Temperature compensatible pressure monitor and sensor construction

• US 4,980,675 A
• Filed: 01/09/1990
• Issued: 12/25/1990
• Est. Priority Date: 01/09/1990
• Status: Expired due to Term

• Current Assignee: Spectrum Associates LLC
• Original Assignee: Spectrum Associates LLC
• Inventors: Meisenheimer, Daniel T. Jr.
• Primary Examiner(s): Orsino, Joseph A.
• Assistant Examiner(s): Negash, Kinfe-Michael
• Application Number:
  US07/462,725
• Time in Patent Office: 350 Days
• Field of Search: 340/626, 73/708, 73/729, 200/83 C, 200/83 J
• US Class Current: 340/626
• CPC Class Codes: G01L 19/04 Means for compensating for effects of changes of temperature , i.e. other than electric compensation
• CPC Class Codes: H01H 35/28 Compensation for variation of ambient pressure or temperature

Abstract

By providing pressure-responsive switch-actuation means constructed for being substantially unaffected by temperature changes, a pressure sensor is attained which is capable of monitoring pressure levels with precision, regardless of the ambient temperature to which the system is subjected. By employing temperature insensitive material to effectively compensate for temperature changes incurred by the remaining sensor components, the actuation control assembly of the sensor is capable of achieving precision monitoring of desired pressure levels regardless of changes in the ambient temperature to which the monitor assembly is exposed. In one preferred embodiment, the pressure sensor of the present invention incorporates a uniquely constructed, machined bellows which further enhances and provides precision pressure sensing capabilities.

Claims

1. A sensor for monitoring the pressure level of a desired pressure source and providing a signal whenever the pressure source level differs from a pre-set level even when exposed to extreme temperature conditions, said sensor comprising:

A. a housing having at least one pressure receiving inlet for connection to the pressure source being monitored;

B. switch means

a. mounted in the housing, and

b. adapted to provide an output signal when activated for indicating a pressure level change outside of the pre-set parameters; and

C. a temperature compensating pressure level monitoring-actuator assembly incorporating

a. an elongated actuating rod

(1) mounted for axial movability in response to changes in the level of the source pressure,

(2) connected at one end to the switch means for activation thereof whenever the source pressure differs from the pre-set level, and

(3) formed from temperature insensitive material, whereby changes in the ambient temperature has negligible effect on the expansion or contraction of said rod, and

b. movement control means

(1) connected to the actuating rod, and

(2) providing an adjustable biasing force to said rod for controllably setting the forces required to move the elongated rod from its first monitoring position to its second alarm-activating position;

whereby an effective precision temperature insensitive sensor is attained which continuously monitors a pressure source within limited pre-set ranges and provides an output indication whenever the source pressure deviates from the pre-set level regardless of temperature conditions to which the sensor is exposed.

2. The pressure sensor defined in claim 1, wherein the movement control means is further defined as comprising

(3) a rod supporting member, mounted in the housing for movement relative to the central axis of the housing in response to changes in the pressure level being monitored, and supportingly holding the elongated rod for controlling the axial movement thereof.

3. The pressure sensor defined in claim 2, wherein said movement control means further comprises

(4) spring means operatively connected at one end thereof to the rod support member for opposing axial movement of the rod support member toward said spring means, and

(5) adjusting means rotationally mounted in the housing in contacting engagement with the opposed end of the spring means for controllably adjusting the force of the spring means on the rod support member by rotational movement thereof.

4. The pressure sensor defined in claim 3, wherein said pressure sensor is further defined as being connected to a single pressure source for monitoring the pressure level within a pre-set range, and the rod support member is further defined as comprising an elongated axially translatable holder peripherally surrounding and containing a substantial length of said elongated rod, with said holder being further defined as comprising

i. a pressure receiving surface formed on one end thereof directly adjacent the pressure receiving inlet, and

ii. a bellows peripherally surrounding a portion of said rod support member with one end thereof mounted to said rod support member, and the opposed end thereof mounted directly to the housing, whereby the axial movement of the rod support member is further controlled and restricted by the compression resistant forces of said bellows.

5. The pressure sensor defined in claim 4, wherein the pressure being monitored ranges between about 2,000 and 4,000 psi and the pre-set range in which said pressure is maintained ranges between one and three percent of said pressure.

6. The pressure sensor defined in claim 4, wherein said bellows is further defined as comprising a machined bellows formed from an open-ended elongated tube with the external annular recesses cut by conventional lathe operation and the internal annular recesses cut by employing a cutting tool constructed for forming each of said internal recesses.

7. The pressure sensor defined in claim 4, wherein said bellows is further defined as being manufactured by employing the steps of:

A. cutting a hollow tube to a desired length;

B. forming a plurality of annular recesses in the external surface of the tube, each of said recesses being parallel to the other and lying in a plane substantially perpendicular to the central axis of the tube; and

C. forming a plurality of annular recesses in the internal surface of the tube, parallel to each other and in alternating selectively spaced relationship to the external recesses.

8. The pressure sensor defined in claim 3, wherein said pressure sensor is further defined as being connected to a single pressure source for monitoring the pressure level within a pre-set range, and the movement control means is further defined as comprising

(6) a substantially circular diaphragm

(a) affixed about its outer peripheral surface to said housing,

(b) defining on one side thereof a pressure receiving chamber connected to the pressure receiving inlet,

(c) being axially movable substantially along the central axis of said housing in response to changes in either the first or the second pressure chambers, and

(d) controllably moving the elongated actuating rod in response to the movement of said diaphragm,

whereby the pressure sensor is capable of monitoring the level of the pressure source and actuating the sensor whenever the pressure level differs from the pre-set desired

9. The pressure sensor defined in claim 8, wherein the housing is further defined as comprising a diaphragm support plate and the diaphragm is further defined as being welded to said support plate about one of its outer peripheral surfaces, thereby assuring that said pressure receiving zones is completely sealed without requiring separate sealing means.

10. The pressure sensor defined in claim 8, wherein the rod supporting member is mounted on the diaphragm for controlled movement thereof and of the rod in response to axial movement of the diaphragm.

11. The pressure sensor defined in claim 8, wherein said switch means is defined as being hermetically sealed in a separate zone to prevent fluid in the housing from contacting the switch means.

12. The pressure sensor defined in claim 3, wherein said sensor is constructed for monitoring differential pressures, the housing is constructed with two pressure receiving inlets and movement control means is further defined as comprising

(6) a substantially circular diaphragm

(a) affixed about its outer peripheral surface to said housing,

(b) defining on one side thereof a first pressure receiving chamber and on the opposed side thereof a second pressure receiving chamber,

(c) being axially movable substantially along the central axis of said housing in response to changes in either the first or the second pressure chambers, and

(d) controllably moving the elongated actuating rod in response to the movement of said diaphragm,

whereby the differential pressure sensor is capable of monitoring the difference between the two pressure sources and actuating the sensor whenever the differential pressure therebetween differs from the pre-set desired range.

13. The pressure sensor defined in claim 12, wherein the housing is further defined as comprising a diaphragm support plate and the diaphragm is further defined as being welded to said support plate about one of its outer peripheral surfaces, thereby assuring that said pressure receiving zones is completely sealed without requiring separate sealing means.

14. The pressure sensor defined in claim 12, wherein the rod supporting member is mounted on the diaphragm for controlled movement thereof and of the rod in response to axial movement of the diaphragm.

15. The pressure sensor defined in claim 12, wherein said switch means is defined as being hermetically sealed in a separate zone to prevent fluid in the housing from contacting the switch means.

16. The pressure sensor defined in claim 12, wherein the switch means is further defined as being sealed by employing a wobble plate, thereby providing accurate precision control of said switch means by movement external of said sealed switch-containing zone.

17. The pressure sensor defined in claim 1, wherein said elongated actuating rod is further defined as being formed from steel having a nickel content of about 36%.

18. The pressure sensor defined in claim 1, wherein said actuating rod is further defined as being formed from invar.

19. The pressure sensor defined in claim 1, wherein said elongated actuating rod experiences negligible contraction at temperatures at least as low as -65°

F. and experiences negligible expansion at deviated temperatures as high as 350°

F., whereby said elongated actuating rod effectively compensates for temperature induced changes in the sensor'"'"'s other component parts and assures continuous, precision monitoring at the pre-set pressure range regardless of the ambient operating temperature.