The World's first practical Johnson Noise Thermometer
developed by .......METROSOL Limited

Metrosol in conjunction with the National Physical Laboratory (NPL) have developed the world's first practical Johnson Noise Thermometer. So far we have developed and patented the technique and instrument concept. We have also produced a desktop proof of principle working prototype and can make measurements in a normal laboratory environment.

The initial phase of this work was part funded by Innovate UK as a feasibility study in their “Development of the Civil Nuclear Supply Chain” competition.“ The outcome of this feasibility study exceeded our expectations.

Johnson Noise Thermometry

Johnson noise thermometry (JNT) is a primary temperature measurement technique based on the fundamental properties of thermal fluctuations in conductors.

A Johnson noise thermometer never needs calibrating and is insensitive to the condition of the sensor material, so is ideally suited to long-term temperature measurements in harsh environments, such as nuclear reactor coolant circuits, nuclear waste management and storage.

Johnson noise (thermal noise, Johnson-Nyquist noise, white noise) is the electronic noise generated by the thermal agitation of the charge carriers (usually the electrons) inside an electrical conductor, which happens regardless of any applied voltage. The generic, statistical physical derivation of this noise is called the fluctuation-dissipation theorem.

Johnson noise in an ideal resistor is white, meaning that the power spectral density is constant throughout the frequency spectrum (except at extremely high frequencies). As the Johnson noise is the results of many independent charge carrier movements, the central limit theorem states that the resulting noise voltage will have a normal or Gaussian distribution.

The most important aspect of Johnson noise from our point of view is that the power of the Johnson noise is directly proportional to absolute temperature. There is no material property or calibration requirement to derive the absolute temperature, just electrical measurements. Therefore this technique is not subject to sensor drift.

Johnson Noise Thermometer

We are now seeking partners or investors to take the project to the next stage, or work with you to help you measure Johnson Noise on your project. Contact Metrosol to register your interest.



Our Ethos can simply be stated as “uncompromising”. We believe that the difference between an adequate (or even a good) product and a world-class product is in the fine detail and at Metrosol we are unflinching in our search for perfection. We employ a continuous improvement approach, refining our designs and manufacturing processes in order to ensure that our products always deliver the highest performance and are of the highest quality.

Our approach is to look for innovative solutions to measurement problems that provide tangible benefits to users of our instruments. We collaborate with a number of partners (National Measurement Institutions and commercial organisations) who are acknowledged leaders in their field in the development of our technology. The extensive range of skills we can deploy allows Metrosol to take a product design from a market requirement to a fully engineered instrument, ready for production.

Our aim is always to exceed our customers’ expectations.

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 Johnson Noise