Temperature measurement in extreme conditions

Andrew Dunbabin, temperature products specialist for ABB’s Measurement Products business, explains what’s involved in building the right equipment for some of the world’s most demanding ambient conditions.

Almost anyone working in industry will be familiar with the IP ratings of instruments that are built to withstand the ingress of certain levels of dust and moisture. But some environments present special challenges that require a bit more thought. When it comes to temperature measurement, there is a growing demand for devices that can offer high accuracy and availability under the harshest operating conditions in some of the most inhospitable regions of the world.

The big chill

For example, oil and gas companies are increasingly looking to very northerly latitudes, from Canada to Russia, in their exploration and recovery operations. The frigid conditions that these facilities have to work in can cause a major headache for electronics, which must be specially rated to operate reliably down to -50oC.

Daily cycles

Another potential problem is presented in dry, desert conditions, where temperatures can easily reach 45oC in the day and plunge to OoC at night. In such environments, temperature cycling can pose a problem for electronics, allowing components to work loose, strain connections and crack as they repeatedly expand and contract. The solution in this case is to opt for potted equipment, which holds everything steady by embedding it in a solid resin.

Hot and steamy Potted equipment is also the preferred solution in tropical operating environments, where high humidity and condensation is the big challenge. An appropriate IP enclosure is the obvious first line of defence, provided it remains firmly sealed.

If the external atmosphere gets inside, however, the night time drop in temperature will be enough for moisture to form and cause condensation. Not only will water cause the obvious problems of corrosion or shorting out circuits, but the warm, damp conditions also provide a perfect environment for the growth of fungus.

Unless an instrument is to remain permanently sealed, potted or epoxy-coated components are thus the only realistic solutions.

Deep water

Offshore operators are increasingly choosing to position production heads on the sea bed, rather than in topside facilities, because it’s more cost-effective and helps to keep more of their equipment in relatively calm waters, rather than having to face storms on the surface. The downside is that the flow, pressure and temperature instrumentation in the production head must be protected against corrosion and pressure at depths of up to 4,000 metres.

Unlike the instruments designed for arctic environments, the electronics of the equipment used in underwater applications can be the same as in standard, good-quality instruments. Where the deep-sea installations differ is in the level of containment and protection required.

Nuclear know-how

The issues in the nuclear industry are different again, with the main challenge being the ability to cope with ionising radiation that can actually alter the chemistry of semiconductors and play havoc with the electronics.

ABB has developed a platinum resistance temperature (PRT) probe that can achieve a 90% response in the measuring element within seven seconds of a step change in temperature. This is wired up to a transmitter using a four-wire circuit that is designed to cancel out the effect of resistance in long cables. This enables operators to position the electronics tens of metres away from the source of radiation.

Growing demand

While attitudes to the expansion of nuclear power have shifted following events at the Fukushima Daiichi plant in Japan, nuclear may yet have a continuing role to play in strategies to tackle global warming. Meanwhile the days of “easy wins” are over for oil and gas companies. Whatever happens, it seems certain that the demand for temperature instrumentation that can operate in challenging conditions will continue to grow.

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