Best-suited sensors

Paul Boughton

Leila Briem explains how to specify encoders and sensors to save space, boost efficiency and cut costs

In an industry where fluctuations in supply and demand can drastically effect drilling operations, the need to design more streamlined feedback systems is greater than ever. This means that all players, from the OEMs of drilling equipment down to the companies that build the components, need to strive to design products that boost efficiency, improve safety and lower the cost of ownership. Top among the demands for position sensing feedback devices for oil and gas operations are features such as space-saving packages, high shock and vibration resistance, extended temperature operation, superb sealing and multiple hazardous area certifications.

Many oil and gas applications exist in potentially explosive atmospheres where having explosion-proof and flame-proof rotary encoders that can operate directly in Division 1, Zone 1 environments is required. Having hazardous area rated encoders and sensors that have been triple-certified (UL, CENELEC/ATEX, and IECEx) helps simplify the certification process of an entire assembly, and saves costs in obtaining additional approvals to comply with international safety regulations. The tricky thing about designing explosion-proof and flame-proof devices is that the housing naturally needs to have a thick and more bulky construction. With the aim of keeping the overall size of equipment (such as top drives) as compact as possible, explosion-proof encoders designed in extremely low profile packages to take up less shaft space provide a more fitting solution (pun intended) than comparable larger alternatives. Compact encoders are also ideal for mud pump applications where the pumps are situated back-to-back because their low profile design allows space for installing a feedback device.

OEMs continue to demand higher performance from industrial encoders especially in drilling applications where shock and vibration are harsh. Encoders with high shock resistance, upwards of 250G, are crucial for reliable operation. Encoders on these applications are often installed behind motors, close to the brake, where a lot of heat is generated. The capability of operating in temperatures of up to +85°C (185°F) is a key requirement to demand of encoders to prevent component failure. Hard-anodised housings and IP66 levels of sealing also help to extend component life by protecting from dirt, moisture and corrosion. Removable terminal boxes simplify installation and minimise time in the field, while improved electronics that protect against wiring errors can prevent encoder failure.

Another way to boost efficiency in applications such as pipe handling and iron roughnecks is to use an explosion-proof Hall effect sensor instead of relying on multiple proximity sensors for positioning. A rotary Hall effect sensor can provide constant and accurate position feedback that allows for better speed control and increased productivity. For example, a Hall sensor would allow pipe-handling equipment to operate faster throughout its movement and then slow as it reaches the end of its travel. Furthermore, using only one Hall sensor on an iron roughneck eliminates the need for multiple proximity sensors, which not only provides more accurate feedback but also reduces cost. Using Hall effect sensors for zone control can also increase safety in drilling equipment operations because the exact location of the moving piece of machinery will be known at all times, reducing the likelihood of a collision, either with equipment or operators.

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Leila Briem is with BEI Sensors, a brand of Custom Sensors & Technologies (CST).

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