Drucella Andersen
Headquarters, Washington, D.C.                                                 
January 5, 1993
(Phone:  202/453-8613)

Nancy Lovato
Ames-Dryden Flight Research Facility, Edwards, Calif.
(Phone:  805/258-3448)


RELEASE:  93-002

NASA INVENTION YIELDS BETTER, FASTER STRESS MEASUREMENTS

     A NASA engineer has developed an idea that could 
revolutionize the way engineers measure strains and stresses on 
products as varied as cars, planes and nuclear reactors.

     Karl Anderson at NASA's Ames-Dryden Flight Research Facility, 
Edwards, Calif., has invented a method to prevent errors caused by 
temperature changes in the wires that connect instruments, called 
strain gages, to recording devices.  Anderson's method uses a 
circuit called a "constant current loop" that produces more 
accurate data while using smaller and sometimes fewer wires. 

     "I had been aware of the problem since coming to NASA in 
1964," said Anderson.  "About a year ago, I came up with a 
different point of view and was able to find a practical 
solution."

     Researchers use strain gages to do structural tests on new 
products.  The common testing method uses a wiring system called 
the "Wheatstone bridge" that has been employed for almost 150 
years.  However, thermal changes in the wires can result in errors 
when specimen temperatures vary greatly.  

     Anderson's new constant current loop circuit suppresses 
unwanted effects from the lead wires and records only the correct 
strain and stress data.  It should produce great cost and time 
savings because engineers now can get valid measurements easily in 
situations where earlier tests had to be repeated and averaged to 
get accurate readings.

     "The constant current loop will tremendously benefit the 
measurement world that relies on electrical resistance to show 
what is going on," said Anderson.
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     NASA has applied for patents on the innovation.  Anderson 
will present the new constant current method for strain gage 
signal conditioning and test results at a Western Regional Strain 
Gage Committee meeting in Pasadena, Calif., in February and at the 
International Instrumentation Symposium in Albuquerque, N.M., in 
May.

     NASA Technical Memorandum 104260, which details Anderson's 
research
results, is available from the National Technical Information 
Service, 5285 Port Royal Road, Springfield, Va. 22161.

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