Digital data acquisition system records steady state and dynamic data of bearing and shaft displacement. Elliptical orbits formed can be reconstructed and the data reduced automatically. System also reads pressures, temperatures, flows, and torque during any one data scan

Rossbach, R. J.

English

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NASA TECH BRIEF 
.
Displacement	 Detectors Sensors 
Bearing Force
Svnchronousf	 I	 I	 I Digital Filter	 Phase I	 WI Data 
	
Meter I	 I System 
October 1970	 Brief 70-10503 
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 progam may be directed to the Tech-
nology Utilization Division, NASA, Code UT, Washington, D.C. 20546. 
New Data Acquisition System Records Bearing Measurements Directly 
Shaft Displacement 	 Average 
Level 
Detector 
Switch 
I—	 I Switch I 	Charge	 I 
I	 I 1j AmplifiedJ 
Load Cells 
1 Tooth 
Gear 
QticJ Pulse 0Synchronous 
kup 	Sine Wave Converter I Converter	 I I
Peak-to
Peak
Detector 
A digital data acquisition system has been developed 
that facilitates the recording of steady state and 
dynamic data of bearing and shaft displacement. 
Conventionally, signals from the displacement 
sensors in the test apparatus are displayed on oscil-
loscopes; the displays are photographed, and dis-
placement measurements are made by hand from the 
photographs. Alternatively, the signals are recorded 
on a multichannel tape recorder, and either played 
back on an oscilloscope and photographed, or printed
out permanently on a high-response strip recorder. 
These methods require a considerable amount of time 
and manual labor to obtain digital data. The new 
acquisition system records the measurements directly 
in digital form in such a way that the elliptical orbits 
formed can be reconstructed and the data can be re-
duced automatically. 
As shown in the figure, readings are obtained by 
the digital data acquisition system from displacement 
sensors and load cells. To read the equilibrium posi-
(continued overleaf) 
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tion of the test shaft, signals from the displacement 
sensors are switched to the average-level detector and 
then into the readout portion of the digital data ac-
quisition system. The average-level detector receives 
the sinusoidal signal from the displacement sensor and 
electronically measures the absolute distance from a 
zero reference point to a reading midway between the 
peak and trough on the sine wave. 
To obtain the orbit size of a particular test point, 
displacement sensor signals are switched to the peak-
to-peak detector and then on to the digital data acqui-
sition system. The peak-to-peak detector electronically 
measures the distance between the peak and the trough 
of the sinusoidal wave set up by the displacement 
sensor. 
The dynamic forces can be read by a series of 
programmed switches which send the load cell signals 
through a charge amplifier, through one channel of a 
synchronous, filter and through the peak-to-peak de-
tector. The synchronous filter is dual-channelled and 
is automatically set to the frequency corresponding 
to the rotative speed of the test. In order to obtain 
the phase angles between the unbalance force and 
either a displacement or a force, a phase meter is 
connected to the digital data acquisition system. A 
single-tooth gear on the test shaft actuates a magnetic 
pickup once each revolution, and this pulse is con-
verted into a sine wave in a pulse-to-sine converter. 
The converter causes the synchronous filter to operate 
at the rotative speed of the test shaft. The signal from 
the pulse-to-sine converter goes through one channel 
of the synchronous filter and into one channel of
the phase meter. Either a displacement or a force signal 
enters the second channel of the synchronous filter 
and the second channel of the phase meter. Thus, 
the phase meter reads the angle of any displacement 
or force signal with respect to the unbalance of the 
test bearing shaft, and sends the signal to the digital 
data acquisition system. 
Notes: 
1. In addition to the dynamic measurements, pres-
sures, temperatures, flows, torque, and steady load 
are read by the digital data acquisition system dur-
ing any one scan of the data. 
2. The system can handle 600 pairs of leads and can 
read instruments at the rate of three per second. 
Readouts can be obtained in the form of punched 
and/or printed tape. 
3. No additional documentation is available. Specific 
questions, however, may be directed to: 
Technology Utilization Officer 
Lewis Research Center 
21000 Brookpark Road 
Cleveland, Ohio 44135 
Reference: B70-10503 
Patent status: 
No patent action is contemplated by NASA. 
Source: R.J. Rossbach of 
General Electric Company 
under contract to 
Lewis Research Center 
'(LEW-10510)
S 
S 
Brief 70-10503
	 Category 06,09 b


New data acquisition system records bearing measurements directly

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