Measuring with the Gauge
39
PROBE USAGE
Cygnus 1 ROV Gauge is supplied with a single Ultrasonic Probe. More than one Probe-type
is available, depending on the application
Probes are not freely interchangeable - if you want to use the Gauge with a Probe of a
different Frequency : the Gauge must be returned to Cygnus, so that it can be configured to
operate with the new Probe
Probe Selection
Probe-diameter - apart from the physical limitations of the Probe size, the diameter of the
crystal affects the probe performance :
¾ Larger diameter crystals produce more energy, which in turn gives better penetration.
¾ Smaller diameter crystals produce a narrower beam, which is a distinct advantage when
looking for small reflectors - they are particularly useful on tubes of small diameter
Probe-frequency :
¾ Lower-frequency Probes are able to penetrate into corroded materials more easily, but
are not suitable to measure thin materials
¾ Higher-frequency Probes are needed to measure thin material, but may not have enough
penetration power to make multiple-echo measurements
Probe face colour
Cygnus 1 ROV Gauge should only be used with soft-face Probes, as supplied by Cygnus.
L The colour of the Probe face indicates the Probe-frequency
See Table of Probe Types, page 12
Using Probes at high temperature
Heat can damage the Probe crystal. In Cygnus Probes the crystal is very near to the face.
The higher the temperature of the test material and the longer the contact with the Probe,
the greater the likelihood of eventual damage to the crystal.
¾ At temperatures above normal, ie : above 75
o
C (170
o
F), always avoid prolonged
contact.
¾ Teflon (PTFE) membranes are available for measurements up to 150
o
C (318
o
F).
¾ Thin oil couplants evaporate rapidly at high temperature – high melting-point grease is
more suitable in such cases.
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