IET Labs 1491 Series High Accuracy All-Purpose Decade Inductor

IET Labs 1491 Series High Accuracy All-Purpose Decade Inductor

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IET Labs 1491-9704

Data Sheet

Features:

Shielded toroidal cores for small mutual inductance
and minimal effect from external fields
Sealed against moisture for long-term stability
Excellent as a moderately precise standard of
inductance
High-Q, 200 and above

Additional Images


Figure 1: Percentage change in normal and incremental inductance with ac and bias current. Incremental curve is limited to and ac excitation less than I₁.		Figure 2: Variation of inductance with frequency for the 1491 Decade Inductors.
Click image to enlarge		Click image to enlarge


Figure 3: Variation to Q for the maximum inductance at low excitation levels. Dashed curves correspond to use with chassis floating.
Click image to enlarge

Description

The 1491 Decade Inductor is an assembly of several Decade-Inductor Units in a single metal cabinet. The units have no electrical connection to the panel, but a separate ground terminal is provided, which can be connected to the adjacent low terminal, leading to the smallest decade.

These inductance decades are convenient elements for use in wave fi lters, equalizers, and tuned circuits throughout the range of audio and low radio frequencies. As components in oscillators, analyzers, and similar equipment, they are especially useful during the preliminary design period, when you need to vary circuit elements over relatively wide ranges to determine optimum operating values. As moderately precise standards of inductance they have values of low-frequency storage factor, Q, that are much larger than those of air-core coils.

Models, Options, & Accessories

Model	Description	List Price	Sale Price
1491-9704	1491-D Decade Inductor, 11.11 H, Bench - Discontinued - no replacement
1491-9707	1491-G Decade Inductor 11.111 H, Bench - Discontinued - no replacement

Specifications:

RMS I₁ (mA)
Switch Settings		0.1% Increase	0.25% Increase
		100 µH	Inductance per Step
		100 µH	10 mH	100 mH	1 H
1	141	17	5.4	1.7	.54
2,3,4	100	12	3.8	1.2	.38
5,6,7,8,9,10	63	8	2.4	0.8	.24
Maximum I	4 A	1.5 A	500 mA	150 mA	50 mA

Frequency Characteristics

Percentage increase in effective series inductance (above the zero-frequency value, Lo) may be obtained by interpolation in accompanying graph (see Figure 2) for any setting to the highest-value decade used, when LOW terminal is grounded to cabinet.

Zero Inductance:

Approximately 1 µH

Maximum Voltage:

500V rms. Switch will break circuit at 500V if turned rapidly, but voltages above 150V may cause destructive arcing with switch between detent positions.

Accuracy (Low Frequency, Low Signal Level)

Inductance Per Step
Model	100 µH	1 mH	10 mH	100 mH	1 H
1491-9704	N/A	±2%	±1.6%	±0.8%	±0.8%
1491-9707	±2%	±2%	±1.6%	±0.8%	±0.8%

Change in Inductance with Current

Fractional change in initial inductance with AC current for each type of toroid is shown in the normal curves, Figure 1, in terms of the ratio of the operating current, I, to I₁ the current for 0.25% change, solid line (0.1%, broken line). For ratios below unity, inductance change is directly proportional to current. Values of I₁, listed below, are approximate and are based on the largest inductor in the circuit for each setting.

Storage Factor Q

See Figure 3 above

dc Resistance

Approximately 45 Ω per Henry.

Temperature Coefficient

Approximately -25 ppm/°C between 16° and 32° C

Terminals

Binding posts on ¾-in centers; separate ground terminal
provided.

Mechanical

Lab-bench cabinet.

Dimensions

22.3 cm H x 43.2 cm W x 16.6 cm D (8.75" x 17" x 6.5 ").

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