Making the best choice

Sensor Review

ISSN: 0260-2288

Article publication date: 1 September 2001

263

Citation

Loughlin, C. (2001), "Making the best choice", Sensor Review, Vol. 21 No. 3. https://doi.org/10.1108/sr.2001.08721caa.001

Publisher

:

Emerald Group Publishing Limited

Copyright © 2001, MCB UP Limited


Making the best choice

Making the best choice

In this issue we look at temperature sensing and have aimed to include systems and techniques that operate near the extremes of hot and cold that are experienced in industrial processes. We also cover methods that can be used for gaining higher accuracy measurements from standard sensors.

As with most fields of sensor technology, for any given application there are usually a number of techniques that can be used successfully to measure the value of interest. However, there will only be one "best" method, and so a detailed knowledge of the application itself and all the various possible methods is required if the optimum choice is to be made.

Of course you will probably get away with it if you do not make the best choice, and indeed I would not be surprised if at least 50 per cent of the sensors currently in use in our factories were not the "best" choice. Not making the best choice may have quite subtle and often long-term impacts on your productivity. For example, if the accuracy is not quite as good as it should be, or if the signal is a bit noisy, then a process may have to be operated with wider tolerances or increased power consumption, all effects that will cost far more than the sensor that is being used to measure the operating characteristics.

Other non-best choices may have more immediate and noticeable impacts. For example, on a system that I have recently been involved with, a wire-wound potentiometer was originally specified to provide a tank level indication as part of a hydraulic system. The system operated under high pressure and sub-sea and the wire-wound sensor was completely submerged in the hydraulic fluid. No problem so far, as the fluid is non-conducting and non-corrosive all should be well. The problem only came about when small quantities of sea water entered the system. It should not have got in, but such things happen in the real world. The sea water was attracted like a magnet to the wire-wound sensor and immediately initiated a violent electrochemical attack on the wire itself and the electrical connections. Life expectancy was drastically reduced to about six weeks. The cost of a replacement sensor was one thing, but this was made completely insignificant by the cost of down time and dismantling needed to replace it. Needless to say an alternative sensing method was adopted after about 12 weeks.

Making the best choice of sensor is, therefore, quite an involved process that goes far beyond the simple requirements of measuring range and accuracy. Can it be linked in to the rest of the system? What are the likely causes of failure? What is the life expectancy? How easy will it be to replace? Is it likely to still be available in ten years' time?

All these and more are fundamental to sensor application, and are particularly important if you are operating under harsh or extreme conditions.

Clive Loughlin

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