Automatic line-reversal pyrometer measures gas temperatures from 2900 degrees to 4500 degrees R. The self-balancing device uses the sodium D-line but replaces the two conventional manual operations of the line-reversal method and can be used by semiskilled personnel

Buchele, D.

English

NASA Technical Reports Server

August 1967	 Brief 67-10268 
NASA TECH BRIEF 
NASA Tech Briefs are issued to summarize specific innovations derived from the U.S. space program, 
to encourage their commercial application. Copies are available to the public at 15 cents each 
from the Clearinghouse for Federal Scientific and Technical Information, Springfield, Virginia 22151. 
Self-Balancing Line-Reversal Pyrometer Automatically

Measures Gas Temperatures 
Hot Gas 
Splitter Plate  
Condensing Lens	
f 
0	 Sodium Compound F_	 Window 
Tungsten Lamp 
Optical Unit'
	
Alinement Lamp	 S2	 I	 Corner Cube Reflector 
	
Photomultiplier	 7	 I 
	
- - - - 
S	 ---Spectroscope Prism 
	
Servomotor	
A^.phfier 
Variable 
Transformer 
A C Line 
Lamp Ammeter 
The problem: 
To develop an automatic line-reversal pyrometer for 
measurement of gas temperatures in the range of 
2900° to 4500 1 R. Conventional line-reversal (sodium 
D-line) pyrometers that have been used for measure-
ment of gas temperatures require critical optical 
alinement of the reversal point by a skilled technician 
to achieve reliable results. 
This document was prepared under the sponsorship of the National 
Aeronautics and Space Administration. Neither the United States 
Government nor any person acting on behalf of the United States
The solution: 
A self-balancing line-reversal pyrometer (using the 
sodium D-line) that replaces the two conventional 
manual operations of the line-reversal method: 
namely, observing the spectral line through a spectro-
scope and controlling the lamp current to produce 
reversal. The self-balancing pyrometer can be used in 
the field by semiskilled personnel.
(continued overleaf) 
Government assumes any liability resulting from the use of the 
information contained in this document, or warrants that such use 
will be free from privately owned rights.
https://ntrs.nasa.gov/search.jsp?R=19670000268 2020-03-11T20:39:20+00:00Z
How it's done: 
The instrument consists of an enclosed optical unit 
alined with a corner-cube reflector; a probe that 
injects a powdered sodium compound into the hot gas 
at an upstream point; and an electrical unit containing 
a self-balancing system, which adjusts the current 
through the tungsten ribbon-filament lamp in the 
optical unit to restore the state of reversal of the 
sodium D-line, and an ammeter which continuously 
monitors the lamp current, related to the gas tempera-
ture by a previous calibration. An alinement lamp 
and small mirror are built into the optical unit to 
enable precise alinement of the optical axes of the 
tungsten lamp and the corner reflector before the 
instrument is used for measuring gas temperatures. 
The spectroscope prism receives light from both the 
hot gas (seeded with an appropriate sodium com-
pound) and the lamp through aperture Si and en-
trance slit S2. Slit S3 vibrates sinusoidally at a 60 Hz 
frequency and is positioned along the continuum (con-
tinuous spectrum from the lamp) to transmit light to 
the photomultiplier from the sodium D- spectral line 
at the slit center position, from a shorter adjacent 
wavelength in the continuum (at one extreme position 
of the slit), and from a longer adjacent wavelength in 
the continuum (at the other extreme position of the 
slit). Flux from the spectral line is compared alter-
nately with flux from the two adjacent wavelengths 
during each vibration cycle of the slit. When the 
spectral line is not at reversal (spectral line brightness 
does not match the continuum brightness), a differ-
ence of light flux between the spectral line and the 
adjacent wavelengths generates a 120 Hz signal. The
signal is transmitted from the photomultiplier to the 
amplifier, servomotor, and variable transformer, 
which then adjusts the tungsten lamp current to 
establish the state of line reversal. At line reversal the 
lamp temperature is uniquely related to the gas tem-
perature when thermal equilibrium exists between 
the gas and the atoms of the injected sodium com-
pound. The lamp calibration data then gives the gas 
temperature in terms of the lamp ammeter reading. 
Notes: 
I. The upper limit of temperature set by the tungsten 
lamp at 4500°R can be extended to 6500°R by use 
of a carbon arc source and absorption wedges to 
control the intensity of the transmitted light. 
2. Inquiries concerning this innovation may be di-
rected to:
Technology Utilization Officer 
Lewis Research Center 
21000 Brookpark Road 
Cleveland, Ohio 44135 
Reference: B67-10268 
Patent status: 
No patent action is contemplated by NASA. 
Source: Donald Buchele 
(Lewis-348) 
Brief 67-10268	 Category 01


Self-balancing line-reversal pyrometer automatically measures gas temperatures

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