FIELD OF THE INVENTION
The invention relates to a square cross section coil based magnetic coil apparatus for producing uniform magnetic field intensity with high accuracy for large application. The cost and ease of manufacturing such a large structure . within close tolerances are of prime concern. The apparatus comprises of four non-magnetic formers over a non-magnetic structure. All four coils with equal square cross section are disposed on the formers and connected in series so as to excite them through a single current source. The inner coil pair is placed at 12.81% of the square dimension distanced from centre. The outer coil pair is placed at 50.54 % of the square dimension distanced from centre. The ampere turn of inner coil pairs are 42.35 % of that of outer coil pairs. The achieved magnetic field distribution over the volume is within 2% tolerance.
BACKGROUND OF THE INVENTION
Many electric and electronic machines along with their controllers is used in wide variety of applications ranging from domestic to industrial front. A few are used in areas like telecommunications, defense etc. Some of the control functions of such machines are more susceptible to electromagnetic fields. Hence, needed to be tested for their compliance with magnetic field obligations. Some small size machines and controllers can be tested in small cavities of uniform test field. But, it is quite complicated and sometimes impractical to produce uniform magnetic field over large size machines along with their controllers.

Usually preferred configuration to provide a uniform, low frequency magnetic field for susceptibility testing of electrical and electronic equipment is a pair of Helmholtz coils. It produces a homogeneous magnetic field at its centre which is directly proportional to the number of turns in the coils and the current. A Helmholtz coil is a parallel pair of identical circular coils spaced one radius apart and wound so that the current flows through both coils in the same direction.
There are many other lab-scale configurations to produce uniform magnetic field intensity but most of them are limited to smaller machines. Some of them can be enlarged to produce uniform magnetic field intensity but the manufacturability of such a large circular and cylindrical configuration within tight tolerances is quite difficult and, most of the time, impractical. Sometimes the testing requirement does not allow ex- situ testing of equipments. In such cases, in-situ arrangements are essential for producing uniform magnetic field intensity in test volume.
OBJECTS OF THE INVENTION:
The object of the invention is to develop a magnetic coil testing device for producing uniform magnetic field intensity with high accuracy over large volumes.
Another object of the invention is to develop a square cross section based magnetic coil system for ease of manufacturing and installation at site wherein all four coils have same square cross section.
Yet, another object of the invention is to develop a coil apparatus comprising of non- magnetic formers over a non-magnetic structure wherein

all four coils are disposed on.
Yet, another object of the invention is to develop an easily foldable non¬magnetic structure for easy in-situ as well as ex-situ testing.
Yet, another object of the invention is to configure all four coils and connect them in series so as to excite them through a single current source.
Yet, another object of the invention is to ensure that inner coil pair is placed at 12.81% of the square dimension distanced from centre.
Yet, another object of the invention is to ensure that outer coil pair is placed at 50.54 % of the square dimension distanced from centre.
Further object of the invention is to ensure that the ampere turn of inner coil pairs are 42.35 % of that of outer coil pairs.
Still another object of the invention is to ensure that the achieved magnetic field distribution over the required volume is within 2% tolerance.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
Fig-1 shows Single Coil on Non-magnetic Former.
Fig-2 shows Side-view of all Four Square Coils on Non-magnetic Former with
Support Structure,
Fig-3 shows Front-view of all Four Square Coils on Non-magnetic Former

with Support Structure.
Fig-4 shows Single Coil on Non-magnetic Former.
Fig-5 shows Equipment under Test.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT:
Figure 1 represents a coil 101 on a non-magnetic former 102.
Fig.2 represents the side view of four square coils on non-magnetic formers. All four coils are having same square cross section. Outer coil-1 201 is placed at 50.54% of its square dimension distanced from centre line 206 in the left side. Outer coil-2 204 is placed at 50.54% of its square dimension distanced from centre line 206 in the right side. Inner coil-1 202 is placed at 12.81% of its square dimension distanced from centre line 206 in the left side. Inner coil-2 203 is placed at 12.81% of its square dimension distanced from centre line 206 in the right side. All four formers are supported by a non-magnetic non-metallic structure 205. The outer coil-1 201 and outer coil-2 204 is termed as outer coil pair while inner coil-1 202 and inner coil-2 203 is termed as inner coil pair.
Fig.3 represents the front view of all four square coils on non-magnetic formers. In the front view, any of the four coils 305 with square cross section can be seen along with their supports. Each coil has four supports; one top side coil support 301, one bottom side coil support 302, one left side coil support 303 and one right side coil support 304. All four formers are supported by a non-magnetic non-metallic structure 205, 307. The complete structure at bottom is supported on non-magnetic non-metallic beams 306 on each side. All four coils are connected in series and only two terminals

308, 309 are left for applying excitation-Fig4 represents the side view of complete magnetic coil assembly. The final assembly of outer coil-1 406 supported on coil former 401, inner coil-1 407 supported on coil former 402, inner coil-2 408 supported on coil former 403 and outer coil-2 409 supported on coil former 404 is shown along with termination of Outer Coil-1410 and termination of Outer Coil-2 411. All four formers 401, 402, 403, 404 are supported by a non-magnetic non-metallic structure 205, 307, 405. The complete structure at bottom is supported on non-magnetic non-metallic beams 306, 412 on each side. The centre line 413 along the length of non-magnetic non-metallic structure is marked for field measurement.
Fig.5 represents the position of 'Equipment under Test' 501 in the constrained volume of non-magnetic coil support structure 503. The complete coil system 502 is connected through external connections 504 to excitation power supply 505. This shows the complete magnetic coil system for producing uniform magnetic field intensity with high accuracy for large applications.

We claim:
1. A magnetic coil apparatus for producing uniform magnetic field intensity for
an electric or electronic machine that comprises of:
- an inner coil pair (202, 203) wound on a non-magnetic former;
- an outer coil pair (202, 204) wound on the non-magnetic former;
wherein the outer coil pair and the inner coil pair are positioned at predefined distance from a centre line (206) and connected in series;
- an external power supply (505);
wherein the coil pair is coupled to the external power supply to provide excitation to the said coil pair that outcomes a magnetic field distribution within 2% tolerance.
2. The magnetic coil apparatus as claimed in claim 1, wherein the coil pair have equal square cross section supported and wounded on four non-magnetic formers.
3. The magnetic coil apparatus as claimed in claim 1 is a foldable structure and can be assembled in-situ and ex-situ for radiative susceptibility testing of heavy weighted electric machines.
4. The magnetic coil apparatus as claimed in claim 1, wherein a coil is
supported on all four sides by means of a nonmagnetic nonmetallic structure
(205,307).
5. The magnetic coil apparatus as substantially descried and illustrated herein
with reference to the accompanying drawings.