The benefits of using inductive sensors

Inductive sensors, on the other hand, use alternating current to 'induce' a current to flow in an opposite direction in a second conductor allowing position and speed to be measured. But, unlike capacitive methods, inductive techniques are much less affected by foreign matter such as water or dirt, and temperature fluctuations which can cause a problem. These are negated by using multiple receive coils to calculate the position from the ratio of the received signals. This robust, reliability has meant that inductive sensors are used in areas where harsh conditions are common such as defence, aerospace, industrial, and oil and gas sectors. However, though a superior sensing technique, it is yet to really be used by the mainstream. The reason is traditional inductive sensors use a series of wound conductors or spools which must be wound accurately to achieve accurate position measurement and achieve strong electrical signals making them bulky, heavy and expensive. To overcome this, Cambridge-based Zettlex's technology, uses printed, laminar constructions rather than wound spools to allow the same inductive principles to be used. This means that the coils can be produced from etched copper or printing on a wide variety of substrates such as polyester film, paper, epoxy laminates and even ceramics. The printed constructions can be made more accurately than windings and offer improved measurement accuracy at a lower cost, bulk and weight while maintaining the stability and robustness of the inductive technique. Since inductive techniques work at greater separation distances than capacitive techniques, this allows the principle components of inductive position sensors to be installed with relatively relaxed tolerances. This helps to minimise the cost of both sensor and host equipment and enables the principal components to be encapsulated to withstand very harsh local environments such as long-term immersion, extreme shock, vibration or the effects of explosive gaseous or dust-laden environments. Electromagnetic noise susceptibility is often cited as a concern by engineers considering inductive position sensors. The concern is misplaced however, given that resolvers have been used for many years within the harsh electromagnetic environments of motor enclosures for speed and position control. Though some engineers are confused between capacitive and inductive position sensors, as both use a non-contact technique to measure position, the underlying physical principles are very different with each technique suitable for particular geometries and applications. However, Zettlex believes many of the disadvantages of using inductive sensors can now be overcome, and that they offer a better solution to capacitive sensing technology. Film in colour A 'low-tech' pressure sensitive film has been introduced by US based Sensor Products. Its Pressurex-micro Green (PMG) is a tactile surface pressure mapping sensor film and can yield both high-resolution and visual detail for fast, accurate surface contact stress analysis. PMG comes on a roll and can easily be cut with scissors to the desired sizes and shapes required for an application. The thin 8mm film can be adhered to bolted interfaces, impressions between rollers or lamination presses and provides a colour changing visual indicator to reveal the surface contact force between any two surfaces. The colour change is instantaneous and permanent, the more intense the colour the higher the pressure. The rolls are consumable and ready to use out of the box with no training, setup, electronics or instruments required.