Capacitance Standards

standard (electrical) capacitors, characterized by highly stable nominal capacitance (constant calibration). Such standards are used mainly for accurate measurements conducted with capacitance meters and q-meters. Capacitance standards are divided into two groups: (1) constant capacitance of 0.5 pF (picofarad) to 0.1μF and (2) variable capacitance of up to 0.002 μF. The dielectric in the standards is usually a high-grade mica, a ceramic with low dielectric losses, and air. The temperature coefficient is usually 10^-5-10^-6 deg^-1 and the loss tangent is tan δ = 10^-3-10^-4. Measures of capacitance are carefully shielded during accurate measurement in order to reduce any capacitive coupling with surrounding objects.