Thermal measuring and testing – Temperature measurement – Combined with diverse art device
Reexamination Certificate
2000-10-06
2002-12-03
Gutierrez, Diego (Department: 2859)
Thermal measuring and testing
Temperature measurement
Combined with diverse art device
C374S183000, C374S208000, C004S496000
Reexamination Certificate
active
06488408
ABSTRACT:
BACKGROUND OF THE INVENTION
A spa (also commonly known as a “hot tub”) is a therapeutic bath in which all or part of the body is exposed to forceful whirling currents of hot water. When located indoors and equipped with fill and drain features like a bathtub, the spa is typically referred to as a “whirlpool bath”. Typically, the spa's hot water is generated when water contacts a heating element in a water circulating heating pipe system.
FIG. 1
shows prior art hot tub spa
1
. Spa controller
7
is programmed to control the spa's water pumps
1
A and
1
B and air blower
4
. In normal operation, water is pumped by water pump
1
A through heater
3
where it is heated by heating element
5
. The heated water then leaves heater
3
and enters spa tub
2
through jets
11
. Water leaves spa tub
2
through drains
13
and the cycle is repeated.
The prior art spa shown in
FIG. 1
includes safety protection devices designed to prevent dangerous overheating conditions. For example, a circuit incorporating temperature sensor
50
serves to protect spa
1
from overheating. Temperature sensor
50
is mounted to the outside of heater
3
. Temperature sensor
50
is electrically connected to comparator circuit
51
A and control circuit
52
A, which is electrically connected to high limit relay
53
A.
As shown in
FIG. 1
, power plug
54
connects heating element
5
to a suitable power source, such as a standard household electric circuit. Water inside heater
3
is heated by heating element
5
. Due to thermal conductivity the outside of heater
3
becomes hotter as water inside heater
3
is heated by heating element
5
so that the outside surface of heater
3
is approximately equal to the temperature of the water inside heater
3
. This outside surface temperature is monitored by temperature sensor
50
. Temperature sensor
50
sends an electric signal to comparator circuit
51
A corresponding to the temperature it senses.
When an upper end limit temperature limit is reached, such as about 120 degrees Fahrenheit, positive voltage is removed from the high temperature limit relay
53
A, and power to heating element
5
is interrupted.
Water Pressure Sensor for Dry Fire Protection
Some conditions may cause little or no flow of water through the pipe containing heating element
5
during the heating process. These problems can cause what is known in the spa industry as a “dry fire”. Dry fires occur when there is no water in heater
3
or when the flow of water is too weak to remove enough heat from the heating element
5
. Common causes of low water flow are a dirty filter or a clogged pipe. For example, referring to
FIG. 1
, if a bathing suit became lodged in pipe
17
clogging the pipe, flow of water through heater
3
would be impeded and a dry fire could occur.
FIG. 1
shows water pressure sensor
15
mounted outside heater
3
. As shown in
FIG. 1
, water pressure sensor
15
is located in a circuit separate from temperature sensor
50
. It is electrically connected to spa controller
7
, which is electrically connected to regulation relay
111
.
In normal operation, when water pressure sensor
15
reaches a specific level, the electromechanical switch of the sensor changes its state. This new switch state indicates that the water pressure inside heater
3
is large enough to permit the heating process without the risk of dry fire. Likewise, in a fashion similar to that described for temperature sensor
50
, when a lower end limit pressure limit is reached, such as about 1.5 −2.0 psi, positive voltage is removed from regulation relay
111
, and power to heating element
5
is interrupted.
Tub Temperature Sensor
It is well known in the spa industry to place a tub temperature sensor inside the spa tub to help monitor and control the temperature of the water inside the spa tub.
FIG. 1
shows temperature probe
112
located inside spa tub
2
. A user of spa
1
can set the desired temperature of the water inside tub
2
to a predetermined level from keypad
200
. Spa controller
7
receives an input from tub temperature probe
112
. When the temperature of the water inside tub
2
reaches the predetermined level, spa controller
7
is programmed to remove the voltage to regulation relay
111
, and power to heating element
5
will be interrupted.
In order to function properly, temperature probe
112
must be correctly mounted to the side of spa tub
2
.
FIG. 2
shows a cut-out perspective view of the side of spa tub
2
. While water is contained in the inside of spa tub
2
, ambient air is allowed to contact the area underneath spa tub skirt
2
A. Hole
150
is drilled into the side of spa tub
2
below the water level for the purpose of mounting a temperature probe.
FIG. 3
shows a side view of spa tub
2
and temperature probe
112
and prior art temperature probe mount assembly
151
.
It is well known in the spa industry to use thermistors to measure the temperature of the water inside the spa tub. The thermistor changes its resistance with changes in temperature. Thermistors typically work over a relatively small temperature range and can be very accurate and precise within that range. An exemplary thermistor temperature probe
112
is made by Gecko Electronics, Inc with offices in San Marcos, Calif. (part no. 9920-400262). It is approximately 2 inches long and ⅜ inches in diameter.
Prior art temperature probe mount assembly
151
is manufactured by Waterway Plastics with offices in Oxnard, Calif. (part no. 400-4360). As shown in
FIG. 3
, temperature probe mount assembly
151
consists of socket
152
, nut
153
, O-ring
154
and rear nut
155
.
FIG. 4
shows temperature probe
112
mounted to the side of spa tub
2
utilizing temperature probe mount assembly
151
. As shown in
FIG. 4
, an ideal distance for the tip of temperature probe
112
to extend beyond the edge of temperature probe mount assembly
151
into the water inside spa tub
2
is approximately ¼ inch. However, this exposes rear end
112
A of temperature probe
112
to ambient air underneath spa tab skirt
2
A. If a spa is located in a cold area, such as at a ski-resort during the winter, the cool air contacting rear end
112
A of temperature probe
112
could cause a signal to be sent to spa controller
7
(
FIG. 1
) that is not representative of the true temperature of the water inside spa tub
2
. This could cause heating element
5
to stay on longer than desired, causing a potential safety hazard to the user of the spa. A prior art solution to the problem of protecting rear end
112
A from ambient cold air is to spray the inside of spa skirt
2
A with foam insulation. However, the foam insulation has been known to deteriorate over time. Or, during maintenance operations, workers have been known to rip the foam insulation out without replacing it when the maintenance is over.
FIG. 5
illustrates another potential problem associated with prior art temperature probe mount assembly
151
. During the installation process, it is possible for temperature probe
112
to be incorrectly installed so that its tip extends too far out into the inside of spa tub
2
. A user of the spa may inadvertently bump into temperature probe
112
and damage it or, by bumping it, cause it to damage or crack temperature probe mount assembly
151
. It is also possible for temperature probe
112
to be pressed so far forward that it is pushed beyond O-ring
154
(
FIG. 3
) causing the seal to break.
Also, while sitting inside the spa, a user may notice that temperature probe
112
is extending too far. He then may decide to press it back it with his finger. By mistake, or due to the possibility that the user may not know the correct distance that temperature probe
112
should extend beyond temperature probe mount assembly
151
, the user could press temperature probe
112
too far so that it is in the position shown in FIG.
6
. In
FIG. 6
, a large portion of rear end
112
A is exposed is exposed to ambient cool air inside spa tub skirt
2
A. The front tip of probe
112
has been pressed in so that
Laflamme Benoit
Ringuet Sylvain
Gecko Electronique, Inc.
Gutierrez Diego
Pruchnic Jr. Stanley J.
Ross John R.
Ross, III John R.
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