The amount of solar radiation incident on a specially prepared bimetallic strip is simply and reliably controlled by a light valve. This device is valuable for systems requiring temperature regulation

Lonborg, J. O.

Randall, J. C.

English

NASA Technical Reports Server

Insulated Mounting 
Bimetallic Strip
Light Valve 
Black Side 
March 1965
	
Brief 65-10061 
NASA TECH BRIEF 
NASA Tech Briefs are issued by the Technology. Utilization Division to summarize specific 
technical innovations derived from the space program. Copies are available to the public from 
the Clearinghouse for Federal Scientific and Technical Information, Springfield, Virginia, 22151. 
Simple Control Device Senses Solar Position 
The problem: Many systems are affected by the 
presence of solar radiation. In those systems adversely 
affected by such radiation beyond a certain level, it is 
necessary to adjust or shield equipment as the relative 
position of the sun changes. The amount of heat and 
light energy received by an area is a function of the 
angle of incidence of the sun's rays on that area. A 
simple and reliable device is needed to provide control 
actuations as a function of solar incidence. 
The solution: A light valve that controls the 
amount of solar radiation incident on a specially pre-
pared bimetallic strip. The axis of the light valve is 
oriented in the direction of normal solar motion as it 
relates to the system or equipment involved. Curva-
ture of the bimetallic strip is a function of angle of 
solar incidence and may be used to actuate control 
mechanisms.
How it's done: The light valve consists of two sec-
tions, resembling venetian blinds, with transverse slots 
and slats of equal width. The two sections are stacked 
with axes parallel and are separated so as to provide 
25% transmission of radiation at normal incidence. 
Transmission typically varies linearly from 0% to 50% 
with small deviations from normal incidence. The bi-
metallic strip is prepared with one black side and one 
highly polished side. The black, high-absorptivity side 
is faced toward the light valve and the polished, low-
emissivity side is faced away, the whole being ther-
mally insulated from its mounting. Angular change in 
position of the bimetallic strip is a function of the 
characteristics of the strip and light valve, the position 
of the sun, and time. 
The important characteristics of the particular con-
figuration used are its gain and time constant which 
are approximately 1/6 and 2500 seconds, respectively, 
(continued ovcr(eal( 
This document was prepared under the sponsorship of the National 
Aeronautics and Space Administration. Neither the United States Govern-
ment, nor NASA, nor any person acting on behalf of NASA: A. Makes 
any warranty or representation, express or implied, with respect to the 
accuracy, completeness, or usefulness of the information contained in
this document, or that the use of any information, apparatus, method, 
or process disclosed in this document may not infringe privately-owned 
rights; or B. Assumes any liabilities with respect to the use of, or for 
damages resulting from the use of, any information, apparatus, method, 
or process disclosed in this document.
https://ntrs.nasa.gov/search.jsp?R=19650000060 2020-03-11T17:18:04+00:00Z
with the solar intensity at earth distance from the sun. 
Although time constant is fairly easily understood, the 
concept of gain may need some clarification. Gain is 
the ratio of the steady state change in the angular 
movement at the tip of the bimetallic strip to the 
change in sun/actuator angle. 
Notes: 
1. Sensitivity and dynamic range can be adjusted by 
varying the slot-to-slat ratio and the separation 
distance between the two venetian blind sections. 
Characteristics such as gain and time constant can 
be adjusted by the selection of different sensitivity 
bimetallic elements or merely changing their phys-
ical size. 
This device may find application where tempera-
tures must be maintained under varying amounts 
of incident sunlight, such as greenhouses or mod-
ern office buildings with their vast expanses of sin-
gle pane glass. It should be pointed out, however,
that the device described was designed to operate 
in a vacuum; thermal isolation of the bimetallic 
strip is critical to its operation. Convection losses 
caused by a surrounding atmosphere may be signi-
ficant and should be investigated further if this 
type of application is planned. 
4. Inquiries concerning this invention may be directed 
to:
Technology Utilization Officer 
Jet Propulsion Laboratory 
4800 Oak Grove Drive 
Pasadena, California, 91103 
Reference: B65-10061 
Patent status: NASA encourages the immediate 
commercial use of this invention. Inquiries about ob-
taining rights for its commercial use may be made to 
NASA, Code AGP, Washington, D.C.. 20546. 
Source: James 0. Lonborg and 
James C. Randall 
(J PL-638) 
Brief 65-10061
	
Category No. 01


Simple control device senses solar position

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