US3777240A
Expired / Lapsed
US
⏱️ 0.0 years remaining
Thermostat chatter protection for refrigeration compressor motors
Assignee: Carrier Corp
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Filing: 1972-09-21
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Granted: 1973-12-04
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Expires: 1992-09-21
Abstract
Abstract The motor of a reciprocating refrigeration compressor is provided with a motor control and protection system, which includes means for preventing the contacts of the motor relay from welding or otherwise being damaged by vibration of the system thermostat. The motor relay is energized or de-energized by a solid state switch, which is controlled by two or more trip circuits in response to a condition of operation of the system. A current sensor provides a signal proportional to motor current which is summed with an opposite polarity reset signal and integrated to provide a signal to a first trip circuit. The room thermostat contacts close in response to a demand for refrigeration and provide a current through the switch means to energize the relay. When the thermostat contacts stay open for a short period of time, the open circuit voltage across them is integrated and eventually trips a second trip circuit which actuates the switch means to a nonconducting condition, thereby de-energizing the relay and preventing damage to the relay contacts. A feedback circuit raises the output of the integration circuit and decreases the trip threshold of the first trip circuit to trip the first trip circuit, whereby a period of time must elapse while the reset signal is integrated to the reset level before the relay contacts can be closed again. If the contact chatter lasts only a very short time, the signal due to integrating the voltage across them will not be sufficient to cause an unnecessary trip.
Inventors
- 👤 D Neill
Bibliographic Details
Application Number
—
Jurisdiction
US
Data Source
google_patents
Last Synchronized
2026-10-23 13:30
CPC Classifications
H; H02; H02H; H02H7/00; H02H7/22; H02H7/222; H02H7/224
Claims Analysis
Total Claims: 6
Claim 1
Independent Claim
290 words
A motor control system for governing the operation of the compressor motor of a refrigeration system; said control system comprising: A. a relay having electrical contacts for connecting and disconnecting a compressor motor with a source of electric current; B. solid state switch means controlling the energizing and deenergizing of said relay; C. a first trip circuit having a trip level for rendering said switch means nonconducting in response to an input signal of a predetermined magnitude being supplied thereto; D. reset time delay means connected to enable the system to energize said relay means and motor after a period of time has elapsed following a trip due to said first trip circuit; E. a second trip circuit having a trip level for rendering said switch means nonconducting in response to an input signal of a predetermined magnitude being supplied thereto; F. thermostat terminal means for connecting a thermostat to said system having a pair of electrical thermostat contacts for supplying a refrigeration demand signal to energize said relay means upon closing of the thermostat contacts due to the occurrence of a refrigeration demand; and G. integration circuit means connected to said thermostat terminal means for integrating an input signal which is functionally related to the presence of an open circuit voltage appearing across said thermostat terminal means upon opening of thermostat contacts connected thereto, said integration circuit means providing an integrated output signal to said second trip circuit, whereby said second trip circuit is tripped and said motor relay is positively de-energized after the interval of time required to integrate the input signal to the trip level of said second trip circuit, to thereby prevent damage to the relay contacts upon opening or excessive chattering of the thermostat contacts.
Claim 2
Dependent Claim
290 words
A motor control system for governing the operation of the compressor motor of a refrigeration system; said control system comprising: A. a relay having electrical contacts for connecting and disconnecting a compressor motor with a source of electric current; B. solid state switch means controlling the energizing and deenergizing of said relay; C. a first trip circuit having a trip level for rendering said switch means nonconducting in response to an input signal of a predetermined magnitude being supplied thereto; D. reset time delay means connected to enable the system to energize said relay means and motor after a period of time has elapsed following a trip due to said first trip circuit; E. a second trip circuit having a trip level for rendering said switch means nonconducting in response to an input signal of a predetermined magnitude being supplied thereto; F. thermostat terminal means for connecting a thermostat to said system having a pair of electrical thermostat contacts for supplying a refrigeration demand signal to energize said relay means upon closing of the thermostat contacts due to the occurrence of a refrigeration demand; and G. integration circuit means connected to said thermostat terminal means for integrating an input signal which is functionally related to the presence of an open circuit voltage appearing across said thermostat terminal means upon opening of thermostat contacts connected thereto, said integration circuit means providing an integrated output signal to said second trip circuit, whereby said second trip circuit is tripped and said motor relay is positively de-energized after the interval of time required to integrate the input signal to the trip level of said second trip circuit, to thereby prevent damage to the relay contacts upon opening or excessive chattering of the thermostat contacts.
Claim 3
Dependent Claim
61 words
A control system as defined in claim 1, including feedback circuit means associated with said switch means for tripping said first trip circuit when the second trip circuit is tripped so that a reset time delay associated with resetting of the first trip circuit is imposed on re-energizing said relay means in the event of tripping of said second trip circuit.
Claim 4
Dependent Claim
70 words
A control system as defined in claim 1, wherein said reset time delay means includes circuit means for providing a reset signal and means for supplying the reset signal to an integration means whereby the system is reset a period of time subsequent to a trip which is determined by the length of time required to integrate a function of the reset signal to the reset level of the system.
Claim 5
Dependent Claim
122 words
A control system as defined in claim 1, including motor current sensing means connected to provide a motor current signal responsive to the magnitude of current drawn by the compressor motor, said reset time delay means including circuit means for providing a reset signal; circuit means for combining and integrating a difference between said motor current signal and said reset signal, and circuit means for providing the resulting integrated difference signal to said first trip circuit to trip said first trip circuit and de-energize said relay after the period of time required to integrate the difference function to the trip level, whereby relatively large motor current overloads cause a trip in a shorter period of time than relatively smaller motor current overloads.
Claim 6
Dependent Claim
130 words
A control system as defined in claim 1, including motor current sensing means connected to provide a motor current signal responsive to the magnitude of current drawn by the compressor motor; said reset time delay means including circuit means for providing a reset signal; circuit means for combining and integrating a difference between said motor current signal and said reset signal, and circuit means for providing the resulting integrated difference signal to said first trip circuit; and said system including feedback circuit means associated with said switch means for tripping said first trip circuit when the second trip circuit is tripped so that reset time delay associated with resetting of the first trip circuit is imposed on re-energizing said relay means in the event of tripping said second trip circuit.
References Cited (Backward Citations)
USPTO Annuity & Maintenance Windows
| Annuity Stage | Window Opens | Payment Deadline | Surcharge Period Until | Estimated Fee | Status |
|---|---|---|---|---|---|
| 3.5 Years (Year 4) | 1976-12-03 | 1977-06-04 | 1977-12-04 | $2000.00 | Window Closed / Lapsed |
| 7.5 Years (Year 8) | 1980-12-03 | 1981-06-04 | 1981-12-04 | $3760.00 | Window Closed / Lapsed |
| 11.5 Years (Year 12) | 1984-12-03 | 1985-06-04 | 1985-12-04 | $7700.00 | Window Closed / Lapsed |