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Manufacture of precision electrical measurement instruments

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The National Measurement Institute (NMI) designs and manufactures a range of unique electrical measurement instruments. We use these instruments in Australia’s national standards. Leading national metrology institutes around the world use these instruments, as well as laboratories accredited by the National Association of Testing Authorities (NATA). 

As the peak body for measurement we’re responsible for developing, maintaining and disseminating Australia’s national standards. We apply the technology and skills we develop though our research to design, manufacture and supply instruments and standards for clients. The devices and systems we manufacture are among the most accurate in the world, and many have no known equivalents.

The instruments currently available are:

  • PBA-1S precision buffer amplifier
  • precision 1000 V inductive voltage divider
  • a range of precision resistive voltage dividers
  • precision multi-range current transformer MCT-1
  • precision current shunts
  • CCS-4S computer controlled switch for ac-dc transfer measurement systems

We can manufacture other precision devices and systems on request. 

For more information email or phone 1800 020 076.  

PBA-1S precision buffer amplifier for thermal voltage converters

The precision buffer amplifier is a three stage voltage follower. It’s designed to drive thermal voltage converters (TVCs) without introducing appreciable contribution to the ac-dc difference. Our unique design ensures closeness of the gain to unity, and low phase shift up to 200 kHz. 


  • maximum voltage: 5 V rms
  • input connector: N-female or BNC
  • output connector: N-male or BNC
  • input impedance: 10 MΩ in parallel with 20 pF
  • ac-dc difference:
    • less than 1 µV/V up to 10 kHz;
    • less than 100 µV/V at 100 kHz
  • output voltage with open input: less than 200 mV
  • power: 16 Vac from included supply or ±12 Vdc from an optional external battery

For more information email or phone 1800 020 076. 

Precision 1000 V inductive voltage divider

The precision inductive voltage divider suits metrological applications that require accurate scaling of ac voltage up to 1000 V rms, such as measurements of electrical power.  


  • type: separately excited three-stage inductive voltage divider
  • number of decades: 3
  • maximum input voltage: 1100 V ac rms or 20 V/Hz, whichever is less
  • connectors: type N-female
  • voltage ratios for isolated outputs (decade “x 0.001”): 0.001, 0.002, 0.003, … 0.010
  • nominal frequency range: 40 Hz to 1 kHz
  • typical ratio errors at power frequencies: 
    • in-phase: 1 part in 109 of input
    • quadrature: 5 parts in 109 of input
  • typical calibration uncertainty and life-time stability at power frequencies:
    • in-phase: 1 part in 1010 of input
    • quadrature: 5 parts in 1010 of input
  • weight: 117 kg

For more information email or phone 1800 020 076.

Precision resistive voltage divider RVD-2

The precision resistive voltage divider accurately converts ac and dc voltage up to 500 V to a lower voltage, where sampling and other techniques deliver accurate measurements. 


  • nominal ratio: 0.002 (other ratios available)
  • nominal input impedance: 100 kΩ 
  • nominal input voltage: 500 V
  • input connector: type N-male
  • output connector: type N-female
  • nominal frequency range: 40 Hz to 1 kHz
  • ac-dc transfer difference and of the ratio at power frequencies: less than 5 parts in 106
  • phase error at power frequencies: less than 5 µrad

Other ratio, input impedance and nominal input voltage combinations are available upon request. 

Precision multi-range current transformer MCT-1

The multi-range current transformer forms part of national standards for electrical power. 

The transformer converts a wide range of alternating currents into a voltage with 0.8 V or 1 V nominal value and can be controlled remotely via a USB interface. It allows full automation of the measurement setup and offers high accuracy. Its long-term stability is determined by one ultra-stable 10 Ω resistor.

We supply the transformer with three precision resistors, connecting and interface cables, driver software a calibration certificate and a manual.


  • input current ranges: 0.125, 0.25, 0.5, 1, 2.5, 5, 10, 20, 50*, 100*, 200* А (* with the Range Extender)
  • nominal output voltage: 0.8 V or 1 V (must be specified at the time of order)
  • frequency range: 10 Hz to 10 kHz
  • maximum in-phase error at 50 Hz: 5 µV/V
  • maximum quadrature error at 50 Hz: 10 µrad
  • typical calibration uncertainty at 50 Hz (95%):
    • transformer ratio: 2 µV/V, 3 µrad
    • resistor ac-dc difference: 1 µV/V
    • resistor phase: 1 µrad
  • interface: USB
  • input connector: 4-pin 30A Amphenol (up to 20 A)
  • 12 mm terminals (above 20 A)
  • output connector: N-type or BNC
  • output resistance: 30 Ω

For more information email or phone 1800 020 076.

Precision current shunts

The precision current shunts are part of standards for ac-dc transfer and ac current.

Each shunt is a coaxial two-port 4 terminal resistor, comprising a parallel combination of precision thick film resistive elements. 


  • nominal output voltage: 1 V
  • input connector: UHF female or N-male
  • output connector: N-female
  • typical lifetime stability of ac-dc difference: less than 10% of calibration uncertainty
  • change of resistance due to self-heating:
    • less than 10 µΩ/Ω/W for ranges up to 2 A
    • less than 1 µΩ/Ω/W for ranges from 5 A to 20 A
  • typical phase error: less than 1 µrad at 1 kHz, less than 10 µrad at 10 kHz


Typical ac-dc difference (µΩ/Ω)

Range1 kHz100 kHz1 MHz
1 mA<3<100n/a
10 mA<3<50n/a
20 mA<3<20n/a
50 mA<3<10<200
100 mA<3<5<200
200 mA<3<5<200
500 mA<3<10<200
2 A<3<50<200
5 A<3<100<1000
10 A<3<100<1000
20 A<3<500<200

Typical uncertainty of ac-dc difference (µΩ/Ω)

Range1 kHz100 kHz1 MHz
1 mA10100n/a
10 mA850n/a
20 mA520n/a
50 mA515100
100 mA515100
200 mA515100
500 mA515100
2 A520100
5 A10100150
10 A20100200
20 A25200n/a

For more information email or phone 1800 020 076.

CCS-4S computer controlled switch for ac-dc transfer measurement systems

The computer controlled switch for ac-dc transfer measurement systems is a two-terminal single-pole double-throw device. It can operate under full remote or manual control, and has a manual off switch. Light emitting diodes indicate the state of the switch.

The switch contains two modules, a control unit (USB or PCI) and either a high voltage relay unit or a high frequency relay unit. We supply the switch with LabView and Visual Basic drivers, and a manual.


  • rated voltage:
    • 1100 V @ 100 kHz reducing to 30 V @ 1 MHz (with high voltage relay unit)
    • 120 V @ 100 kHz reducing to 10 V @ 100 MHz (with high frequency relay unit)
  • input and output connectors: N-female
  • switching time: < 5 ms
  • on-resistance repeatability: < 20 mΩ@10 mA
  • interface: USB

For more information email or phone 1800 020 076.

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  • Email
  • Phone 1800 020 076
  • Write to us at National Measurement Institute, GPO Box 2013, Canberra ACT 2601

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Last updated: 13 September 2019

Content ID: 64446