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New SR785 ROM Version Available!
Version 219 of the SR785 firmware is now available. This version correctsproblems with the j-Omega math function and the Octave total power bin.Please contact SRS for an upgrade to the latest firmware version.
SR785 Overview
The SR785 Two Channel Dynamic Signal Analyzer is a precision,full-featured signal analyzer that offers state-of-the-art performance anda wide selection of features at a price that's less than half that ofcompetitive analyzers. Building on its predecessor, the SR780, the SR785incorporates new firmware and hardware that make it the ideal instrumentfor analyzing both mechanical and electrical systems. For measurementsinvolving modal analysis, machinery diagnostics, vibration testing, servosystems, control systems, or acoustics, the SR785 has the features andspecifications to get the job done.
Standard measurement groups include FFT, order tracking, octave,swept-sine, correlation, time capture and time/histogram. The SR785 bringsthe 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 atypical dual channel analyzer with measurements like cross spectrum,frequency response, coherence, etc. Alternatively, the instrument can beconfigured so that each input channel functions as a single channelanalyzer with its own span, center frequency, resolution, and averaging.This allows you to view a wideband spectrum and simultaneously zoom in onspectral details. The same advanced architecture provides storage of allmeasurement building blocks and averaging modes. Vector averaged, RMSaveraged, unaveraged and peak hold versions of all measurements aresimultaneously acquired and can be displayed without re-taking data.
Averaging
The SR785 comes equipped with a wide selection of averaging techniques toimprove your signal to noise ratio. Choose RMS averaging to reduce signalfluctuations, vector averaging to actually eliminate noise fromsynchronous signals, or peak hold averaging. In the order-trackingmeasurement group, time averaging is available. Both linear andexponential averaging are provided for each mode.
Because the SR785 is so fast, there's no need for a separate "fastaveraging" mode. For instance, in a full span FFT measurement with a 4 mstime record, 1000 averages take exactly 4 seconds, during which the SR785still operates at its maximum display rate.
For impact testing, the average preview feature allows each time record orspectrum 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 shaftfrequency (orders), rather than absolute frequency. Combined with awaterfall plot, the SR785 provides a complete history or "order map" ofyour data as a function of time or RPM. Using the slice feature, theamplitude profile of specific orders in the map can be analyzed.
In tracked order mode the intensity of individual orders vs. RPM ismeasured. Unlike other analyzers, there's no need to track a limitednumber of orders to ensure full speed measurements. The SR785's speedallows simultaneous tracking of up to 400 orders.
Run-up and run-down measurements are available in both polar andmagnitude/phase formats. RPM profiling is provided to monitor variationsof RPM as a function of time. A complete selection of time and RPMtriggering modes is included allowing you to make virtually any rotatingmachinery measurement.
Octave Analysis
Real-time 1/1, 1/3, 1/12 octave analysis at frequencies up to 40 kHz(single channel), or 20 kHz (2 channel) is a standard feature of theSR785. 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 wellas A, B and C weighting math functions are included. Averaging choicesinclude exponential time averaging, linear time averaging, peak hold andequal confidence averaging. Broadband sound level is measured anddisplayed as the last band in the octave graph. Total power, impulse, peakhold and Leq are all available. Exponentially averaged sound power (Leq)is calculated according to ANSI S1.4-1983, Type 0.
Octave displays can be plotted as waterfalls with a fast 4 ms storageinterval. Once data is stored in the waterfall buffer, the SR785 candisplay centile exceedance statistics for each 1/1, 1/3 or 1/12 octaveband as well as for Leq.
Swept-Sine Measurements
Swept-sine mode is ideal for signal analysis that involves high dynamicrange or wide frequency spans. Gain is optimized at each point in themeasurement producing up to 145 dB of dynamic range. A frequencyresolution of up to 2000 points is also provided. Auto-ranging can be usedwith source auto-leveling to maintain a constant input or output level atthe device under test (to test response at a specific amplitude, forinstance).
Auto-resolution ensures the fastest possible sweeps and adjusts thefrequency steps in the scan based on the DUT's response. Phase andamplitude changes that exceed user-defined thresholds are measured withhigh frequency resolution, while small changes are measured using widerfrequency steps between points. A choice of linear sweeps with highresolution, or logarithmic sweeps with up to eight decades of frequencyrange is provided.
Time/Histogram
Use the time/histogram measurement group to analyze time domain data. Ahistogram of the time data vs. signal amplitude is provided for accuratetime domain signal characterization. Statistical analysis capabilitiesinclude both probability density function (PDF) and cumulative densityfunction (CDF). The sample rate, number of samples and number of bins canall be adjusted.
Time Capture
The SR785 comes with 2 Msamples of memory (8 Msamples optional). Analogwaveforms can be captured at sampling rates of 262 kHz or any binarysubmultiple, allowing you to optimize sampling rate and storage for anyapplication. For example, 8 Msamples of memory will capture 32 seconds oftime domain data at the maximum 262 kHz sample rate, or about 9 hours ofdata at a 256 Hz sample rate. Once captured, any portion of the signal canbe played back in any of the SR785's measurement groups except swept-sine.The convenient Auto Pan feature lets you display measurement resultssynchronously with the corresponding portion of the capture buffer toidentify important features.
Unit Conversion
Automatic unit conversion makes translating transducer data easy. Enteryour transducer conversion directly in V/EU, EU/V or dB (1V/EU). TheSR785 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 powermeans you don't need an external power supply for your accelerometer.Acoustic measurement results can be displayed in dBSPL, while electricalunits include V, V², dBV and dBm.
Source
The SR785 comes standard with five precision source types. Generate lowdistortion (-80 dBc) single or two-tone sine waves, white noise, pinknoise, chirps, and arbitrary waveforms. The chirp and noise sources can bebursted to provide activity over a selected portion of the time record forFFT measurements, or to provide impulse noise for acoustic measurements.The digitally synthesized source produces output levels from 0.1 mV to 5 Vand offsets from 0 to ±5 V, and delivers up to 100 mA of current.
Arbitrary waveform capability is standard with the SR785. Use thearbitrary source to playback a section of a captured waveform, play aselected FFT time record or upload your own custom waveform from yourcomputer.
User Math
Create your own measurement in each of the SR785's measurement groupsusing the math menu. Enter any equation involving RMS averaged, vectoraveraged or unaveraged time or frequency data, stored files, constants, ora rich array of supplied operations including arithmetic functions, FFT,inverse FFT, jw, d/dw, exp, ln x, and many others. Because all theaveraging modes are available as user math operands, non-repeatable runoutmeasurements (used in analyzing disk drives) can be performed in a singlepass by entering the equation MAG(RMS<F1>)-MAG(Vec<F1>). Unlike many otheranalyzers, the SR785's measurement rate is virtually unaffected when usermath is selected. For instance, the function exp(ln(conj(FFT2/FFT1))) canbe calculated with a 100 kHz real-time bandwidth.
Waterfall
Waterfall plots are a convenient way of viewing a time history of yourdata. Each successive measurement record is plotted along the z-axismaking it easy to see trends in the data. All FFT, octave and ordertracking measurements can be stored in the SR785's waterfall buffermemory. You can choose to save all measurements and averaging modes orjust the current measurement to conserve memory. Waterfall traces can bestored every n time records for FFT and order tracking measurements. Fororder tracking measurements new records can be acquired at a specific timeinterval or change in RPM. In octave measurements, the storage interval isin seconds (as fast as every 4 ms). While displaying waterfall plots, youcan adjust the skew angle to reveal important features, or change thebaseline threshold to eliminate low-level clutter. Any z-axis slice orx-axis record can be saved to disk or displayed separately for analysis.
Analysis
The SR785 includes a wide variety of built-in analysis features. Markeranalysis lets you easily measure the power contained in harmonics,sidebands or within a given band of frequencies. Important informationsuch as THD, THD+N, sideband power relative to a carrier, or totalintegrated power are calculated in real-time and displayed on the screen.The front/back display feature allows you to display live data from bothsignal inputs on one graph. You can also simultaneously display savedtraces and live data. The peak-find marker allows you to quickly locatefrequency peaks with the click of a button. The marker statistics featurecalculates the maximum, minimum, mean and standard deviation of data inany section of the display. For modal analysis, the cursor can beconfigured to display the resonant frequency and damping of a singleselected mode.
Use data tables to display up to 100 selected data points in tabularformat. Limit tables allow you to define up to 100 upper and lower limitsegments in each display for GO/NO GO testing. Data and limit tabledefinitions can also be saved to and recalled from disk for quick setup.
Curve Fit and Synthesis
The SR785 has a standard 20-pole, 20-zero curve fitter that can fitfrequency domain data from both the FFT and swept-sine measurement groups.Curve models can be displayed in pole/zero, pole/residue and polynomialformats. Synthesis reverses the process: enter a model in any of the aboveformats and the SR785 synthesizes the required curve. The curvefit/synthesis menu allows you to change gain, delay and frequency scale,set pole and zero locations and instantly see the response of the modeledsystem.
Output
The SR785's built-in 3.5" 1.44 MB disk drive, GPIB and RS-232 computerinterfaces and Centronics printer port combine to allow almost unlimitedflexibility in saving, printing, plotting or exporting your measurementdata. Displays and setups can be printed or plotted to disk, GPIB, RS-232or Centronics port in PCX, GIF, PCL (LaserJet® and DeskJet®), dot-matrix,Postscript, HP-GL or ASCII formats. An annotation editor lets you addtext, time and date, or filenames to any portion of the plot. For modalanalysis applications, nodal degree-of-freedom information is stored withthe data files to simplify transfer to external analysis programs.
Data Conversion Utilities
The SR785 contains a complete suite of data conversion utilities for bothWindows® and DOS® operating systems. These versatile utilities make datatransfer to and from external programs fast and simple. SR785 files can beconverted to ASCII for use with spreadsheets, or Universal File Format(UFF) and HP SDF for use with modal analysis programs. SR785 Files canalso be converted to MAT file format for use with MATLAB. Conversion fromexternal file types is also supported. Both HP SDF and SR780 files can beconverted to SR785 format.
DataViewer
The SRS DataViewer is a Windows 95 program that allows you to quicklyupload SR785 files into a graphical environment, perform simple editingand cut and paste into other applications. You can add pointers and text,change scaling, and perform simple math operations. Graphs can be saved inPCX, BMP or GIF formats.
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