National Physical Laboratory

High accuracy measurement at work

NPL has developed the 'industry' Primary Impedance Microwave Measurement System - iPIMMS.


This new software provides businesses with National Measurement System (NMS)-levels of measurement accuracy that minimises downtime by ensuring instruments do not need to leave the workplace to be calibrated.


Laboratories needing traceable measurements are required to periodically send their standards to be calibrated at a National Measurement Institute (NMI) such as NPL. They need to receive a certificate and correction values on a regular basis to continue to operate effectively.

This downtime can be disruptive and expensive for laboratories, with instruments unusable as they are off site. It can also take time for equipment to be reinstated, checked and the new calibration figures incorporated.


The 'industry' Primary Impedance Microwave Measurement System (iPIMMS) is a piece of software that provides industry with NMS-levels of measurement accuracy without the need to regularly send equipment to an NMI.

It was designed by NPL in 2001 for microwave network analyser users to achieve uncertainties which are equivalent to those of measurements performed at NPL. iPIMMS is used in conjunction with a vector network analyser to calibrate RF and microwave devices and calculates both the result and its associated uncertainties

It takes into account many key preferences for any calibration laboratory; namely traceability to National Standards, a very short traceability chain, low uncertainties and reduced cost of calibration.

Originally, users would access iPIMMS remotely over the NPL server, but firewalls and security meant that connectivity became an issue, and a new solution was sought. In 2010 NPL transferred the code onto a CD ROM with dongles used to store key parameters to offer an improved remote service.

The iPIMMS software can be used to measure: verification kits; calibration kits; terminations; air lines; attenuators and power sensors.


iPIMMS disseminates the measurement expertise of the NMS to industry in a way that minimises downtime to save companies time and money. It employs the same algorithms and techniques that are used by NPL for its own RF and microwave impedance calibration services.

Agilent Technologies is a global company that designs and manufactures instruments and equipment for measurement and evaluation that has moved its microwave centre of excellence to the UK. It has signed a licencing agreement to use iPIMMS to provide reflection and transmission coefficient measurements.

This work was funded by the National Measurement System, the UK's national infrastructure for measurement, which delivers world-class measurement science and technology. It is overseen by the National Measurement Office (NMO), an Executive Agency of the Department for Business, Innovation and Skills and is responsible for stimulating good measurement practice and enabling business to make accurate and traceable measurements, for the benefit of the nation.

Find out more about NPL's work in the Digital Economy sector

Last Updated: 18 Sep 2017
Created: 22 Dec 2010


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