Normal Mode Noise Research Articles

Characteristics of a special-isolation transformer capable of protecting from high-voltage surges and its performance

Rapidly expanding computer-control systems and information networks must be protected from high voltage surges and made immune from noise. The usual method employed for this purpose is isolation transformers. Conventional electrostatic-shielded transformers, however, are insufficient for a number of reasons. The first is that many fine and complicated local resonant circuits are created by the inhomogeneously distributed circuit parameters inside the coil. The second is that common-mode surge noises traveling on both the active conductor of the line through some common-mode component, change into normal-mode noise because of the unbalance between their respective impedance values to ground. The third is the problem that component changed into normal mode, propagate due to the electromagnetic inductance from the primary to the secondary coil. In order to remedy this set of problems, one must eliminate the high-frequency magnetic flux linking the primary coil to the secondary coil through the air. In this paper, the authors propose a design for a transformer that does not propagate high-frequency components, even noise in a normal mode. They demonstrate dramatic noise reduction in their experiments with the new design. They thus validate the utility of the coil arrangement for the purpose of noise reduction.

An analysis of normal‐mode noise caused by braided shield current flowing on coaxial cable attached by a ferrite core

Since coaxial cables have excellent electromagnetic shielding characteristics, they are widely used as interconnecting cables for digital information equipment. However, since braided lines are used in the shield layer of most coaxial cables, if an RF current flows, a noise voltage (normal mode noise) is induced between the core wire and the braided wire by electromagnetic coupling. Electromagnetic noise is also radiated from the common mode current of the braided shield. It has been considered that ferrite core loading is effective for reduction of the electromagnetic noise, and such loading is frequently used. In this article, in order to study whether ferrite core loading is effective in reducing normal mode noise, the normal mode noise generated by the braided shield current is analyzed with respect to the core loading location. Next, a formula for the noise-reduction effect due to ferrite core loading is derived and its validity is demonstrated experimentally. © 1998 Scripta Technica, Electron Comm Jpn Pt 1, 82(2): 1–10, 1999

An analysis of normal-mode noise caused by braided shield current flowing on coaxial cable attached by a ferrite core

Since coaxial cables have excellent electromagnetic shielding characteristics, they are widely used as interconnecting cables for digital information equipment. However, since braided lines are used in the shield layer of most coaxial cables, if an RF current flows, a noise voltage (normal mode noise) is induced between the core wire and the braided wire by electromagnetic coupling. Electromagnetic noise is also radiated from the common mode current of the braided shield. It has been considered that ferrite core loading is effective for reduction of the electromagnetic noise, and such loading is frequently used. In this article, in order to study whether ferrite core loading is effective in reducing normal mode noise, the normal mode noise generated by the braided shield current is analyzed with respect to the core loading location. Next, a formula for the noise-reduction effect due to ferrite core loading is derived and its validity is demonstrated experimentally. © 1998 Scripta Technica, Electron Comm Jpn Pt 1, 82(2): 1–10, 1999

High performance step-down noise-reduction transformer constructed with C-core

Noise-reduction transformers have a filter function against conductive noise transmission. Several types of noise-reduction transformers have been presented. Few papers, however, have reported a noise-reduction transformer for direct power supply to electronics equipments. In this paper, we propose a prototype step-down noise-reduction transformer suitable for digital circuit. The input voltage of the transformer is 100 V and the output voltage is 5 V. Frequency characteristics of noise attenuation are discussed and prevention of pulse noise transmission is demonstrated. The results of the experiments can be summarized as follows: (1) Normal mode noise attenuation is -70 dB, and common mode exceeds -80 dB; (2) Prototype step-down noise-reduction transformer eliminates pulse noise efficiently. Our noise-reduction transformer has a good noise attenuation characteristic and is an efficient noise attenuator.

Acoustic Receiver with Co-Sensor

This paper describes a practical method of a new type of an acoustic receiver using the co-sensor with no vibration sensor in order to decrease the influence of the equi-status noise (NMN : normal mode noise). The co-sensor is physically arranged close to the acoustic sensor as a counter measure for the noise circumstances. The acoustic signal is only received by the acoustic sensor and NMN is separately detected by both the acoustic sensor and the co-sensor. Then the recieved noise can be eliminated or canceled without the phase processing. From the experimental results using this method, SNR (signal noise ratio) increases around 35dB in the air 13dB under the water respectively.

A method to estimate normal mode noise voltage induced on indoor telecommunication lines due to adjacent AC supply lines

AbstractWhen metallic telecommunication lines carrying digital signals are laid adjacent to ac supply lines in an office or a house, then the noise generated by the ac supply lines is induced on the telecommunication lines and the quality of transmission may be degraded. To calculate the induced voltage generated directly between the cores of a telecommunication line requires accurate values of the coupling admittance or coupling impedance between the two lines corresponding to the cable construction and the problem becomes very complicated.This paper proposes a simple method of estimating the voltage induced between the cores of a telecommunication line when the telecommunication line is laid adjacent to an ac supply line. The amount of coupling from the primary circuit with an open‐circuited terminal and with a short‐circuited terminal to the secondary circuit is measured. Using this value, the characteristics of the induced voltage corresponding to an arbitrary value of terminal impedance of the primary or secondary circuit simply are estimated. The validity of the estimation method was confirmed by experiments.

An optical instrumentation using a sensor with a sensordummy against noises on sensor and transmission line

This short paper discusses the method of effectively canceling equal status normal mode noise not only on a sensor line but also on a transmission line of an optical instrument using a sensor with a sensordummy resistance.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Methods of alternating noise canceling for an instrumentation using strain gages

A description is given of methods of noise canceling in instrumentation using strain gages, such as a sensor-sensordummy, a dual sensor, and a single sensor. As an example, two signals were produced by alternating the switching between the sensor and sensordummy output signals. The data processing of the two signals made a reliable signal without any noise on the signal line. In this case, 'any noise' means normal mode noise (NMN) under a quarter frequency of the switching. The accuracy of this method, called alternating noise canceling, has been verified with experiments. >

Noise and array configuration considerations for matched‐field processing in phone and mode space

The conditions under which mode space matched‐field processing offers performance gains relative to phone space matched‐field processing are investigated. Particular emphasis is placed on determining the effects of spatially correlated versus spatially uncorrelated noise fields and choice of array configuration on signal detection. Varying amounts of homogeneous white noise and spatially correlated noise as calculated by a normal mode noise model were combined with the field due to a submerged source to produce simulated phone space covariance matrices for a range of array configuration parameters. A phone‐to‐mode spacing mapping was then used to obtain the corresponding cross‐amplitude correlation matrices. The results of both conventional and MLM processing were analyzed and the trade‐off between the number of phones and percent of the water column spand was investigated.