The Stanford Research Systems SR785 is a two-channel, dynamic signal analyzer designed for advanced signal processing, acoustics, vibration testing, and electronic design. It features a high real-time bandwidth of 102.4 kHz on both channels simultaneously and supports multiple measurement modes including FFT, octave analysis, swept-sine, and order tracking.
Specifications
General
| Parameter | Value |
|---|---|
| Interfaces | GPIB (IEEE-488.2), RS-232, Centronics Parallel Printer Port |
| Display | 7-inch monochrome CRT, 640 × 480 pixels |
Physical
| Parameter | Value |
|---|---|
| Power Supply | 90 to 132 VAC or 198 to 264 VAC, 47 to 63 Hz, 150 W |
| Operating Temperature | 0 to 40 |
| Dimensions (W×H×D) | 432 × 210 × 565 |
| Weight | 25.4 |
Frequency Specifications
| Parameter | Value |
|---|---|
| Frequency Range (Single/Dual Channel) | DC to 102.4 kHz |
| Frequency Resolution | 100, 200, 400, 800 lines |
| Frequency Accuracy | ±25 ppm (0 °C to 40 °C) |
| Real-Time Bandwidth (Single Channel) | 102.4 kHz |
| Real-Time Bandwidth (Dual Channel) | 102.4 kHz |
| Dynamic Range | 90 dB (typical) |
Measurement Modes & Functions
| Parameter | Value |
|---|---|
| FFT Analyzer Mode | Yes |
| Octave Analysis Mode | 1/1, 1/3, 1/12 octave (ANSI S1.11-1983 Class 3) |
| Swept-Sine Mode | Yes |
| Order Tracking Mode | Yes |
| Time Capture Mode | Yes (up to 8 MSamples RAM) |
| Correlation Mode | Yes |
| Histogram / Probability Density Mode | Yes |
| Measurement Types | FFT, Time Record, Windowed Time, Orbit, Cross Spectrum, FRF, Coherence, Coherent Output Power, Auto Correlation, Cross Correlation, Histogram, PDF, CDF |
Analog Input Channels
| Parameter | Value |
|---|---|
| Number of Inputs | 2 |
| Input Coupling | AC, DC, ICP (4 mA, 24 V source) |
| Input Configuration | Single-ended, Differential |
| Input Impedance | 1 MΩ + 50 pF |
| Full-Scale Input Range | -50 dBV (3.16 mVp) to +34 dBV (50 Vp) in 2 dB steps |
| A/D Converter Resolution | 16-bit (256 kHz sigma-delta) |
| Common Mode Rejection Ratio (CMRR) | >90 dB (at 1 kHz, -50 dBV to -14 dBV range) |
| Crosstalk (Ch-to-Ch Isolation) | <-145 dBFS (100 kHz) |
| Input Noise Floor | <-160 dBVrms/√Hz (typical, above 1 kHz, -50 dBV range) |
| Amplitude Accuracy | ±0.2 dB or ±2% of reading |
Signal Source (Generator)
| Parameter | Value |
|---|---|
| Signal Source Types | Sine, Two-Tone, Swept-Sine, Chirp, White Noise, Pink Noise, Arbitrary |
| Source Frequency Range | DC to 102.4 kHz |
| Source Amplitude Range | 0.1 mVp to 5 Vp |
| Source Amplitude Resolution | 0.1 mVp |
| Output Impedance | <5 Ω (50 mA max current) |
| Harmonic Distortion | <-80 dB (at <10 kHz), <-70 dB (at <100 kHz) |
| DC Offset Range | 0 to 5 V |
FFT and Signal Processing
| Parameter | Value |
|---|---|
| FFT Resolution (Lines) | 100, 200, 400, 800 lines |
| Averaging Modes | RMS, Vector, Peak Hold |
| Averaging Types | Linear, Exponential, Equal Confidence |
| Waveform Math | Add, Subtract, Multiply, Divide, Integrate, Differentiate, Conjugate, Square Root, Log, Exp, FFT, dFFT |
Triggering
| Parameter | Value |
|---|---|
| Trigger Sources | Free Run, Internal (Ch 1/Ch 2), External, External TTL |
| Trigger Modes | Continuous, Single, Arm, Armed, Triggered |
| Trigger Level Range | ±100% of full scale (Internal), ±5 V (External) |
| Trigger Slope | Positive, Negative |
| Pre-Trigger Delay Range | Up to 8192 samples |
| Post-Trigger Delay Range | Up to 131,072 samples |
Display & User Interface
| Parameter | Value |
|---|---|
| Display Formats | Single, Dual (Split-screen), Waterfall |
| Vertical Scale Formats | Linear, Log (dBV, dBm, dBre, dBV/√Hz, dBm/√Hz, dBre/√Hz, V, V², V/√Hz, V²/Hz) |
| Horizontal Scale Formats | Linear, Log |
Connectivity & I/O Interfaces
| Parameter | Value |
|---|---|
| External Trigger Input | TTL levels or analog (±5 V, BNC) |
| Analog Monitor Outputs | Yes (Ch 1 and Ch 2, BNC) |
Storage & Memory
| Parameter | Value |
|---|---|
| Internal Memory Capacity | 8 MB standard (expandable to 32 MB) |
| Removable Storage Type | 3.5-inch 1.44 MB floppy disk drive (DOS format) |
Physical & Environmental
| Parameter | Value |
|---|---|
| Enclosure Form Factor | Benchtop with rackmount option |
| Cooling Mechanism | Internal fan |
Input Channels
| Parameter | Value |
|---|---|
| ICP Transducer Power | 4 mA source current, 24 V compliance, selectable on/off |
Analysis Features
| Parameter | Value |
|---|---|
| Curve Fitting & Synthesis Capacity | Up to 20 poles and 20 zeros |
| Waterfall Memory Capacity | Up to 3450 traces |
Octave Analysis
| Parameter | Value |
|---|---|
| Octave Analysis Standards | Conforms to ANSI S1.11-1986 Order 3 Type 1-D and IEC 225-1966 |
Signal Source
| Parameter | Value |
|---|---|
| Arbitrary Source Memory | 2 MSamples (8 MSamples with Option 01) |
| Source D/A Converter Resolution | 16-bit |
| Source D/A Converter Sampling Rate | 262.144 kHz |
| Sine Source Distortion (<10 kHz) | < -90 dBc |
| Sine Source Distortion (<100 kHz) | < -80 dBc |
| White Noise Source Flatness | < 1.0 dB (50 mHz to 102.4 kHz) |
| Pink Noise Source Flatness | < 2.0 dB (20 Hz to 20 kHz) |
| Chirp Source Flatness | < 1.0 dB (50 mHz to 102.4 kHz) |
| Source Phase Noise | < -80 dBc/Hz at 1 kHz offset |
Data Capture
| Parameter | Value |
|---|---|
| Standard Capture Buffer Size | 2 MSamples (8 MSamples with Option 01) |
Interfaces
| Parameter | Value |
|---|---|
| Printer Port | Centronics parallel |
Input & Acquisition
| Parameter | Value |
|---|---|
| A/D Converter Sampling Rate | 262.144 kHz |
| Anti-Aliasing Filter Stopband Attenuation | 115 dB |
| Anti-Aliasing Filter Type | Multi-stage elliptic |
Connectivity & Interface
| Parameter | Value |
|---|---|
| GPIB Transfer Rate | Up to 100 kB/s |
| RS-232 Baud Rates | Up to 115.2 kbps |
| External Clock Input Frequency | 2.048 MHz or 256 × Fs (TTL level) |
| Preamp Power Output | ±15 VDC at up to 100 mA |
Technology
DSP-based Dynamic Signal Analysis
Applications
Vibration, Acoustics, Noise, and Electronic Signal Analysis