National standard of capacitance

Name: National standard of capacitance

Code designation: ECM 250-1/04-029

Year of publication: 2004 (nominal value of 10 pF), 2007 addition (extended by 100 pF)

Department: dpt. 6011 ČMI Regional Inspectorate Brno

Guarantor: Doc. Ing. Jiří Horský, CSc. (2003 – 2009), Ing. Lubomír Mičánek (2009 – 2013), Ing. Jana Horská, Ph.D. (2013-2017), Ing. Stanislav Mašláň, Ph.D. (2017 - )

Related KCDB CMC lines: 4

National Standard of Electrical Capacitance (SEC) comprises of set of high stability fused silica capacitors. Metrological traceability is ensured by periodical calibration of three capacitors (2x 100pF and 1x 10pF) at BIPM every two years. BIPM calibration is traceable to Quantum Hall Effect. The value of SEC between the BIPM calibrations is obtained as a mean value of entire group of capacitors using prediction from the historical data.

In 1995, SEC comprised of set of locally manufactured fused silica capacitors 10 pF developed by national company TESLA in 1970s and one fused silica capacitor 10 pF, type AH11 (Andeen Hagerling). The capacitors were periodically measured by ultraprecision capacitance bridge AH2500A. The TESLA capacitors have to be placed in the oil bath with temperature stability ±0.005 °C in order to reduce their temperature dependence below 0,1 ppm/°C. Two most stable TESLA capacitors were placed into air bath. These capacitors form a first reference group of 10 pF.

In 2001, the SEC was extended by another four fused silica AH11 capacitors 100 pF, which are forming second reference group as addition to the 10 pF group. AH11 capacitors have their own thermostats, so they are placed in chassis without need for oil or air bath. This group is used for calibration of AH2500A capacitance bridge, which is used to build capacitance scale up to 1 µF. The step-up or step-down process of the capacitance scale buildup is traceable to ratio 10:1 provided by ratio of SEC groups 10 a and 100 pF.