SRS Tool — Shock Response Spectrum Analyser
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SRS Tool — Shock Response Spectrum Analyser
SRS Tool is a professional Shock Response Spectrum (SRS) analysis application built for structural dynamics engineers working with OROS NVGate data acquisition systems. It reads shock recordings directly from NVGate measurement folders, computes SRS using the Smallwood (1981) recursive digital filter, and pushes results back into NVGate as live TCP result channels — all from a single application.
What sets SRS Tool apart
Most SRS tools require manual import/export and ship with no built-in normative database. SRS Tool is built around the idea that an engineer should go from raw measurement to qualification verdict in under one minute.
| Feature | OROS SRS Tool | Typical alternatives |
|---|---|---|
| 30+ normative limit curves built-in — MIL-STD-810H, ECSS, NASA-STD, DEF-STAN, ready to use with no setup | ✔ Included | ✘ Manual entry only |
| Multi-channel Pass/Fail with per-channel verdict — x, y, z compared simultaneously in one run | ✔ Included | ✘ One channel at a time |
| NVGate TCP result injection — log-log display, autoscaled, direct to project | ✔ Native | ✘ Not available |
| Automatic shock zone detection — envelope algorithm, runs on load | ✔ Automatic | ~ Manual only |
| Primary + Residual SRS in a single computation pass | ✔ One click | ~ Two separate runs |
| SRSS + Worst-case Envelope — triaxial multi-axis combination | ✔ Included | ✘ Paid add-on |
| Interactive dB cursor on Pass/Fail chart — frequency, SRS, limit, margin at a glance | ✔ Included | ✘ Rarely available |
Full feature list
- Signal acquisition: reads NVGate signal files directly
- Multi-channel: up to 10+ simultaneous channels; channel labels read from NVGate recording metadata (e.g. x, y, z)
- Smallwood recursive filter: vectorised NumPy implementation; all frequencies computed in a single forward pass
- Frequency axis: 1/3, 1/6, 1/12 or 1/24 octave resolution; user-defined f_min / f_max
- SRS types: Maximax (absolute maximum), Positive, Negative
- Physical quantities: Acceleration SRS + derived Pseudo-Velocity SRS + Pseudo-Displacement SRS
- Shock zone: auto-detection + manual override (drag on plot or type Start/End in seconds)
- Residual SRS: computes SRS on the signal segment after the shock ends
- Multi-axis combination: SRSS and/or Worst-case Envelope across all loaded channels
- Pass/Fail: 30+ built-in normative curves; user CSV; scale factor (dB); multi-channel worst-case
- CSV export: full table (per-channel SRS, SRSS, limit, per-channel margin, worst margin, status)
- PNG export: Pass/Fail chart at 150 dpi
- NVGate injection: injects all SRS curves into NVGate on log-log display, autoscaled
- Preprocessing: DC offset removal, noise floor suppression
- Dark theme: optimised for lab-room screen visibility
Quick Start
Installation
Note: NVGate does not need to be running to load signals or compute SRS. It is only required for Inject into NVGate.
User Interface
Main Tab
NVGate connection indicator
A coloured dot in the NVGate box shows connection status, polled every 3 seconds automatically:
| 🟢 Connected | NVGate reachable. Injection available. |
| 🔴 Disconnected | NVGate not running. SRS computation still fully functional. |
Signal
Click Select signal folder… to open a folder browser (default root: C:\OROS\NVGate data\Projects). Select the Measurement subfolder — channels are listed and the signal is plotted immediately.
Channels
One checkbox per recorded channel, showing label, sampling rate, duration and unit:
☑ x (25 600 Hz 13.86 s m/s²) ☑ y (25 600 Hz 13.86 s m/s²) ☑ z (25 600 Hz 13.86 s m/s²)
Channel labels (x, y, z…) come from the Name field set by the operator in NVGate at recording time.
Uncheck a channel to exclude it. ↺ Reload channels re-reads files from disk after a new recording.
Calculation parameters
| Parameter | Description | Recommended default |
|---|---|---|
| Frequency range | f_min to f_max of the SRS output | 1 Hz → 10 000 Hz |
| Q / Damping | Q factor or damping ratio ζ (linked: Q = 1/2ζ) | Q = 10 (ζ = 5 %) |
| Resolution | Octave subdivision: 1/3, 1/6, 1/12, 1/24 oct | 1/12 octave |
Q = 10 (ζ = 5%) is the universal standard for aerospace shock SRS — MIL-STD-810H, ECSS-E-ST-10-03C, NASA-STD-7003A all specify this value. f_max is auto-clamped to Nyquist (f_s / 2).
Output
- Type
- Acc — Acceleration SRS. Always available. Vel — Pseudo-velocity SRS. Disp — Pseudo-displacement SRS. (Vel and Disp require an acceleration input.)
- Curve
- Maximax — max(positive, |negative|). The standard curve required by most norms. Positive — max tensile response. Negative — max compressive response.
Signal and SRS plots
Advanced Tab
Shock Zone
The shock zone is auto-detected every time a signal loads — you normally do not need to touch these settings. Use manual override only to fine-tune the boundary.
Auto-detection
The detection algorithm:
- Compute a smoothed envelope: rolling mean of |signal| over a 3 ms window
- Trigger threshold = Threshold % × peak envelope
- Zone = first to last sample above threshold
- Expand by Padding ms on each side, clamped to signal bounds
| Parameter | Effect | Default |
|---|---|---|
| Threshold (% of peak) | Lower → wider zone; higher → core impact only | 5 % |
| Padding (ms) | Symmetric margin added on both sides of detected zone | 20 ms |
Padding example: shock detected at 8.055 s – 9.978 s with 20 ms padding → zone becomes 8.035 s – 9.998 s, ensuring ring-down is fully captured.
Manual override
Type Start and End (seconds, 3-decimal precision) — the yellow markers on the signal plot update immediately. Dragging on the signal plot synchronises the spinboxes in return.
Residual SRS
Check Also compute residual SRS to run a second computation on the signal after the shock zone end. This captures the free-vibration decay required by MIL-STD-810H Method 517 and ECSS-E-ST-10-03C for fragility assessment. Residual curves appear on the SRS plot labelled "(residual)".
Advanced Preprocessing
| Option | Effect | Typical use |
|---|---|---|
| Remove DC offset (N ms) | Subtracts the mean of the first N ms from the whole signal | Sensor bias, thermal drift |
| Noise floor (N ms) | Zeroes the first N ms | Pre-trigger noise before impact |
Multi-axis Combination
Enabled automatically when ≥ 2 acceleration channels are loaded. Check one or both options before computing:
| Option | Formula | Display |
|---|---|---|
| SRSS — Square Root Sum of Squares | √(SRS_x² + SRS_y² + SRS_z²) | White dashed curve, Maximax only |
| Worst-case Envelope | max(SRS_x, SRS_y, SRS_z) at each frequency | Orange dash-dot curve, all types |
Pass / Fail Tab
The Pass/Fail tab compares computed SRS against any normative or user-defined limit curve.
Built-in limit curve library
30+ normative curves are pre-programmed — select a standard from the grouped drop-down and run immediately. No other standalone SRS tool provides this library out of the box.
| Standard | Curves included |
|---|---|
| MIL-STD-810H — Method 517 | Near-field (< 0.3 m), Mid-field ★ (0.5–1.5 m), Far-field (> 1.5 m), Gunfire, Tall vehicles |
| ECSS-E-ST-10-03C | Protoflight, Proto+, Acceptance, Qualification, Protoqualification (equipment & system level) |
| NASA-STD-7003A | Payload near/far-field, structure-borne near/far |
| DEF-STAN 00-35 | Land vehicle, Ship (deck), Airborne external/internal |
| MIL-S-901D | High-impact shock Grade A / Grade B |
| IEST-RP-DTE032 | Light / medium / heavy equipment |
| RTCA DO-160G | Avionics Cat. A / B / C |
★ MIL-STD-810H Mid-field is the default — the most common qualification specification.
User-defined CSV
Select ← User-defined (CSV), load a two-column file (Hz, g). Interpolation is log-log linear between breakpoints. Example:
10, 5 100, 50 2000, 50 10000, 50
Scale factor (dB)
Scales the limit curve before comparison: L_scaled(f) = L_nominal(f) × 10^(dB/20)
| dB | Multiplier | Typical use |
|---|---|---|
| +6 | ×2.00 | Conservative / tighter requirement |
| +3 | ×1.41 | Standard qualification margin check |
| 0 | ×1.00 | Nominal — no change |
| −6 | ×0.50 | Relaxed limit |
Pass/Fail results
Top panel — SRS vs Limit
Each channel plotted in a distinct colour. Limit curve: red dashed. Red fill = exceedance (SRS > limit). Orange fill = caution zone (0 ≤ margin < 3 dB).
Bottom panel — Margin (dB)
Margin M(f) = 20 × log₁₀( Limit(f) / SRS(f) )
| Colour | Condition | Meaning |
|---|---|---|
| Green | M ≥ 3 dB | Well within specification |
| Orange | 0 ≤ M < 3 dB | Caution — low margin |
| Red | M < 0 dB | FAIL — exceedance |
Interactive cursor
Hover anywhere on either panel to see a floating readout snapped to the nearest frequency band, showing frequency, SRS value, limit value, margin in dB, and PASS/FAIL status. The readout border turns green, orange or red accordingly.
Verdict text
The result box below the chart shows global verdict, per-channel minimum margin, and the 10 worst exceedance frequencies. Example output:
PASS — Maximax SRS Limit: MIL-STD-810H Meth.517 — Mid-field (0.5–1.5 m) Per-channel result: PASS x min +42.1 dB @ 500 Hz PASS y min +38.7 dB @ 342 Hz PASS z min +45.3 dB @ 1000 Hz Worst margin (all channels): +38.7 dB @ 342.0 Hz No exceedance detected over the computed frequency range.
Export
| Button | Output | Content |
|---|---|---|
| Export CSV… | .csv | Per-channel SRS · Worst SRS · Limit · Per-channel margin · Worst margin · Status. Header block includes curve name and scale factor for traceability. |
| Export graph PNG… | .png / .pdf | Both panels at 150 dpi. |
NVGate Integration
Reading signal files
SRS Tool reads NVGate data with NVGate closed, using no additional DLL. File layout:
Measurement8/
Record_1_1/
Channel_1_0_XXXXXXXX/
Channel_1.orm ← JSON: sampling rate, unit, channel Name
Part_0.ors ← binary: float32 little-endian, SI units
Channel_2_0_XXXXXXXX/ …
Channel label comes from the Name field in .orm (set in NVGate at recording time). Falls back to SourceName ("Input 1", "Input 2"…) if empty.
Injecting results into NVGate
Click Inject into NVGate (or the duplicate button in the Advanced tab) to send all computed curves via the NVDrive TCP protocol as NVD REAL SPECTRUM channels:
- All SRS curves → separate TCP result channels
- X and Y axes: log scale (set automatically)
- Y axis: autoscaled
- All curves displayed in window SRS_Results of Layout1
NVGate channel naming convention:
SRS Acc Shock AbsMax: x SRS Acc Shock AbsMax: y SRS Acc Shock AbsMax: z
Calculation Reference
Shock Response Spectrum
The SRS is the peak response of a bank of Single Degree Of Freedom (SDOF) oscillators, each with a different natural frequency f_n, driven by a common base acceleration x(t):
z(t) + 2ζωₙz'(t) + ωₙ²z(t) = −x(t)
| Curve | Definition | Standard? |
|---|---|---|
| Positive SRS | maxt[ ωₙ² z(t) ] | Supplementary |
| Negative SRS | maxt[ −ωₙ²z(t) ] | Supplementary |
| Maximax SRS | max(Positive, Negative) | Required by most norms |
Smallwood Recursive Filter
The Smallwood (1981) filter avoids step-by-step numerical integration, giving an exact discrete-time equivalent with coefficients computed once per frequency:
| E = exp(−ζωₙΔt) K = ωd·Δt (ωd = ωₙ√(1−ζ²)) |
| b₀ = 1 − E·sin(K)/K b₁ = 2(E·sin(K)/K − E·cos(K)) b₂ = E² − E·sin(K)/K |
| a₁ = 2E·cos(K) a₂ = −E² |
| y[k] = b₀x[k] + b₁x[k−1] + b₂x[k−2] + a₁y[k−1] + a₂y[k−2] |
All N natural frequencies are processed in a single forward pass through the signal using NumPy broadcasting — typically 50–100× faster than a frequency-by-frequency loop.
Frequency axis
Log-spaced at 1/n octave: f_k = f_min × 2^(k/n)
| Resolution | Bands 1–10 000 Hz |
|---|---|
| 1/3 octave | 40 |
| 1/6 octave | 80 |
| 1/12 octave (default) | 160 |
| 1/24 octave | 320 |
Q factor and damping
Q = 1/(2ζ) ↔ ζ = 1/(2Q)
| Q | ζ | Use |
|---|---|---|
| 10 | 5 % | Aerospace standard — MIL-STD-810, ECSS, NASA |
| 50 | 1 % | Lightly damped structures |
| 5 | 10 % | Rubber-mounted, heavily damped |
Primary and Residual SRS
| Zone | Signal segment | Required by |
|---|---|---|
| Primary | [t_start → t_end] — the shock transient | All norms |
| Residual | [t_end → end] — free vibration decay | MIL-STD-810H §517, ECSS §8.4.3 |
Pseudo-velocity and pseudo-displacement
| Quantity | Formula | Unit (SA in m/s²) |
|---|---|---|
| Pseudo-velocity | SV(fn) = SA(fn) / (2π·fn) | m/s |
| Pseudo-displacement | SD(fn) = SA(fn) / (2π·fn)² | m |
Multi-axis combination
| Method | Formula | Applied to | Use case |
|---|---|---|---|
| SRSS | √(SA_x² + SA_y² + SA_z²) | Maximax only | Euclidean resultant, triaxial sensor |
| Worst-case Envelope | max(SA_x, SA_y, SA_z) at each f | All types | Space programmes (ECSS App. H) |
Supported Input Units
| Unit | Physical quantity | Vel/Disp SRS available |
|---|---|---|
| m/s², g | Acceleration | ✔ Yes |
| m/s, mm/s | Velocity | ✘ No |
| m, mm, µm | Displacement | ✘ No |
| N, kN | Force | ✘ No |
| V, mV | Voltage | ✘ No |
| Pa, N/m² | Pressure | ✘ No |
| rad/s, RPM | Angular velocity | ✘ No |
Glossary
| Term | Definition |
|---|---|
| SRS | Shock Response Spectrum. Peak SDOF response as a function of natural frequency. |
| Maximax | Negative|). The absolute peak response — required by most norms. |
| SDOF | Single Degree Of Freedom. A mass–spring–damper system with one resonant frequency. |
| Q factor | Quality factor. Q = 1/(2ζ). Q = 10 is the universal aerospace standard. |
| ζ | Damping ratio. Fraction of critical damping. ζ = 5 % ↔ Q = 10. |
| Primary SRS | SRS over the shock transient [t_start, t_end]. |
| Residual SRS | SRS on the post-shock free vibration [t_end, end]. |
| SRSS | Square Root Sum of Squares: √(SRS_x² + SRS_y² + SRS_z²). |
| Envelope | Point-by-point max across channels at each frequency. |
| Margin (dB) | 20·log₁₀(Limit/SRS). Positive → PASS, negative → FAIL. |
| Padding | Symmetric time margin added around the auto-detected shock zone. |
| Pyroshock | Shock from explosive devices: separation bolts, pyrocutters, pin pullers. |
| .orm | NVGate JSON channel metadata: sampling rate, unit, name. |
| .ors | NVGate binary signal: float32 little-endian samples, SI units. |
| NVDrive | OROS TCP protocol for programmatic communication with NVGate. |
Algorithm: D.O. Smallwood, An Improved Recursive Formula for Calculating Shock Response Spectra, Shock and Vibration Bulletin, 1981. · Standards referenced: MIL-STD-810H (2019) · ECSS-E-ST-10-03C (2012) · NASA-STD-7003A (2011) · DEF-STAN 00-35 Part 3 (2021).