Atec Labworks-SC-121 - Manual (Page 3)

Analog outputs make recording or plotting test profiles easy.
2 Channel Average Control. When large test
articles must be tested beyond their fundamental
resonance frequency, an over test condition can
occur where the control accelerometer is physi-
cally located at a resonance node. For this situation
and others that would benefit from a sine test
based on control of the average of two accelera-
tions, the SC-121 has average control capability.
Sine signals cannot be simply combined to form
an average acceleration because of phase coher-
ence. The detected scalar sine amplitudes must
be used, but are not normally available from sine
analysis instrumentation. The SC-121 solves this
problem by providing for control on the average
acceleration of both of its channels.
Calibration or Relative Acceleration.
The analog data output can be switched to provide
a linear DC voltage proportional to the ratio of the
two acceleration inputs. A semi log formatted
output is automatically presented to make accel-
eration transducer calibration or linear
transmissibility curves easy to plot. This output
voltage is normalized to 1.00 Vdc when the ratio of
the two different accelerations is equal to 1. This
allows the output to be read and interpreted by a
common volt meter for inexpensive calibration or
recorded or plotted by analog/digital conversion
or analog recorder-plotters. The output ranges
from 0 to 200% (0 to 2.00 Vdc) in the linear
difference (ratio) plotter output mode.
are more precisely controlled by optionally using the
average of the two channels for servo feedback.
The frequency generator and servo control sections are
independent in order to allow either manual or automatic
frequency control with the output under either manual or
servo control.
In the manual frequency and output modes, the SC-121
functions as a high quality sine signal source with simulta-
neous control of frequency and amplitude. This mode is
required for manual investigation of vibration response or
general sine signal applications.
Flexible programming allows internal storage of up to three
independent 2, or 4 level test profiles. Stored test profiles
are easy to modify or replace and are maintained
internally when the power is removed. This feature
eliminates the need for external disks or memory cards
and there are no batteries to wear down or replace.
Large displays indicate frequency, acceleration and
displacement at all times without the need to manually
switch the display function after a cross-over.
A programmable test cycle counter keeps track of the
accumulated test time or can be set to terminate the test
after a specific number of test sweep cycles.
Digitally generated analog outputs for frequency and
acceleration, facilitate plotting or recording test profiles,
responses and transfer functions.
Transmissibility. Plotting transmissibility and
acceleration response curves is a snap with the
Labworks SC-121 sine servo controller. Simply
place the control (channel 1) accelerometer on
the input member, base or fixture and mount a
response accelerometer (channel 2) on the ac-
tive portion of the test load. Set the SC-121 to
control on channel 1 and program for a constant
acceleration output. Program the SC-121 for a
frequency sweep over the band of interest and
initiate a servo controlled frequency sweep.
Switching the plotter output control to channel 2
allows recording or plotting the acceleration re-
sponse on channel 2, producing a log
transmissibility curve automatically.