Calibration; Why Should I Calibrate My Thickness Gauge; Calibration Options - Cygnus 1 Ex Manual

Calibration

Why should I Calibrate my Thickness Gauge?

Ultrasonic thickness gauges measure time in order to measure the thickness of the
material being tested. It relies on the principal that sound travels through a
material at a constant velocity or speed. If you can accurately measure the time it
takes to travel through a material, and you know its velocity, then you can
calculate its thickness.
Modern thickness gauges are easily capable of measuring time accurately to 10
Nano seconds (0.000,000,01 seconds) so this is considered to be more than
sufficiently accurate.
This means the accuracy of any thickness gauge measurement relies principally on
the velocity of sound value being correct for the material being measured.
There are tables listing the velocity of sound of most common metals and
materials, but these velocities are only "typical" values. For example, Mild Steel
has a typical velocity of 5920 m/s – but in practice when measuring a variety of
mild steel samples, the velocity can range anywhere from 5860 to 5980 m/s.
This means if you want to achieve the most accurate thickness measurements you
must calibrate your thickness gauge to a sample of the same material you will be
testing – and a sample that you can accurately measure the thickness of with a
Vernier or Micrometer.
Remember - your measurements are only as good as your calibration!
Instructions for calibrating the gauge can be found on page 44.

Calibration Options

The Cygnus 1 Ex gauge is supplied calibrated with a calibration certificate. The
Gauge will have been calibrated to measure thickness through steel (grade
S355JO) with a velocity of sound of 5920 m/s.
Either a 15mm or 1/2" Test Block is supplied with the kit so the Gauge can be
quickly checked for correct operation. Note, this test block is not intended to be
used for calibration of the Gauge.
The best way to calibrate the Gauge is to Calibrate using a Known Thickness
using a sample of the material you intend to measure. This method
determines the velocity of sound for the material sample, which will always
Cygnus 1 Ex Operating Manual
Thickness = time x velocity
Page 41 of 91
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