Convection thermocouple vacuum gauge

• US 5,351,551 A
• Filed: 05/27/1993
• Issued: 10/04/1994
• Est. Priority Date: 05/27/1993
• Status: Expired due to Fees

• Current Assignee: Meridian Bank Texas (UMB Financial Corporation)
• Original Assignee: The Fredericks Co.
• Inventors: Woshczyn, Leonard, Drubetsky, Emil, Taylor, Donald R. Jr.
• Primary Examiner(s): Chilcot, Jr., Richard E.
• Assistant Examiner(s): FELBER, JOSEPH LEON
• Application Number:
  US08/068,328
• Time in Patent Office: 495 Days
• Field of Search: 73/755, 374/45
• US Class Current: 73/755
• CPC Class Codes: G01L 21/14 using thermocouples

Abstract

A thermocouple vacuum gauge includes a first thermocouple element spaced below a second thermocouple element. The two thermocouple elements are electrically connected in series in a back-to-back manner by connecting together their respective negative ends. A pulse generator supplies a pulsing on-off current only to the first thermocouple element. During the off intervals, a switch connects the positive ends of both thermocouple elements to a voltage measuring and comparing circuit which measures a thermally generated voltage signal between the positive ends of the thermocouple elements and compares the measured voltage signal to a reference signal. The result of the comparison is used to vary the output current of the pulse generator so as to supply an amount of current to the first thermocouple element sufficient to cause the measured voltage signal to approach the reference signal. The amount of current supplied sufficient to cause the measured voltage signal to approach the reference signal is proportional to the amount of pressure or vacuum in an enclosure in which the thermocouples of the vacuum gauge are placed. A method for measuring pressure at partial vacuum which employs these features is also described.

Claims

1. A thermocouple vacuum gauge comprising:

(a) a heated and a non-heated thermocouple element, the heated thermocouple element being spaced below the non-heated element;

(b) a pulse generator for generating on-off electrical heating pulses to the heated thermocouple element, the heated and non-heated thermocouple elements being electrically connected in series in a back-to-back manner by having one of their respective like ends connected together at least during off periods, the off periods being the time between the end of a heating pulse and the beginning of a subsequent heating pulse;

(c) a voltage measuring and comparing circuit for measuring a thermally generated voltage difference between the other respective like ends of the thermocouple elements during the off periods, generating a voltage signal related to the difference and comparing the voltage signal to a reference signal;

(d) switch means for connecting said other respective like ends of the thermocouple elements to the voltage measuring and comparing circuit only during the off periods of the heating pulses so as to allow the voltage measuring and comparing circuit to make its measurement and comparison only during said off periods; and

(e) means for varying the output current of the pulse generator so as to supply an amount of current to the heated thermocouple element sufficient to cause the voltage signal to approach the reference signal, the amount of supplied current being proportional to the vacuum level.

2. The thermocouple vacuum gauge of claim 1, wherein the thermocouple elements are mounted on a support, the non-heated thermocouple element overlying the heated thermocouple element and spaced therefrom by a preselected distance.

3. The thermocouple vacuum gauge of claim 2, wherein each thermocouple has a hot junction, the hot junctions overlying each other and being spaced apart by the preselected distance.

4. The thermocouple vacuum gauge of claim 3, wherein the thermocouple elements are skew to one another.

5. The thermocouple vacuum gauge of claim 1, wherein the pulse generator provides a pulsatile current output of on-off intervals.

6. The thermocouple of claim 1, wherein the thermocouple elements are substantially identical.

7. A system for measuring pressure at partial vacuum comprising:

(a) a first and a second thermocouple element in the partial vacuum, the thermocouple elements each having hot and cold junctions, the hot junction of the first thermocouple element being spaced below the hot junction of the second thermocouple element, the thermocouple elements each having positive and negative ends corresponding to the cold junctions;

(b) a pulse generator for supplying a pulsing on-off current to the first thermocouple element, the negative ends of the thermocouple elements being connected together at least during off intervals of said on-off current, the off intervals being the time between the end of a pulse of current and the beginning of a subsequent pulse of current;

(c) a voltage measuring and comparing circuit for measuring a thermally generated voltage difference between the positive ends of the thermocouple elements during the off intervals, generating a voltage signal related to the difference and comparing the voltage signal to a reference signal;

(d) switch means for connecting the positive ends of the thermocouple elements to the voltage measuring and comparing circuit during said off intervals so as to allow the voltage measuring and comparing circuit to make its measurement and comparison, the switch means disconnecting the positive ends of the thermocouple elements from the voltage measuring and comparing circuit during on intervals of said on-off current, the on intervals being the time between the beginning and end of a pulse of current; and

(e) means for varying the output current of the pulse generator so as to supply an amount of current to the first thermocouple element sufficient to cause the voltage signal to approach the reference signal, the amount of current supplied being proportional to the pressure.

8. The system of claim 7, wherein the thermocouple elements are mounted on a support, the second thermocouple element overlying the first thermocouple element and spaced therefrom by a preselected distance.

9. The system of claim 8, wherein the hot junctions overlie each other and are spaced apart by the preselected distance.

10. The system of claim 9, wherein the thermocouple elements are skew to one another,

11. The system of claim 7, wherein the pulse generator provides a pulsatile current output of on-off intervals.

12. The system of claim 7, wherein the thermocouple elements are substantially identical.

13. A method for measuring pressure at partial vacuum comprising the steps of:

(a) providing an electrically generated heating current to a first thermocouple element which alternates between an on state and an off state;

(b) connecting the first thermocouple element to a second thermocouple element in series in a back-to-back manner at least when the heating current is off by connecting together one of their respective like ends, the first thermocouple element being spaced below the second thermocouple element;

(c) measuring thermally generated EMF between the other respective like ends of the thermocouple elements when the heating current is off;

(d) comparing the thermally generated EMF to a reference signal; and

(e) varying the heating current so as to cause the thermally generated EMF to approach the reference signal, the heating current being proportional to the pressure.

14. The method of claim 13, wherein each thermocouple has a hot junction, the hot junctions overlying each other and being spaced apart by a preselected distance.