Instrumentation • Electronics


decision. In such instances, when the financial impact on a producer’s brand or reputation is considered, the few pounds’ difference in BOM costs pales into insignificance.


the changeover is not at all straightforward. A major issue is that potentiometers are physically compact and so the space previously occupied by a potentiometer will usually be too small or not the correct shape for a non-contact replacement. The change to non-contact may require a complete mechanical redesign and hence re-testing and re-qualification of the host product.


Second, non-contact devices consume more power than


Fig. 2. Add a tiny piece of foreign matter - such as sand, grit or dirt - between the contact and track and the resulting abrasion has a dramatic effect on a potentiometer’s lifetime and reliability.


There is a further aspect to be considered in any such financial analysis. Buyers of equipment are increasingly aware of the unfortunate reputation that potentiometers have. No doubt that this is somewhat unfair but nevertheless there is a tendency for equipment that uses potentiometers to be more closely scrutinised and hence there are more pressure on cost compared to alternatives that offer non- contact sensing solutions. This widespread perception can put equipment manufacturers on the back foot when they are selling equipment that relies on potentiometers - since they are often forced to defend or justify the reliability and quality of their product. Consequently, many equipment builders are looking to replace potentiometers with non-contact solutions for marketing, rather than strictly technical, reasons. The unfortunate reality is that partially ill founded market perception as a driving force for change is just as real and just as brutal as any technical reason. Nevertheless, not everyone is changing from potentiometers to non-contact solutions. The reason is that


a potentiometer and tend to produce a digital electrical output compared to a potentiometer’s analogue output. Similarly, such a changeover may require the host electrical system to be re-engineered, re-tested and re-qualified. Third, potentiometers are classed as ‘simple devices’ in safety-related or ATEX environments, whereas a non-contact device is unlikely to be classified as such and only infrequently are such devices ATEX-certified. In order to minimise the impact of changing to a non-


contact alternative, a common shortcut is to use a new generation inductive sensor. These sensors work in a similar way to traditional resolvers or linear transformers but crucially are just as compact as a potentiometer. Rather than a traditional inductive sensor’s wire spools, these new generation devices use printed circuits to generate the inductive fields. This means that they can be readily arranged in a wide variety of compact shapes and sizes to suit the mechanical constraints of the host equipment. Such compactness and form flexibility can eradicate the need for a mechanical redesign to accommodate the changeover. These new sensors can also generate a high accuracy voltage or current analogue output to mimic a potentiometer and hence avoid re-engineering the host electrical system. The sensors are well suited to harsh environments with operating temperatures between -55 deg C to +230 deg C and can be encapsulated for long-term submersion or operation in explosive environments. Since they are lightweight and non-contact, vibration and shock have negligible effect. ●


Mark Howard is General Manager, Zettlex UK Ltd, Newton, Cambridge, UK www.zettlex.com


Analytical electronic valves C


lippard Instrument Laboratory Inc’s new Analytical Series electronic valves are available in 2/2 or 3/2,


normally-closed or fully ported. The valves are designed for the specific needs of the analytical industry and for applications where cleanliness is especially important. The A-E Series pneumatic valves utilise a patented valve system that has been used and proven throughout many industries. With a low power consumption of only 0.67 watts, a response time of 5 to 10 milliseconds, and voltages of 6, 12, or 24VDC, these new valves offer unlimited


flexibility in design.


Special materials, manufacturing and assembly processes make this valve perfectly-suited for applications where internal cleanliness, bubble-tight operation, and long life are imperative. For complete details on the A-E series electronic valves that provide safety of operation with quick response, low power consumption and long life. ●


Enter 31 or ✔ at www.engineerlive.com/ede


Clippard Europe SA is based in Louvain-la-Neuve, Belgium. www.clippard.com/analytica


www.engineerlive.com 31


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