SR785 – 100 kHz 2-ch. FFT analyzer


  • 100 kHz 2-ch. FFT analyzer


SR785 – 100 kHz 2-ch. FFT analyzer


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.


• DC to 102.4 kHz bandwidth
• 90 dB dynamic range
• 145 dB dynamic range (swept-sine)
• Order tracking
• 20-pole/20-zero curve fitting
• Real-time octave analysis
• Up to 32 Mbyte memory
• GPIB and RS-232 interfaces


Technical Specifications

Measurement Groups
Groups: FFT, Correlation, Time Histogram, Swept-Sine, Order Tracking

Range: 102.4 kHz or 100 kHz (both displays have the same range)
FFT spans: 195.3 mHz to 102.4 kHz or 191 mHz to 100 kHz. The two displays can have different spans and start frequencies.
FFT resolution: 100, 200, 400 or 800 lines
Real-time bandwidth: 102.4 kHz (highest FFT span with continuous data acquisition and averaging)
Accuracy: 25 ppm from 20 ?C to 40 ?C

Dynamic Range
Dynamic range: 90 dB typical, 80 dB guaranteed (FFT and Octave). 145 dB typical (Swept-Sine). Includes spurs, harmonics, intermodulation distortion, and alias products. Excludes alias responses at extremes of span.
Harmonic distortion: <-80 dB (single tone in band)
Intermod. Distortion: <-80 dB (two tones in band, each less than -6.02 dBfs)
Spurious: <-80 dBfs
Alias responses: <-80 dBfs (single tone outside of span, -30 dBV, Hanning window, 64 rms averages)
Residual DC response: <-30 dBfs (FFT with Auto-Cal on)

Amplitude Accuracy
Single channel: ?0.2 dB (excluding window effects)
Cross channel: ?0.05 dB, DC to 102.4 kHz (frequency response measurement, both inputs on the same range, rms averaged)
Phase Accuracy
Single channel: ?3.0 deg. relative to external TTL trigger (-50 dBfs to 0 dBfs, freq <10.24 kHz, center of frequency bin, DC coupled). For Blackman-Harris, Hanning, Flat-Top and Kaiser windows, phase is relative to a cosine wave at center of time record. For Uniform, Force and Exponential windows, phase is relative to a cosine wave at beginning of the time record.
Cross channel: ?0.5 deg. (DC to 51.2 kHz)
?1.0 deg. (DC to 102.4 kHz)
(frequency response measurement, both inputs on same range, vector averaged)

Signal Inputs
Number of inputs: 2
Full-scale input range: -50 dBV (3.16 mVp) to +34 dBV (50 Vp) in 2 dB steps
Maximum input level: 57 Vp
Input configuration: Single-ended (A) or differential (A-B)
Input impedance: 1 M? + 50 pF
Shield to chassis: Floating mode: 1 M? + 0.01 ?F
Grounded mode: 50 ? (shields grounded in (A-B) mode)
Max. shield voltage: 4 Vp
AC coupling: 0.16 Hz cutoff frequency
CMRR: 90 dB at 1 kHz (input range <0 dBV)
80 dB at 1 kHz (input range <10 dBV)
50 dB at 1 kHz (input range ?10 dBV)
ICP signal conditioning: Current source: 4.8 mA
Open circuit voltage: +26 V
A-weight filter: Type 0 tolerance, ANSI standard S1.4-1983; 10 Hz to 25.6 kHz
Crosstalk: <-145 dB below signal (input to input and source to inputs, 50 ? receiving input source impedance)
Input noise: <10 nVrms/?Hz above 200 Hz (<-160 dBVrms/?Hz)

Trigger Input
Modes: Free Run, Internal, External, or External TTL
Internal: Level adjustable to ?100 % of input scale, positive or negative slope. Min. trigger level: 5 % of input range
External: Level adjustable to ?5 V in 40 mV steps, positive or negative slope.
Input impedance: 1 M?
Max. input: ?5 V
Min. trigger amplitude: 100 mV
External TTL: Requires TTL level to trigger (low 3.0 V)
Post-trigger: Measurement record is delayed up to 100,000 samples after the trigger.
Pre-trigger: Measurement record starts up to 8000 samples prior to the trigger.

Tachometer Input
Pulses per revolution: 1 to 2048
RPM accuracy: ?50 ppm (typ.)
Tach level range: ?25 V, ?5 V, TTL
Tach level resolution: 20 mV @ ?25 V, 4 mV @ ?5 V
Max. tach input level: ?40 Vp
Min. tach pulse width: 100 ns
Max. tach pulse rate: 750 kHz (typ.)

Transient Capture
Mode: Continuous data recording
Maximum rate: 262,144 samples/s for both inputs
Maximum capture length: 2 Msamples (single input)
8 Msamples with optional memory
Octave Analysis
Standards: Conforms to ANSI standard S1.11- 1986, Order 3, Type 1-D
Frequency range: (Band centers)

Single channel
1/1 Octave 0.125 Hz to 32 kHz
1/3 Octave 0.100 Hz to 40 kHz
1/12 Octave 0.091 Hz to 12.3 kHz
Two channels
1/1 Octave 0.125 Hz to 16 kHz
1/3 Octave 0.100 Hz to 20 kHz
1/12 Octave 0.091 Hz to 6.17 kHz
Accuracy: <0.2 dB (1 second stable average, single tone at band center)
Dynamic range: 80 dB (1/3 Octave, 2 second stable average) per ANSI S1.11-1986
Sound level: Impulse, Peak, Fast, Slow and Leq per ANSI S1.4-1983 Type 0 and IEC 651-1979 Type 0

Order Tracking
Delta order: 0.0075 to 1
Resolution: up to 400 lines
Amplitude accuracy: ?1 dB (typ.)
Displays: Order map (mag. and phase), order track (mag. and phase), orbit
Curve Fit and Synthesis
Type: 20 poles/20 zeros curve fit (non-iterative rational fraction)
Order selection: Auto or manual
Output format: Pole-zero, polynomial, pole-residue

Source Output
Amplitude range: 0.1 mVp to 5 Vp
Amplitude resolution: 0.1 mVp
DC offset: <10.0 mV (typ.)
Offset adjust: ?5 VDC (sine, two-tone, swept-sine)
Output impedance: <5 ?, ?100 mA peak output current
Sine Source
Amplitude accuracy: ?1 % of setting, 0 Hz to 102.4 kHz , 0.1 Vp to 5 Vp into High-Z load
Harmonics, sub-harm.
& spurious signals: 0.1 Vp to 5 Vp
<-80 dBc (fundamental <30 kHz)
<-75 dBc (fundamental <102 kHz)

Two-Tone Source
Amplitude accuracy: ?1 % of setting, 0 Hz to 102.4 kHz, 0.1 Vp to 5 Vp into High-Z load
Harmonics, sub-harm.: <-80 dBc, 0.1 Vp to 2.5 Vp

White Noise Source
Time Record: Continuous or burst
Bandwidth: DC to 102.4 kHz or limited to span
Flatness: <0.25 dBpp (typ.), 5000 rms averages (<1.0 dBpp (max.))

Pink Noise Source
Bandwidth: DC to 102.4 kHz
Flatness: <2.0 dBpp, 20 Hz to 20 kHz (measured using averaged 1/3 Octave Analysis)

Chirp Source
Time record: Continuous or Burst
Output: Sine sweep across the FFT span
Flatness: ?0.25 dB (1.0 Vp)

Swept-Sine Source
Auto functions: Source Level, Input Range and Frequency Resolution
Dynamic range: 145 dB

Arbitrary Source
Amplitude range: ?5 V
Record length: 2 Msamples (playback from arbitrary waveform memory or capture buffer). Variable output sample rate.

CRT monitor: Monochrome, 800H by 600V resolution
Interfaces: IEEE-488.2, RS-232 and Printer interfaces standard. All instrument functions can be controlled through computer interfaces. A PC (XT) keyboard input is provided for additional flexibility.
Hardcopy: Print to dot matrix and PCL compatible printers. Plot to HP-GL or postscript plotters. Print/plot to RS-232 or IEEE-488.2 interfaces or to disk file. Additional file formats include GIF, PCX and EPS.
Data storage: USB drive
Preamp power: Power connector for SRS preamps
Power: 70 W, 100/120/220/240 VAC, 50/60 Hz
Dimensions: 17″” ? 8.25″” ? 24″” (WHL)
Weight: 56 lbs.
Warranty: One year parts and labor on defects in materials and workmanship