Cygnus 1 Operation Manual page 42

If there is up to three fixed bars plus one flashing bar, but never any reading - this means
the Gauge is receiving unrelated echoes from more than one reflector :
on heavily corroded areas this is often a problem :
try check measurements on an adjacent area of the same material
check the Gauge and Probe together on a test block :
if there is still no reading the Gauge may require servicing
If readings obtained are erratic or unstable
Check that the Probe-assembly is properly connected to both Probe and Gauge, and that
the O-Rings are properly seated in their correct positions
False readings can occur if the Probe-assembly has not been fully screwed onto the
Gauge-body
See : Fitting the Probe-module, page 18
Check that the Probe and its membrane are correctly assembled with sufficient couplant
Air bubbles inside the membrane can cause false readings
Membrane stretched too tightly over the Probe-face can cause false readings
Ensure that the Probe-frequency is suitable for the probable minimum thickness of the
material being measured
Probe-frequency too low causes doubling and tripling of the actual thickness
See Probe Usage, page 39
Common reasons which cause difficulty getting readings
Is the Probe-membrane fitted correctly ?
See : Probe/Knurled Ring Assembly, page 20
Check that there is a thin layer of oil between the membrane and Probe-face, and
with no air-bubbles trapped
Check that the membrane has not been stretched too tightly over the Probe-face
Is the Probe-cable OK ?
Check that the cable is in good condition
Check that the Probe-assembly is correctly fitted onto the Gauge-body
Is the material measurable at all ?
Are the front and back faces of the material parallel ?
Is the material not too corroded ?
Is the material not too thin for the Probe being used ?
It is often worth confirming that the Gauge is operating OK using a test sample – and
also to confirm that the material can actually be measured by ultrasonic multiple-echo
thickness measurement.
Measuring with the Gauge
41