CSIR-National Physical Laboratory

सीएसआईआर-राष्ट्रीय भौतिक प्रयोगशाला

LF & HF Voltage, Current and Microwave Metrology

Precise and traceable measurements are important across all areas of life to ensure the performance and reliability of the measurement results. CSIR-NPL measures electrical quantities that are accurate, reliable and traceable to the SI units. The National standards are realized, established, maintained, upgraded and disseminated to support industry, govt. sector, research and academia. We maintain LF & HF Voltage, Current, Microwave Power and Phasor Measurement Unit (PMU) parameters of electrical metrology. To maintain the international traceability, a number of international & bilateral intercomparisons under the umbrella of BIPM and APMP have been carried out. At CSIR-NPL, PMU-CAL system traceable to its national standards carries out a comprehensive calibration of a PMU as per IEEE Standard C37.118.1. It plays a vital role in power distribution sector through the PMU calibration and measurement system.

CSIR-NPL provides apex level calibration services in LF & HF Voltage, LF Current, Microwave power and PMU parameters as per ISO/IEC 17025 standards to the industry, strategic sectors, STQC labs & private organizations of the country by maintaining their respective primary standards. We are disseminating measurement traceability in the above-mentioned parameters along with the other derived parameters and their measurement capabilities. We have 26 registered CMC’s and participated in more than 13 BIPM/APMP key/Supplementary comparisons to establish mutual degree of equivalence with the corresponding standards of the leading NMIs having internationally recognized traceability.

This section also includes an important metrological activity “Josephson Voltage Standard”, which is one of the Quantum standards established at CSIR-NPL. ‘Programmable Josephson Voltage Standard’ (PJVS) system, serves as the primary standard of voltage. This system also plays an important role in electrical metrology as it is used to disseminate unit ‘Volt’ throughout the nation to maintain traceability. The quantum accuracy of voltage levels in this system is derived from the ‘Josephson Effect’, due to which the superconducting junctions in the PJVS chip produces a voltage precisely proportional to the frequency of the applied microwave bias signal. Presently this system is used for dissemination of unit ‘volt’ in India through calibration of national standards (bank of Zener-diode based dc reference standard) at 1.018 V and 10 V as per the ISO/IEC 17025:2005. These Zener standards further provide traceability to all DC instruments to this primary standard.

The fabrication of various novel structures/patterns and prototype devices for metrology is also carried out at CSIR-NPL through the FIB (Focused Ion Beam) Laboratory. The FIB instrument at CSIR-NPL consists of dual-beam system i.e. focused ion beam and scanning electron microscope which enable the precise micro-nano imaging and machining of samples with nanometer-scale control. Dimensional measurements (lateral X and Y) performed using this instrument is accurate and traceable to SI unit (meter). FIB lab also produces superconducting junctions, weak links, nanostructures and nano-devices that are used in the metrology’s program for developing new standards and technologies.

a. LF Voltage & Current Banks of Multi-Junction thermal converters (MJTC) are used for assigning AC DC transfer difference to the primary standard (MJTC) at 2 Volt and 5mA with the best uncertainty of ±5ppm. Therefore, the thermal transfer standard or thermal converters are designed to cover voltage range of 1mV volts to 1000 volts in the frequency range 10 Hz to 1 MHz with an uncertainty of ± (7 to 1000) ppm and current range of 1mA to 20 A in the frequency range of 40 Hz to 10 kHz with an uncertainty of ± (10 to 92) ppm.

Fig.1: a) Bank of multijunction thermal converters b) AC-DC Voltage Transfer Difference

b. HF Voltage High frequency (HF) voltage primary standard at NPLI has been realized using a twin resistance coaxial power mount in the frequency range of 1 MHz to 1000 MHz. The rf/dc transfer difference has been assigned at the input reference plane of the primary standard. The overall uncertainty in assigning RF DC transfer difference has been estimated to be within ±0.50% in the frequency range up to 1 GHz. With the establishment of the RF voltage primary standard, one can calibrate and assign the RF DC transfer difference to the transfer standard thermal voltage converters. HF Voltage standard is used to calibrate the RF Voltage meters, high frequency thermal converters using the well-established technique.

c. Microwave Power Coaxial Microcalorimeter system in 2.4mm connector, established as the primary standard of Microwave Power in the frequency range of 1 MHz to 50 GHz is an absolute method based on thermocouple principle for the determination of effective efficiency to the thermocouple sensor. This section provides apex level calibration services in microwave power parameter to the industry & user organizations of the country. In order to meet the growing demand for calibration of microwave equipments in this era of continuously growing technology, CSIR-NPL disseminates the traceability of microwave power from 1MHz up to 50 GHz. The absolute value of the effective efficiency has been assigned to the microwave power standard from 1 MHz to 50 GHz using coaxial microcalorimeter and Vector network analyzer. The expanded uncertainty of microwave power primary standard at 50 GHz is ±1.9%.

Fig.2 : a) 2.4mm Coaxial Microcalorimeter b) Coaxial Thermocouple sensor

d. Phasor Measurement Unit Calibration System Today’s smart grid relies on phasor measurement units (PMUs) to deliver real-time critical data on the voltage, current, frequency and phase mainly within the power grid. It is mandatory that PMUs must be calibrated from a traceable calibrator system to ensure its consistency, accuracy and reliability. The CSIR-NPL Phasor Measurement Unit Calibration System (PMU-CAL) is capable of providing perfect solutions for PMU users, manufacturers, electrical power utilities and organizations associated with electrical power transmission. The automated PMU-CAL system fully complies with the IEEE C37.118.1a-2014. The compliance testing of Phasor Measurement Unit (PMU) from 50V to 150V and 1A to 5A at 50 Hz with a frame rate of 10, 25 and 50 frame/seconds has become possible with the establishment of PMU-CAL system serving the nation through power sector. The CSIR-NPL PMU calibration system has an uncertainty of ±0.005% to ±0.010%. We use PMU-CAL system to generate a wide variety of complex signals, including flicker, harmonics. This feature gives us flexibility to calibrate PMUs by different manufacturers.

Fig.3: Phasor Measurement Unit Calibration System

e. Nanofabrication Facility: FIB Lab FIB lab work on the synthesis and fabrication of nanodevices and nanostructures to study the quantum transport properties, understanding the enhancement in the device functionality and validating their future implementation for establishing quantum metrology related activities and applications. It is believed that nanofabrication will be very essential tool for the next generation’s technologies and metrological standards will be truly based on quantum phenomena. As per this mandate, we have fabricated superconducting meander lines, very thin superconducting nanowires or nanostructures, proximity coupled 2D layered material-based junctions, superconductor 2D electronic gas superconductor junctions, topological insulators-based devices etc. that have very useful metrology applications. Further, FIB lab also works on the fabrication and characterization of calibration artifacts, samples from the textile, pharma and biotech industries e.g. Drug Eluting Stent System (DES).

Fig.4: Focused Ion Beam System

f. Josephson Voltage Standard PJVS forms the basis for standard of the unit ‘Volt’ in India at par to the international level”. The uncertainty in measurement of Zener Reference Standards is ± 350 nV at k=2 (inclusive of noise of Zener) at 10V level as per the ISO/IEC 17025:2005. CMC: DC voltage (single value) Range: 1 V to 10 V. The PJVS system is based on ‘Quantum Phenomena’ (Josephson effect) given by the relation 2eVn = nhf where n = 0, ± 1, ± 2, ± 3.., Vn = quantized voltage, f = frequency of irradiation, h = Planck’s constant, e = electron charge.