Effects Of Vibration And Mechanical Shock; Metal Free Zone - Thermo Scientific Apex Service Manual

Effects of
Vibration and
Mechanical

Metal Free zone

Thermo Fisher Scientific
REC 4258 Rev C
The metal case screens the magnetic field of the search head avoiding
false detections from nearby moving metallic objects. Obviously this
ensures reliable operation. However, the case is metal and can produce
signals that may cause false detection.
When product effect is negligible, APEX eradicates case effects
Shock
because they have a phase angle characteristic like most products and
can be learnt by lightly vibrating the case. The phase angle from the
case is usually about 89 degrees.
When phasing a wet product, the dominant signal to be eradicated is
the product itself, which is typically around 0 degrees. This is totally
at-odds with the signal from the case and traditionally, you can't phase
out a product and simultaneously phase out the vibration effects of the
metal case.
What you may find in many wet applications are search heads that can
be prone to the effects of vibration. Obviously the product effect needs
to be eradicated to achieve best performance but this leaves the effects
from the case largely unchecked.
APEX recognizes this problem and for many wet applications,
vibration or shock to the case will not be a problem. The characteristic
of case vibration or shock is that it usually produces a high initial
impulse signal that APEX removes before it can be detected.
By applying APEX's new impulse reduction system, most applications
dogged by vibration problems are fixed. This feature is not in DSP3.
Previously it was mentioned that the case screens the search head
magnetic field to prevent false detections. In truth the aperture
openings remain unscreened i.e. the magnetic field extends beyond
aperture openings and can be affected by metallic reject arms when
they operate. This will cause a false detection and fire the reject arm
after the delay and the cycle repeats.
This sort of problem has affected a few systems in the past but
APEX's new impulse reduction system should fix this in most
applications allowing the search head to operate at lower detection
thresholds.
Reference Material
Reference Material 6-9