ELECTRICAL TIME LOCK-OUT SYSTEM
United States Patent 3721866
A time lock-out system including an operator circuit having a normally open lock-out switch therein. A control circuit is provided which includes a holding switch that is responsive to the absence of an electrical signal to assume a first position and responsive to the presence of such electrical signal to assume a second position. Current sensing means is provided for sensing current in the operating circuit and is responsive to the current sensed to produce a triggering signal to hold the holding switch to its second position. A time delay device is connected with the holding switch and is responsive to an electrical signal in the control circuit to, after a selected time delay, produce a triggering signal to switch the holding switch to its second position. The control circuit connects the holding switch with the lock-out switch and time delay device to complete a circuit to the lock-out switch when the holding switch is in its second position to thereby close such lock-out switch and to, further, complete a circuit to the time delay device when the holding switch is in the first position whereby the lock-out switch will be closed as long as both the control and operator circuits are energized but will be opened any time current is discontinued in either the operator or control circuit and will remain open until the timed delay device is re-energized for the pre-determined timed delay.
US Patent References:
Control circuits for electric motors
Kyle - June 1965 - 3192463
AUTOMATICALLY RESETTING MOTOR PROTECTION CIRCUIT RESPONSIVE TO OVERCURRENT AND OVERTEMPERATURE
Pinckaers - May 1972 - 3660718
Control circuits for electric motors
Kyle - June 1965 - 3192463
AUTOMATICALLY RESETTING MOTOR PROTECTION CIRCUIT RESPONSIVE TO OVERCURRENT AND OVERTEMPERATURE
Pinckaers - May 1972 - 3660718
Application Number:
05/173905
Publication Date:
03/20/1973
Filing Date:
08/23/1971
View Patent Images:
Export Citation:
Assignee:
Robertshaw Controls Company (Richmond, VA)
Primary Class:
Other Classes:
318/485, 62/158, 361/22, 361/194, 318/474
International Classes:
H02H3/06; H02H7/08; H02H3/02; G05D23/32; H01H47/18
Field of Search:
317/141R,13A 318/473,474,484,485
Primary Examiner:
Hix L. T.
Claims:
What is claimed is
1. An electrical time lock-out system comprising:
2. An electrical time lock-out system as set forth in claim 1 wherein:
3. An electrical time lock-out system as set forth in claim 1 wherein:
4. An electrical time lock-out system as set forth in claim 1 wherein:
5. An electrical time lock-out system as set forth in claim 1 wherein:
6. An electrical time lock-out system as set forth in claim 1 wherein:
7. An electrical time lock-out system as set forth in claim 1 wherein:
8. An electrical time lock-out system as set forth in claim 1 wherein:
9. An electrical time lock-out system as set forth in claim 1 wherein:
10. An electrical time lock-out system as set forth in claim 1 wherein:
11. An electrical time lock-out system comprising:
12. An electrical time lock-out system as set forth in claim 11 wherein:
13. An electrical time lock-out system as set forth in claim 11 wherein:
14. An electrical time lock-out system as set forth in claim 11 wherein:
1. An electrical time lock-out system comprising:
2. An electrical time lock-out system as set forth in claim 1 wherein:
3. An electrical time lock-out system as set forth in claim 1 wherein:
4. An electrical time lock-out system as set forth in claim 1 wherein:
5. An electrical time lock-out system as set forth in claim 1 wherein:
6. An electrical time lock-out system as set forth in claim 1 wherein:
7. An electrical time lock-out system as set forth in claim 1 wherein:
8. An electrical time lock-out system as set forth in claim 1 wherein:
9. An electrical time lock-out system as set forth in claim 1 wherein:
10. An electrical time lock-out system as set forth in claim 1 wherein:
11. An electrical time lock-out system comprising:
12. An electrical time lock-out system as set forth in claim 11 wherein:
13. An electrical time lock-out system as set forth in claim 11 wherein:
14. An electrical time lock-out system as set forth in claim 11 wherein:
Description:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an electrical control system that includes a time delay device for delaying re-energization of the system once such system has been de-energized to thereby positively prevent fast cycling of the system.
2. Description of the Prior Art
In thermostat controlled air-conditioning systems it is desirable to prevent re-energization of an air-conditioner compressor motor for about 5 minutes after such motor has been de-energized to enable the pressure in the compressor lines to equalize so the motor is not started against high pressures which may cause stalling of such motor. Many efforts have been made to provide a satisfactory protective time delay device for this purpose and the systems proposed normally include relatively expensive and inconvenient to use timing motors. Prior art devices of this type are shown in U. S. Pat. No. 3,053,057 and No. 3,054,271.
SUMMARY OF THE INVENTION
The time lock-out control system of the present invention is characterized by a holding switch means that is responsive to the absence of a triggering signal to assume a first position and to a triggering signal to move to a second position to close a lock-out switch in an operator circuit. Sensing means is provided for sensing current in the operator circuit to hold the holding switch in such second position and maintain the lock-out switch closed. A time delay device is provided for preventing application of such triggering signal for a predetermined time after the system is energized.
The objects and advantages of the present invention will become apparent from the consideration of the following detailed description when taken in conjunction with the accompanying drawings.
DESCRIPTION OF THE DRAWINGS
FIG. 1 is a schematic view of an electrical time lock-out system embodying the present invention;
FIG. 2 is a schematic view of a second embodiment of the time lock-out system of the present invention; and
FIG. 3 is an electrical schematic of a third embodiment of the time lock-out system of the present invention.
DESCRIPTION OF THE PREFERRED EMBODIMENT
The time lock-out system of the present invention is particularly useful for controlling an operator in the form of an air-conditioner motor 11 and includes a lock-out relay having a switch 13 in the operator circuit, generally designated 14. The coil 15 of the lock-out relay is included in a holding circuit, generally designated 16 and is controlled by a holding relay including a holding switch 19. The holding switch 19 includes a first contact 21 connected with such lock-out relay 15 and a second contact 23 connected with a time delay device, generally designated 25. The coil 29 of the holding relay has current thereto controlled by a silicon controlled rectifier (SCR) 31, which SCR has its triggering circuit connected with a ferro-magnetic current sensing loop 33 and a parallel connected switch 37 controlled by the time delay device 25. The current sensing loop 33 is responsive to current flow to the compressor motor 11 to maintain a gating signal on the SCR 31 to maintain such SCR conductive and the holding coil 29 energized to maintain the switch 19 on the contact 21 to maintain the lock-out coil 15 energized and the lock-out switch 13 closed. However, anytime the compressor motor 11 is de-energized the gating current to the SCR 31 will be discontinued thereby de-energizing the holding coil 29 and causing the switch 19 to engage the contact 23 thereby deenergizing the lock-out coil 15 to open the switch 13 and also energizing the time delay device 25. Consequently, even if the circuit for the compressor motor 11 is immediately re-energized, such motor will not be energized since the lock-out switch 13 remains open until the time delay device effects closure of the switch 37 to provide a gating signal to the SCR 31 to energize the holding coil 29 and switch the switch 19 to the contact 21 to thereby re-energize the lock-out coil 15 and close the switch 13 to initiate energization of the motor 11 after the predetermined time delay. Further, if at any time the control current to the lock-out coil 15 is discontinued, the lock-out switch 13 will be opened to effect the same time delay dictated by the timed delay device before the motor 11 can be re-energized.
The compressor motor 11 is connected across the high voltage primary coil 41 of a transformer, generally designated 43, by means of leads 45, 47 and 49. The compressor motor 11 includes a thermostatic overload switch 50 which is responsive to overloading of the motor to heat and open.
The lock-out coil 15 is connected across the secondary low voltage coil 51 of the transformer 43 by means of leads 53, 55 and 57 and holding switch 19.
Series connected high and low pressure switch 58 and 59 and a thermostat switch 60 are connected in series with the holding relay coil 29 by means of an actuating circuit including leads 61 and 62.
The gate electrode 63 of the SCR 31 is connected with one end of a sensing coil 55 by means of a lead 67, such sensing coil being wound on one side of the sensing loop 33. The opposite end of the sensing coil 65 is connected with the cathode electrode 71 of the SCR 31 by means of a lead 73.
The cathode 71 and gate 63 of the SCR 31 are also connected across the secondary transformer coil 51 by means of a readiness lead 75, a lead 77 and resistor 79, the lead 75 includes the time delay switch 37 which readies the circuit 14 for energization.
The time delay device 25 is in the form of a dash pot including a viscous fluid chamber 83 which has a plunger 85 reciprocatably disposed therein. The plunger 85 includes a relatively small bleed orifice 87 and a relatively large return orifice 89 having a flapper valve 91 disposed adjacent thereto. The plunger 85 is biased downwardly by means of a coil spring 95 wound about a switch actuating post 97. The plunger includes a solenoid core 101 projecting from its bottom side and having a solenoid coil 103 wound thereon. The solenoid coil 103 is connected across the transformer secondary coil 51 by means of leads 105, 57 and 107 and the contact 23 of the holding switch 19.
In operation, when the transformer 43 is energized and the thermostat switch 60 closes to call for cooling, the time delay solenoid coil 103 will be energized through leads 57, 105 and 107 and contact 23 of switch 19 to urge the plunger 85 upwardly. Upward travel of the plunger 85 causes the flapper valve 91 to close and the viscous fluid in the chamber 83 will flow through the bleed port 87 to enable the plunger 85 to move upwardly at a relatively slow speed. After approximately 5 minutes, the actuator post 97 will engage the time delay switch 37 to close such switch and energize the lead 75 to impose a gating current on the gate 63 of the SCR 31 to thereby render such SCR conductive to energize the holding switch coil 29 and switch the switch 19 to the contact 21. Engagement of the switch 19 with the contact 21 completes a circuit through leads 57, 55 and 53 to energize the lock-out switch coil 15 to thereby close the lock-out switch 13 and initiate current flow in the operator circuit 14 to the compressor motor 11 thereby energizing such motor to commense operation of the compressor to actuate the air-conditioner (not shown). Switching of the switch 19 from the contact 23 to the contact 21 will de-energize the time delay solenoid coil 103 thereby enabling the return spring 95 to bias the plunger 85 rapidly downwardly to open the flapper valve 91 to enable the viscous fluid to escape through the return port 89 and opening the time delay switch 37.
After the environment has been cooled sufficiently to cool the control thermostat to the desired temperature and effect opening of the thermostat switch 60, the holding switch coil 29 will be de-energized to enable the holding switch 19 to disengage the contact 21 and engage the contact 23 thereby opening the circuit through the lock-out switch coil 15 and completing the circuit through the time delay coil 103. De-energization of the lock-out switch coil 15 enables the lock-out switch 13 to open thereby discontinuing current to the air-conditioning compressor motor 11 to thereby discontinue operation of the air-conditioner and also discontinuing current in the lead 49 thereby discontinuing the gating signal in the sensing coil 65 to thereby render the SCR 31 non-conductive. Consequently, if the thermostat switch 60 is closed immediately after opening thereof, as by an operator turning the thermostat adjustment dial to a lower temperature setting, the holding switch coil 29 will not be energized because the SCR 31 is non-conductive. However, it will be appreciated that after the selected time delay, as for instance 5 minutes, the time delay solenoid 103 will raise the time delay plunger 85 to close the time delay switch 37 thereby supplying a gating voltage to the SCR 31 to render such SCR conductive to then energize the holding switch coil 29 to switch the switch 19 from the contact 23 to the contact 21. Such switching of the holding switch 19 will complete a circuit through the lock-out switch coil 15 to close the lock-out switch 13 and again energize the compressor motor 11 and produce a gating signal on the sensing coil 65 for gating the SCR 31. Also, switching of the holding switch 19 to the contact 21 de-energizes the time delay solenoid coil 103 thereby enabling the spring 95 to bias the time delay plunger downwardly to enable the time delay switch 37 to open and discontinue imposition of the gating signal therethrough to the SCR gate 63.
It is noted that if at any time the motor 11 overloads the operator circuit 14, the overload switch 50 will be heated to open the operator circuit 14 and discontinue operation of the motor and also discontinue the gating current to the SCR 31 to de-energize the holding switch coil 29. Thus, the holding switch 19 will disengage the contact 21 and engage the contact 23 to de-energize the lock-out switch coil 15 and energize the time delay coil 103. Consequently, if the overload switch 50 closes immediately after opening, the 5 minute time delay produced by the time delay device 25 will prevent re-energization of the motor 11 for the desired 5 minute period as described hereinabove.
The lock-out control system shown in FIG. 2 is similar to that shown in FIG. 1 except that the time delay switch 37 is in the form of a thermostatic blade 108 and is connected in series with the lock-out switch coil 15 and switches 58, 59 and 60 by means of readiness leads 110 and 111, and actualing leads 112 and 113. A heating resistor is connected across the transformer secondary coil 51 by means of leads 119, 121 and 123 and the holding switch 19.
In operation when the system shown in FIG. 2 is energized the heating resistor 117 will heat the thermostatic switch blade 108 to, after approximately 5 minutes, close such switch 108 to ready the lock-out coil 15 for energization. Consequently, when the thermostat switch 60 is closed to call for cooling, the lock-out coil 15 will be energized through the readiness lead 110 to close the switch 13 and energize the compressor motor 11. Current flow in the compressor motor lead 49 will impose a triggering signal on the coil 65 to provide triggering current to the gate 63 of the SCR 31 to thereby render such SCR conductive to energize the holding switch coil 29. Energization of the coil 29 will switch the switch 19 from the contact 23 to the contact 21 thereby de-energizing the heat resistor 117 and maintaining a circuit through the leads 123 and 110 to the lock-out coil 115 irrespective of the fact that the time delay switch 108 is opened.
When the holding circuit 16 is de-energized, as by opening of the high or low pressures switches 58 or 59 or the thermostatic switch 60, the circuit to the holding switch coil 29 will be opened to thereby cause the holding switch 19 to switch from the contact 21 to the contact 23 to thereby de-energizing the lock-out switch coil 15 and reenergizing the heating resistor 117. Again, even if the switch 58, 59 or 60 which was open to break the circuit is closed immediately, the SCR 31 will remain non-conductive because the lack of current in the motor lead 49 thereby preventing energization of the holding switch coil 29 until such time as the resistor 117 heats the thermostatic switch 108 to close such switch and energize the lock-out coil 15 to thereby close the lock-out switch 13 and provide a current in the lead 49 to produce a triggering signal in the sensing coil 65 to render such SCR 31 conductive. Also, as described hereinabove, if the compressor motor 11 is overloaded to cause the overload switch 50 to open the triggering signal from the sensing coil 65 to the SCR 31 will be discontinued thereby rendering such SCR non-conductive and de-energizing the holding switch coil 29 to cause the holding switch 19 to switch from the contact 21 to contact 23. This switching of the switch 19 will be de-energize the lock-out coil 15 and energize the heating resistor 17 as described hereinabove to produce the 5 minute delay period before the system can be re-energized.
The lock-out control system shown in FIG. 3 is substantially the same as that shown in FIG. 2 except a time delay device 25 is substituted for the heating resistor 117. The coil 103 of the time delay device 25 is connected across the secondary transformer coil 51 by means of leads 135, 137 and 139 and the contact 23 of the holding switch 19.
Consequently, when the system is de-energized, as by opening up of the thermostat switch 60, the holding coil 29 will be de-energized to cause the switch 19 to disengage the contact 21 and engage the contact 23 to de-energize the lock-out coil 15 and ready the time delay coil 103 for energization. De-energization of the lock-out coil 15 will cause the lock-out switch 13 to open thereby discontinuing current to the motor 11 and discontinuing the triggering signal from the sensing coil 65 to the SCR 31. Concurrently, the time delay coil 103 will be energized through the leads 135, 137, switch 19 and lead 139. Energization of the time delay coil 103 drives the plunger 85 upwardly at a speed dictated by the bleed orifice 87 to, after approximately a five minute interval, engage the actuating post 97 with the time delay switch 37 to close such switch and, if the thermostat switch 60 has already closed, energize the lock-out coil 15 to close the lock-out switch 13. Closure of the lock-out switch 13 will again energize the compressor motor 11 and provide a gating current from the sensing coil 65 to the SCR 31 thereby rendering such SCR conductive to energize the holding coil 29 and switch the holding switch 19 from the contact 23 to the contact 21 to thereby maintain the lock-out coil 15 energized even after the time delay coil 103 has been de-energized and the time delay switch 37 opened.
From the foregoing it will be apparent that the time lock-out of the present invention provides an economical and straight forward means for delaying re-energization of a compressor motor for a specified period of time after such motor has been de-energized to thereby protect such motor from stalling due to attempted start-up against a pressure head remaining the compressor. Such time delay is effected irrespective of whether the motor circuit or the control circuit has been de-energized momentarily and is then reenergized.
Various modifications and changes may be made with regard to the foregoing detailed description without departing from the spirit of the present invention.
1. Field of the Invention
The present invention relates to an electrical control system that includes a time delay device for delaying re-energization of the system once such system has been de-energized to thereby positively prevent fast cycling of the system.
2. Description of the Prior Art
In thermostat controlled air-conditioning systems it is desirable to prevent re-energization of an air-conditioner compressor motor for about 5 minutes after such motor has been de-energized to enable the pressure in the compressor lines to equalize so the motor is not started against high pressures which may cause stalling of such motor. Many efforts have been made to provide a satisfactory protective time delay device for this purpose and the systems proposed normally include relatively expensive and inconvenient to use timing motors. Prior art devices of this type are shown in U. S. Pat. No. 3,053,057 and No. 3,054,271.
SUMMARY OF THE INVENTION
The time lock-out control system of the present invention is characterized by a holding switch means that is responsive to the absence of a triggering signal to assume a first position and to a triggering signal to move to a second position to close a lock-out switch in an operator circuit. Sensing means is provided for sensing current in the operator circuit to hold the holding switch in such second position and maintain the lock-out switch closed. A time delay device is provided for preventing application of such triggering signal for a predetermined time after the system is energized.
The objects and advantages of the present invention will become apparent from the consideration of the following detailed description when taken in conjunction with the accompanying drawings.
DESCRIPTION OF THE DRAWINGS
FIG. 1 is a schematic view of an electrical time lock-out system embodying the present invention;
FIG. 2 is a schematic view of a second embodiment of the time lock-out system of the present invention; and
FIG. 3 is an electrical schematic of a third embodiment of the time lock-out system of the present invention.
DESCRIPTION OF THE PREFERRED EMBODIMENT
The time lock-out system of the present invention is particularly useful for controlling an operator in the form of an air-conditioner motor 11 and includes a lock-out relay having a switch 13 in the operator circuit, generally designated 14. The coil 15 of the lock-out relay is included in a holding circuit, generally designated 16 and is controlled by a holding relay including a holding switch 19. The holding switch 19 includes a first contact 21 connected with such lock-out relay 15 and a second contact 23 connected with a time delay device, generally designated 25. The coil 29 of the holding relay has current thereto controlled by a silicon controlled rectifier (SCR) 31, which SCR has its triggering circuit connected with a ferro-magnetic current sensing loop 33 and a parallel connected switch 37 controlled by the time delay device 25. The current sensing loop 33 is responsive to current flow to the compressor motor 11 to maintain a gating signal on the SCR 31 to maintain such SCR conductive and the holding coil 29 energized to maintain the switch 19 on the contact 21 to maintain the lock-out coil 15 energized and the lock-out switch 13 closed. However, anytime the compressor motor 11 is de-energized the gating current to the SCR 31 will be discontinued thereby de-energizing the holding coil 29 and causing the switch 19 to engage the contact 23 thereby deenergizing the lock-out coil 15 to open the switch 13 and also energizing the time delay device 25. Consequently, even if the circuit for the compressor motor 11 is immediately re-energized, such motor will not be energized since the lock-out switch 13 remains open until the time delay device effects closure of the switch 37 to provide a gating signal to the SCR 31 to energize the holding coil 29 and switch the switch 19 to the contact 21 to thereby re-energize the lock-out coil 15 and close the switch 13 to initiate energization of the motor 11 after the predetermined time delay. Further, if at any time the control current to the lock-out coil 15 is discontinued, the lock-out switch 13 will be opened to effect the same time delay dictated by the timed delay device before the motor 11 can be re-energized.
The compressor motor 11 is connected across the high voltage primary coil 41 of a transformer, generally designated 43, by means of leads 45, 47 and 49. The compressor motor 11 includes a thermostatic overload switch 50 which is responsive to overloading of the motor to heat and open.
The lock-out coil 15 is connected across the secondary low voltage coil 51 of the transformer 43 by means of leads 53, 55 and 57 and holding switch 19.
Series connected high and low pressure switch 58 and 59 and a thermostat switch 60 are connected in series with the holding relay coil 29 by means of an actuating circuit including leads 61 and 62.
The gate electrode 63 of the SCR 31 is connected with one end of a sensing coil 55 by means of a lead 67, such sensing coil being wound on one side of the sensing loop 33. The opposite end of the sensing coil 65 is connected with the cathode electrode 71 of the SCR 31 by means of a lead 73.
The cathode 71 and gate 63 of the SCR 31 are also connected across the secondary transformer coil 51 by means of a readiness lead 75, a lead 77 and resistor 79, the lead 75 includes the time delay switch 37 which readies the circuit 14 for energization.
The time delay device 25 is in the form of a dash pot including a viscous fluid chamber 83 which has a plunger 85 reciprocatably disposed therein. The plunger 85 includes a relatively small bleed orifice 87 and a relatively large return orifice 89 having a flapper valve 91 disposed adjacent thereto. The plunger 85 is biased downwardly by means of a coil spring 95 wound about a switch actuating post 97. The plunger includes a solenoid core 101 projecting from its bottom side and having a solenoid coil 103 wound thereon. The solenoid coil 103 is connected across the transformer secondary coil 51 by means of leads 105, 57 and 107 and the contact 23 of the holding switch 19.
In operation, when the transformer 43 is energized and the thermostat switch 60 closes to call for cooling, the time delay solenoid coil 103 will be energized through leads 57, 105 and 107 and contact 23 of switch 19 to urge the plunger 85 upwardly. Upward travel of the plunger 85 causes the flapper valve 91 to close and the viscous fluid in the chamber 83 will flow through the bleed port 87 to enable the plunger 85 to move upwardly at a relatively slow speed. After approximately 5 minutes, the actuator post 97 will engage the time delay switch 37 to close such switch and energize the lead 75 to impose a gating current on the gate 63 of the SCR 31 to thereby render such SCR conductive to energize the holding switch coil 29 and switch the switch 19 to the contact 21. Engagement of the switch 19 with the contact 21 completes a circuit through leads 57, 55 and 53 to energize the lock-out switch coil 15 to thereby close the lock-out switch 13 and initiate current flow in the operator circuit 14 to the compressor motor 11 thereby energizing such motor to commense operation of the compressor to actuate the air-conditioner (not shown). Switching of the switch 19 from the contact 23 to the contact 21 will de-energize the time delay solenoid coil 103 thereby enabling the return spring 95 to bias the plunger 85 rapidly downwardly to open the flapper valve 91 to enable the viscous fluid to escape through the return port 89 and opening the time delay switch 37.
After the environment has been cooled sufficiently to cool the control thermostat to the desired temperature and effect opening of the thermostat switch 60, the holding switch coil 29 will be de-energized to enable the holding switch 19 to disengage the contact 21 and engage the contact 23 thereby opening the circuit through the lock-out switch coil 15 and completing the circuit through the time delay coil 103. De-energization of the lock-out switch coil 15 enables the lock-out switch 13 to open thereby discontinuing current to the air-conditioning compressor motor 11 to thereby discontinue operation of the air-conditioner and also discontinuing current in the lead 49 thereby discontinuing the gating signal in the sensing coil 65 to thereby render the SCR 31 non-conductive. Consequently, if the thermostat switch 60 is closed immediately after opening thereof, as by an operator turning the thermostat adjustment dial to a lower temperature setting, the holding switch coil 29 will not be energized because the SCR 31 is non-conductive. However, it will be appreciated that after the selected time delay, as for instance 5 minutes, the time delay solenoid 103 will raise the time delay plunger 85 to close the time delay switch 37 thereby supplying a gating voltage to the SCR 31 to render such SCR conductive to then energize the holding switch coil 29 to switch the switch 19 from the contact 23 to the contact 21. Such switching of the holding switch 19 will complete a circuit through the lock-out switch coil 15 to close the lock-out switch 13 and again energize the compressor motor 11 and produce a gating signal on the sensing coil 65 for gating the SCR 31. Also, switching of the holding switch 19 to the contact 21 de-energizes the time delay solenoid coil 103 thereby enabling the spring 95 to bias the time delay plunger downwardly to enable the time delay switch 37 to open and discontinue imposition of the gating signal therethrough to the SCR gate 63.
It is noted that if at any time the motor 11 overloads the operator circuit 14, the overload switch 50 will be heated to open the operator circuit 14 and discontinue operation of the motor and also discontinue the gating current to the SCR 31 to de-energize the holding switch coil 29. Thus, the holding switch 19 will disengage the contact 21 and engage the contact 23 to de-energize the lock-out switch coil 15 and energize the time delay coil 103. Consequently, if the overload switch 50 closes immediately after opening, the 5 minute time delay produced by the time delay device 25 will prevent re-energization of the motor 11 for the desired 5 minute period as described hereinabove.
The lock-out control system shown in FIG. 2 is similar to that shown in FIG. 1 except that the time delay switch 37 is in the form of a thermostatic blade 108 and is connected in series with the lock-out switch coil 15 and switches 58, 59 and 60 by means of readiness leads 110 and 111, and actualing leads 112 and 113. A heating resistor is connected across the transformer secondary coil 51 by means of leads 119, 121 and 123 and the holding switch 19.
In operation when the system shown in FIG. 2 is energized the heating resistor 117 will heat the thermostatic switch blade 108 to, after approximately 5 minutes, close such switch 108 to ready the lock-out coil 15 for energization. Consequently, when the thermostat switch 60 is closed to call for cooling, the lock-out coil 15 will be energized through the readiness lead 110 to close the switch 13 and energize the compressor motor 11. Current flow in the compressor motor lead 49 will impose a triggering signal on the coil 65 to provide triggering current to the gate 63 of the SCR 31 to thereby render such SCR conductive to energize the holding switch coil 29. Energization of the coil 29 will switch the switch 19 from the contact 23 to the contact 21 thereby de-energizing the heat resistor 117 and maintaining a circuit through the leads 123 and 110 to the lock-out coil 115 irrespective of the fact that the time delay switch 108 is opened.
When the holding circuit 16 is de-energized, as by opening of the high or low pressures switches 58 or 59 or the thermostatic switch 60, the circuit to the holding switch coil 29 will be opened to thereby cause the holding switch 19 to switch from the contact 21 to the contact 23 to thereby de-energizing the lock-out switch coil 15 and reenergizing the heating resistor 117. Again, even if the switch 58, 59 or 60 which was open to break the circuit is closed immediately, the SCR 31 will remain non-conductive because the lack of current in the motor lead 49 thereby preventing energization of the holding switch coil 29 until such time as the resistor 117 heats the thermostatic switch 108 to close such switch and energize the lock-out coil 15 to thereby close the lock-out switch 13 and provide a current in the lead 49 to produce a triggering signal in the sensing coil 65 to render such SCR 31 conductive. Also, as described hereinabove, if the compressor motor 11 is overloaded to cause the overload switch 50 to open the triggering signal from the sensing coil 65 to the SCR 31 will be discontinued thereby rendering such SCR non-conductive and de-energizing the holding switch coil 29 to cause the holding switch 19 to switch from the contact 21 to contact 23. This switching of the switch 19 will be de-energize the lock-out coil 15 and energize the heating resistor 17 as described hereinabove to produce the 5 minute delay period before the system can be re-energized.
The lock-out control system shown in FIG. 3 is substantially the same as that shown in FIG. 2 except a time delay device 25 is substituted for the heating resistor 117. The coil 103 of the time delay device 25 is connected across the secondary transformer coil 51 by means of leads 135, 137 and 139 and the contact 23 of the holding switch 19.
Consequently, when the system is de-energized, as by opening up of the thermostat switch 60, the holding coil 29 will be de-energized to cause the switch 19 to disengage the contact 21 and engage the contact 23 to de-energize the lock-out coil 15 and ready the time delay coil 103 for energization. De-energization of the lock-out coil 15 will cause the lock-out switch 13 to open thereby discontinuing current to the motor 11 and discontinuing the triggering signal from the sensing coil 65 to the SCR 31. Concurrently, the time delay coil 103 will be energized through the leads 135, 137, switch 19 and lead 139. Energization of the time delay coil 103 drives the plunger 85 upwardly at a speed dictated by the bleed orifice 87 to, after approximately a five minute interval, engage the actuating post 97 with the time delay switch 37 to close such switch and, if the thermostat switch 60 has already closed, energize the lock-out coil 15 to close the lock-out switch 13. Closure of the lock-out switch 13 will again energize the compressor motor 11 and provide a gating current from the sensing coil 65 to the SCR 31 thereby rendering such SCR conductive to energize the holding coil 29 and switch the holding switch 19 from the contact 23 to the contact 21 to thereby maintain the lock-out coil 15 energized even after the time delay coil 103 has been de-energized and the time delay switch 37 opened.
From the foregoing it will be apparent that the time lock-out of the present invention provides an economical and straight forward means for delaying re-energization of a compressor motor for a specified period of time after such motor has been de-energized to thereby protect such motor from stalling due to attempted start-up against a pressure head remaining the compressor. Such time delay is effected irrespective of whether the motor circuit or the control circuit has been de-energized momentarily and is then reenergized.
Various modifications and changes may be made with regard to the foregoing detailed description without departing from the spirit of the present invention.