SRS Tool — Shock Response Spectrum Analyser

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 SRS Tool

Developer OROS / Gemini Platform Windows 10 / 11 Language Python 3.9+ UI PySide2 · Qt 5.15 Algorithm Smallwood 1981 File I/O .ors / .orm (NVGate) Standards 30+ built-in curves Licence Free / open-source

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.

Figure 1 — SRS Tool main window. Time signal with auto-detected shock zone (top right, yellow markers) and log-log SRS plot (bottom right). Three-channel triaxial measurement loaded: channels x, y, z.

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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	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
Direct NVGate signal read — no DLL, no NVGate open, no export step	✔ Native	✘ Manual export required
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
No dongle, no subscription, no cloud	✔ Free	✘ Licence required

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Quick Start

⚡ Five steps from measurement folder to qualification verdict

1. Main tab → Select signal folder… → navigate to the NVGate Measurement folder
2. Channels appear automatically — shock zone is auto-detected (yellow markers on signal plot)
3. Set Q = 10, range 1–10 000 Hz, resolution 1/12 oct → click Compute SRS
4. Pass / Fail tab → limit curve is pre-set to MIL-STD-810H Mid-field → click ▶ Run Pass / Fail
5. Read the per-channel verdict, export CSV / PNG, or click Inject into NVGate

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Installation

Requirements

Component	Minimum version	Notes
Python	3.9	3.12 not yet tested
PySide2	5.15	Qt5 Python binding
NumPy	1.22	Vectorised SRS engine
Matplotlib	3.5	Embedded plot canvases
pywin32	any	Windows only — for NVGate injection
pynvdrive	OROS Toolkit NVdrive	Required only for NVGate injection

Launch

<syntaxhighlight lang="bash"> cd C:\OROS\Gemini\SRS python -m src.main </syntaxhighlight>

Note: NVGate does not need to be running to load signals or compute SRS. It is only required for Inject into NVGate.

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User Interface

The window is split into two zones:

• Left panel (340 px fixed) — three tabs: Main, Advanced, Pass / Fail
• Right panel (expandable) — signal + SRS plots when on Main/Advanced; Pass/Fail chart when on Pass/Fail tab

The status bar at the bottom tracks every operation. A progress bar appears during computation.

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Main Tab

Figure 2 — Main tab controls. From top: NVGate connection indicator, Signal folder, channel checkboxes with Reload, Calculation parameters, Output type selectors, Compute and Inject buttons.

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

Figure 3 — Time signal plot. Three channels (x/y/z) overlaid. Yellow dashed lines mark the auto-detected shock zone. Drag horizontally anywhere on the plot to redefine the zone manually.

Figure 4 — SRS log-log plot. Channels x (blue), y (orange), z (green). Each curve is the Maximax acceleration SRS over the detected shock zone. Q = 10, 1/12 octave, 1–10 000 Hz.

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Advanced Tab

Figure 5 — Advanced tab. Shock zone section (auto-detection parameters + manual Start/End override), Residual SRS option, preprocessing, and multi-axis SRSS / Envelope.

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:

1. Compute a smoothed envelope: rolling mean of |signal| over a 3 ms window
2. Trigger threshold = Threshold % × peak envelope
3. Zone = first to last sample above threshold
4. 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

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Pass / Fail Tab

Figure 6 — Pass/Fail controls. Grouped limit curve library (30+ curves), user CSV option, scale factor, channel selector, Run button, and export buttons.

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

Figure 7 — Pass/Fail chart. Three channels (x/y/z) vs MIL-STD-810H Mid-field limit (red dashed). All channels are well within spec: the margin subplot (bottom) shows 30–60 dB positive margin throughout the full frequency range.

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.

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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

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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)

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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

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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.

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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).