Jim Ralston, Wireless Sales Engineer ProSoft Technology- Mechanical failure of motors, drives and other vital electromechanical equipment are among the most common reasons for production stoppages.
Fortunately, recent advancements in vibration monitoring and data analysis have lead to condition monitoring systems that can accurately detect a problem before failure, thus reducing costly machine shutdowns and maximizing production output.
These systems are installed on the monitored equipment and are typically networked back to a central computer for data analysis and alarm annunciation. Because the machines may be in remote locations where network infrastructure is not available, or on moving platforms where hardwired network connectivity is not practical, wireless communications is a networking alternative that offer installation cost savings, quicker deployment and even improved reliability in certain situations.
For many industries, the purchase of a condition monitoring system is easily justified with a simple return-on-investment (ROI) calculation. For a relatively nominal cost, vital machines may be retrofitted with condition monitoring to reduce operating failures. However, there are additional costs to consider when network infrastructure is not available or practical.
This extra expense can include fiber optic cable installation, conduit engineering/installation, trenching between buildings, leasing phone lines for remote sites, and installation of festooning or slip rings for moving equipment. These additional costs may push the ROI out beyond what management will accept.
If the monitored machine is in a remote location within the factory where network infrastructure is not available, cable installation is necessary. The installation costs of cable in an industrial plant can vary greatly based upon the type of plant and physical configurations.
For example, studies have shown that average cable installation in a chemical plant is $40 per foot ($120 per meter), while cable installation within a nuclear power plant can be as much as $2,000 per foot ($6,000 per meter)'. The actual cable cost depends on the location of the machine relative to existing network infrastructure, type of cable needed (e.g. fiber optic), conduit engineering (if needed), labor cost rates and if trenching is required.
If the machine is in a remote location several miles (kilometers) or more away, then leasing phone lines for communications is required. Leased phone line costs usually include an initial activation/installation fee and then a monthly fee based upon speed of service.
Since vibration monitoring is continuous and typically data intensive, the phone line service must support a high enough speed for continuous monitoring. Phone line service to remote sites such as pump stations are also prone to communication failures due to poor line quality and reliability may be of concern. Wireless cellular services are sometimes an option for remote sites, but are subject to service availability and limited in speed. Cellular data subscription costs may also be expensive.
If the machine is on a moving platform (such as an overhead crane, transfer car or conveyor system), then connecting the condition monitoring system to the plant network is a particular challenge. Depending on the speed and distance that the platform travels, traditional cabling methods such as festooning may be possible.
However, festooning is subject to wear and tear, and is itself a reliability concern as cables may break. For spinning platforms, slip rings with Ethernet support are available but are expensive and require periodic maintenance. Some machines may move so fast, that the only practical communication method is wireless RF.
Given the challenges of networking condition monitoring systems, wireless communications offer lower installation costs (shorten ROI time), eliminate phone lines and remotely monitor machines that were not practical before. But wireless technologies and equipment vary widely in performance and reliability in industrial installation. Designing a successful wireless network requires an examination of current wireless usage, RF paths and environmental challenges of the industrial plant.