New furnace calibrates unknown thermocouple by comparing its electrical output to a reference thermocouple /previously calibrated by optical pyrometry/, as both are heated simultaneously. Thermocouples may be radioactive, thus heat source must be accessible by remote manipulation and inspection measurements. Advantages of furnace operation are cited

Gracey, C. M.

Hoff, R. G.

English

NASA Technical Reports Server

March 1971
	
Brief 71-10046 
ICY co.
AEC-NASA TECH BRIEF 
TES	 Space Nuclear Systems Office 
AEC-NASA Tech Briefs announce new technology derived from the research and development program of the U.S. 
AEC or from AEC-NASA interagency efforts. They are issued to encourage commercial application. Tech Briefs are 
available on a subscription basis from the National Technical Information Service, Springfield, Virginia 22151. Requests 
for individual copies or questions relating to the Tech Brief program may be directed to the Technology Utilization 
Office, NASA, Code KT, Washington, D.C. 20546. 
Inexpensive High-Temperature Furnace for Thermocouple Calibration 
A commercial inert-gas arc torch used in a furnace 
configuration provides an inexpensive solution to 
high-temperature thermocouple calibration problems. 
Thermocouples used in nuclear rocket development are 
Height Adjustment 
Pyrometer 
View Port 
Thermocouples 
(2)
>"
	 f
.Graphite 
Felt 
Molybdenum 
Susceptor Block 
10.16x 6.35 cm 
Tantalum Foil 
Copper Housing 
20.32 x 12.70 cm dia. 
Calibration Furnace 
subjected to temperatures approaching 2755°K 
(4500nF) and must be calibrated periodically at high 
temperatures, under inert atmospheres to prevent con-
tamination and corrosion. Because the thermocouples 
may also be radioactive, the heat source must not only 
be simple but must be accessible by remote manipula-
tors and inspection instruments. Commercial furnaces 
previously used were expensive and only partially 
capable of satisfying the calibration requirements. 
The new furnace calibrates the unknown thermo-
couple by comparing its electrical output to that of a 
reference thermocouple (previously calibrated by 
optical pyrometry), as both are heated simultaneously. 
The thermocouples are mounted in a molybdenum 
"susceptor" block (see fig.) which evenly distributes 
the heat delivered by the 4145°K (7000n17) arc of a 
helium-shielded arc torch mounted on a bracket above 
the furnace. A screw adjustment on the bracket allows 
the torch to be raised or lowered as desired. The sus-
ceptor temperature is monitored through a viewing 
port, using an optical pyrometer. 
Molybdenum is used for the susceptor because of its 
machinability and its ability to withstand the 2755°K 
temperatures indefinitely, with cooling. The block 
is physically supported and electrically grounded 
by three tungsten welding rods, which are in turn con-
nected to the water-cooled copper jacket housing the 
furnace. Three layers of tantalum foil and three layers 
of graphitic felt provide intermediate thermal insula-
tion. The foil blocks radiated heat and prevents the 
formajion of a molybdenum-graphite eutectic which 
would ruin the insulation effects. 
The two boron nitride inserts into which the 
thermocouples are placed provide electrical insulation 
bet'.veen the probes and the outer jacket so that most 
of the current from the arc returns to ground through 
the welding-rod supports rather than through the 
thermocouple sheaths. The inserts are closely fitted to 
minimize gas leakage around the thermocouples and to 
ensure that gas from the torch escapes through the 
viewing port.
(continued overleaf) 
Boron Nitride 
Inserts (2) 
Coolant 
Tubes 
•
Tungsten Welding Rods 
This document was prepared under the sponsorship of the Atomic 
Energy Commission and/or the National Aeronautics and Space 
Administration. Neither the United States Government nor any per-
son acting on behalf of the United States Government assumes any
liability resulting from the use of the information contained in this 
document, or warrants that the use of any information, apparatus, 
method, or process disclosed in this document may not infringe pri-
vately owned rights.
https://ntrs.nasa.gov/search.jsp?R=19710000046 2020-03-17T02:18:27+00:00Z
	Operationally, the furnace has several advantages:
	
Patent status: 
	
the thermocouples are easily inserted; the arc is con-
	 No patent action is contemplated by AEC or NASA.

trolled by a single rotary adjustment; the view of the 
	
optical pyrometer is unobstructed; and the outside of
	
Source: R. G. Hoff and C. M. Gracey of 
	
the furnace remains cool during operation, making
	
Aerojet-General Corp. 
	
manual control possible. Use of tungsten for the sus-
	
under contract to 
	
ceptor block would yield 3310°K (550017). With modi-
	
AEC-NASA Space Nuclear Systems Office 
	
fications, the furnace could be used to test materials
	
(NUC-10372)
for melting or heat treating effects. 
Note: 
Requests for further information may be directed 
to:
Technology Utilization Officer 
AEC-NASA Space Nuclear Systems Office 
U.S. Atomic Energy Commission 
Washington, D. C. 20545 
Reference: B71-10046
is 
Brief 71-10046 Category 03


Inexpensive high-temperature furnace for thermocouple calibration

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