Vibration monitoring is essential for predictive maintenance of rotating machinery. This is no less true in hazardous locations where standard sensors don’t meet safety requirements – fortunately, certified sensors designed for these hazardous locations are available. Below, we’ll focus on intrinsically safe sensors: what they are, how they work, and why to use them.
A hazardous area is essentially a location where there's a risk of explosion or fire. In North America, hazardous areas are classified according to the Class/Division system defined by NFPA Publication 70 and the NEC/CEC (National/Canadian Electrical Codes). The similar (but not interchangeable) Class/Zone system is used outside of North America.
Electrical equipment in a hazardous area must meet certain requirements to reduce explosion risk. Three things are necessary to cause an explosion: a flammable substance, an oxidizer (usually oxygen), and an ignition source. The classification of hazardous areas depends on the specifics of that combination and is intended to describe a) the hazardous material that may be present, b) the likelihood that it’s present, and c) the conditions that affect the chance of explosion or fire. These conditions can be other characteristics of the surrounding area or properties such as the design or installation method of the electrical equipment itself.
There are several ways of reducing explosion risk – confining the explosion in an enclosure, isolating the equipment to prevent ingress of explosive mixtures, and limiting the energy so that the electrical equipment can't cause ignition. Intrinsically safe hazardous area protection focuses on controlling the ignition source by limiting the available energy and preventing, rather than containing, explosions. Intrinsic safety is most often used as a protection method where there are flammable liquids, gases, or vapors (Class I) present in ignitable concentrations under normal operating conditions (Division 1, or Zone 0/1).
Intrinsically safe sensors are energy-limiting, meaning that the sensor is, by design, incapable of developing enough energy to ignite the surrounding atmosphere. This makes IS sensors suitable for Class I, Division 1 locations (and thereby suitable for lower classes or divisions). Wilcoxon’s IS sensors are certified for temperature class T4 (equipment surface temperatures up to 120°C), which is acceptable for a significant portion of Class I, Division 1 areas.
Intrinsically safe systems limit the energy even under worst-case scenarios of multiple fault conditions. The major advantage of an intrinsically safe sensor over other methods is that it solves all the problems of hazardous areas for equipment requiring limited power and is the only technique which meets these criteria.
Other upsides include:
Intrinsic safety meets the requirements for hazardous locations found in chemical processing facilities, refineries, mills – facilities where flammable materials, in any quantity, are processed or handled. It’s a globally accepted standard, and Wilcoxon’s IS sensors hold CSA, ATEX and IECEx certifications.
When a transducer is electrically connected to other equipment, an electrical safety barrier must be installed outside the hazardous area in series with the connection to prevent fault conditions from introducing excess energy. This is often the only accessory equipment needed specifically when using IS sensors. (Wilcoxon manufactures safety barriers and we’ll be happy to supply them, although barriers from other manufacturers will also work just fine.) The technical note Installation guide for hazardous areas has more information on this topic.
Predictive maintenance in general is a great practice. It’s even better for machines in hazardous areas. Critical machines are less likely to fail at inconvenient times when you can reliably schedule repairs and downtime, which is done much more efficiently with the use of vibration data. Scheduled maintenance improves safety, since there’s less need to enter the hazardous area during normal operation, and increases plant uptime.
Rotating machines such as pumps, motors, compressors, fans, and anything with bearings are all used in hazardous areas and should all be monitored for changes in vibration levels. Intrinsically safe vibration sensors provide this information with high reliability and significant ROI, giving you more peace of mind.
And check out our expanded line of dual-output vibration and temperature sensors with hazardous area certifications.
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