Straight Beam Modes; Angle Beam Modes - Olympus EPOCH 650 User Manual

9.2.1

Straight Beam Modes

Straight beam calibrations can be performed by two methods. For the purposes of this
calibration discussion, straight beam refers to all zero-degree probes, including contact,
dual, delay line, immersion, etc. The two methods of straight beam calibration are:
• Thickness
This standard straight beam calibration mode requires you to provide two
different, known material thicknesses to properly calibrate the instrument. The
thin material thickness allows for zero offset calibration, and the thick material
thickness allows for velocity calibration.
• Echo-to-echo
This calibration mode allows you to use any echo-to-echo measurement to
calibrate for material velocity only. In echo-to-echo calibration, the effects that
cause zero offset are eliminated by gating a particular indication that represents
the start point of the measurement. A second gate is set to track that gated
indication to acquire a measurement.This means that you must only calibrate for
the material velocity of the sample to acquire accurate echo-to-echo
measurements. You can perform echo-to-echo measurements between G2–G1,
and this calibration mode will only be available if Gate 2 tracking is turned on (see
"Gate Tracking and Echo-to-Echo Measurements" on page 130).
9.2.2

Angle Beam Modes

Angle beam calibrations can be performed by two methods:
• Sound path
This standard angle beam calibration mode uses the sound path measurement of
two different, known material thicknesses to properly calibrate the instrument.
Typically, these sound path measurements are made from the radius of a
calibration test block. The smaller (thin) sound path measurement allows for zero
offset calibration, and the larger (thick) sound path measurement allows for
velocity calibration.
• Depth
This angle beam calibration mode uses the known depth of two different
reflectors to properly calibrate the instrument. Typically, these depth
measurements are made from side-drilled holes of equal size. For accurate
measurements, you must first verify the refracted angle of the transducer, as the
EPOCH 650 calculates depth values based on sound path and known refracted
DMTA-10055-01EN, Rev. A, February 2015
Calibration 145