CSIR-National Physical Laboratory

सीएसआईआर-राष्ट्रीय भौतिक प्रयोगशाला

LF, HF Impedance and DC Metrology

This activity is maintaining the LF & HF impedance standards, DC standards and DC High Voltage standards.

LF & HF Impedance Standard: This activity is maintaining the standards of capacitance, inductance and ac resistance. Value to the 10 pF capacitor is assigned through primary standard, calculable cross capacitor, with an uncertainty of 0.6 ppm using precision ac bridges. Scale of capacitance is build up from 10 pF to 1 F using transformers bridges. The unit of inductance, Henry, is realized from capacitance and resistance using Maxwell-Wien bridge. Value to 100 µH to 10 H is assigned through this bridge. The unit of ac resistance, Ohm, is also realized from capacitance, using Quadrature Bridge and other precision ac bridges at 1kΩ. The scale of resistance from 1 Ω to 1 MΩ builds up with Kelvin double arms ac bridge.

The Precision Coaxial air-lines are taken as the primary standard of HF capacitance standard, traceable to length standards. The capacitance values of these air lines at high frequencies have been evaluated from their dimensions by using the transmission line theory1 and taking into account the distributive effects associated with the coaxial lines. A set of seven air-lines of different lengths from 3 cm to 30 cm exhibit capacitance values which varies from 2 pF to 20 pF respectively has been employed in the frequency range of 10 kHz-100 MHz. Transfer standards of capacitance at high frequency include a set of four coaxial capacitors (1 pF to 20 pF) and four 4-TP (Terminal Pair) air dielectric capacitors (1 pF to 1000 pF) which are calibrated against the primary standard. These transfer standards are then used to calibrate the LCR meters and Impedance analyzer in the range of 1 pF – 1000 pF from 10 kHz – 10 MHz and 1 pF to 20 pF from 10 MHz to 100 MHz respectively.

DC standards: This activity is maintaining National Standards of DC voltage, DC current and DC resistance. The apex level calibr