US3772617A - Method and arrangement for setting the remanent flux density in magnetic circuits and equalizer utilizing same - Google Patents

Method and arrangement for setting the remanent flux density in magnetic circuits and equalizer utilizing same Download PDF

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Publication number
US3772617A
US3772617A US00303137A US3772617DA US3772617A US 3772617 A US3772617 A US 3772617A US 00303137 A US00303137 A US 00303137A US 3772617D A US3772617D A US 3772617DA US 3772617 A US3772617 A US 3772617A
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flux density
accordance
error signal
air gap
signal
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US00303137A
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A Ciesielka
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AT&T Corp
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Bell Telephone Laboratories Inc
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    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04B—TRANSMISSION
    • H04B3/00—Line transmission systems
    • H04B3/02—Details
    • H04B3/04—Control of transmission; Equalising

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  • ABSTRACT The remanent flux density in a selected portion of a magnetic circuit is precisely set to a desired value by comparing the flux density in the selected portion to a predetermined reference, generating an error signal based on the comparison, integrating the error signal, and inducing an H field in the magnetic circuit in accordance with the integrated error signal. Integration of the error signal is performed only when the flux density has a substantially remanent value, i.e., only when the H field in the magnetic circuit is substantially zero. Thus, error in setting the flux density due to imperfect remanence in the magnetic circuit is substantially eliminated.
  • I density in the air gap is utilized to precisely set the resistance value of a magnetoresistor, which in turn determines the gain of the equalizer.
  • My invention relates generally to magnetic circuits and, more particularly, to a method and arrangement for precisely setting remanent flux density in magnetic circuits.
  • a magnetic circuit is an arrangement in which magnetic flux is produced in response to an applied magnetic field.
  • a particular magnetic circuit may include one or more paths of magnetic material and a coil for applying the magnetic field thereto.
  • the magnetic circuit may also include an air gap or gaps in one or more of the paths. The flux density in a particular path or portion of the circuit is determined principally by the circuit geometry, the strength of the applied magnetic field and the previous magnetic history of the circuit.
  • the flux density, or B field, in a selected portion of a magnetic circuit is generally set to a desired value by inducing a magnetic field, or H field, in the circuit such that the desired flux density is attained.
  • a magnetic field or H field
  • Many magnetic materials for example, ferromagnetic materials, exhibit substantial remanence, so that theI-I field in the magnetic circuit can be reduced to zero without the flux density being reduced to zero as well.
  • a nonzero flux density can be permanently established in a selected portion of a magnetic circuit (for example, an air gap or a section of magnetic material). without expending energy to maintain same.
  • One known arrangement for precisely setting flux density in a magnetic circuit maintains an H field in the circuit at all times. This arrangementprecludes advantageous utilization of magnetic remanence, as described above. Moreover, a failure in the H field supply will change the flux density from the desired value.
  • a magnetic circuit comprising a magnetic core having an air gap interrupting its continuity, can be utilized'in an arrangement'for controlling the gain of a transmission cable equalizer.
  • a magnetoresistor is positioned in the air gap, its resistance value thus being determined by the remanent flux density in the gap.
  • the equalizer gain is determined by the resistance value of the magnetoresistor.
  • an object of the invention is to provide a method and arrangement for precisely setting remanent flux density in magnetic circuits.
  • a more specific object of the invention is to provide a method and arrangement for precisely setting the remanent flux density in an air gap in a magnetic circuit.
  • a further object of the invention is to provide a method and arrangement for precisely setting the flux density in the air gap of a magnetic core and thus the resistance value of a magnetoresistor positioned in the gap.
  • Another object of the invention is to provide a method and arrangement for precisely setting the flux density in the air gap of a magnetic core to precisely set the resistance value of a magnetoresistor to, in turn, precisely set the gain of a transmission cable equalizer.
  • An important feature of the invention is that the above-mentioned integrating and field inducing steps are performed independently in sequence; when the error signal is being integrated, no H field is induced in the magnetic circuit and when the H field is being induced in the magnetic circuit, no integration of the error signal is performed.
  • the sequence of integrating and field inducing is performed repetitively until the flux density inthe selected portion of the magnetic circuit attains the desired value.
  • An illustrative embodiment of the invention precisely sets the flux density in the air gap of a magnetic core.
  • the flux density is sensed by a magnetoresistor positioned in the gap, and the resistance value of the magnetoresistor establishes the amplitude of a control signal.
  • the above-mentioned error signal is generated by determining the difference between the control signal and the above-mentioned predetermined reference.
  • the magnetoresistor is advantageously utilized as a gain-determining element in a transmission cable-equalizer.
  • a pilot frequency tone is transmitted down the cable to be equalized, and is thereby extended to the input of A an amplifier included in the equalizer.
  • the pilot tone detected at the equalizer output, is rectified and filtered to provide the above-mentioned control signal.
  • a subtractor determines the difference between the control signal and a predetermined reference voltage proportional to that value of air gap flux density which provides a predetermined equalizer output amplitude.
  • the resultant error signal is processed in accordance with the invention, as described above, to set the remanent flux density in the air gap, by which the resistance value of the magnetoresistor and hence the gain of the equalizer are set.
  • FIG. 1 depicts an arrangement according to the invention, illustratively employed in a transmission cable equalizer
  • FIGS. 2A and 2B show graphs useful in describing the operation of the arrangement of FIG. 1.
  • FIG. 1 depicts a magnetic circuit comprising a magnetic core 378, an air gap 379 interrupting the continuity thereof, and core windings 377.
  • FIG. 1 further depicts circuitry in accordance with'the invention for precisely setting the remanent flux density in a selected portion of the magnetic circuit, viz. gap 379.
  • the magnetic circuit is utilized illustratively in an automatic transmission cable equalizer 30 which includes an operational amplifier 31.
  • the magnitude of the flux density in gap 379 determines the gain of amplifier 31 and hence of equalizer 30 for a predetermined pilot frequency.
  • the present invention by providing precise setting of the flux density in gap 379, assures precise setting of the gain of equalizer 30 at that pilot frequency.
  • the gain of equalizer 30 is a function of input frequency and is adjusted at each of (illustratively) four pilot frequencies f,, f f and f (which are distributed across the frequency band over which equalizer 30 is to operate) by adjusting the impedance of one of four equalizer input networks 34-37.
  • networks 34-37 include variable resistances 34a-37a, respectively.
  • Equalizer 30 is adapted for equalizing a transmission path comprising transmission cable 20 over which signals are extended from an information source to a utilization circuit.
  • the frequencydependent gain characteristic of equalizer 30 is adjusted to correspond to frequency-dependent attenuation in cable 20.
  • the frequency characteristic of signals from source 10 is substantially preserved at the input of the utilization circuit.
  • equalizer 30 When equalizer 30 is to be aligned, that is, when its gain characteristic is to be adjusted in accordance with the frequency-dependent attenuation in cable 20, tones at each of the abovementioned pilot frequencies are transmitted down cable 20 from a pilot tone'source 15.
  • the impedances of networks 34-37 are adjusted by adjusting variable resistances 34a-37a, respectively such that the signal at output terminal 38 of amplifier 31 has a predetermined amplitude at each pilot frequency.
  • this adjustment of variable resistances 34a-37a is effected automatically.
  • connections between terminal 38 and each variable resistance are provided via taps off lead 33.
  • Each of the variable resistances 34a-37a comprises a magnetic core having an air gap, circuitry in accordance with the invention for precisely setting the flux density in the air gap, and a magnetoresistor positioned in the air gap.
  • the magnetoresistor in each variable resistor comprises the resistive element thereof while the magnetic core and its associated circuitry control the resistance value of the magnetoresistor.
  • variable resistance 37a for example, includes magnetic core 378, magnetoresistor MR positioned in gap 379, and circuitry for setting the flux density in gap 379.
  • the latter comprises rectifying and filtering circuit 370, subtractor 371, error signal lead ER, switch 372, integrator 373, amplifier 374, switches 375 and 376 all connected in series in the order named.
  • Switch 376 is connected to core windings 377.
  • Variable resistance 37a also includes a pilot tone detector 380 which is coupled to output terminal 38 of equalizer 30, as is rectifying and filtering circuit 370. Detector 380 fcloses switch 376 when a tone at pilot frequency f is present at terminal 38.
  • Circuit 370 provides a dc. control signal proportional to the amplitude of the ac pilot signal (of frequency f4) at Output terminal 38.
  • Subtractor 371 determines the difference between the control signal and a predetermined d.c. reference.
  • the resultant error signal is extended along lead ER to integrator 373 and therefore to amplifier 374.
  • the voltage at output terminal R of amplifier 374 generates a current in windings 377.
  • the H field induced in windings 377 and thus in core 378 adjusts the flux density in gap 379, thus the resistance value of magnetoresistor MR and thus the gain of equalizer 30 at pilot frequency f.,.
  • the gain of amplifier 374 is chosen, based on the parameters of the other components of variable resistance 37a to ensure that the system is stable and that the error signal on lead ER will converge to zero.
  • equalization of cable 20, i.e. alignment of equalizer 30 at pilot frequency f, is complete.
  • the signal at terminal R and, accordingly, the H field induced in core 378 become constant.
  • the H field in core 378 is not zero. If the H field in core 378 is thereafter reduced to zero to take advantage of the magnetic remanence of core 378, the flux density in gap 379 drops (assuming first quadrant operation) somewhat because the remanence in core 378 is not perfect. This, of course, lowers the resistance value of magnetoresistor MR and destroys the equalization. The remanence even of so-called square hysteresis loop materials, is generally too imperfect for precise equalization.
  • switch 372 is opened and switch 375 is closed so that current flows in windings 377 proportional to the equalization error that obtained when the flux density in gap 379 was at its last remanent value.
  • the resultant l-I field induced in core 378 changes the flux density in gap 379, thereby adjusting the resistance value of ma'gnetoresistor MR and reducing the equalization error.
  • This two-step cycle of integration and induction is performed repetitively until the desired flux density is achieved.
  • the error signal on lead ER is zero at the start of a cycle, i.e. with switch 375 open, the flux density in gap 379 is assured to have the desired remanent value which provides alignment of equalizer 30 at pilot frequency )2.
  • this same value of flux density would be attained with some nonzero H field induced in core 378.
  • the present invention substantially eliminates equalization error due to imperfect remanence in core 378.
  • switches 372 and 375 are illustratively shown in FIG. 1 as mechanical elements, other known arrangements, for example, electronic switches, as'well as circuitry for operating them in the manner described above, will be apparent to those skilled in the art.
  • FIGS. 2A and 2B show graphs exemplifying the operation of equalizer 30 and, in particular, of variable resistance 37a, during alignment of the former at pilot frequency f,.
  • FIG. 2A depicts variations in the gap 379 flux density in response to H field pulses induced in core 378 via windings 377.
  • FIG. 2B depicts a time graph of those H pulses, as well as the signal at terminal R which generates them.
  • the H scale along the ordinate of FIG. 2B is aligned with the H scale along the abscissa of FIG. 2A.
  • the voltage at terminal R is initially zero and the flux density in gap 379 is B,.
  • the flux density necessary to equalize cable 20 at pilot frequency f is B,,.
  • ten magnetization cycles designated I, II...X
  • the integration steps of cycles I, II...X are performed in time periods designated Ia, IIa...Xa, respectively.
  • the induction steps are performed in time periods designated Ib, IIb,...Xb, respectively.
  • switches 372 and switches 375 are closed and opened, respectively.
  • periods Ib, IIb,...Xb the opposite relationship obtains.
  • the rise time of the H field pulses in FIG. 2B are shown as substantially zero to simplify illustration, some nonzero rise time elapses before the pulses attain their full magnitude. It will be appreciated that this rise time is not an important consideration as long as periods Ib, Ilb...Xb have sufficient duration.
  • the flux density in gap 379 rises to point C in response to the H field pulse of period I'b. Since core 378 has imperfect remanence, the flux density in gap 379 falls back to point D when switch 375 opens at the start of period IIa. The flux density at point D is less than B so that the error signal on lead ER is still negative. Thus, the voltage at terminal R further increases during period IIa. In period IIb a pulse of magnitude H is induced in windings 377, driving the flux density in gap 379 to point E.
  • the flux density falls back to point P as period IIIa begins.
  • the flux density is now greater than B so that the error signal on lead ER is positive and the voltage at terminal R decreases during period IIIa.
  • the pulse induced during period III! has magnitude H the flux density rising to point G but dropping back to point F as period IVa begins.
  • the voltage at terminal R increases during period VIIa.
  • the flux density thus goes to point N in period VIIb, returns to and remains at point M during cycle VIII and rises to point 0 in cycle IX, from which it falls back to point P and finally rises to point Q in cycle X.
  • the flux density in gap 379 falls to B Thereafter, the error signal on lead ER is zero when switches 372 and 375' are closed and open, respectively, and accordingly, the voltage at terminal R stays constant.
  • the flux density oscillates between points Q and B, during any magnetization cycles which follow cycle X, such as cycle XI.
  • the number of magnetization cycles which will be needed to attain a particular remanent flux density, such as B, is not known beforehand, and some number of magnetization cycles corresponding to an anticipated maximum will occur during alignment at each pilot frequency.
  • a method for setting the flux density in a selected portion of a magnetic circuit comprising the steps of,
  • said integrating step is performed only when the flux density in said selected portion has substantially a remanent value.
  • a method in accordance with claim 2 wherein said generating step comprises the steps of,
  • said selected portion is an air gap and wherein said sensing step is performed using a magnetoresistor positioned in said air gap.
  • control signal providing step comprises the steps of extending a predetermined signal to the input of an amplifier and adjusting the gain of said amplifier based on the resistance value of said magnetoresistor, said control signal being derived from the output signal of said amplifier.
  • An arrangement forsetting the flux density in a selected portion of a magnetic circuit comprising, means for generating an error signal corresponding to the difference between the flux density in said selected portion and a desired value therefor, means operative for integrating said error signal, and means operative for inducing an H field in said magnetic circuit in accordance with the integrated error signal, the improvement comprising means for operating said integrating means only when the flux density in said selected portion has substantially a remanent value.
  • said last-mentioned means comprises means for operating said integrating means and said inducing 9.
  • said selected portion is an air gap and wherein said sensing means includes a magnetoresistor positioned in said air gap.
  • control signal providing means comprises an amplifier, means for extending a predetermined signal to the input of said amplifier and means for adjusting the gain of said amplifier in accordance with the resistance value of said magnetoresistor, said control signal being derived from the output of said amplifier.
  • an equalizer including circuit means adapted for insertion into a transmission path and operative for varying the gain of said path the combination comprising, a magnetic core having an air gap interrupting its continuity and providing remanent magnetic flux in said air gap, means for operating said circuit means in accordance with the density of magnetic flux in said air gap, means coupled to said circuit means fordetecting a pilot signal applied to said path, means for comparing the detected pilot signal to a predetermined reference signal and for generating an error signal based on the comparison, means operative for integrating said error signal only when the flux density in said gap has substantially a remanent value, and means operative for applying a magnetic field to said core to adjust the density of the flux in said air gap, said magnetic field being proportional to the output of said integrating means.
  • An equalizer in accordance with claim 11 wherein said last-mentioned means comprises means for operating said integrating means and said applying means independently in sequence.
  • An equalizer in accordance with claim 12 wherein said means for operating said circuit means includes magnetoresistive means positioned in said air gap.
  • An equalizer in accordance with claim 14 further comprising means for amplifying the output of said integrating means, said magnetic field being proportional to the output of said amplifying means.

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  • Engineering & Computer Science (AREA)
  • Computer Networks & Wireless Communication (AREA)
  • Signal Processing (AREA)
  • Soft Magnetic Materials (AREA)
  • Filters And Equalizers (AREA)
  • Networks Using Active Elements (AREA)
  • Tone Control, Compression And Expansion, Limiting Amplitude (AREA)
US00303137A 1972-11-02 1972-11-02 Method and arrangement for setting the remanent flux density in magnetic circuits and equalizer utilizing same Expired - Lifetime US3772617A (en)

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JP (1) JPS4979146A (de)
CA (1) CA981347A (de)
DE (1) DE2354730A1 (de)
FR (1) FR2205692B1 (de)
GB (1) GB1415422A (de)

Cited By (10)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
FR2385270A1 (fr) * 1977-03-21 1978-10-20 Rca Corp Circuit d'equilibrage automatique de signaux transmis par un cable
EP0004054A1 (de) * 1978-03-10 1979-09-19 Siemens Aktiengesellschaft Schaltungsanordnung zur automatischen Entzerrung eines Signals
US4383535A (en) * 1979-11-03 1983-05-17 Siemens Aktiengesellschaft Method for preventing remanence phenomena from interfering with magnetic field sensing systems and a device for implementation of the method
US4897599A (en) * 1985-03-27 1990-01-30 Createc Gesellschaft Fur Elektrotechnik Mbh Signal processing device with a level adapter circuit
US6097244A (en) * 1998-12-17 2000-08-01 Centillium Communications, Inc. Highly-linear continuous-time filter for a 3-volt supply with PLL-controlled resistor and digitally-controlled capacitor
US6160697A (en) * 1999-02-25 2000-12-12 Edel; Thomas G. Method and apparatus for magnetizing and demagnetizing current transformers and magnetic bodies
US6522517B1 (en) 1999-02-25 2003-02-18 Thomas G. Edel Method and apparatus for controlling the magnetization of current transformers and other magnetic bodies
US7242157B1 (en) * 2005-02-11 2007-07-10 Edel Thomas G Switched-voltage control of the magnetization of current transforms and other magnetic bodies
US7289575B1 (en) 1999-02-12 2007-10-30 Andrew Corporation Signal processing means
US7595689B1 (en) * 1998-07-02 2009-09-29 Andrew Llc Predistorter

Families Citing this family (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4450427A (en) * 1981-12-21 1984-05-22 General Electric Company Contactor with flux sensor

Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2908873A (en) * 1957-08-05 1959-10-13 Bell Telephone Labor Inc Automatic phase equalizer
US3257628A (en) * 1963-05-21 1966-06-21 Bell Telephone Labor Inc Resetting circuitry for a square-loop ferromagnetic core utilizing the output of a hall plate
US3359511A (en) * 1964-11-04 1967-12-19 Ampex Automatic gain control system with pilot signal
US3458769A (en) * 1965-08-27 1969-07-29 Lucifer Sa Electrically controlled valve

Patent Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2908873A (en) * 1957-08-05 1959-10-13 Bell Telephone Labor Inc Automatic phase equalizer
US3257628A (en) * 1963-05-21 1966-06-21 Bell Telephone Labor Inc Resetting circuitry for a square-loop ferromagnetic core utilizing the output of a hall plate
US3359511A (en) * 1964-11-04 1967-12-19 Ampex Automatic gain control system with pilot signal
US3458769A (en) * 1965-08-27 1969-07-29 Lucifer Sa Electrically controlled valve

Cited By (11)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
FR2385270A1 (fr) * 1977-03-21 1978-10-20 Rca Corp Circuit d'equilibrage automatique de signaux transmis par un cable
EP0004054A1 (de) * 1978-03-10 1979-09-19 Siemens Aktiengesellschaft Schaltungsanordnung zur automatischen Entzerrung eines Signals
US4383535A (en) * 1979-11-03 1983-05-17 Siemens Aktiengesellschaft Method for preventing remanence phenomena from interfering with magnetic field sensing systems and a device for implementation of the method
US4595022A (en) * 1979-11-03 1986-06-17 Siemens Aktiengesellschaft Method for preventing remanence phenomena from interfering with magnetic field sensing systems and a device for implementation of the method
US4897599A (en) * 1985-03-27 1990-01-30 Createc Gesellschaft Fur Elektrotechnik Mbh Signal processing device with a level adapter circuit
US7595689B1 (en) * 1998-07-02 2009-09-29 Andrew Llc Predistorter
US6097244A (en) * 1998-12-17 2000-08-01 Centillium Communications, Inc. Highly-linear continuous-time filter for a 3-volt supply with PLL-controlled resistor and digitally-controlled capacitor
US7289575B1 (en) 1999-02-12 2007-10-30 Andrew Corporation Signal processing means
US6160697A (en) * 1999-02-25 2000-12-12 Edel; Thomas G. Method and apparatus for magnetizing and demagnetizing current transformers and magnetic bodies
US6522517B1 (en) 1999-02-25 2003-02-18 Thomas G. Edel Method and apparatus for controlling the magnetization of current transformers and other magnetic bodies
US7242157B1 (en) * 2005-02-11 2007-07-10 Edel Thomas G Switched-voltage control of the magnetization of current transforms and other magnetic bodies

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FR2205692B1 (de) 1977-08-12
CA981347A (en) 1976-01-06
GB1415422A (en) 1975-11-26
JPS4979146A (de) 1974-07-31
FR2205692A1 (de) 1974-05-31
DE2354730A1 (de) 1974-05-09

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