The 1422 Variable Air Capacitor.
Variable Air Capacitor is a stable and precise variable air capacitor intended for use as a continuously
adjustable standard of capacitance.
One of the most important applications is in AC bridge measurements, either as a builtin standard or as an
external standard for substitution measurements.
It is available in a variety of ranges, terminal configurations, and scale arrangements to permit selection of
precisely the required characteristics.
1422 Air Variable Capacitor
Model  Description 

1422  1422 Capacitor Variable. Air Capacitance. 
Stability: better than 0.02% full scale per year
Settable to 40ppm
Low Temperature coefficient, low losses
Wide selection to suit needs
3 different models
Laboratory Standard
Working Standard
Calibrating Working Standards
Capacitance Measurement Functions
Substitution Measurements
Calibrating Instrumentation
Twoterminal  The 1422D is a dualrange, twoterminal capacitor, direct reading in total capacitance at the terminals.
Threeterminal  The 1422CB and CL are threeterminal capacitors with shielded coaxial terminals for use
in threeterminal measurements. The calibrated direct capacitance is independent of terminal capacitance
to ground, and losses are very low.
The 1422CL has particularly low, constant terminal capacitance, making it suitable for measurement circuits
in which high capacitance to guard cannot be tolerated.
Construction  The capacitor assembly is mounted in a cast frame for rigidity.
This frame and other critical
parts are made of aluminum alloys selected to give the strength of brass with the lightness of aluminum.
The plates of most models are also aluminum, so that all parts have the same temperature coefficient of
linear expansion.
A worm drive is used to obtain high precision of setting.
To avoid eccentricity, the shaft and the worm are accurately machined as one piece.
The worm and worm wheel are also lapped into each other to improve smoothness.
The dial end of the worm shaft runs in a selfaligning ball bearing, while the other end is supported by an
adjustable spring mounting, which gives positive longitudinal anchoring to the worm shaft through
the use of a pair of sealed, selflubricating, preloaded ball bearings.
Similar pairs of preloaded ball bearings
provide positive and invariant axial location for the main or rotor shaft.
Electrical connection to the rotor is
made by means of a silveralloy brush bearing on a silveroverlay drum to assure a lownoise electrical
contact.
Stator insulation in all models is a crosslinked thermosetting modified polystyrene having low
dielectric
losses and very high insulation resistance.
Rotor insulation, where used (Types 1422CB and CL), is grade L4 steatite, silicone treated.
Accuracy  The errors tabulated in the specifications are possible errors, i.e., the sum of error contributions
from setting, adjustment, calibration, interpolation, and standards.
When the capacitor is in its normal position
with the panel horizontal, the actual errors are almost always smaller.
The accuracy is improved when the readings are corrected using the 12 calibrated values of capacitance given
on the correction chart on the capacitor panel and interpolating linearly between calibrated points.
Even better accuracy can be obtained from a precision calibration of approximately 100 points on the capacitor
dial, which permits correction for sight residual eccentricities of the worm drive and requires interpolation over
only short intervals. This precision calibration is available for the 1422CL model.
A plastic enclosed certificate
of calibration is supplied, giving corrections to one more figure than the tabulated accuracy.
1422 Precision Capacitors  Two Terminal 1422D  ThreeTerminal 1422CB 
ThreeTerminal
1422CL 

Capacitance Range (Min/Max) 
100/1150pF 35/115 
50/1100pF 10/110pF 

Scale, pF/Division 
0.2 0.02 
0.2 
0.02 
Initial Accuracy: ± Picofarads
DirectReading (Adjustment): Total Capacitance 
1.5* 0.3* 
1.5 
0.1 
With Corrections from Calibration Chart (supplied) Total Capacitance 
n/a n/a 
n/a 
0.04 
With Corrections from Precision Calibration (extra charge) Total Capacitance 
n/a n/a 
n/a 
0.01 
Residuals (typical values):
Series Inductance, µH 0.06 Series Resistance, V at 1MHz 0.04 
0.10 0.05 
0.14 0.1 
0.13 0.1 
Terminal Capacitance, pF, typical
high terminal to case low terminal to case 
min/max scale min/max scale 
36/35
58/53 
34/33
58/55 