Nova Eclipse TG950 - Users Manual
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inches (0.25 to 25 cm), it must have highly stable and accurate timing
circuitry. Think of it as a highly sophisticated, super-accurate stop-watch.
Attached to the NOVA is a cable connected to an ultrasonic transducer, or
probe. The transducer has a thin wafer of a piezoelectric material at its
surface. Piezoelectric materials convert short pulses of electrical energy
into tiny mechanical displacements, and, conversely, from mechanical
displacements into electrical impulses. The probe acts both as transmitter
and receiver
W hen coupled to the surface of the test object – call it the
entry surface
–
the probe receives a short-duration electrical pulse from the pulser in the
NOVA. Fundamentally, the “clock” starts with this pulse. The ultrasonic
sound-beam begins its transit within the test object, induced by the
electrical-to-mechanical impulse generated by the transducer. The
ultrasonic impulse travels through the test object at a velocity characteristic
of the material. W hen it reaches a boundary – for example, the side of the
test object opposite the entry surface – the
back surface
– it reflects
(
echoes
) back toward the entry surface. As it impinges on the entry
surface, the transducer senses the tiny mechanical echo displacement and
converts it into a small electrical signal. In the receiver section of the
NOVA, the “clock” is signaled to stop. The time interval between the start
and stop is converted into a thickness measurement. The characteristic
velocity of the test material – distance divided by time (e.g., inches or
millimeters per microsecond) – divided by the round-trip transit time
(microseconds) yields total distance traveled. Since the total transit path is
twice the actual thickness, it is automatically divided by one-half and
displayed as a decimal thickness. On test objects with smooth, parallel
surfaces, the displayed thickness is true within the resolution of the last
decimal place displayed.
Nova Eclipse TG950 - Users Manual
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Functional Diagram
This round-trip time of the echo is linearly correlated to the test material's
thickness – the thicker the material, the longer the round-trip time. The
NOVA’s sophisticated circuitry precisely measures the round trip-time and
compensates for the characteristic ultrasonic velocity of the material being
gaged. The measured thickness is displayed, virtually instantaneously, on
the digital display and in the units selected, either inches or millimeters.
1.2 General Applications
The NOVA TG950 gages a wide range of thicknesses on metals, plastics,
ceramics, glass or virtually any other material which satisfactorily conducts
ultrasound, and has relatively parallel (or concentric) surfaces. Its high-
resolution capabilities make the NOVA TG950 uniquely applicable to gaging
very thin materials – for metals, as thin as 0.005 inch (0.13 mm) – with
resolution of 0.0001 inch (0.001 mm). However, it can also be effectively
used to gage thickness up to 20 inches (500 mm).
Small, local thickness variations, such as those caused by corrosion,
erosion, and certain types of internal flaws may also be detected.
[9xx
Model-dependent: Later sections of this manual will detail a unique
