Parameters

This page describes every editable Analysis-tab field and every operator-controlled parameter.

Experiment Fields

These fields are shown in the Experiment box on the Analysis tab.

Field Unit Meaning
npoint samples Number of samples in each windowed incident, reflected, and transmitted pulse.
diam_bar / bar diameter m Diameter of the incident/transmitted bars. Used to compute bar cross-sectional area and force.
E Pa Bar Young's modulus. Used in force calculation.
x1 m Distance from gauge 1 to the specimen. Used to locate the reflected pulse and to apply dispersion correction.
x2 m Distance from the specimen to gauge 2. Used to locate the transmitted pulse and to apply dispersion correction.
c0 m/s Bar wave speed. Used for pulse timing, velocity, strain rate, and dispersion correction.
gfact dimensionless Strain-gauge factor. Used to convert bridge voltage to strain.
vbridge V Bridge excitation voltage. Used with gfact in the voltage-to-strain conversion.
diam_spec / specimen diameter m Specimen diameter. Used to compute specimen area and stress.
long_spec / specimen length m Specimen length. Used to compute engineering strain rate.
tdelay_us microseconds Acquisition delay for the transmitted signal. Hopki pads the transmitted record by this delay before windowing.
pretr_pct percent Pre-trigger percentage. Used to guess the initial tim_cut when an experiment loads.
damp_f coefficient Amplitude damping coefficient used during frequency-domain correction.

Derived Values

Value Source Notes
tpp Signal time column Time per point. This is intentionally not editable because it belongs to the recorded signal.
x1 estimate Signals Used only when x1 is absent from all config layers. Usually more reliable than x2.
x2 estimate Signals Used only when x2 is absent from all config layers. Treat as best-effort and verify with Pick x2 (2 clicks) when needed.

Operator Parameters

Parameter Control Default Meaning
tim_cut Vertical line on Signals Initial guess from pretr_pct Pulse-start time. The incident pulse window starts here; reflected and transmitted windows are positioned from x1, x2, c0, and tdelay_us.
invert_signals invert signal polarity off Negates both input channels before analysis.
nu Poisson nu 0.29 Poisson ratio used by the Bancroft phase-velocity table for dispersion correction.
reflect_shift reflect shift spinbox/slider 0 Sample shift applied to the reflected pulse after correction. Positive values delay it; negative values advance it.

How Hopki Uses The Values

The core pipeline runs in four stages:

  1. Window pulses using tim_cut, x1, x2, c0, tdelay_us, nlong, and npoint.
  2. Correct dispersion and damping using nu, diam_bar, c0, x1, x2, tpp, npoint, and damp_f.
  3. Align the reflected pulse using reflect_shift.
  4. Compute mechanics using diam_bar, E, gfact, vbridge, diam_spec, long_spec, c0, and tpp.

Configuration Files

Modern configuration uses hopki.toml. Ancestor files are applied before the experiment-local file, so a campaign-level file can hold shared bar constants and each experiment can hold only specimen-specific values.

[bar]
nlong = 1000
npoint = 450
diam_bar = 1.27e-2
E = 1.9e11
x1 = 0.558
x2 = 0.230
c0 = 4800
gfact = 2.13
vbridge = 10.15
damp_f = -1.8e-2

[specimen]
diam = 4e-3
length = 4e-3
tdelay_us = 0.0
pretr_pct = 10.0

[signals]
incident = "WAVE0003.FLT"
transmitted = "WAVE0004.FLT"

Legacy folders with no hopki.toml can still use incid.exp, incid.spec, and DAMP_F.