Compressor control module

[0002] This invention relates generally to pressurization systems, and more particularly to control of such systems.

[0003] Generally, a pressurization system may be constructed using a compressor and a pressure switch. In such a system, the compressor is typically configured to pressurize a gas, such as air, or a liquid. The pressure switch is configured to measure the pressure created by the compressor and turn the compressor on and off to maintain a desired pressure. In certain applications, it may be desirable to accurately or precisely control the pressure provided by the pressurization system. An exemplary application of a precisely controlled pressurization system may be a pressurization system that provides dry pressurized air to an antenna housing or radome to prevent the ingress of contamination, such as moisture. Such precision pressurization systems are often desirable as the housings or radomes used on many antennas are often fragile and easy fractured.

[0004] One approach to controlling pressure from a compressor uses a diaphragm pressure switch. A diaphragm pressure switch generally includes a diaphragm, a spring supporting the diaphragm, and a set of electrical contacts coupled to the diaphragm. Pressurized air in the system presses against the diaphragm, opposing a bias from the spring. Once the pressure reaches a desired point, the electrical contacts are opened, de-energizing the compressor. Later, as pressure in the system decreases, the contacts are closed, re-energizing the compressor and thereby maintaining a constant pressure in the system.

[0005] Diaphragm pressure switches are not particularly well suited to accurately regulating pressure due to the spring force within such switches varying with temperature, vibration, and wear due to cyclical use. Sample-to-sample consistency of springs may also impart unacceptable variations in pressure. Further, diaphragm pressure switches tend to be sensitive to gravity or physical orientation; therefore, implementation of a diaphragm pressure switch may be critical in accurately controlling pressure.

[0006] Other approaches for regulating pressure in a pressurization system involve the use of strain gauge transducers and microprocessors. In these approaches, a transducer may be used to provide a voltage that varies in proportion to the pressure in the system created by a compressor. The variable voltage from the transducer is then processed either directly or indirectly, after an analog-to-digital conversion is performed, by a microprocessor to control the operation of the compressor, thereby maintaining a given pressure.

[0007] Approaches utilizing transducers have the advantage of regulating pressure accurately but are of limited utility due to the microprocessors used therewith. Often, pressurization systems are needed in applications where moisture, vibration, and power consumption are of concern. Pressurization systems incorporating microprocessors in such applications may be prone to failure, while requiring additional power. Moreover, the use of a microprocessor in a pressurization system may increase the cost of such a system, sometimes prohibitively so.

[0008] Therefore, it would be desirable to provide a pressurization system having accurate pressure sensing and reliability. It would be further desirable to achieve such accuracy and reliability with reduced cost and power consumption.

[0009] The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments of the invention and, together with the detailed description given below, serve to explain the principles of the invention.

[0010] FIG. 1 is a pneumatic diagram of an embodiment of a pressurization system in accordance with the principles of the present invention; and,

[0011] FIG. 2 is a schematic diagram of an embodiment of a compressor control module adapted for use with the pressurization system shown in FIG. 1 and consistent with the present invention.

[0012] With reference to FIGS. 1 and 2, wherein like numerals denote like parts, there is shown a pressurization system 10 and a compressor control module 40 for use therewith that relies on a strain gauge transducer 26 to sense the pressure in the system 10 accurately and reliability with reduced cost and power consumption. More specifically, strain gauge transducer 26 provides a voltage that varies in proportion to the pressure in the system 10. The voltage is then compared to set points, (i.e., variable voltages), to control the operation of a compressor 14, and optionally provide additional controls and alarms.

[0013] Referring first to FIG. 1, a pneumatic diagram of an embodiment 10 of a pressurization system in accordance with principles of the present invention is illustrated. Pressurization system 10 comprises a compressor 14 coupled with a strain gauge transducer 26. Strain gauge transducer 26 exemplifies a transducer that provides a voltage that varies in proportion to pressure, as is well known in the art. Thus, as configured in system 10 and as shown in FIG. 1, the voltage provided by strain gauge transducer 26 varies in proportion to the pressure created in system 10 by compressor 14, the voltage being used to control the operation of compressor 14 as will be discussed hereinafter.

[0014] Strain gauge transducers are available in a number of standard pressure ranges from SenSym ICT, located at 1804 McCarthy Boulevard, Milpitas, Calif. 95035. Measurement Specialties, Inc., located at 80 Little Falls Road, Fairfield, N.J. 07004 also manufactures a number of standard pressure ranges, as well as custom pressure range, transducers. Those skilled in the art will appreciate that any one of these transducers, as well as others, may be used without departing from the spirit of the present invention.

[0015] System 10 may optionally include an intake air filter 12 coupled to the compressor 14. System 10 may further comprise one or more filters 18, 20, a check valve 22, a tank 24, and a pressure regulator 28, all of which are in fluid communication intermediate compressor 14 and strain gauge transducer 26. Solenoid valves 16, 30 and/or alarms 32, 34 may also be advantageously included as will also be discussed hereinafter.

[0016] As configured in FIG. 1, ambient air is drawn into system 10 through intake air filter 12 by compressor 14. The filtered intake air then flows downstream through filters 18 and 20. Filters 18 and 20 dry the intake air, the moisture in the intake air accumulating at the bottom of the filters 18, 20. Filters 18 and 20 may be coupled to a valve actuated by a solenoid 16 for purposes of draining the accumulated moisture from the filters 18, 20 as will be discussed hereinafter. The dry intake air then flows downstream through check valve 22 and into tank 24. Check valve 22 functions to prevent dry pressurized air in tank 24 from flowing upstream into filters 18 and 20 when compressor 14 is de-energized.

[0017] Compressor 14 builds pressure in tank 24, tank 24 functioning as a reservoir for dry pressurized air. When the pressure in tank 24 exceeds a given pressure associated with pressure regulator 28, pressure regulator 28 provides a source of accurately controlled dry pressurized air, as indicated at reference numeral 36. Such a source of accurately controlled dry pressurized air 36 may be used to prevent the ingress of moisture and other contaminants in pressure sensitive devices such as an antenna 38 having a housing or radome 60, the radome including a window 62. System 10 may also be used for waveguides 64, conduits or cable troughs 66 or antenna systems 68 with enclosed portions which are pressurized. Those skilled in the art will appreciate that pressurization system 10 may also be used for other applications requiring a source of accurately controlled dry pressurized air.

[0018] System 10 may advantageously include an over pressure relief valve 30. Over pressure relief valve 30 may be used to release pressure in system 10 to protect pressure sensitive components, such as a window in an antenna housing or radome, should an over pressure condition occur within system 10. System 10 may also advantageously include a low pressure alarm 32 and/or a high pressure alarm 34. Low pressure alarm 32 and high pressure alarm 34 may be used to provide indications of low and high pressure conditions in system 10. In FIG. 1, over pressure relief valve 30, low pressure alarm 32, and high pressure alarm 34 are shown downstream from pressure regulator 28; however, those skilled in the art will appreciate that any or all of an over pressure relief valve, low pressure alarm, and high pressure alarm may be located upstream from a pressure regulator without departing from the spirit of the present invention.

[0019] Referring now to FIG. 2, a schematic diagram of an embodiment 40 of a compressor control module adapted for use with pressurization system 10 shown in FIG. 1 and consistent with principles of the present invention is illustrated. Compressor control module 40 comprises variable voltage references 42a-e, comparator circuits 44a-e, control logic circuit 46, relays 48a-e, delay timer circuit 50 and indicators 52a-e.

[0020] To control the operation of compressor 14, compressor control module 40 uses variable voltage references 42a, 42b, comparator circuits 44a, 44b, control logic circuit 46, and relay 48a. Variable voltage reference 42ais associated with a low-pressure limit for pressurized air from compressor 14, and variable voltage reference 42bis associated with a high-pressure limit for the pressurized air. Comparator circuit 44ais coupled to strain gauge transducer 26 and variable voltage reference 42aand is configured to compare the voltage from strain gauge transducer 26 and variable voltage reference 42aand output a first logic signal 54afor energizing compressor 14. Similarly, comparator circuit 44bis coupled to the strain gauge transducer 26 and variable voltage reference 42band is configured to compare the voltage from strain gauge transducer 26 and variable voltage reference 44band output a second logic signal 54b. Control logic circuit 46 is coupled to comparator circuits 44aand 44band is configured to logically combine the first and second logic signals 54a, 54band provide a control signal 54c. Relay 48ais coupled to the control logic circuit 46 and is configured to apply power to the compressor 14 in response to the control signal 54c.

[0021] Control logic circuit 46 may include one or more logic gates or other suitable logic components configured to logically combine logic signals 54aand 54b, providing control signal 54c, for purposes of energizing compressor 14 when the pressure in system 10 is below the low pressure limit and de-energizing compressor 14 when the pressure in system 10 is above the high pressure limit. The one or more logic gates may be further configured to maintain the operational status, i.e., energized or de-energized, of compressor 14 should the pressure in system 10 be between the low and high pressure limits.

[0022] Such a configuration of logic gates will be readily apparent to those of skill in the art when faced with the design constraints associated with the selection of other components in system 10. Constraints may include, but are not limited to, the selection of the strain gauge transducer 26, the selection of the comparator circuits 44a-e, and the availability of devices or components within integrated circuits should integrated circuits be selected for comparators circuits 44a-eand/or variable voltage references 42a-e.

[0023] As configured in FIG. 2, indicator 52ais coupled to control logic circuit 46 and indicates the operational status of compressor 14. As mentioned hereinbefore and shown in FIG. 1, solenoid valve 16 may be used to drain moisture and contaminants from filters 18 and 20. As shown in FIG. 2, relay 48bis coupled to control logic circuit 46 and actuates solenoid valve 16 in response to control signal 54c. Delay timer circuit 50 coupled intermediate control logic circuit 46 and relay 48bmay used to delay the application of control signal 54cto solenoid valve 16 thereby providing an opportunity for moisture to condense in filters 18 and 20 prior to being drained. Delay timer circuit 50 may be an integrated circuit timer such as a 555 timer/oscillator. Those skilled in the art will appreciate that other timers and/or oscillators may also be used without departing from the spirit of the present invention.

[0024] Control module 40 advantageously includes control circuits 56a-c. Each control circuit 56a-ccomprises a respective variable voltage reference 42c-e, a comparator circuit 44c-e, and a relay 48c-e. Each control circuit 56a-cmay further comprise a respective indicator 52b-d. The variable voltage references 42c-emay be associated with either an under pressure limit or an over pressure limit. As configured in FIGS. 1 and 2, variable voltage references 42cand 42dare associated with an over pressure limit, whereas variable voltage reference 42eis associated with an under pressure limit.

[0025] Comparator circuits 44c-eare coupled to strain gauge pressure transducer 26 and variable voltage references 42c-e, respectively. Comparator circuits 44c-eare configured to compare the voltage from strain gauge transducer 26 and the respective variable voltage reference 42c-eand output a respective logic signal 54d-f. Relays 48c-eare coupled respectively to comparator circuits 44c-eand include a set of switch contacts that operate in response to the respective logic signals 54d-f. Indicators 52b-dcoupled to respective comparator circuits 44c-eindicate the state of the relay, such as the position of respective relay 48c-eswitch contacts.

[0026] As shown in FIGS. 1 and 2, control circuit 56ais coupled to over pressure relief valve 30 for purposes of releasing pressure in system 10 in the event of an over pressure condition, variable voltage 42ccorresponding to the pressure at which valve 30 opens. Control circuit 56bis coupled to a high pressure alarm 34, variable voltage reference 42dcorresponding to the pressure at which the high pressure alarm occurs. Similarly, control circuit 56cis coupled to a low pressure alarm 32, variable voltage reference 42ecorresponding to the pressure at which the low pressure alarm occurs.

[0027] Variable voltage references 44a-emay be provided using potentiometers, a resistor arrays, or digital-to-analog converters used with a series of switches, such as dual inline package (DIP) switches, or a processor. Those skilled in the art will appreciate that other devices providing a variable voltage may also be used without departing from the spirit of the present invention. Comparator circuits 44a-emay be differential amplifiers, operational amplifiers, or other devices capable of comparing two voltages and providing a logical output and known to those skilled in the art. Indicators 52a-dmay be incandescent lamps, light emitting diodes (LEDs), or other indicators having similar functionality.

[0028] While the present invention has been illustrated by the description of the embodiments thereof, and while the embodiments have been described in considerable detail, it is not the intention of the applicants to restrict or in any way limit the scope of the appended claims to such detail. For example, it will be understood that a valve actuated by a solenoid for purposes of draining accumulated moisture from one or more filters, an over pressure relief valve configured to relieve pressure from a pressurization system should an over pressure condition occur within a system, and high and/or low pressure alarms and the circuitry associated therewith are all optional, and may be omitted from embodiments consistent with the present invention. Further, a strain gauge pressure transducer may be used to sense pressure in practically any pressurized region of a pressurization system. Moreover, multiple strain gauge pressure transducers may also be used to sense pressures in multiple regions of a pressurization system. Additional advantages and modifications will readily appear to those skilled in the art. Therefore, the invention in its broader aspects is not limited to the specific details representative apparatus and method, and illustrative examples shown and described. Accordingly, departures may be made from such details without departure from the spirit or scope of applicants' general inventive concept.