Atec SR785 User Manual

· DC to 102.4 kHz bandwidth

· 90 dB dynamic range

· Low-distortion synthesized source

· 145 dB dynamic range in
swept-sine mode

· Order tracking

· 20-pole/20-zero curve fitting

· Real-time octave analysis

· Up to 32 Mbyte memory

· GPIB and RS-232 interfaces

· SR785 ... $11,950

(U.S. list)

Stanford Research Systems phone: [phone]

www.thinkSRS.com

The SR785 Two-Channel Dynamic Signal Analyzer is a
precision, full-featured signal analyzer that offers state-of-the-art
performance at a price that's less than half that of competitive
analyzers. Building on its predecessor, the SR780, the SR785
incorporates new firmware and hardware that make it the ideal
instrument for analyzing both mechanical and electrical
systems. For measurements involving servo systems, control
systems, acoustics, vibration testing, modal analysis, or
machinery diagnostics, the SR785 has the features and
specifications to get the job done.

Standard measurement groups include FFT, order tracking,
octave, swept-sine, correlation, time capture, and
time/histogram. The SR785 brings the power of several
instruments to your application: a spectrum analyzer, network
analyzer, vibration analyzer, octave analyzer and oscilloscope.

A unique measurement architecture allows the SR785 to
function as a typical dual-channel analyzer with
measurements like cross spectrum, frequency response,
coherence, etc. Alternatively, the instrument can be configured
so that each input channel functions as a single-channel
analyzer with its own span, center frequency, resolution and
averaging. This allows you to view a wide-band spectrum and
simultaneously zoom in on spectral details. The same
advanced architecture provides storage of all measurement
building blocks and averaging modes. Vector averaged, rms
averaged, unaveraged, and peak hold versions of all

SR785 Dynamic Signal Analyzer

FFT Spectrum Analyzers

SR785  100 kHz 2-channel dynamic signal analyzer

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measurements are simultaneously acquired and can be
displayed without re-taking data.

Averaging

The SR785 comes equipped with a wide selection of
averaging techniques to improve signal-to-noise ratio. RMS
averaging reduces signal fluctuations, while vector averaging
minimizes noise from synchronous signals. Peak hold
averaging is also available. Both linear and exponential
averaging are provided for each mode.

Because the SR785 is so fast, there's no need for a separate
“fast averaging” mode. For instance, in a full-span FFT
measurement with a 4 ms time record, 1000 averages take
exactly 4 seconds, during which the SR785 still operates at its
maximum display rate.

For impact testing, the average preview feature allows each
time record or spectrum to be accepted or rejected before
adding it to the measurement.

Order Tracking

Order tracking is used to evaluate the behavior of rotating
machinery. Measurement data is displayed as a function of

multiples of the shaft frequency (orders), rather than absolute
frequency. Combined with a waterfall plot, the SR785
provides a complete history or "order map" of your data as a
function of time or rpm. Using the slice feature, the amplitude
profile of specific orders in the map can be analyzed.

In tracked order mode, the intensity of individual orders vs. rpm
is measured. Unlike other analyzers, there's no need to track a
limited number of orders to ensure full speed measurements.
The SR785's speed allows simultaneous tracking of up to
400 orders.

Run-up and run-down measurements are available in both
polar and magnitude/phase formats. RPM profiling is
provided to monitor variations of rpm as a function of time.
A complete selection of time and rpm triggering modes is
included, allowing you to make virtually any rotating
machinery measurement.

Octave Analysis

Real-time 1/1, 1/3 and 1/12 octave analysis, at frequencies up
to 40 kHz (single channel) or 20 kHz (dual channel), is a
standard feature of the SR785. Octave analysis is fully
compliant with ANSI S1.11-1986 (Order 3, type 1-D) and
IEC 225-1966. Switchable analog A-weighting filters, as well
as A, B and C weighting math functions, are included.
Averaging choices include exponential time averaging, linear
time averaging, peak hold, and equal confidence averaging.
Broadband sound level is measured and displayed as the last
band in the octave graph. Total power, impulse, peak hold and
L

eq

are all available. Exponentially averaged sound power

(L

eq

) is calculated according to ANSI S1.4-1983, Type 0.

Octave displays can be plotted as waterfalls with a fast 4 ms
storage interval. Once data is stored in the waterfall buffer, the
SR785 can display centile exceedance statistics for each
1/1, 1/3 or 1/12 octave band, as well as for L

eq

.

Swept-Sine Measurements

Swept-sine mode is ideal for signal analysis that involves high
dynamic range or wide frequency spans. Gain is optimized at

SR785 Dynamic Signal Analyzer

Stanford Research Systems phone: [phone]

www.thinkSRS.com

Order map (top), tracked order (bottom)

Octave analysis

Narrow band FFT (top), wide band FFT (bottom)

each point in the measurement, producing up to 145 dB of
dynamic range. A frequency resolution of up to 2000 points is
also provided. Auto-ranging can be used with source auto­leveling to maintain a constant input or output level at the device
under test (to test response at a specific amplitude, for instance).

Auto-resolution ensures the fastest possible sweeps, and
adjusts the frequency steps in the scan based on the DUT's
response. Phase and amplitude changes that exceed user­defined thresholds are measured with high frequency
resolution, while small changes are measured using wider
frequency steps between points. A choice of linear sweeps
with high resolution, or logarithmic sweeps with up to eight
decades of frequency range, is provided.

Time/Histogram

The time/histogram measurement group is used to analyze
time-domain data. A histogram of the time data vs. signal
amplitude is provided for accurate time domain signal
characterization. Statistical analysis capabilities include both
probability density function (PDF) and cumulative density
function (CDF). The sample rate, number of samples, and
number of bins can all be adjusted.

Time Capture

The SR785 comes with 8 Mbytes of memory (32 Mbytes
optional). Analog waveforms can be captured at sampling
rates of 262 kHz or any binary sub-multiple, allowing you to
optimize sampling rate and storage for any application. For
example, 8 Msamples of memory will capture 32 seconds of
time domain data at the maximum 262 kHz sample rate, or
about 9 hours of data at a 256 Hz sample rate. Once captured,
any portion of the signal can be played back in any of the
SR785's measurement groups except swept-sine. The
convenient Auto-Pan feature lets you display measurement
results synchronously with the corresponding portion of the
capture buffer to identify important features.

Transducer Units

Automatic unit conversion makes translating transducer data
easy. Enter your transducer conversion directly in V/EU,
EU/V or dB (1V/EU). The SR785 will display the result in

units of meters, inches, m/sec2, in/sec2, m/s, in/s, mil, g, kg,
lbs., N, dynes, pascals or bars. Built-in ICP power is provided
for accelerometers. Acoustic measurement results can be
displayed in dBSPL, while electrical units include V, V

2

, dBV

and dBm.

Source

The SR785 comes with six precision source types: low­distortion (−80 dBc) single or two-tone sine waves, white
noise, pink noise, chirp, and arbitrary waveforms. The chirp
and noise sources can be bursted to provide activity over a
selected portion of the time record for FFT measurements, or
to provide impulse noise for acoustic measurements. The
digitally synthesized source produces output levels from

0.1 mV to 5 V, DC offset from 0 to ±5 V, and delivers up to
100 mA of current.

Arbitrary waveform capability is standard with the SR785.
Use the arbitrary source to playback a section of a captured
waveform, play a selected FFT time record, or upload your
own custom waveform from your computer.

User Math

Custom measurements can be created in each of the SR785's
measurement groups using the math menu. Enter any equation
involving rms averaged, vector averaged or unaveraged time

SR785 Dynamic Signal Analyzer

Stanford Research Systems phone: [phone]

www.thinkSRS.com

Swept-sine Bode plot of low pass filter response

User Math

Burst noise source (top), arbitrary waveform source (bottom)