Taking A Reading - Elcometer CG30 Operating Instructions Manual

5.2.3 Known velocity calibration
This procedure requires that the operator knows the sound-velocity of the material to be measured.
A table of common materials and their sound-velocities can be found in "Sound velocities of
common materials" on page 24.
1. Press ON/OFF key to switch on the gauge.
2. Press the CAL key to enter calibration mode. If the MM (or IN) symbol is flashing, press the
CAL key again, so that the M/s (or IN/µs) symbols are flashing.
3. Use the UP and DOWN arrow keys to adjust the displayed velocity up or down, until it matches
the sound-velocity of the material to be measured.
4. Press the CAL key once more to exit the calibration mode. The gauge is now ready to perform
measurements.
Note: At any time during the gauge calibration procedure (IN, MM, IN/µs, or M/s flashing in the
display), pressing the PRB-0 key will restore the gauge to the factory default sound-velocity for
steel, 5918 m/s (0.233 in/µs).
To achieve the most accurate measurements possible, it is generally advisable to calibrate the
gauge to a sample piece of known thickness. Material composition (and thus, its sound-velocity)
sometimes varies from lot to lot and from manufacturer to manufacturer. Calibration to a sample of
known thickness will ensure that the gauge is set as closely as possible to the sound-velocity of the
material to be measured.

6 TAKING A READING

Disclaimer: Inherent in ultrasonic thickness measurement is the possibility that the instrument will
use the second echo rather than the first echo from the back surface of the material being measured
while in standard pulse-echo mode. This may result in a thickness reading which is TWICE what it
should be.
The responsibility for proper use of the instrument and recognition of these types of phenomenon
rests solely with the user of the instrument.
6.1 BEFORE YOU START
• Set the zero point of the gauge.
See "Transducer - Zeroing" on page 8.
• Calibrate the gauge.
See "Calibration" on page 9.
• Prepare the surface.
See "Condition and preparation of surfaces" on page 22.
6.2 PROCEDURE
1. Apply couplant
For the gauge to work correctly there must be no air gaps between the transducer and the
surface of the material to be measured. This is achieved using a material called a couplant.
Before the transducer is placed on the surface, put a small amount of the couplant supplied
with the gauge on the surface of the material. Typically a single drop is sufficient.
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