Fail safe electronic pressure switch for compressor motor

Details Fail safe electronic pressure switch for compressor motor Fail safe electronic pressure switch for compressor motor

2000-12-20

2002-12-24

Freay, Charles G. (Department: 3746)

Pumps

Condition responsive control of pump drive motor

By control of electric or magnetic drive motor

C417S902000, C418S055100

Reexamination Certificate

active

06497554

ABSTRACT:

BACKGROUND OF THE INVENTION
This invention relates to an electronic switch for stopping operation of a compressor motor if certain pressure conditions are not met.
Compressors are typically driven by an electric motor to compress a fluid, such as a refrigerant, and move that fluid to a downstream use. In a refrigerant compressor, typically, the compressed refrigerant is sent into a refrigerant cycle.
In a refrigerant compressor, there are many potential concerns that can arise. As one example, the refrigerant can be over pressured due to a number of conditions. For that reason, pressure sensors have typically been incorporated somewhere adjacent the discharge portion of the compressor to monitor the discharge pressure. If the discharge pressure exceeds a predetermined amount, then the compressor motor may be stopped. Typically, these pressure sensors have included mechanical elements that move against a spring force, etc., to open a cutoff switch.
While a mechanical switch is relatively inexpensive, it is not as reliable as would be desired. Thus, a more reliable safety switch with fail-safe features would be desirable.
SUMMARY OF THE INVENTION
In the disclosed embodiment of this invention, a pressure sensor communicates with an electronic control to send a signal to a switch to stop operation of a compressor motor should a sensed pressure be outside an acceptable range. Most preferably, the pressure sensor is sensing a discharge pressure, and the condition which is outside the acceptable range would typically be an overly high discharge pressure.
In the disclosed embodiment, a microprocessor based control receives a voltage signal from a pressure sensor which is related to the compressor discharge pressure. A transducer is typically included into the electronic pressure sensor such that the pressure is transferred into a related voltage amount. The voltage amount is sensed by the microprocessor based control. If the voltage amounts indicates that the pressure exceeds a particular predetermined high pressure, then a signal is sent to a first switch to stop operation of the compressor. Most preferably the compressor is stopped by opening a relay which is part of the compressor motor control.
Such a system provides benefits when compared to the prior art. However, with such an electronically controlled system it would still be desirable to include a fail-safe mode to ensure proper operation of the electronic control. Thus, in a most preferred embodiment, the signal from the pressure sensor, which is preferably a voltage signal, is sent to a comparing circuit. The comparing circuit sends a signal to a second switch. If the comparing circuit senses that the pressure voltage signal is less than, or more than, predetermined boundaries, then the relay is left open. The compressor motor is again stopped from operating. In this way, should the microprocessor or pressure sensor fail, this fail-safe portion of the circuit will stop operation of the motor.
In a preferred embodiment, the first switch, which communicates with the microprocessor based control is a triac. The second switch is preferably an output relay. The second switch relay is preferably in series with the triac, and is controlled by the comparing circuit. The comparing circuit is preferably a bandwidth comparing circuit.
These and other features of the present invention can be best understood from the following specification and drawings, the following of which is a brief description.


REFERENCES:
patent: 4527953 (1985-07-01), Baker et al.
patent: 4538422 (1985-09-01), Mount et al.
patent: 4863355 (1989-09-01), Odagiri et al.
patent: 5321957 (1994-06-01), Moore
patent: 8-313123 (1996-11-01), None

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