Model 1412-BC: The wide capacitance
range
and high resolution of this decade capacitance
box make it exceptionally useful in both
laboratory and test shop. Owing to its fine
adjustment of capacitance, it is a convenient
variable capacitor to use with an impedance
comparator. The polystyrene dielectric used
in the decade steps is necessary for applications
requiring low dielectric absorption and
constancy of both capacitance and dissipation
factor with frequency.
For decades of polystyrene capacitors and a variable air capacitors
are used, mounted in a double-shield box. The double shielding
provides 2-terminal and 3-terminal capacitances that are the same
except for the capacitance between the terminals. The variable
air
capacitor with a linear ΔC of 100 pF and a resolution of better
than
1 pF provides continuous adjustment between the 100 pF steps of
the smallest decade.
Figure 1
The double shielding used in the 1412-BC Decade Capacitor keeps
CHG very small. This capacitance is the difference between the
3-terminal and 2-terminal capacitance of the box; CLG is approx.
125 pF. |
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