Data from record tracks of all accelerometers is injected simultaneously into electronic circuits which convert inputs into single, composite graphical representation. Three adequate methods of processing data: peak acceleration at a frequency, average of all channels, and quad-mean of all channels

Reddeman, E. E.

English

NASA Technical Reports Server

March 1973	 B73-10139 
•	 NASA TECH BRIEF 
NASA Pasadena Office	 -dr 
NASA Tech Briefs announce new technology derived from the U.S. space program. 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. 
Simultaneous Processing of Vibration Test Data 
Specifications for conducting vibration qualification 
tests on large objects (e.g., aircraft structures) require 
that determination be made of the forces actually ap-
plied to the test object by analyzing recordings of 
the output of sensors disposed either on the test object 
or test fixture to which the. object is attached. Typ-
ically, recordings of the outputs of sensors, such as 
accelerometers, are made on multichannel magnetic 
tapes, utilizing one channel for each of the sensors 
and one for the frequency spectrum. 
Generally, data are transferred from each of the 
tracks in sequence and transcribed by means of an 
X-Y recorder to obtain a visible record of the forces 
sensed by each accelerometer. As each channel out-
put is transcribed, it is superposed on one X-Y 
recording to form a master graphical representation 
of the test results. Considerable time is required to 
produce the master record because each channel must 
be recorded separately, but in recent work it has been 
found possible to reduce the time required by inject- 
ing data from the record tracks of all of the acceler-
ometers simultaneously into electronic circuits which 
convert inputs into a single, composite graphical rep-
resentation. Three methods of processing the data 
have been found adequate. 
Method I: Peak acceleration at a frequency. The ac 
waveforms , from analog FM-recorded tapes of eight 
control channels are played into an eight-channel 
detector-averager which converts the ac waveform 
into a proportional dc voltage level. Each of the eight 
channels is patched into an analog computer board 
which provides buffering and amplification. The chan-
nels are then fed into a circuit of eight cascaded com-
parator relays; sensitivity of the relays is set so that a 
difference of 10 mV between channels will trip a relay 
and direct the higher voltage to the next comparator 
set. The output of the last comparator is the highest 
voltage present in the eight input channels. Final 
scaling is performed by an output amplifier which 
provides suitable voltage inputs to the Y axis of an 
X-Y recorder for plotting the output. The X axis of 
the X-Y recorder represents the shaker sweep fre-
quency as recorded on a separate tape channel and 
converted to a dc voltage by a frequency-to-voltage 
meter. 
Method II: Average of all channels. To determine 
the average of the inputs from the control channels 
with respect to frequency, data from the analog con-
trol channels are fed into detector-averagers and con-
verted into equivalent dc levels;' each channel input 
is brought into the analog computer via a buffer ampli-
fier. The individual voltages are summed and divided 
by the number of channels to determine the average 
value; the output is also plotted by an X-Y recorder. 
Method III: Quad-mean of all channels. The inputs 
from eight control channels are detected and then 
patched to an analog program board. Inputs are again 
buffered and, in this case, the individual voltages 
with respect to frequency are squared, summed, di-
vided by the number of channels, and the square root 
is then taken. The output is plotted on an X-Y recorder. 
The average and the quad-mean of eight channels 
are usually plotted simultaneously during a single 
pass of the analog tape. The analog computer inputs 
are paralleled to perform the calculations and to pro-
vide both average and quad-mean outputs for separate 
(continued overleaf) 
This document was prepared under the sponsorship of the National 	 Government assumes any liability resulting from the use of the 
Aeronautics and Space Administration. Neither the United States 	 information contained in this document, or warrants that such use 
Government nor any person acting on behalf of the United States	 will be free from privately owned rights.
https://ntrs.nasa.gov/search.jsp?R=19730000139 2020-03-17T07:08:33+00:00Z
plotters. Plots can be scaled in engineering units for 
peak, rms, or average terms. Plots can also be dis-
played logarithmically on the Y axis. 
Note: 
Requests for further information may be directed 
to:
Technology Utilization Officer 
NASA Pasadena Office 
4800 Oak Grove Drive 
Pasadena, California 91103 
Reference: TSP 73-10139
Patent status: 
NASA has decided not to apply for a patent. 
Source: Eugene E. Reddeman of 
Caltech/JPL 
under contract to 
NASA Pasadena Office 
(NPO-11616)
1)0 
B73-10139	 Category 01


Simultaneous processing of vibration test data

Abstract

Similar works

Full text

Available Versions

NASA Technical Reports Server