ELECTRICAL

The primary resistance standard is derived from the quantum Hall effect. The quantum Hall effect is observed when a current-carrying semiconductor heterostructure device is placed perpendicular to a large magnetic field at a sufficiently low temperature. Under this experimental condition, for certain magnetic fields B_z, the quantized Hall resistance (QHR) R_H became quantized and appears as plateaux at values that only depend on fundamental constants.

where the number i=1,2,3,4… denotes the resistance plateaux of R_H .

Services Provided:

• Standard resistors.

The volt V is realized using the Josephson effect and the following value of the Josephson constant K_J: 483 597.848 416 984 GHz V^–1.

When a junction created by two superconductors separated by a thin insulating barrier of a few nanometer in thickness is irradiated with microwaves, a discrete voltage level V is generated between the superconductors depending only on the frequency f of the microwaves and the Josephson constant K_J.

The Josephson constant K_J = 2e/h is the ratio of two fundamental constants - the Planck’s constant h and elementary charge e. The number n=1,2,3,…. denotes the total number of the constant voltage steps.

The Josephson array voltage standard at the National Metrology Centre provides calibrations for voltage up to 10 V at typical expanded measurement uncertainties (k=2) for calibration of Zener voltage standard at 1.018 V and 10 V of 0.1 μV/V and 0.05 μV/V respectively.

Services Provided:

• Zener voltage standard
  

The primary standard for dc voltage is derived from the Josephson effect.

Measurement system based on the Josephson array is used as absolute voltage reference for the calibration of dc voltage standards such as Zener voltage standards.

The Josephson array voltage standard calibrates voltage range from -10 V to +10 V. Typical expanded measurement uncertainties (k=2) for calibration of Zener voltage standard at 1.018 V and 10 V are 0.1 μV/V and 0.05 μV/V respectively.

The reference standard for dc voltage is maintained by periodic intercomparison of a group of 10 Zener references.

Zener references and voltage divider are used to transfer the 10 V standard into electrical multifunction calibrator which will then source any dc voltage from zero up to approximately 1100 V.

The voltage ratio of a resistive divider with equally dividers resistance chain that are used for scaling of the dc voltage is determined using the reference voltage source bootstrap method, an absolute calibration method in the form of a “self-calibration” arrangement.

Services Provided:

• Voltage divider
•  Voltage meter
• Standard voltage source

A typical current measurement setup consists of a resistance standard or current shunt and a voltmeter to measure the voltage across the resistor or shunt.

NMC is able to calibrate dc current source and meter from 100 mA to 20 A at expanded measurement uncertainties (k=2) from 4 to 65 mA/A.

NMC has set up systems to calibrate small current measuring equipment based on high resistance shunt and charging capacitor techniques. Equipment such as Electrometer, high-resistance meter, sub-femto-ampere remote source meter, and picoammeter can now be calibrated in NMC in the range of 1 pA to 0.1 mA A at expanded measurement uncertainties (k=2) range from 300 to 5 μA/A.

Services Provided:

• Standard current source
• Dc current shunt
• Low current meter
• Low current source

The quantized Hall resistance is used as an absolute 12.906 4035 kΩ resistance reference and maintained by a bank of 100 Ω resistance standards. A dual SQUID cryogenic current comparator resistance bridge is used to calibrate resistance standards against the quantized Hall resistance standard at typical expanded measurement uncertainties (k=2) better than 0.1 μΩ/Ω.

Standard resistors and direct current comparator resistance bridges are used to transfer the unit of resistance to standard resistors from 0.1 mΩ to 1 TΩ. The scaling of resistance standard periodically verified by intercomparison of groups of 1 Ω and 10 kΩ standard resistors.

The range of resistance standards are used to calibrate multifunction calibrators or meters.

Services Provided:

• Resistance standard
• Resistivity meter

The capacitance standards in NMC are maintained by groups of capacitance standards. Standard capacitors are compared to the reference standards using capacitance bridges. Capacitor from 1 pF to 1 mF is calibrated with expanded measurement uncertainties (k = 2) from 1 to 60 mF/F.

The inductance standards in NMC are maintained by groups of inductance standards. Standard inductors are compared to the reference standards using impedance bridges. Inductor from 100 mH to 10 H is calibrated with expanded uncertainties (k = 2) from 150 to 340 mH/H.

Services Provided:

• Capacitance meter
• Capacitance standard
• Inductance meter
• Inductance standard
• Impedance meter

AC-DC transfer standards are used to establish traceability for AC voltage (current) to the DC voltage (current) based on equivalence in power dissipation of the applied AC and DC voltages (currents) by means of a transfer standard such as a thermal converter (TC).

Measurement systems are used to compare the AC-DC differences of TC and to scale the measurement for voltage and current up to 1000 V and 20 A respectively.

The AC-DC voltage and current difference values are used to derive the traceability of AC voltage and current for frequency range up to 1 MHz and 100 kHz respectively at best expanded measurement uncertainties (k = 2) better in a few parts in 10⁶.

Services Provided:

• AC-DC current transfer device
• AC-DC voltage transfer device
• Standard AC current source
• Current shunt

The AC voltage and current standards are derived in NMC, by using AC-DC voltage and current transfer standards with known AC-DC difference values. This values are used for corrections when trace AC quantities to DC ones.

AC voltage from 2 mV to 1 kV, from 10 Hz to 1 MHz can be derived at expanded uncertainties (k = 2) ranged from 9 x 10^-6 to 0.59 %. AC current, range from 0.2 mA to 10 A, from 10 Hz to 10 kHz can be derived at expanded uncertainties (k = 2) ranged from 40 to 400 x 10^-6.

Services Provided:

• AC voltage/current meter
• Standard AC voltage/current source
• AC Current Shunt

The measurement traceability in electrical power is achieved by characterising and maintaining a group of standard watt converters with reference to AC voltage, AC current and phase standards, and frequency standard for electrical energy calibrations.

Digital sampling method is used to perform harmonics measurement for power quality characterization, calibration of power meter, power analyser, and energy meter under sinusoidal and non-sinusoidal conditions. This is to support electrical power metering, power quality evaluation and electronic energy meter's characterisation for power range up to 20 kW, at expanded measurement uncertainties (k = 2) from 40 to 900 μW/VA.

Besides, NMC also maintains standards for phase angle calibrations, at expanded measurement uncertainties (k = 2) from 4 to 50 m° for sinusoidal signals at 10 to 100 000 Hz.

Services Provided:

• Power converter
• Power calibration standard
• Power analyser
• Power meter
• Energy meter
• Phase standard
• Phase meter

NMC’s high voltage laboratory has the capability for measuring high DC and AC voltages up to 200 kV respectively. Resistive dividers are used as reference standards for high DC voltage, with expanded measurement uncertainties (k = 2) between 30 to 70 μV/V. Standard voltage transformers and standard capacitance are used as reference standards for high AC voltage, with expanded measurement uncertainties (k = 2) of 0.06 %.

The high voltage capability supports high voltage tests and measurements in electrical power and energy related industries, but also dielectric characterization and insulation design for new product developments.

Services Provided:

• High voltage divider
• High voltage meter
• High voltage generator
• High voltage tester
• Impulse tester
• Electrostatic analyser
• Electrostatic detector

Electricity Metering

Accurate measurements of energy and power are essential for energy supply custody transfer billing from energy suppliers to the users, and for energy efficiency monitoring and evaluating to support schemes on energy sustainability.

Accuracy verification of Electricity Meter

Calibration of an electricity meter assures fair trading of electricity.   Standard power values are generated  at defined voltages, currents and power factors for calibrations of such meters. International standards such as IEC 62053-21/22 are referred to for proper operations and definitions of the accuracy of the units under test.

Power reference systems with best uncertainty better than 0.01 % in one-phase or poly-phase at voltage up to 1000 V and current up to 100 A. The frequency is normally 50 Hz but may be varied up to 400 Hz to suit different applications. Harmonics up to 99th can be imposed for simulating various real waveforms. 

Power Measurement for Green Mark

The laboratory is working with government agencies and the industry to support energy efficiency related measurements and verification. The laboratory provides electrical measurement validation, consultancy and knowledge transfer services on green building energy efficiency measurement and verification and smart grid condition monitoring applications to industry and research institutes.

In response to the trend in safety and quality assurance to reduce the probability of false acceptance, as well as performance validation of prototype products, industry often require specialised expertise to ensure the measurements produce relevant, reliable and accurate results.

Some of the electrical measurement verification and characterisation work NMC carried out for the industry:

• High voltage measurement system verification
• Surface resistivity measurement for ESD controlled product
• Characterization of stun devices
• Aircraft battery charger/analyzer
• Dry cell battery production testing systems
• Welding current verification for oil and gas equipment company
• Test station verification
• Characterization of a passive network filter
• Touch current simulation network verification
• Impedance spectroscopy measurement of devices

Evaluation of Charge Characteristics on Dielectric Surfaces

Friction or rubbing on objects can easily induce surface charge. This accumulated charge may trigger sparks as effective ignition sources in explosive environments. It is important to investigate the charging characteristics to identify possible ignition source for explosion prevention. The NMC performs such investigations for various applications of dielectric materials, including those for use on marine off-shore platforms environment.

Evaluation of Dielectric Characteristics of Encapsulation Material

New power electronics devices can potentially operate with minimal cooling requirements at high temperatures. To develop this technology for more electrical aircraft, the limiting factors lie in the packaging and interconnections of the dice in power module.  The NMC supports R&D work in high temperature and high voltage encapsulation design and tests for such devices. We also evaluate the encapsulation’s performance and life span under harsh conditions.

Electrical Impedance Characterisation of Devices

DC parametric and impedance spectrum measurement systems for electrical characterisation of MEMS and semiconductor devices. The characterisation capabilities system includes DC electrical parameters measurement system for voltage-current, power and pulse measurement at low level signal, Low frequency impedance (L, C, R) measurement system for precision measurement impedance measurement up to 1 MHz, and high frequency impedance and frequency response analyser system for measurement up to 100 MHz. Measurement capabilities are also available for small signals and impedance spectroscopy characterisations of devices and materials.

Characterisation of Measuring Network such as body impedance network, perception and reaction network, let-go network as specified in IEC 60990 for measurement of touch current and protective current for safety evaluation of apparatus are done using equivalent circuit network. Leakage current and patient auxiliary currents network as specified by IEC60601 for medical electrical equipment, and resistivity measurement system is using equivalent circuit network to calibrate the 4-point surface.