In this case there is said to be hysteresis in the readings.
Hence in performing a cycle there is a waste of energy corresponding to what has been termed hysteresis-loss.
Owing to hysteresis the part of the band magnetized is not symmetrically placed with regard to the magnetic poles, but advanced in the direction of motion of the band.
When the oscillations pass through the coil they annul the hysteresis and cause a change of magnetism within the coil connected to the telephone.
A well-known example of hysteresis is presented by the case of permanent magnets.
A notable feature in both classes of curves is that, owing to hysteresis, the ascending and descending limbs do not coincide, but follow very different courses.
The ballistic method is largely employed for determining the relation of induction to magnetizing force in samples of the iron and steel used in the manufacture of electrical machinery, and especially for the observation of hysteresis effects.
The downward course of the curve is, owing to hysteresis, strikingly different from its upward course, and when the magnetizing force has been reduced to zero, there is still remaining an induction of 7500 units.
The closed figure a c d e a is variously called a hysteresis curve or diagram or loop. The area f HdB enclosed by it represents the work done in carrying a cubic centimetre of the iron through the corresponding magnetic cycle; expressed in ergs this work is I HdB.
When a hysteresis curve is to be obtained, the procedure is as follows: The current is first adjusted by means of R to such a strength as will fit it to produce the greatest + and - values of the magnetizing force which it is intended to apply in the course of the cycle; then it is reversed several times, and when the range of the galvanometer throws has become constant, half the extent of an excursion indicates the induction corresponding to the extreme value of H, and gives the point a in the curve fig.
Fleming, Magnets and Electric Currents, p. 193) are shown three very different types of hysteresis curves, characteristic of the special qualities of the metals from which they were respectively obtained.
Several arrangements have been devised for determining hysteresis more easily and expeditiously than is possible by the ballistic method.
Ewing's hysteresis-tester, 2 which is specially intended for testing the sheet iron used in transformers.
[[[Magnetic Measurements]] introduced the method of measuring hysteresis by means of an electro-dynamometer used ballistically.
When the magnetizing current is twice reversed, so as to complete a cycle, the sum of the two deflections, multiplied by a factor depending upon the sectional area of the specimen and upon the constants of the apparatus, gives the hysteresis for a complete cycle in ergs per cubic centimetre.
Steinmetz's formula may be tested by taking a series of hysteresis curves between different limits of B,' measuring their areas by a pianimeter, and plotting the logarithms of these divided by 47r as ordinates against logarithms of the corresponding maximum values of B as abscissae.
Working with two different specimens, he found that the hysteresis loss in ergs per cubic centimetre (W) was fairly represented by o 00125B 1 6 and o o0101B 1 ' 6 respectively, the maximum induction ranging from about 300 to 3000.
Baily showed that hysteresis ceased to increase when B was carried beyond 23,000.
Low hysteresis is the chief requisite for iron which is to be used for transformer cores, and it does not necessarily accompany high permeability.
In response to the demand, manufacturers have succeeded in producing transformer plate in which the loss of energy due to hysteresis is exceedingly small.
Parshall quotes tests of six samples of iron, described as of good quality, which showed an average hysteresis loss of 3070 ergs per c.cm.
The standard induction in reference to determinations of hysteresis is generally taken as 2500, while the loss is expressed in watts per lb at a frequency of ioo double reversals, or cycles, per second.
In many experiments, however, different inductions and frequencies are employed, and the hysteresis-loss is often expressed as ergs per cubic centimetre per cycle and sometimes as horse-power per ton.
The third column shows the relative amount of hysteresis deduced by Ewing as a general mean from actual tests of many samples (Journ.
If now the alternations are performed so rapidly that time is not allowed for more than the first sudden change in the magnetization, there will be no hysteresis loss, the magnetization exactly following the magnetizing force.
In hardened iron and steel the effect can scarcely be detected, and in weak fields these metals exhibit no magnetic hysteresis of any kind.
The complicated hysteresis effects which attend magnetic elongation and retraction have been studied by H.
After one of the rings had been annealed at 840°, its maximum permeability at ordinary temperatures was 4000 for H =1.84; when it had been subsequently annealed at 1150°, the maximum permeability rose to 4680 for H =1.48, while the hysteresis loss for 2 B = t 4000 was under 500 ergs per c.cm.
The effects of temperature upon hysteresis were also care fully studied, and many hysteresis loops were plotted.
The results of a typical experiment are given in the annexed table, which shows how greatly the hysteresis loss is diminished as the critical temperature is approached.
Hysteresis Loss in Ergs per c.cm.
No evidence of hysteresis could [[[Temperature And Magnetization]] found to be 780°, 360° and 1090° respectively, but these values are not quite independent of the magnetizing force.
Soc., 1896, 60, 81) were the first to experiment on the permeability and hysteresis of iron at low temperatures down to that of liquid air (-186° C.).
8 The hysteresis of the soft annealed iron turned out to be sensibly the same for equal values of the induction at - 186° as at 15°, the loss in ergs per c. cm.
The hysteresis-loss in Swedish iron was decreased for inductions below about 9000 and increased for higher inductions; in tungsten-steel, nickel and cobalt the hysteresis-loss was always increased by cooling.
Claude (C. R., 1899, 129, 409) found that for considerable inductions (B =15,000) the permeability and hysteresis-loss remained nearly constant down to - 186°; for weak inductions both notably diminished with temperature.
6 A small percentage of aluminium produced still higher permeability (µ=6000 for H=2), the induction in fields up to 60 being greater than in any other known substance, and the hysteresis-loss for moderate limits of B far less than in the purest commercial iron.
Its hysteresis-loss for B =9000 was o 236 per pound.
There was considerable hysteresis, the energy-loss per cycle being fairly represented by W =0.000549513 2 ' 238.
Rhoads obtained a cyclic curve for iron which indicated thermo-electric hysteresis of the kind exhibited by Nagaoka's curves for magnetic strain.
The results of experiments as to the effect of magnetization were for long discordant and inconclusive, sufficient care not having been taken to avoid sources of error, while the effects of hysteresis were altogether disregarded.
Changes of elasticity are in all cases dependent, not only upon the field, but also upon the tension applied; and, owing to hysteresis, the results are not in general the same when the magnetization follows as when it precedes the application of stress; the latter is held to be the right order.
Supposing Ewing's hypothesis to be correct, it is clear that if the magnetization of a piece of iron were reversed by a strong rotating field instead of by a field alternating through zero, the loss of energy by hysteresis should be little or nothing, for the molecules would rotate with the field and no unstable movements would be possible.'
With small magnetizing forces the hysteresis was indeed somewhat larger than that obtained in an alternating field, probably on account of the molecular changes being forced to take place in one direction only; but at an induction of about 16,00o units in soft iron and 15,000 in hard steel the hysteresis reached a maximum and afterwards rapidly diminished.
In one case the hysteresis loss per cubic centimetre per cycle was 16,100 ergs for B =1 5,900, and only 1200 ergs for B = 20,200, the highest induction obtained in the experiment; possibly it would have vanished before B had reached 21,000.2 These experiments prove that actual friction must be almost entirely absent, and, as Baily remarks, the agreement of the results with the previously suggested deduction affords a strong verification of Ewing's form of the molecular theory.
2 His well-known modification 3 of Weber's molecular theory, published in 1890, presented for the first time a simple and sufficient explanation of hysteresis and many other complexities of magnetic quality.
Other effects of " hysteresis " occur in alloys of iron, which have been studied by W.
524) has given the name of hysteresis (Gr.
II) or the hysteresis curve (figs.
Induction and Hysteresis Curves.
They found that the hysteresis-loss, which at ordinary temperatures is very small, was increased in liquid air, the increase for the alloys containing less than 30% of nickel being enormous.