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Site Survey
The site survey is the first step needed to design a shield. It is necessary to establish the shape and strength of the magnetic field in order to make any design decisions. The basic equipment needed to accomplish this goal is a gauss meter and/or a field probe (EP-102A) w/ Fluke multi-meter (or equivalent). Magnetic Shield Corporation recommends an easy two-step process.
Step 1
Establish the source or sources of the interference.
Step 2
Apply a grid approach to measurement reading. Map the field strengths at intervals of one meter or 3 feet in each direction. Measure from floor to ceiling and from one end of the wall to the other.
This grid will provide you with an overall map of the field and any "hot spots". This map (matrix) of the field can then be used to calculate the type and thickness of material required to deliver adequate shielding.
Materials
The shielding materials that MSC uses for the mitigation of magnetic (low frequency) interference are the proprietary alloys NETIC and CONETIC. These were developed by MSC specifically for this purpose and have proven to be the most effective means for remediation.
Both are available in either foil and sheet form and in a range of thickness to accommodate the specific application. For fields of low intensity CO-NETIC AA is recommended. Its high initial permeability and corresponding high attenuation characteristics make it the ideal solution. In fields of high intensity NETIC S3-6 is preferred because of its high magnetic saturation characteristics. In some applications, combinations of the two materials may be useful, with NETIC® always placed closer to the source of interference.
Foil with adhesive backing is used to seal seams against leakage. All material supplied by MSC is what we term "Perfection Annealed". That indicates that in its final annealed state, these materials are ready to perform as a shield without any further anneal processing.
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| Physical and Magnetic Data on Shielding Alloys |
| | NETIC S3-6 STRESS ANNEALED* | CO-NETIC AA PERFECTION ANNEALED |
| Specific Gravity |
7.86 |
8.74 |
| Coefficient of Expansion, per oC x 10-6 |
13.7 |
12.6 |
| Tensile Strength, PSI x 103 |
42 |
64 |
| Yield Strength, PSI x 103 |
27 |
18.5 |
| Modulus of Elasticity, PSI x 106 |
30 |
25 | | Hardness, Rockwell B |
50 Ref. |
50 Ref. |
| Elongation in 2 inches |
38% |
27% |
| Melting Point |
2790°F
1532°C |
2650°F
1454°C |
| Thermal Conductivity (cal/sec/cm2/cm/°c) at 20° |
.118 |
.138 |
| Electrical Resistivity Micro-ohm-centimeter |
1 |
55 |
| Saturation Induction (Gauss) |
21,400 |
8,000 |
| Initial Permeability |
200 |
30,000 |
| Permeability at 40 B |
300 |
75,000 |
| Permeability at 200 B |
500 |
135,000 |
| Maximum Permeability |
4,000 |
450,000 |
| Induction at µ max. |
8,000 |
3,000 |
| Coercive Force Hc,Oersteds |
1.0 |
.015 |
| Curie Temp. |
1420°F
770°C |
850°F
454°C |
| Minimum Operating Temp. |
4°K |
4°K |
| Note: Magnetic data is for sheet material measured in a D.C. field. |
| *Stress annealed material must be annealed after fabrication for optimum magnetic shielding properties. |
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