D E V I C E FOR M E A S U R I N G H Y S T E R E S I S L O O P C O E F F I C I E N T S

(UDC 621.317.43)

V. V. Klimov, Ya. V. Kovalin, and N. A. Netsvetailov

Translated from I zmer i t e l ' n aya Tekhnika, No. 9, pp. 39-41, September, 1965

In testing ferromagnet ic mater ia ls by their hysteresis loop with its character is t ic quantities B m, H m, B r , and H c (Fig. l a ) , it is often also necessary to know the quadrature factor Brs/B m for H = �89 H m, the rectangular i ty factor

Br/B m, and the factor H c / H m. These factors are ca lcula ted following the measurements of B m, H m, B r, H c, and Brs for H = 1 H m [1], or they are measured as the ratio of the distances between the corresponding points on osc i l lo- grams [2], which requires measurements of long duration and is not sufficiently precise.

For a direct measurement of the above factors with the possibil i ty of reading them off scales, a special de - v ice is used which is based on the ferrograph principle. Measurements are then made by the "reflected loop" me- thod [3].

"Reflected loop" method. The ca thode- ray oscil loscope plates are fed with voltages (Fig. l a ) which are pro- port ional to induction I3 (Y axis) and to field strength H (X axis), thus producing on the oscil loscope screen the hy- steresis-loop image of the tested ferr i te core.

If the vol tage proportional to field strength H (let us ca l l i t vol tage H, Fig. lb) is rect i f ied, the vol tage pro- port ional to induction B (vol tage B) will he scanned on the screen only to the right of axis B (the image seen on the screen is shown in the r ight-hand part of Fig. lb) . The hysteresis loop part which was previously to the left of axis

B (the r ight-hand part of Fig. l a ) wil l now be superposed on the

r ight-hand part of the hysteresis loop. The image on the CROscreen

(Fig~ lb) can be considered as consisting of a part of the hysteresis loop over which the other ("ref lec ted") part is superposed, thus or igi- nating the name of "reflected loop" given to this method.

By adjusting vol tage H as shown in Fig. l c , it is possible to convert the reflected part of the loop into a ver t ica l l ine. Segment Om b will then correspond to max imum induction Bin, and segment O r to residual induction B r (r ight-hand side of Fig. lc ) . By adjust- ing vol tage B as shown in Fig. l c , it is possible to make points mb and r coincide. The coincidence of the points means that the ratio of the ampl i tude of vol tage B at the instant when H equals zero to

its ampl i tude corresponding to the posit ive hal f -per iod of H, is equal to the ratio of segments Or /Ore b, which in turn is equal to the rec- tangulari ty factor BrA3 m .

By adjusting vol tage 13 as shown in Fig. l d , i t is possible, in a s imilar manner, to convert the ref lected part of the loop into a hori- zontal line. Segment Om h wil l then correspond to the maximum

field strength H m, and segment OC to the coerc ive force H c (right- hand side of Fig. ld) . By adjusting vol tage H (see Fig. ld) , i t is pos- sible to make points m h and C coincide. The coinc idence of the points means that the ratio of the ampl i tude of vol tage H at the in- stant when vol tage 13 equals zero to its max imum ampl i tude is equiva- lent to the rat io of segments OC/Om h, which in turn is equal to fac- tor H c / H m .

Fig. I.

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oo

Fig. 2.

+ 250 V

Out s

I ~ Inll~.

-250 V ~220 V

Fig. 3.

D1

Fig. 4.

Out

r

over at the instant when the sinusoidal voltage passes shift circuit PSC connected to the electronic switch.

When the quadrature factor Brs/B m is measured for H = �89 m, this condition is set by voltage H on a coupled po- tentiometer (Fig. le). The reflected part of the loop in this case is scanned to the right only up to the value of H which is equal to �89 m. Segment O ' m ' then corresponds to induc- tion B m, and segment O's to induction Brs for H = �89 H m. By adjusting voltage 8 as shown in Fig. le , it becomes possible to make points m ' and s coincide. The coincidence of points means that the ratio of the amplitude of voltage B at the in- stant when H = �89 Hm to its maximum amplitude is equivalent to the ratio of segments ,O 's /O 'm' , which in turn is equal to

1 the quadrature factor Brs/Bm for H = ~ H m.

In all three cases the comparison and adjustment of voltages can be made by precision potentiometers whose scales are calibrated respectively in units of factors Br/B m, H c / H m, and of the quadrature factor.

Measurements by the "reflected loop" method are made by means of a normal ferrograph whose cathode-ray tube plates are preceded by a ratio-measuring unit (Fig. 2).

Channel y is connected to electronic commutator switch S (Fig. 3) in the ratio-measuring unit (Fig. 2), and channel x to the rectifying and control circuit B, which con- sists of four diodes and a twin variable resistor R~ (Fig. 4). Voltage H (see Figs. lb , l c , and ld) is rectified by means of a rectifying and control circuit in such a manner that its in- put resistance remains constant for any position of the poten- tiometer sliders, thus keeping the total resistance consisting of R and the potentiometer resistance (Fig. 2) at a constant value. The circuit is suitable for adjusting the rectified half- period of the sinusoidal voltage from zero to its maximum value.

Voltage B (see Figs. l c , ld, and le) is adjusted by means of (see Fig. 2) potentiometer Pl and electronic switch S. The electronic switch is synchronized with the sinusoidal magnet iz- ing voltage. The inputs of the electronic switch are changed

through its zero value. This is arranged by means of the phase- The electronic switch connects either the full voltage B or a

part of it through potentiometer Pl, thus serving to provide any of the values of B shown in Figs. lc , ld, and le .

The sinusoidal voltage, having passed through the phase shifter, synchronizes multivibrator MV, tube T 1. Trigger T, tube T2, is switched at the instants corresponding to the leading and trailing edges of the multivibrator pulses. The trigger energizes in turn tubes Ts, T4, Ts, and T 6, thus serving to connect to the output the signals from input I or input II.

In measuring the rectangularity factors Brs/B m, the sliders of potentiometers P2 (see Fig. 4) are set to their extreme right-hand position and voltage H is rectified (see Fig. lc) . Voltage B is set by potentiometer P1 so as to make points m b and r coincide (Fig. lc) . The ratio of the potentiometer resistance between its slider and ground to its total resistance is then equal to rectangularity factor Br/Bm.

In order to measure factor H c / H m, the slider of potentiometer P1 is set to its extreme bottom position, with voltage B having the shape shown in Fig. ld. Points T h and c (Fig. ld) are brought to coincidence by potentiometer P2. Factor H c / H m is then equal to the ratio of the resistance of potentiometer P2 between its slider and ground to its full resistance.

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In measuring the quadrature factor Brs/Bm, the sliders of potentiometer P2 are set to their middle position, and potentiometer Pt is used to bring points m ' and s to coincidence (Fig. I.~,). Factor Brs/Bm for H = �89 m is then equal to the ratio of the resistance between the slider of potentiometer Pl and ground to its full resistance.

The quadrature factor can be measured with thesliders of potentiometer P2 in a position away from its middle. In such a case, the quadrature factor will correspond to a value of H distinct from �89 m. Such measurements are of interest in evaluating the magnetizing field for which the quadrature factor becomes smaller than the given value.

This device measures with adequate simplicity. With a high-quality integrating amplifier the measuring error of the device does not exceed 6-7%

The device operates at 50 Hz, but the electronic switch and the circuit shown in Fig. 4 are suitable for meas- uring at higher frequencies.

L I T E R A T U R E C I T E D

1. V.V. Kobelev, "Equipment for oscillographic recording of plane ferromagnetic film hysteresis loops, ~ Collection: Magnetic Elements in Computer Devices [in Russian] (Izd. ITM i VT AN SSSR, 1961).

2. L .A. Pil 'kevich, ~Instruments for measuring the characteristic of ferrites with a rectangular hysteresis loop, which are used in electronic computers," Collection: Problems of Computer Techniques [in Russian] (Gostekhizdat, UkrSSR, Kiev, 1961).

3. F. Bernstein, T. H. Bonn, and R. D. Torey, Electronics Engineering, No. 3, 31 (1958).

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