Integral water heater and water temperature sensor

A screwplug type water heater (10) has a heating element (12) immersible in a water heater tank (T) to heat water (L). Electrical terminals (28) on the outer end of the heater connect the heating element into a heater circuit (H) for a control unit (14). The control unit also includes a sensing circuit (S) for the unit to be responsive to water temperature inputs to turn-on the heater to heat water to a desired temperature and maintain it there. A thermistor (16) provides a temperature input to the control circuit. The thermistor is encapsulated in a bracket (32) mounted in, or integrally formed with, the screwplug to sense water temperature. Terminals (36) on the outer end of the heater allow the thermistor to be connected into the control circuit.

CROSS-REFERENCE TO RELATED APPLICATIONS 
Not applicable. 
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
Not applicable. 
BACKGROUND OF THE INVENTION 
This invention relates to heater units for hot water heaters such as found 
in homes, and more particularly, to a water heater assembly with a heater 
element and temperature sensor installed with the heater unit. In one 
embodiment, the temperature sensor device is integrally formed with the 
unit. In another embodiment the sensor can be removed and replaced without 
having to remove and reinstall the heater unit. 
Water heaters have an associated control system by which water temperature 
is monitored so the water can be heated to a desired temperature as 
efficiently as possible, and then maintained at that temperature. A 
thermistor, or other temperature responsive sensing device, is used to 
provide an input to the control system representative of water 
temperature. Heretofore, location of the sensing element has been separate 
from a water heater, and the sensor location has not always been readily 
accessible so the sensor could be readily replaced. Combining a 
temperature sensor with a water heater unit therefore has certain 
advantages of cost, ease of installation, and maintenance or replacement. 
Further, there are certain advantages in making, the assembly an integral 
assembly. 
BRIEF SUMMARY OF THE INVENTION 
Among the several objects of the present invention may be noted the 
provision of a water heater assembly including a heater element in 
combination with a temperature sensor such as a thermistor; 
the provision of such an assembly in which the temperature sensor is 
readily installed with the water heater element as an integral unit; 
the provision of such a temperature sensor to be readily installable and 
removable from the heater assembly, this being accomplished without the 
entire heater assembly having to be removed and reinstalled; 
the provision of such an assembly in which the thermistor is formed as a 
molded part having a snap-fit insertion into a base portion of the 
assembly, the thermistor further including male quick connect pins for 
ready connection into temperature sensing circuitry of the control system; 
the provision of such a combination in which the value of the thermistor 
rating is variable in accordance with the requirements of the electronic 
control circuitry to which it is attached; 
the provision of such a combination having an increased sensitivity to the 
water temperature to effect better temperature control; 
the provision of such a combination to employ an off-center heating element 
mounting configuration so to accommodate the temperature sensor; 
the provision of such a combination in which the sensing device is located 
at the end of a bracket tongue extending from a connector end of the 
sensor element into a cavity formed in a screwplug portion of the sensor 
to position the sensor in, or adjacent to, a threaded portion of the 
screwplug; 
the provision of such an assembly to reliably provide accurate water 
temperature measurements to the control system; and, 
the provision of such a combination to be easily installed and removed and 
to provide a low cost water temperature measurement capability. 
In accordance with the invention, generally stated, a water heater is a 
screwplug type assembly having a heating element immersible in the water 
in a water tank to heat the water to a desired temperature. Electrical 
terminals on an outer end of the assembly allow the heating element to be 
connected into a heater circuit. A control circuit responsive to water 
temperature controls operation of the heater to heat the water. An input 
to the control circuit is provided by a thermistor or other temperature 
sensor installed in an outer end portion of the heater assembly. The 
thermistor is either integrally formed with the water heater; or, can be a 
separate element readily inserted into the outer end of the assembly. The 
thermistor is encapsulated in a support sized to extend from the outer end 
of the heater into the screwplug portion of the heater, or adjacent 
thereto, for the thermistor to sense water temperature. Terminals on the 
outer end of the assembly allow the thermistor to be connected into the 
control circuit Other objects and features will be in part apparent and in 
part pointed out hereinafter.

Corresponding reference characters indicate corresponding parts throughout 
the drawings. 
DETAILED DESCRIPTION OF THE INVENTION 
Referring to the drawings, a tank T holds a liquid such as water. A 
threaded opening O is formed in a sidewall W of the tank for installation 
of an immersion type water heater 10. The heater includes a 
resistance-type heating element 12 of conventional design electrically 
connected to a control unit 14. The control unit is responsive, inter 
alia, to inputs from a temperature sensor 16, such as a thermistor 
connected in a sensing circuit S of the control unit, to supply electrical 
power to the heating element via a heater circuit H. The heating element 
heats water in the tank to a desired temperature (e.g., 140.degree. F.) 
and maintains the water temperature at that level. 
Referring to FIG. 3, heater 10 comprises three main elements; heating 
element 12, a mounting means 18 for installing the heater assembly in the 
tank sidewall, and a housing 20 attached the mounting means and located on 
the outside of the tank. Mounting means 18, comprises a screwplug having a 
sidewall matingly threaded with opening O to screw the heater into place. 
Heater element 12, which is generally U-shaped has legs 12a, 12b extending 
into housing 20 through the screwplug. A hexagonal flange 22 formed at the 
outer end of the screwplug is useful in installing and replacing the 
heater. 
Housing 20 is a generally circular shaped housing with a truncated or 
flattened section 20a as shown in FIG. 4. The housing includes a Y-shaped 
divider 24 formed on an outer end face 26 of the housing. The divider has 
two arms 24a, 24b of equal length, and a leg 24c shorter than the arms. 
The dividers divide the outer face of housing 20 into three separate 
segments. Respective segments defined by divider sections 24a-24c, and 
24b-24c, have electrical terminals 28 for the respective ends of heater 
element 10 to be connected in the heating circuit of control unit 14. 
Referring to FIG. 11, it will be seen that the legs of the heater element 
extend through longitudinal channels 30 in the screwplug. It will further 
be seen that, unlike convention-cheaters, the channels are offcenter of 
the screwplug. This is to accommodate installation of temperature sensor 
16 in the heater assembly. 
In FIGS. 5-7, a first embodiment of the temperature sensor includes the 
thermistor 16 encapsulated in a bracket 32. Specifically, the bracket 
either fits in an oval shaped opening 33 formed in the outer end of the 
housing; or, the bracket/thermistor assembly is integrally formed with the 
housing. Regardless, bracket 32 includes a tongue 34. The thermistor is 
encapsulated at the inner end of the tongue (when the bracket is installed 
in the housing). Electrical leads for the thermistor are also encapsulated 
in the tongue and extend through the length of the tongue to electrical 
terminals 36 which project from an outer end 38 of the bracket These 
terminals are quick disconnect terminals and allow the thermistor to be 
connected in sensing circuit S of the control unit. For heater control 
purposes, it is important that the thermistor be positioned in a 
temperature sensing relationship with the water. Accordingly, the length 
of tongue 34 is such that the thermistor is located adjacent the inner end 
of the screwplug (i.e., at the level of flange 22 when the heater is 
installed. Or, as shown in FIG. 12, a recess or blind bore 40 extends into 
the body of the screwplug, from an inner end of the screwplug, with the 
inner end of tongue 34, fitting in this recess. As noted, bracket 32 is 
either integrally formed with the housing, or it can, be a separate piece. 
The bracket 32 of FIGS. 5-7 is for a separate piece. As shown therein, at 
the outer end of the bracket is an oval shaped flange 42 sized to be fit 
in opening 33 in the outer end of housing 20. Inwardly of this flange, at 
the inner end of tongue 34, a circumferential seal 44 is formed. The seal 
has a central section 44a, and upper and lower beveled sections 44b, 44c. 
When installed, the thermistor is readily replaced by disconnecting wiring 
leads from the terminals 36 and pulling the bracket/thermistor assembly 
out of housing 20. A new assembly is the inserted in opening 33 and the 
wiring leads reconnected to the terminals of the nests assembly. 
Referring to FIGS. 8-10, another embodiment of the bracket is indicated 
generally 52. Now, two separate thermistors 16a, 16b are encapsulated in 
the bracket which, again, either fits in the oval shaped opening 33 in the 
outer end of housing 20; or is integrally formed with tire housing. 
Bracket 52 includes a tongue 54 and the thermistors are encapsulated in 
the inner end of the tongue. Electrical leads for each thermistor are also 
encapsulated in the tongue and extend through the length of the tongue 
respective sets of electrical terminals 56a, 56b, and 56c, 56d all of 
project from an outer end 58 of the bracket. Again, the terminals allow 
the thermistors to be connected in sensing circuit S of control unit 14. 
Also again, the length of tongue 54 is such that the thermistors are 
located adjacent the inner end of the screwplug, or in the recess 40 in 
the body of the screwplug. At the outer end of the bracket is an oval 
shaped flange 62 sized to fit in opening 33, and inwardly of this flange 
is a circumferential seal 64 having a central section 64a, and upper and 
lower beveled sections 64b, 64c. Installation and removal of bracket 52, 
or the housing/bracket assembly is as above described. 
What has been described is a water heater assembly in which a thermistor 
for sensing water temperature is incorporated. The thermistor is 
encapsulated at one end of a housing which can be integrally formed with a 
housing portion of the heater, or which is readily installed and removed 
from the housing. The thermistor extends either into, or is positioned 
adjacent the outer end of the screwplug so to be in a heat sensing 
relationship with the water. The thermistor is electrically connected into 
the sensing circuit of a control unit which operates the water heater to 
heat the water to a desired temperature and maintain it there. In a second 
embodiment of the heater assembly, a pair of thermistors are employed with 
both thermistors being encapsulated and located in the housing to sense 
water temperature. 
In view of the foregoing, it will be seen that the several objects of the 
invention are achieved and other advantageous results are obtained. 
As various changes could be made in the above constructions without 
departing from the scope of the invention, it is intended that all matter 
contained in the above description or shown in the accompanying drawings 
shall be interpreted as illustrative and not in a limiting sense.