Thermocouple, multiple junction reference oven

An improved oven (10) for maintaining the junctions of a plurality of reference thermocouples at a common and contant temperature. The oven (10) is characterized by a cylindrical body (12) defining a heat sink having an axially extended cylindrical cavity (14), a singularized heating element comprising a unitary cylindrical heating element consisting of a resistence heating coil (20) wound about the surface of a metallic spool (18) having an axial bore (22) defined therein and seated in the cavity, an annular array of radially extended bores (30) defined in the cylindrical body (12) and a plurality of reference thermocouple junctions (32) seated in the bores in uniformly spaced relation with the heating element, and a temperature sensing device (28) seated in the axial bore for detecting temperature changes as they occur in the spool and circuit (46) for applying a voltage across the coil in response to detected drops in temperatures of the spool.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The invention generally relates to a system including remotely related 
thermocouples employed in detecting and measuring temperatures by 
providing electrical output signals to be compared with the electrical 
output signals derived from reference thermocouples maintained at known 
temperatures, and more particularly to an improved oven for maintaining 
the junctions of a plurality of reference thermocouples at a common and 
constant temperature. 
2. Description of the Prior Art 
As is well known by those familiar with temperature measuring procedures 
commonly employed in industrial operations, such as are employed in the 
aerospace industry, thermocouples often are used to measure temperatures 
because of their relatively low cost and high reliability. Unfortunately, 
in order to provide for accurate measurements of temperature utilizing 
such devices, however, it is necessary to provide in combination therewith 
reference thermocouples maintained at constant temperatures throughout the 
duration of the temperature measuring operation in which the devices are 
employed. 
Numerous devices have been proposed for use in heating reference 
thermocouples and many have been employed for this purpose. For example, 
see U.S. Pat. Nos. 2,559,571; 3,069,909; 3,345,540; and 3,648,523 which 
generally typify devices utilized in simultaneously heating the junctions 
of a multiplicity of reference thermocouples, herein referred to as a 
mulitple junction reference oven, or simply oven. 
Heretofore, it has been common practice to provide in a multiple junction 
reference oven individual reference junctions displaced at uneven 
distances from a common source of heat. Alternatively, multiple heating 
elements are sometimes employed in heating the junctions. Such 
arrangements, of course, inherently result in temperature gradients being 
established between the various reference thermocouples with an attendent 
necessity that the gradients be, in some manner, taken into account or 
accommodated. Often, such requires the use of ovens of increased weight, 
size and complexity. 
Moreover, in certain applications, such as in airborne data acquisition 
systems used in conducting flight tests, a relatively large number of 
temperature sensing thermocouples are required. Because of the inherent 
bulk and weight of the ovens of the prior art, as well as power 
requirements, limitations frequently are imposed on the number of 
reference junctions which can be accommodated, with an attendant reduction 
in the number of temperature sensing thermocouples which can be made 
available for a given test flight or similar operation. 
It should therefore be apparent that there currently exists a need for a 
small, economic, and lightweight oven having capabilities for 
accommodating large numbers of thermocouple junctions, without temperature 
gradients being established between the various junctions employed to 
provide standard signals to which signals derived from temperature sensing 
thermocouples are compared. 
It is therefore the general purpose of the instant invention to provide an 
improved oven for use in maintaining the junctions of reference 
thermocouples at constant temperatures in combination with a temperature 
sensing sytem characterized by a multiplicity of remotely related 
temperature sensing thermocouples. 
OBJECTS AND SUMMARY OF THE INVENTION 
It is an object of the instant invention to provide an improved oven for 
simultaneously controlling the temperature of a multiplicity of the 
junctions for reference thermocouples. 
It is another object to provide an improved, multiple junction reference 
oven having a capability for accommodating an increased number of 
reference thermocouple junctions. 
It is another object to provide a multiple junction reference oven 
particularly suited for maintaining an increased number of reference 
thermocouples at uniform temperatures. 
It is another object to provide an improved, relatively small, lightweight, 
economical oven having enhanced capabilities for accommodating increased 
numbers of junctions for reference thermocouples, without an attendant 
reduction in operational accuracy. 
These and other objects and advantages are achieved through a provision of 
an oven for heating reference thermocouples, said oven being characterized 
by a cylindrical body defining a heat sink having an axially extended 
cylindrical cavity, a singularized heating element comprising an unitary 
cylindrical heating element consisting of a resistance heating coil wound 
about the surface of a metallic spool having an axial bore defined therein 
and seated in said cavity, an annular array of radially extended bores 
defined in the cylindrical body and a plurality of reference thermocouple 
junctions seated in the bores in uniformly spaced relation with the 
heating element, and a temperature sensing device seated in the axial bore 
for detecting temperature changes as they occur in the spool and a circuit 
connected to the sensing device for applying a voltage across the coil in 
response to detected drops in the temperatures of the spool, as will 
become more readily apparent by reference to the following description in 
claims in light of the accompanying drawings.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
Referring now to the drawings, with more particularity, wherein like 
reference characters designate like or corresponding parts throughout the 
several views, there is shown in FIG. 1 an oven, generally designated 10, 
which embodies the principles of the instant invention. 
The oven 10 includes a cylindrical wall 12, formed of a good thermal 
conductive material, such as brass or the like. Within the wall 12 there 
is provided a cylindrical cavity 14 having a substantially uniform 
diameter. The purpose of the cavity 14 is to receive in supporting 
relation an electrical resistance heater, generally designated 16. The 
heater 16 includes a spool 18, also formed of brass or similar material, 
about which is wound a cylindrical coil 20. As a practical matter, the 
coil is formed of a suitable wire and comprises a resistance heating 
element, in a manner fully understood by those familiar with such devices. 
It is important here to note that the spool 18 also includes an axial 
cavity 22 which serves to receive therein a temperature sensing pad 24. 
Preferably, the temperature sensing pad 24 is seated in a cap 26, provided 
as a closure member for the cavity 14. 
As shown, the temperature sensing pad 24 includes a temperature sensing 
element 28 which, preferably, comprises a thermocouple. However, it is to 
be understood that any suitable temperature sensing device may be employed 
in lieu of the thermocouple depicted in the drawings. Moreover, it is to 
be understood that the cap 26 also is fabricated from a good thermal 
conductive material similar to that from which the wall 12 and spool 18 
are fabricated. Consequently, the temperature of the spool 18 closely 
follows the temperature of the wall 12 and, because of the proximity and 
conductivity of the materials from which the spool and cap are fabricated, 
the sensing element 28 readily detects changes occuring in the temperature 
of the spool 18, and therefore, the temperature of the oven 10. 
The wall 12 is provided with a large number of bores 30 extended radially 
into the wall 12. Preferably, the bores extend to a depth of approximately 
one-half the thickness of the wall 12 and collectively comprise an annular 
array circumscribing the external surface of the wall 12. Within each bore 
30 there is seated a junction 32 of a reference thermocouple. Because of 
the cylindrical shape of the wall 12, the cavity 14, and the heater 16, a 
positioning of a large number of reference thermocouple junctions at a 
common distance from a common coil 20 is accommodated. Thus the 
temperature to which the thermocoupled junctions 32 are heated by an 
outwardly flowing thermal flux, comprises a temperature which is 
substantially common to all the junctions. Hence, the junctions 32 are 
heated with substantially no temperature gradient being established 
therebetween. 
It is to be understood that the thermocouple junctions 32 are supported 
within the bores 30 by any suitable means, including a use of adhesives 
including epoxy and the like. 
Referring for a moment to FIG. 4, there is depicted, for exemplary 
purposes, a temperature measuring circuit within which the oven 10 is 
connected. It can be seen that this circuit includes a junction 34 for a 
temperature sensing thermocouple. This junction is connected to a pair of 
junctions 32 for a pair of reference thermocouples through leads 36 and 
38. As shown, the lead 36 is formed of chromel while the lead 38 is formed 
of alumel. Other types of thermocouple wire available can also be used. 
The leads 36 and 38, in turn, are connected at junction 32 with copper 
leads 40 and 42 for thus forming the thermocouple junctions 32 within the 
bores 30. The leads 40 and 42 are connected across a suitable volt meter, 
designated 44, for purposes fully understood by those familiar with the 
art. 
Additionally, the coil 20 is connected via a suitable control circuit 46 to 
a suitable voltage source, designated 48. In practice, the control circuit 
46 is connected to the sensing element 28 by leads 50 in order that the 
circuit between the voltage source 48 and the coil 20 may be opened and 
closed in response to electrical signals derived from the sensing element 
28, generated in response to temperature changes occuring in the spool 18. 
Since the details of the circuit shown in FIG. 4 form no part of the 
hereinafter claimed invention, and, further since the design and 
construction of the circuit is well within the skill of the art, a 
detailed description of the circuit is omitted in the interest of brevity. 
It suffices to understand that the output signal received from the 
thermocouple junction 34 is applied across the volt meter 44 via the 
thermocouple junctions 32, and that the temperature of the device 10 is 
controlled by the sensing device 28, the output of which initiates an 
opening and closing of the circuit 46 for selectively applying a voltage 
across the coil 20 in response to detected temperature changes occuring in 
the device. 
The wall 12 of the over 10, in practice functions as a heat sink within 
which the reference thermocouple junctions 32 are seated in close 
proximity with the coil 20. As is well known, the direction of transfer of 
heat is always in a direction from hot to cold and the rate of 
transference is, for small differences, directly proportional to the 
differences in temperature. Hence, the flow of thermal flux from the coil 
20 to the thermocouple junctions 32 will be substantially uniform, for 
most operational environments. Thus gradient between the junctions are 
substantially avoided during the operation of the oven 10. Moreover, the 
cylindrical shape of the wall 12, of course, makes it possible to 
accommodate large numbers of reference junctions without increasing the 
size, weight, or complexity of the oven, while the inclusion of the 
temperature sensing thermocouple 28 in close proximity with the spool 18 
tends to assure early detection of changes in temperature occuring within 
the oven 10 so that corrective measures may be expedited. 
Hence, in view of the foregoing, it is believed to be apparent that the 
instant invention provides a practical solution to many of the various 
problems heretofore encountered by those attempting to accommodate a large 
number of reference junctions, while utilizing a single oven.