claim 1 , wherein:
the isolation wall forms a wall of the process vessel; and
the process temperature sensor is in contact with an exterior surface of the isolation wall.

4. The transmitter according to claim 3 , wherein the process vessel is selected from the group consisting of a pipe and a tank.

5. The transmitter according to claim 3 , wherein the secondary temperature sensor measures a terminal block temperature of the transmitter contained within the housing.

6. The transmitter according to claim 3 , wherein:
the temperature sensing unit includes at least one analog-to-digital converter configured to convert the process temperature signal in an analog form into a digital process temperature signal and to convert the secondary temperature signal in an analog form into a digital secondary temperature signal;
the processing circuit produces the temperature signal in a digital form based on the digital process temperature signal and the digital secondary temperature signal; and
a digital-to-analog converter configured to convert the compensated temperature signal in a digital form to an analog compensated temperature signal;
wherein the output circuit is configured to produce the temperature output as a function of the analog compensated temperature signal.

7. The transmitter according to claim 1 , comprising a thermowell including the isolation wall that extends into the process medium and defines a cavity, wherein the process temperature sensor is contained in the cavity.

8. The transmitter according to claim 1 , wherein:
the temperature sensing unit includes an analog-to-digital converter configured to convert the process temperature signal in an analog form into a digital process temperature signal to produce the temperature signal in a digital form; and
a digital-to-analog converter configured to convert the compensated temperature signal in a digital form to an analog compensated temperature signal;
wherein the output circuit is configured to produce the temperature output as a function of the analog compensated temperature signal.

9. The industrial process temperature transmitter according to claim 1 , wherein:
the industrial process temperature transmitter includes a stem portion having a first end attached to the process vessel and a second end displaced from the process vessel and the isolation wall;
the housing is attached to the second end of the stem portion; and
the compensation circuit compensates the temperature signal for the response time of the temperature measurement based on a thermal impedance of the stem portion.

10. The industrial process temperature transmitter according to claim 1 , wherein the process temperature sensor comprises a thermistor.

11. An industrial process temperature transmitter for measuring a temperature of a process medium contained in a process vessel through an isolation wall, the transmitter comprising:
a temperature sensing unit comprising:
a process temperature sensor separated from the process medium by the isolation wall and in contact with the exterior surface of the isolation wall, the process temperature sensor configured to produce a process temperature signal based on the temperature of the process medium;
a secondary temperature sensor configured to produce a secondary temperature signal based on a temperature at a location spaced from the process medium and the isolation wall; and
processing electronics configured to produce a temperature signal that is indicative of the temperature of the process medium based on the process temperature signal and the secondary temperature signal;

a compensation circuit configured to provide a dynamic compensation to the temperature signal for a response time of the temperature measurement and a rate of change of the temperature measurement, and output a compensated temperature signal;
an output circuit configured to produce a transmitter output as a function of the compensated temperature signal;
a stem portion having a first end attached to the process vessel and a second end that is displaced from the process vessel and the isolation wall; and
a housing attached to the second end of the stem portion and containing the secondary temperature sensor.

12. The transmitter according to claim 11 , wherein:
the response time of the temperature measurement is dependent on at least one property of the isolation wall selected from the group consisting of a mass of the isolation wall, a thermal conductivity of the isolation wall, and a thickness of the isolation wall; and
the compensation circuit compensates the temperature signal and produces the compensated temperature signal based on the at least one property of the isolation wall.

13. The transmitter according to claim 11 , wherein the isolation wall forms a wall of the process vessel.

14. The transmitter according to claim 13 , wherein the process vessel is selected from the group consisting of a pipe and a tank.

15. The transmitter according to claim 13 , wherein the compensation circuit compensates the temperature signal for the response time of the temperature measurement based on a thermal impedance of the stem portion.

16. The transmitter according to claim 13 , wherein:
the temperature sensing unit includes a first analog-to-digital converter configured to convert the process temperature signal in an analog form into a digital process temperature signal, and a second analog-to-digital converter configured to convert the secondary temperature signal in an analog form into a digital secondary temperature signal;
the processing circuit produces the temperature signal in a digital form based on the digital process temperature signal and the digital secondary temperature signal; and
a digital-to-analog converter configured to convert the compensated temperature signal in a digital form to an analog comp

Assignees

• Rosemount Inc

Inventors

• Rud Jason Harold
• Trimble Steve Richard

Classifications

• G01K1/143

  for measuring surface temperatures · CPC title

• G01K7/10

  Arrangements for compensating for auxiliary variables, e.g. length of lead · CPC title

• G01K7/42 Primary

  Circuits effecting compensation of thermal inertia; Circuits for predicting the stationary value of a temperature · CPC title

• G01K7/04 Primary

  the object to be measured not forming one of the thermoelectric materials · CPC title

• G01K7/22

  the element being a non-linear resistance, e.g. thermistor (G01K7/26 takes precedence) · CPC title