Difference between revisions of "SRS Tool — Shock Response Spectrum Analyser"

{DISPLAYTITLE:SRS Tool — Shock Response Spectrum Analyser}}

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|+ style="background:#1565C0; color:#ffffff; font-size:13px; font-weight:bold; padding:8px 12px; letter-spacing:0.5px; text-align:left;" | &nbsp;SRS Tool

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{| style="width:100%;"

| style="color:#555; white-space:nowrap; padding-right:8px;" | '''Developer'''

| OROS / Gemini

| style="color:#555;" | '''Platform'''

| Windows 10 / 11

| style="color:#555;" | '''Language'''

| Python 3.9+

| style="color:#555;" | '''UI'''

| PySide2 · Qt 5.15

| style="color:#555;" | '''Algorithm'''

| Smallwood 1981

| style="color:#555;" | '''File I/O'''

| .ors / .orm (NVGate)

| style="color:#555;" | '''Standards'''

| 30+ built-in curves

'''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.

[[File:11_main_full.png|center|800px|thumb|'''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.]]

== 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.

{| class="wikitable" style="width:100%; font-size:12px; border-collapse:collapse;"

! style="width:54%; background:#f0f4f8;" | Feature

! style="width:23%; background:#f0f4f8; text-align:center;" | SRS Tool

! style="width:23%; background:#f0f4f8; text-align:center;" | Typical alternatives

| '''30+ normative limit curves built-in''' — MIL-STD-810H, ECSS, NASA-STD, DEF-STAN, ready to use with no setup

| style="background:#e8f5e9; color:#1b5e20; text-align:center; font-weight:bold;" | ✔ Included

| style="background:#ffebee; color:#b71c1c; text-align:center;" | ✘ Manual entry only

| '''Multi-channel Pass/Fail with per-channel verdict''' — x, y, z compared simultaneously in one run

| style="background:#e8f5e9; color:#1b5e20; text-align:center; font-weight:bold;" | ✔ Included

| style="background:#ffebee; color:#b71c1c; text-align:center;" | ✘ One channel at a time

| '''Direct NVGate signal read''' — no DLL, no NVGate open, no export step

| style="background:#e8f5e9; color:#1b5e20; text-align:center; font-weight:bold;" | ✔ Native

| style="background:#ffebee; color:#b71c1c; text-align:center;" | ✘ Manual export required

| '''NVGate TCP result injection''' — log-log display, autoscaled, direct to project

| style="background:#e8f5e9; color:#1b5e20; text-align:center; font-weight:bold;" | ✔ Native

| style="background:#ffebee; color:#b71c1c; text-align:center;" | ✘ Not available

| '''Automatic shock zone detection''' — envelope algorithm, runs on load

| style="background:#e8f5e9; color:#1b5e20; text-align:center; font-weight:bold;" | ✔ Automatic

| style="background:#fff8e1; color:#7a5200; text-align:center;" | ~ Manual only

| style="background:#e8f5e9; color:#1b5e20; text-align:center; font-weight:bold;" | ✔ One click

| style="background:#fff8e1; color:#7a5200; text-align:center;" | ~ Two separate runs

| '''SRSS + Worst-case Envelope''' — triaxial multi-axis combination

| style="background:#e8f5e9; color:#1b5e20; text-align:center; font-weight:bold;" | ✔ Included

| style="background:#ffebee; color:#b71c1c; text-align:center;" | ✘ Paid add-on

| '''Interactive dB cursor''' on Pass/Fail chart — frequency, SRS, limit, margin at a glance

| style="background:#e8f5e9; color:#1b5e20; text-align:center; font-weight:bold;" | ✔ Included

| style="background:#ffebee; color:#b71c1c; text-align:center;" | ✘ Rarely available

| No dongle, no subscription, no cloud

| style="background:#e8f5e9; color:#1b5e20; text-align:center; font-weight:bold;" | ✔ Free

| style="background:#ffebee; color:#b71c1c; text-align:center;" | ✘ Licence required

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<div style="background:#2e7d32; color:#fff; font-weight:bold; padding:7px 14px; font-size:12px;">⚡ Five steps from measurement folder to qualification verdict</div>

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# Channels appear automatically — shock zone is '''auto-detected''' (yellow markers on signal plot)

# Set '''Q = 10''', range '''1–10 000 Hz''', resolution '''1/12 oct''' → click '''Compute SRS'''

# Read the per-channel verdict, export CSV / PNG, or click '''Inject into NVGate'''

! 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

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

The window is split into two zones:

* '''Left panel''' (340 px fixed) — three tabs: [[#Main Tab|Main]], [[#Advanced Tab|Advanced]], [[#Pass / Fail Tab|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.

[[File:04_left_panel_main.png|right|300px|thumb|'''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:

| style="padding:2px 8px;" | 🟢 '''Connected''' || NVGate reachable. Injection available.

| style="padding:2px 8px;" | 🔴 '''Disconnected''' || NVGate not running. SRS computation still fully functional.

Click '''Select signal folder…''' to open a folder browser (default root: <code>C:\OROS\NVGate data\Projects</code>). Select the Measurement subfolder — channels are listed and the signal is plotted immediately.

One checkbox per recorded channel, showing label, sampling rate, duration and unit:

<pre>  ☑  x  (25 600 Hz  13.86 s  m/s²)

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

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'''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).

: '''Acc''' — Acceleration SRS. Always available. &nbsp; '''Vel''' — Pseudo-velocity SRS. &nbsp; '''Disp''' — Pseudo-displacement SRS. (Vel and Disp require an acceleration input.)

: '''Maximax''' — max(positive, |negative|). The standard curve required by most norms. &nbsp; '''Positive''' — max tensile response. &nbsp; '''Negative''' — max compressive response.

[[File:05_signal_plot.png|center|760px|thumb|'''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.]]

[[File:06_srs_plot.png|center|760px|thumb|'''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.]]

[[File:09_left_panel_adv.png|right|300px|thumb|'''Figure 5 — Advanced tab.''' Shock zone section (auto-detection parameters + manual Start/End override), Residual SRS option, preprocessing, and multi-axis SRSS / Envelope.]]

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'''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 ===

# Trigger threshold = ''Threshold %'' × peak envelope

# Zone = first to last sample above threshold

# Expand by ''Padding ms'' on each side, clamped to signal bounds

| '''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.

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.

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)".

| '''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

Enabled automatically when ≥ 2 acceleration channels are loaded. Check one or both options before computing:

{| class="wikitable" style="font-size:12px;"

| '''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

|}

[[File:07_left_panel_pf.png|right|300px|thumb|'''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 ==

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'''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.

Select '''← User-defined (CSV)''', load a two-column file (Hz, g). Interpolation is log-log linear between breakpoints. Example:

<pre>10, 5 &nbsp; &nbsp; 100, 50 &nbsp; &nbsp; 2000, 50 &nbsp; &nbsp; 10000, 50</pre>

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 ==

[[File:13_passfail_chart_only.png|center|760px|thumb|'''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

| style="background:#e8f5e9; color:#1b5e20;" | Green || M ≥ 3 dB || Well within specification

| style="background:#fff8e1; color:#7a5200;" | Orange || 0 ≤ M < 3 dB || Caution — low margin

| style="background:#ffebee; color:#b71c1c;" | Red || M < 0 dB || '''FAIL''' — exceedance

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.

The result box below the chart shows global verdict, per-channel minimum margin, and the 10 worst exceedance frequencies. Example output:

{| class="wikitable" style="font-size:12px;"

| '''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.

== Reading signal files ==

SRS Tool reads NVGate data with NVGate closed, using no additional DLL. File layout:

       Channel_1.orm    ← JSON: sampling rate, unit, channel Name

       Part_0.ors      ← binary: float32 little-endian, SI units

     Channel_2_0_XXXXXXXX/ …</pre>

Channel label comes from the <code>Name</code> field in <code>.orm</code> (set in NVGate at recording time). Falls back to <code>SourceName</code> ("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: z</pre>

= 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):

<code>z''(t) + 2ζωₙz'(t) + ωₙ²z(t) = −x''(t)</code>

! Curve !! Definition !! Standard?

| Positive SRS || max_t[ ωₙ² z(t) ] || Supplementary

| Negative SRS || max_t[ −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:

{| style="font-size:12px; font-family:monospace; border-collapse:collapse; margin:8px 0;"

| style="padding:2px 10px;" | E = exp(−ζωₙΔt) &nbsp;&nbsp; K = ωd·Δt &nbsp;&nbsp; (ωd = ωₙ√(1−ζ²))

| style="padding:2px 10px;" | b₀ = 1 − E·sin(K)/K &nbsp;&nbsp;&nbsp; b₁ = 2(E·sin(K)/K − E·cos(K)) &nbsp;&nbsp;&nbsp; b₂ = E² − E·sin(K)/K

| style="padding:2px 10px;" | a₁ = 2E·cos(K) &nbsp;&nbsp;&nbsp; a₂ = −E²

| style="padding:2px 10px; font-weight:bold;" | y[k] = b₀x[k] + b₁x[k−1] + b₂x[k−2] + a₁y[k−1] + a₂y[k−2]

== 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 ==

<code>Q = 1/(2ζ)  ↔  ζ = 1/(2Q)</code>

! Q !! ζ !! Use

| '''10''' || '''5 %''' || '''Aerospace standard — MIL-STD-810, ECSS, NASA'''

| 50 || 1 % || Lightly damped structures

| 5 || 10 % || Rubber-mounted, heavily damped

! 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 ==

{| class="wikitable" style="font-size:12px;"

! 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 =

{| class="wikitable" style="font-size:12px; width:100%;"

! Unit !! Physical quantity !! Vel/Disp SRS available

| '''m/s², g''' || Acceleration || style="background:#e8f5e9; color:#1b5e20; text-align:center;" | ✔ Yes

| m/s, mm/s || Velocity || style="background:#ffebee; color:#b71c1c; text-align:center;" | ✘ No

| m, mm, µm || Displacement || style="background:#ffebee; color:#b71c1c; text-align:center;" | ✘ No

| N, kN || Force || style="background:#ffebee; color:#b71c1c; text-align:center;" | ✘ No

| V, mV || Voltage || style="background:#ffebee; color:#b71c1c; text-align:center;" | ✘ No

| Pa, N/m² || Pressure || style="background:#ffebee; color:#b71c1c; text-align:center;" | ✘ No

| rad/s, RPM || Angular velocity || style="background:#ffebee; color:#b71c1c; text-align:center;" | ✘ No

! style="width:20%;" | Term !! Definition

| '''SRS''' || Shock Response Spectrum. Peak SDOF response as a function of natural frequency.

| '''Maximax''' || max(Positive, |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].

| '''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.

<div style="margin-top:28px; padding-top:12px; border-top:1px solid #ddd; font-size:11px; color:#888; text-align:center;">

Algorithm: D.O. Smallwood, ''An Improved Recursive Formula for Calculating Shock Response Spectra'', Shock and Vibration Bulletin, 1981. &nbsp;·&nbsp;

Standards referenced: MIL-STD-810H (2019) · ECSS-E-ST-10-03C (2012) · NASA-STD-7003A (2011) · DEF-STAN 00-35 Part 3 (2021).