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 makes SRS Tool unique

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	✘ Rarely available
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

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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

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SRS V1.3 here Extract and launch the SRS_Tool.exe

( You need to select the folder of the signal measurement. )

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.

Signal

Click Select signal folder… to open a folder browser (default root: C:\OROS\NVGate data\Projects). Select the Measurement folder — 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.

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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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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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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Appendix SRS Limit Curves — Normative Reference

This page documents all predefined SRS limit curves available in the SRS Tool. Each curve is identified by a confidence level tag shown next to its name in the interface.

Confidence level indicators

Tag	Meaning	What to expect
[normative]	Curve taken directly from the published standard as an SRS specification.	Breakpoints are faithful to the document. Use for compliance testing.
[approximate]	Standard defines a time-domain waveform (half-sine, sawtooth…), not an SRS.	The SRS envelope is computed from the pulse shape. For exact results, import the waveform and run compute_srs() on it.
[indicative]	Levels depend on mounting position, equipment mass or mission profile, or the exact document version was not available.	Use as a first-pass estimate only. Always verify with the applicable programme document.

All curves use Q = 10 (damping ζ = 5 %) and acceleration units (g). Between breakpoints, interpolation is log-log linear (constant dB/octave slope).

Summary table

Standard	Sector	Tag	Application	Peak level	Freq. range
NASA GEVS 2500 g	Space	normative	Hardware on primary structure	2 500 g	20–10 000 Hz
NASA GEVS 1000 g	Space	normative	Hardware on panel or bracket	1 000 g	20–10 000 Hz
NASA GEVS 3750 g (Qual.)	Space	normative	Qualification unit (dedicated test article)	3 750 g	20–10 000 Hz
Ariane 5 Equipment Bay	Space	indicative	Satellite equipment bay, component level	2 000 g	100–10 000 Hz
Ariane 6	Space	indicative	All payload positions, component level	1 600 g	100–10 000 Hz
VEGA-C	Space	indicative	Small satellite missions, component level	1 200 g	100–10 000 Hz
ECSS-E-ST-10-03C Protoqual.	Space	indicative	European space programmes, proto-qualification	2 000 g	20–10 000 Hz
MIL-STD-810H M517 Near-field	Military / Pyro	normative	Equipment < 0.5 m from pyrotechnic source	10 000 g	100–10 000 Hz
MIL-STD-810H M517 Mid-field	Military / Pyro	normative	Equipment 0.5–1.5 m from pyrotechnic source	1 000 g	100–10 000 Hz
MIL-STD-810H M517 Far-field	Military / Pyro	normative	Equipment > 1.5 m from pyrotechnic source	100 g	100–10 000 Hz
MIL-STD-810H M516 Functional 40 g	Military / Mech	approximate	Functional shock — must operate before and after	80 g (2×A)	5–2 000 Hz
MIL-STD-810H M516 Crash 40 g	Military / Mech	approximate	Crash hazard — must not endanger personnel	60 g	5–2 000 Hz
MIL-STD-810H M516 Bench 15 g	Military / Mech	approximate	Bench handling — drops during maintenance	30 g	5–2 000 Hz
MIL-S-901D Grade A	Military / Naval	indicative	US Navy lightweight shipboard equipment (< 136 kg)	2 000 g	20–10 000 Hz
MIL-S-901D Grade B	Military / Naval	indicative	US Navy medium-weight equipment (136–2 268 kg)	1 000 g	20–10 000 Hz
DO-160G Cat. B 6 g	Aviation	approximate	Airborne equipment — operational flight shock	12 g	5–2 000 Hz
DO-160G Cat. C 15 g	Aviation	approximate	Avionics — bench handling during maintenance	30 g	5–2 000 Hz
DO-160G Cat. D 20 g	Aviation	approximate	Airborne equipment — crash / emergency landing	40 g	5–2 000 Hz
DEF STAN 00-35 Cat. M	European Defence	indicative	UK defence — general military ground equipment	1 000 g	10–10 000 Hz
DEF STAN 00-35 Cat. P	European Defence	indicative	UK defence — aircraft store / weapon release	2 000 g	100–10 000 Hz
GAM EG-13 Choc sévère	European Defence (DGA)	indicative	French military — pyrotechnic devices, ejection seats	2 000 g	20–10 000 Hz
GAM EG-13 Choc modéré	European Defence (DGA)	indicative	French military — vehicle impacts, transport drops	500 g	10–5 000 Hz
STANAG 4370 AECTP-201 M417	NATO	indicative	NATO — pyroshock, severity level 3	2 000 g	100–10 000 Hz
STANAG 4370 AECTP-201 M403	NATO	approximate	NATO — mechanical shock, severity level 3	50 g	5–2 000 Hz
IEC 60068-2-27 15 g / 11 ms	Industrial	approximate	General industrial / commercial equipment qualification	30 g	5–2 000 Hz
IEC 60068-2-27 50 g / 11 ms	Industrial	approximate	Rugged industrial equipment — severe shock	100 g	5–2 000 Hz
IEC 60068-2-27 100 g / 6 ms	Industrial	approximate	Harsh shock environments — impacts, sudden accelerations	200 g	5–2 000 Hz
IEC 61373 Cat.1 Class B	Railway	approximate	Railway — equipment mounted on vehicle body (interior)	6 g	2–2 000 Hz
IEC 61373 Cat.1 Class A	Railway	approximate	Railway — bogie-mounted equipment (running gear)	15 g	2–2 000 Hz
IEC 61373 Cat.2 Under-body	Railway	approximate	Railway — under-body / axle-box mounted equipment	50 g	2–2 000 Hz

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How the SRS Tool uses these curves

1. Select a curve in the Pass/Fail tab.
2. The tool interpolates the curve at the same frequency resolution as the measured SRS using log-log linear interpolation.
3. Margin is computed point-by-point: Margin (dB) = 20 × log₁₀(limit / SRS)
4. The overall result is PASS only if the margin is positive at all frequencies.

Adding a custom curve

You can import your own limit curve via a two-column CSV file (frequency Hz, level g) using the Load CSV button in the Pass/Fail tab. The SRS Tool applies the same log-log interpolation as built-in curves.

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).