GenRad 1409 Series Standard Capacitor

The GenRad 1409 Standard Capacitor is series of highly stable, cost-effective capacitance standards. With a low temperature coefficient and low losses, these standard capacitors come in a wide range of capacitance values from 1 nF - 1,000 µF.

Feature of the 1409 Series of Standard Capacitors:

• Excellent stability of better than 100 ppm/year
• Accurate and repeatable measurements of high capacitance values
• Calibrated for both 2 and 3 terminal configurations at 100 Hz or 1 kHz depending upon capacitance value
• Excellent sales and applications support at IET Labs and sales@ietlabs.com

Design
From 1 nF to 1 µF, the standard capacitors are constructed with silvered-mica and foil  for use as two- or three-terminal lab standard.

IET Labs manufacturers the 1409 using the same fixtures and techniques as used by GenRad in 1957 when the 1409 Series was originally developed.

Each 1409 is handmade in the USA using the best available silvered-mica sheets which are alternately stacked to create the correct capacitance.
Every sheet of silvered-mica is individually tested to ensure the dissipation factor is low enough to ensure the final dissipation factor will meet specifications.
Once the stacking is complete, the entire assembly is placed into a clamping structure to compress the mica stack and maintain mechanical stability.

Each 1409 element is artificially aged by temperature cycling to improve stability. The clamping structure is then placed in the the housing.

A final capacitance adjustment is then made to bring the capacitor into specifications.

A thick desiccant sheet is placed over the entire assembly and a coating of potting material is applied to minimize the effect of humidity on the capacitance value and Df. The combination of artificial aging, desiccant and potting material ensures the 1409 will be stable for decades.

From 1 µF to 10 µF the units are made of hermetically sealed polystyrene for 10 μF. Above 10 μF the capacitor is hermetically sealed MPPS metallized polypropylene sulfide type.

Typical capacitors, observed over decades, have shown random fluctuations of less than + 0.01% in measured capacitance with no evidence of systemic drift.

The elements used in 1409 Standard Capacitors are selected for low dissipation factor and are stabilized by heat cycling. They are housed in cast aluminum cases, along with silica gel which provides continuous desiccation. These cases are sealed with high-temperature potting material.  

Three gold plated low thermal EMF binding posts are provided on the top of the case, and removable banana plugs on the bottom, for convenient parallel connection without error.

More information on the 1409 Series of Capacitor Standards can be found in at the link 1409 GR Experimenter July 1957