Computer program simplifies and clarifies random noise vibration test results. It also varies PSD test specifications, sets up automatic equalization equipment, and calculates an exact accleration level for the random noise prior to the test

Chapman, C. P.

English

NASA Technical Reports Server

June 1967	 Brief 67-10160 
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. 
A Power-Spectral-Density Computer Program 
The problem: 
When an engineer receives a random-noise test 
specification in the form of a PSD (Power-Spectral-
Density) sketch on log—log coordinates, he may spend 
several hours or days on slide rule calculations to 
verify and interpret the data. A faster method for 
verification and interpretation was needed. A general 
computer program was required that would: (1) be 
easy to use; (2) give accurate results for any random-
noise test specification without requiring modification 
other than changing data cards; (3) have an easy-to-
read output; and (4) be self-explanatory. 
The solution: 
A computer program in which random-noise vibra-
tion test results can be simplified and made more 
meaningful for the test requester. The program can 
also be used to verify PSD test specifications, and 
set up automatic equalization equipment. An exact 
acceleration level for the shaped random noise can 
be calculated prior to the test. 
How it's done: 
Spectra ratios appear to simplify the interpretation 
of the test results; however, to synthesize a meaningful 
spectra ratio, it is necessary to have the exact accelera-
tion densities of the ideal PSD spectrum for the 
vibration test at small frequency increments across 
the PSD spectrum. Spectra ratios are obtained when 
the ideal g2/cps is ratioed against the vibration test 
92/cps. The results can be expressed in decibels as: 
10 log10 Xratio. 
The program is written in three segments. The first 
segment, labeled $IBFTC MAIN, reads the data cards
into the computer and prints out the results of the 
calculations. The calculations for acceleration density 
are performed in the second segment, labeled $IBFTC 
SUBPSD. This segment is a subprogram called SUB-
ROUTINE PWR. 
The third segment, labeled $IBFTC RMS, calcu-
lates the area under each slope ( g2rms), then sums 
each area and takes the square root of the sum to 
obtain the total acceleration Grms TOTAL. This is 
performed in a subprogram called SUBROUTINE 
GRMS. 
To use the program, it is only necessary to under-
stand what the variables are and how to represent 
them by numbers on card or code form sheet. There 
is one data card for each slope of the PSD specifica-
tion, including zero slopes. 
Notes: 
1. Machine requirements are an IBM 7090/94 com-
puter system. 
2. Fortran IV was the programming language used. 
3. Inquiries concerning this innovation may be di-
rected to:
COSMIC 
Computer Center 
University of Georgia 
Athens, Georgia 30601 
Reference: B67-10160 
Patent status: 
No patent action is contemplated by NASA. 
Source: C. P. Chapman 
Jet Propulsion Laboratory 
(NPO-10126) 
Category 01 
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
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=19670000160 2020-03-11T20:47:48+00:00Z


A power-spectral-density computer program

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