12 January 2024

All of Synaptec’s sensors are passive

Intuitively, we all know what ‘passive’ means: not doing anything. An engineer might get more technical and say it means being incapable of power gain. A scientist might get even more esoteric and say it means being ‘energy neutral’.

Of these potential definitions, I think ‘energy neutral’ is probably the most accurate. While every physical process in the universe does use energy (by converting it from one form to another), passive processes don’t require the addition of new energy into the system to perform their function.

Think of your bathroom mirror. It accurately reflects an image of your face in reverse. That is its function, and it performs it well (when not misted up). You don’t need to plug it in – it just works. The energy contained in the light that reflects from the mirror is sufficient for the whole process to work.

In fact, the bathroom mirror isn’t an arbitrary example: our optical sensors use precisely the same mechanism to convey information from a remote location. We send light down optical fibre, and we look at the reflection that returns. Just like your bathroom mirror, that whole process is passive.

Why is passivity important in a sensor?

Passive processes are less costly than active ones for several reasons. If you can perform a function passively, you do not need a power source to be available at that location. You also won’t have any need for electronics for digitisation or amplification. Because of this minimisation of resources, passive processes are simpler and more robust than active ones. They are usually materially and chemically simpler too, making them more resilient to harsh external environments such as high electric or magnetic fields, radiation, and extreme temperatures. In short, passive devices will generally be smaller, weigh less, last longer, and cost less than active ones.

Ensuring a passive measurement process for voltage and current is one of the principal innovations Synaptec’s engineers and physicists developed to enable Distributed Electrical Sensing (DES). In practice, it means DES sensor networks can be installed throughout power networks in the harshest outdoor conditions, in the most remote and inaccessible locations, and where regular maintenance isn’t an option.

Aside from the measurement itself, we also needed to develop a means to passively synchronise all measurements to a central clock. This is important because precise synchronisation of waveforms and phasors is needed for certain metrics and functions for grid protection and control to be performed. Providing a means to passively measure a signal but then relying on active distribution of a clock signal would obviously be counter-productive!

Although light is pretty darn fast (see Measuring at the Speed of Light), a signal from a sensor 50 km away will still take about a quarter of a second to reach you. That potential delay between local and distant signals just isn’t good enough for the power industry, which relies on precision measurements and timings (down to a single microsecond). We needed to develop a practical solution to time synchronisation that didn’t compromise the passivity of the sensors. This innovation resulted in our Synchromerger patent suite which ensured networks of passive electrical sensors remain time-synchronised over extreme distances.

Putting both of these concepts together delivers a practical platform for synchronised measurement of voltage and current at multiple locations over wide geographic areas. This platform has become known as Distributed Electrical Sensing, or DES.

I hope this article has given you an appreciation of why passivity is a key concept in DES, and of the innovations Synaptec developed to ensure passivity in all its sensors. The concept makes DES a unique technology in voltage and current measurement, allowing us to serve our customers with a highly reliable and commercially competitive means to protect and monitor complex, modern power networks.

Dr Philip Orr, Synaptec CEO