External burner shut-off

The present invention provides an external burner shut-off for oil fired heating systems. More specifically, the present invention provides a burner control circuit interrupt for a burner control circuit. The interrupt includes a pair of switches controlled by a relay coil. One of the switches opens the power supply to the burner control circuit and the other switch provides power to a timer circuit of the interrupt. The timer circuit counts down from a predetermined time to allow sludge in an oil holding tank to resettle after an oil delivery. The interrupt provides a fail-safe feature to insure that the burner control circuit is not inadvertently interrupted.

FIELD OF THE INVENTION 
The present invention relates to a control circuit interrupt. More 
particularly, the present invention relates to a control circuit interrupt 
for an oil fired heating system including a fail-safe feature. 
BACKGROUND OF THE INVENTION 
Oil fired heating systems typically incorporate a primary burner control 
that controls the ignition and the supply of oil to the system burner. The 
primary burner control, in response to a signal from an aquastat or air 
thermostat, will activate the burner and supply oil to the burner. When 
the system reaches the desired temperature, the burner will shut off. 
A common problem with oil fired heating systems is that over time sludge 
accumulates and settles to the bottom of the oil tank. Because the sludge 
settles below the pickup line, it does not typically create problems 
during regular operation of the heating system. However, during an oil 
delivery the sludge gets churned up when oil is added to the heating tank. 
If the burner control actives and supplies oil from the holding tank to 
the burner, the sludge will be drawn into the pickup tube to the burner. 
While the pickup line or burner usually includes a filter, this filter is 
only intended to prevent microparticles from reaching the burner. A 
significant amount of the sludge will clog the filter and prevent the fuel 
from reaching the burner, the burner flame will be extinguished and the 
system will shut down until the filter is cleaned or replaced. 
A way to prevent clogging of the filter is to inhibit operation of the 
heating system during and directly after an oil delivery for a time 
sufficient to allow any sludge present in the holding tank to settle back 
down to the bottom of the tank. 
U.S. Pat. No. 3,976,421 to Lee et al. discloses a sediment control 
apparatus as described above. The apparatus has an internal interrupt 
timer that incorporates a normally closed switch into the burner control 
circuit. The system also includes an initiation switch, connected to the 
timer, that an oil delivery person activates to start the interrupt timer. 
When the initiation switch is activated, the timer opens the normally 
closed switch to interrupt the control circuit. 
A disadvantage of this device, however, is that the timer is integrated 
with and receives power from the same power supply as the burner control 
circuit. If the timer fails, for whatever reason, after being activated 
the normally closed switch will remain open. That will prevent operation 
of the heating system even after the elapsed interrupt period has passed, 
and the home will be without heat until the timer circuit can be repaired. 
SUMMARY OF THE INVENTION 
The present invention provides a mechanism to interrupt a burner control 
circuit for a predetermined period of time, and includes a fail-safe 
feature to prevent unwarranted interruption of the control circuit. 
The present invention provides a burner control circuit interrupt including 
a relay coil, a normally closed relay switch controlled by the relay coil, 
a normally open timer switch, and a timer that controls the normally open 
timer switch. 
The present invention provides a burner control circuit interrupt including 
a control circuit connection port, a power supply connection port and a 
normally open initiate switch, wherein the normally closed relay switch is 
connected across the control circuit connection port and the initiate 
switch couples the timer and the power supply connection port.

DESCRIPTION OF THE INVENTION 
In the drawings, where like numerals identify like elements, a control 
circuit interrupt of the present invention is generally designated by the 
numeral 10. 
As illustrated in FIG. 1, the interrupt 10 is connected to a power supply 
12 at a power supply connection port 14. The interrupt 10 is connected to 
a control circuit 16 at a control circuit connection port such as burner 
control connection port 18. When used with a hot air system, a temperature 
sensor or room thermostat 20 is connected between the control circuit 16 
and interrupt 10. Typically, the temperature sensor 20 will include a 
normally open switch. The switch will close when the sensor 20 achieves 
the preselected temperature thereby supplying power to the oil burner 
supply pump. If, however, the control circuit 16 is for a hot water system 
then the sensor 20 will not be present. 
The interrupt 10, as shown in more detail in FIG. 2, includes a switching 
element 22 and a timing element 24. The interrupt 10 may also include its 
own transformer 26 for converting line voltage to low voltage to operate 
the interrupt components. In this embodiment, the transformer 26 is 
connected across the power supply connection port 14. The interrupt 10 
also includes an initiate switch 28. The initiate switch 28 provides a 
connection between the timing element 24 and the power supply. As 
illustrated in FIG. 2, the initiate switch 28 is connected to the 
transformer 26. 
In its steady state, the initiate switch 28 provides an open circuit 
between timing element 24 and the transformer 26. The initiate switch 28 
may be any type of switch that provides a momentary connection between the 
transformer 26 and the timing element 24, for example, a spring loaded 
toggle switch. 
The switching element 22 includes a relay coil 30. The relay coil 30 
controls a normally closed relay switch 32 and a normally open relay 
switch 34. The term "normally" is determined as the state when the 
interrupt 10 is inactive and is not operating to interrupt the control 
circuit 16. 
The normally closed relay switch 32 is connected across the control circuit 
connection port 18 providing a short circuit across the port 18 allowing 
the control circuit 16 and the sensor 20 to operate according to their 
defined parameters. The normally open relay switch 34 is connected to the 
transformer 26 at one lead and to the timing element 24 at the other lead. 
When the relay coil 30 is energized the normally closed relay switch 32 is 
forced open and the normally open relay switch 34 is forced closed. 
The timing element 24 includes a clock 36 and a normally open timed switch 
38 controlled by the clock 36. The timing element 34 is individually 
coupled to the transformer 26 through both the initiate switch 28 and 
normally open relay switch 34. Furthermore, both the clock 36 and the 
timed switch 38 are coupled to the transformer 26 separately through the 
initiate switch 28 and the normally open relay switch 34. The normally 
open timed switch 38 is also connected to the relay coil 30. The clock 36 
is preset to a specified delay period, for example 20-40 minutes, that 
would allow any sludge that is stirred by an oil delivery to settle back 
to the bottom of the oil holding tank during the preset delay period. The 
timing element 24 closes the normally open timed switch 38 upon receiving 
power from the power supply. 
Once the control circuit interrupt 10, as illustrated in FIG. 2 is 
connected to a power supply 12 and a control circuit 16 it operates in the 
following manner. Upon delivering an oil shipment, the delivery person 
activates the initiate switch 28 thereby closing the switch 28. When the 
initiate switch 28 is activated the timing element 24 is connected to the 
power supply, thereby providing power to the timing element 24. Once the 
timing element 24 receives power, the clock 36 begins to run and the timed 
switch 38 closes. Once the timed switch 38 closes, the relay coil 30 
receives power and is energized. Once the relay coil 30 is energized and 
while the initiate switch 28 is still closed, the relay coil 30 opens the 
normally closed relay switch 32 and closes the normally open relay switch 
34. The relay coil 30 has been energized and changes the state of the 
relay switch 32,34 by the time the initiate switch 28 springs back open. 
With the normally open relay switch 34 closed, the timing element 24 now 
receives power through the relay switch 34 and the relay coil 30 now 
receives power through the relay switch 34 and the timed switch 38. 
As long as the relay coil 30 is energized and the relay switch 32 is open, 
the control circuit 16 will be prevented from activating the burner or 
burner supply. 
Once the clock 36 counts through the preset time period, the timing element 
34 will open the timed switch 38. Once the timed switch 38 is open, power 
to the relay coil 30 will be cut and the relay coil 30 will de-energize. 
Once the relay coil 30 de-energizes, the relay switches 32,34 will return 
to their normal states. Once the normally closed relay switch 32 closes, 
the control circuit 16 will again be able to operate. 
The design of the interrupt 10 of the present invention provides a highly 
desirable fail-safe feature. As described above, the timed switch 38 is 
normally open and will only close under direction and control of the 
timing element 24. Furthermore, the timed switch 38 must be closed in 
order for the relay coil 30 to receive power which in turn opens relay 
switch 32. If for any reason the timing element 24 fails, the timed switch 
38 will open and consequently de-energize the relay coil 30 and thereby 
closing the relay switch 32. If this feature were not present and the 
timed switch 38 were not to open upon failure of the timing element 24 
then the relay coil 30 would remain energized and the relay switch 32 
would remain open. This would prevent operation of the control circuit 16 
well after the oil delivery had been completed. By including such a 
fail-safe feature, the present invention overcomes one of the drawbacks of 
conventional systems. 
In an alternate embodiment, illustrated in FIG. 3, the initiate switch 28 
is not positioned in parallel with the normally open relay switch 34. 
Instead, the initiate switch 28 is connected directly between the 
transformer 26 and the timing element 36. 
FIG. 4 presents another alternate embodiment of the present invention. In 
this embodiment, power is supplied to the control circuit 16 through the 
interrupt 10. The normally closed relay switch 32 couples the control 
circuit 16 to the power supply (not shown). When the relay coil 30 is 
energized, the normally closed relay switch 32 opens and the normally open 
relay switch 34 closes. When the relay switch 32 opens, power is cut to 
the control circuit 16. As long as the relay coil 30 is energized the 
control circuit 16 will be inoperative. 
The present invention may be embodied in other specific forms without 
departing from the spirit or essential attributes thereof and, 
accordingly, reference should be made to the appended claims, rather than 
to the foregoing specification, as indicating the scope of the invention.