2. OPERATING THE Y7 YOKE
2.1 PRINCIPLE OF OPERATION
When the Yoke is connected to a suitable power source, depressing the ‘Push to
test’ switch creates an intense magnetic field between the Yoke legs. As the Yoke
is applied to a steel plate, the magnetic circuit is closed, and the magnetic field
enters the plate between the legs of the Yoke at and near the surface. A surface
crack across this field cuts the magnetic circuit, the two sides of the crack become
opposite poles of a magnet and a leakage field occurs in the air above the crack.
Magnetic particles are attracted by this leakage field and mark its location.
2.2 SAFE USE OF THE YOKE
Our yokes manufactured to the highest technical standards. You can ensure safe
operation of your yoke by observing general safety and accident prevention regu-
lations, including the advice outlined below.
Before using the Yoke:
• Familiarise yourself with thE yoke’s construction and method of operation. If
necessary, contact the manufacturer - Magnaflux GmbH - for instruction/training.
• Ensure it is physically undamaged.
• Ensure the cable is free from cuts which expose the wiring.
• Tighten the articulated joints if they are excessively loose.
During use:
• Follow the operating instructions carefully.
• Observe the safety distances (see section 1.1) and time limit for usage.
• Wear appropriate personal protective equipment to protect yourself from over
exposure to electromagnetic fields.
• Do not allow untrained personnel to operate the yoke; improper use of the
yoke can be hazardous to health.
• Only allow authorised personnel who are aware of the potential dangers of
electromagnetic exposure into the areas where the yoke is being used.
• Do not attempt to repair or rebuild the yoke unit.
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2.3 INSTRUCTIONS FOR USE
1. Adjust the leg spacing to 125 - 175mm and place the Yoke firmly on the work
piece, ensuring the best contact possible, with the suspected defect at right
angles to the poles. If the direction of the potential defect is not known, two
inspections of the area should be made, turning the Yoke approximately 90° for
the second inspection.
2. With the selector switch in either the AC or DC position, depress the test switch
to energise the Yoke.
3. Apply the magnetic ink/powder to the area between the Yoke legs and inspect
closely for cracks or defects. The current should remain ON (continuous
method) to ensure maximum sensitivity.
4. Repeat the process until the entire area of the part is inspected.
5. Demagnetisation: With the Yoke in the AC mode, place the part across the
poles and, whilst the current is flowing, withdraw the part from the field to a
distance of at least 0.75m before turning o the magnetising current.
Dierent parts and surfaces will dictate the best magnetising current, current magni-
tude, particle application and testing procedures to achieve good inspection results.
Always use the lowest magnetising current necessary to provide distinct indications,
as excessively high fields may magnetically saturate the test piece and cause a
‘masking eect’, hiding the defects.
2.4 MAGNETISING FIELD SELECTION
AC magnetisation
This induced field only detects surface cracks. It is particularly useful for inspecting
thick and irregular sections for surface defects. Best results are usually obtained
using the drymethod.
Pulsed DC magnetisation
This induced field penetrates the work piece and detects both surface and slightly
subsurface cracks. Best results are usually obtained using the wet method.
