ECA RS-348-1968 Magnetic Field Polarity Including Definitions and Determination of Polarity《磁场密度极性 包括极性的定义和确定》.pdf

1、EIA 348 68 3234600 O065783 9 w. _- c- - . MARCH 1968 il EIA STANDARD on Magnetic Field Polarity, Including Definitions and Determination of Polarity ELECTRONIC INDUSTRIES ASSOCIATION STANDARD RS-348 Formulated by /EDEC Electron Tube Council EIA 348 68 m 3234600 0065784 O m NOTICE These standards, ad

2、opted and issued by the Electronic Industries Association were formulated by the Electron Tube Council of the Joint Electron Device Engineering Councils. EIA engineering standards are designed to serve the public interest through eliminating mis- understandings between manufacturers and purchasers,

3、facilitating interchangeability and improve- ment of products, and assisting the purchaser in selecting and obtaining with minimum delay the proper product for his particular need. Existence of such standards shall not in any respect preclude any member or non-member of EIA from manufacturing or sel

4、ling products not conforming to such standards. Recommended standards adopted by EIA are without any regard to whether or not their adop tion may in any way involve patents on articles, materials, or processes. By such action, EIA does not assume any liability to any patent owner, nor does it assume

5、 any obligation whatever to parties adopting the recommended standards. Published by ELECTRONIC INDUSTRIES ASSOCIATION Engineering Department 2001 Eye Street, N. W., Washington, D. C. 20006 Electronic Industries Association 1968 All rights reserved Price $.60 Printed in U.S.A. - EIA 348 b8 = 3234bOO

6、 0065785 2 1 -. RS-348 Page 1 MAGNETIC FIELD POLARITY, INCLUDING DEFINITIONS AND DETERMINATION OF POLARITY (From Standards Proposal No. 95 7, formulated under the cognizance of JEDEC Committee JT-13 on Microwave Devices.) 1. PURPOSE The purpose of this standard is to eliminate confusion, by providin

7、g definitive statements of the con- ventions involved in determining the polarity of a magnetic field, and by describing basic practical methods that may be used, with necessary precautions. While it might be considered that the conven- tions are basic text-book material, it is found that few text-b

8、ooks state them explicitly, and disagree- ment among engineers is observed as a result. Since some electrical or electronic devices may be destroyed, if the magnetic field polarity is incorrectly determined, it is important that disagreement or confusion be avoided. 2. DEFINITIONS 2.1 2.2 2.3 The No

9、rth (N) pole of a magnet is that pole which points toward the geographic North of the earth, when the magnet is freely suspended. No distinction is made between ?North? and ?North-seeking?. The implication that the earth?s pole in the North of Canada is a magnetic South (S) pole is an accepted parad

10、ox. The direction of a magnetic field at any point, whether due to a permanent magnet or to a solenoid, is the direction of the force on the North pole of a small magnet at that point. Hence, it is the direction in which the N end of a compass needle points when placed in the field. The direction of

11、 the external field of a permanent magnet is away from the North pole, toward the South pole. However, the ends of a solenoid should not be marked N or S, because both the internal and external fields are accessible, and run in opposite directions, so that any such marking is ambiguous. Coil marking

12、s, if used, should relate the direction of the internal field directly to the polarity of the current supply, without reference to N or S poles. For example, ?Internal field direction when black lead is positive.? EIA 348 68 W 3234600 0065786 4 W RS-348 Page 2 3. METHOD 3.1 Permanent magnet: bring a

13、 compass or suspended test magnet near to one end of the perma- nent magnet. This end is North (N) if the compass points away from it. 3.2 Solenoid or coil: with a current of known polarity flowing in the solenoid or coil, bring a compass into the region of interest (normally inside the coil“); the

14、field direction is the direc- tion in which the compass points, assuming that the current is sufficient for the solenoid field to mask the earths field. (See Figure 1 .) “ Even when the region of interest is inside, it may be more convenient to check the polarity externally (provided thereis no iron

15、 return path), to avoid removal of a tube or other component within the coil. In this case, the polarity should be checked close to the coil and in any plane, perpendicular to the axis, which passes through the working region; (near the ends the field has strong radial components). The internal fiel

16、d direc- tion is then the opposite of that observed externally. 3.3 If the winding direction of a coil is known or can be seen, the magnetic field direction can be determined by the right hand rule: with the right thumb along a wire, pointing in the direction of current flow, the fingers curl around

17、 the wire in the direction of the magnetic field. Al- ternatively, to an observer looking along the coil axis, a clockwise flow of current produces a magnetic field directed along the coil axis and away from the observer. 4. PRECAUTIONS A compass or small test magnet can be remagnetized in the rever

18、se direction if it is suddenly exposed to a large field from a permanent magnet or solenoid. Therefore, the compass or test magnet should be checked before and after a measurement by taking it a short distance away from local magnetic in- fluences, and making sure that the N or marked end points tow

19、ard geographic North. 5. CONVENTION FOR MAGNETRONS Non-packaged magnetrons (Le. magnetrons operated in a permanent magnet which is separate from the tube) should be mounted with the cathode terminal of the tube adjacent to the North pole of the magnet. c- . i . -* EIA 348 b8 = 3234b00 0065787 b - RS-348 Page 3 I- t- 1 r- I I I Working I I I I I 1 I I I I I- - Region I ! I I - -I i I I I I I I I I I I I use compass in this region for external Polar ty check I 1 I I I I I 1 I I FIGURE 1 : External Polarity Check when Working Region is Inaccessible