Arnold - Glossary of Terms

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Glossary

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DC Bias
Direct Current (DC) applied to the winding of a core in addition to any time-varying current. Inductance with DC bias is a common specification for powder cores. The inductance decreases or "rolls-off" gradually and predictably with increasing DC bias.

DC Filters
A filter circuit that removes the AC ripple from a mostly DC current.

DC Stress
Annealing a magnetic material in the presence of a DC magnetic field to enhance magnetic properties.

Decoupling
Refers to a magnetic circuit where comparatively more of the flux generated by the MMF fringes around the magnetic material instead of entering it.

Demagnetization Curve
That portion of the hysteresis loop which lies between the residual induction point, Br, and the coercive force point, Hc (normal curve) or Hci (intrinsic curve). Points on the normal curve are designated by the coordinates Bd and Hd.

Demagnetized
A material condition where a ringing AC field has reduced the remanent induction to or near zero. A ringing AC field is a continually decreasing sinusoidal field. A pulsed DC field can be used to achieve gross demagnetization, but with much effort and with residual local magnetization.

Depth of Winding
The distance from the outside diameter of a winding to the inside diameter of a winding.

Discrete Air Gap
Mechanical air gap created by a small number of breaks in the magnetic path. In a standard C-core this number is generally two.

Distortion
Any deviation from the mathematical ideal of a real-world periodic waveform, which is specified as a per cent of the desired signal. Distortion can be expressed mathematically in terms of the harmonics of the fundamental frequency. This parameter is of considerable importance in instrumentation transformers.

Distributed Air Gap
Major feature of powder cores. It is the cumulative effect of many small gaps distributed evenly throughout the core. In a typical MPP core, the number of separate air gaps results from the use of powder to construct the core and numbers in the millions. The result is minimal fringing flux density compared to a core with one or two air gaps in the magnetic path. (Flux that passes around a discrete air gap and through the sides of a core is "fringing." Fringing flux enters the surrounding winding and causes a substantial amount of eddy current loss.)

Distribution Transformer
The transformer that is immediately "upstream" of the wall outlet.

Drive Transformer
A low-power isolation transformer used in electronic circuits to control semiconductors.

Duty Cycle
Maximum recommended usage (cycles) per unit time. Alternatively, the fraction of percent of "on" time, between 0 and 1 or 0 to 100%.