GenRad 1482 Series Inductance Standard

3 Terminal 1482 Primary Standard Inductor

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Photo represents example of series. See datasheet for more details on any specific model.

  • Stable within ±0.01% per year
  • 18 Models values from 1 µH to 10 H
  • Low, known temperature coefficient
  • 3 year warranty included
  • Calibration accredited to ISO-17025 included
  • Minimized connection errors
  • Toroidal - free from external fields
Prices range from $3785 to $5626

Estimated Delivery is 3 to 7 weeks

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Why Buy
  • Used by most national and primary laboratories
  • Excellent long-term stability
  • Insensitive to applied voltage and current
  • ISO-17025 accredited calibration via transfer method using 1482s calibrated at NPL for most values

  • The GenRad 1482 Standard Inductors are the standard of choice in metrology labs due to their stability and insensitivity to signal level and external magnetic fields. Used today by national metrology institutes and primary standards bodies around the world, these inductors have no peer or equivalent.

    IET continues to produce the 1482 standard inductors to the same exacting specifications and utilizing the same winding machines as General Radio. These standard inductors are accurate, highly stable standards of self inductance for use as a low frequency reference of working standard in the laboratory.

    Records extending over 50 years, including those of standard inductors that traveled to national laboratories in several countries for calibration, show long-term stability well within ±0.01%/year, typically <10 ppm/year.

    Story of the IET (General Radio) Model 1482 Standard Inductor

    Ever since the basic electrical components, R, L*, and C (Resistance, Inductance and Capacitance) have been understood, it has been known that physical implementations of the of the three components can be far from ideal.

    GenRad's quest for an ideal (well almost) inductor
    Of the three RLC elemental components, the inductor is the least ideal. An ideal inductor would need to have no resistance, and no capacitance components, dimensional stable, be insensitive to orientation and external magnetic fields, temperature, and aging. For example, it is easier to construct a capacitor with an almost ideal dielectric by using air, but inductors require real wire with finite resistance. Also at issue are capacitance of the physical construction, field geometry, pickup, frequency response, magnetic saturation, temperature affects.

    GenRad's Solution
    The Type 1482 Standard Inductors were released in 1952 by General Radio.
    Additional technical details on the release of the 1482 can be found in the GenRad Experimenter from 1952.

    The 1482 Standard Inductors replaced the Type 106 Standard Inductors.
    GenRad also produced a Type 1481 Standard Inductor which was smaller than the 1482 however the use of a ferromagnetic core in the 1481 results in the inductance changing with applied voltage or current which limited the 1481's use as a standard.

    Each standard inductor is a uniformly wound toroid using Litz wire on a Steatite L5 ceramic core. Steatite L5 ceramic core was chosen due to dimensional stability over time and temperature and is non ferromagnetic. The cores on lower value inductors have additional holes drilled in the core to allow for partial turns so that the inductance value can be precisely adjusted to the nominal inductance value.

    1482 Winding
    GenRad Custom Winding Machine

    Most 1482 are wound using a duplex winding process which creates two identical windings one on each half of the toroid. The two winding are closely matched and placed in parallel to achieve the final inductance value. The use of duplex winding results in results in current flowing equally and in opposite directions around the toroid. This minimizes the affects from external magnetic field and hence essentially no pickup from external fields.

    1482 Duplex Winding
    Duplex Winding General
    1482 Duplex Winding
    Duplex and Single Winding

    The inductor is resiliently supported in a mixture of ground cork and silica gel, after which the whole assembly is cast with a potting compound into a cubical aluminum case. This as well helps with dimensional stability of the inductor.

    Frequency Response
    The 1482 can used used over a wide frequency range and are calibrated at 100 Hz, 200 Hz, 400 Hz, 1 kHz and for lower inductance values at 10 kHz. The resonance frequency of each inductor is shown on the calibration certificate. More information on resonant frequency can be view at The Determination of resonance

    Terminals and Connections
    Values of 500 µH and above have three terminals, 2 for inductor leads and the third connected to the case, to provide either a 2 or 3 terminal standard.

    Inductors with <500 µH inductance values have three additional terminals to allow for switching between a short circuit and the inductance value. This allows the user to perform short compensation without disconnecting leads from the inductor which minimizes errors due to cable movement during connection. A ground strap is moved to the Lo terminal when short compensation is performed and back to L for measurement of the inductance. When the same connections are used in both measurements, the inductance value is independent of the external lead inductance even for values much less than 200 µH.

    Note: Early GenRad 1482 Standard Inductors for values less than 500 µH had 3 terminals until this issue was discovered. For comparing other inductors with the 1482 Standard Inductors, the 1689 or 1693 Digibridge is recommended.
    Watch a video about the

    GenRad 1482 Series Inductance Standard

    BASIC SPECIFICATION (Full specifications can be found on the datasheet)

    Calibration: A certificate of calibration that is accredited by A2LA to ISO-17025 is provided with each unit, giving measured values of inductance at 100, 200, 400, and 1000 Hz, with test conditions and method of measurements specified. These values are obtained by comparison, to a precision, typically, of better than 0.005%, with standards whose absolute values, traceable to the International System of Units (SI), are known to an accuracy typically of (0.02%+0.1μH) at 100 Hz; (0.1%+0.1 μH for the 1482-B).

    Stability: Inductance change is less than 0.01% per year.

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