Application in Temporary Situation
In some cases it may be necessary to monitor gas in situations in which the cost of setting up a wired solution is completely unfeasible. A planned maintenance turnaround, for example, might involve activities which could potentially introduce gas leaks into the area. A wireless system could be deployed during such operations and relocated once the shutdown is complete. Other temporary situations might include the aftermath of a natural disaster, a security breach or a plant expansion project.
The ability to deploy multiple sensors wirelessly can also provide predictive and preventive maintenance capabilities that wired systems cannot provide cost-effectively. Measuring the amount of background hydrogen sulfide and methane in the air and comparing it over time trends can detect an early indication of a problem. The sensor would pick up on this and send it to an asset management application, which might track increases in methane and/or H2S and compare it to other areas, and historical norms. Analysis of changes could reveal potential dangerous trends early enough so that they can be corrected. Maintenance can be dispatched to affected areas for detailed investigation and needed repair in lieu of checking everywhere during routine maintenance rounds. For systems carrying risk of gas leakage, wireless technology can be the heart of a cost-effective reliability-centered maintenance program.
In addition to the basic sensing technology, battery life and inter-connectivity represent two of the most critical operating issues that wireless gas monitoring will raise.
Battery life is a key variable in both the economics and performance of a wireless monitor. The more remote the location being monitored, the greater the role of the battery in maximizing safety at a low cost. Newer systems use lithium metal technology which, combined with low-power components and advanced power modules, can extend life well beyond 5 years, significantly greater than current offerings operating under the same conditions. Affecting battery life in addition to its metallic composition, is how well low-power components like display and sensory assemblies feed the circuit board, how often they are pinged for a message, and the speed at which the message is transmitted. A typical gas monitor could be configured to send readings at any interval, from seconds to hours or more, depending on the need for information and the desired battery life and the speed at which the sensor can actually collect data. Furthermore, prudent wireless network design (how the wireless sensors are laid out) should be considered, and can help to maximize battery life.
Your plant IT personnel will need to be involved in the deployment of a wireless gas monitoring system in order to connect the wireless network to plant monitoring and control systems. They will need to know exactly how the device will join their network and how it is communicating data, which is a function of the communications protocols.
How the system ties into the control system depends on the wireless protocol selected. A device supporting WirelessHART, for example, would automatically join an existing HART network, which is the most commonly deployed protocol. WirelessHART is a globally approved standard (IEC 62591) that promotes an interoperable, self-organizing and healing, mesh technology, which is secure, reliable, and easy to use (Figure 2). A communication protocol like this can improve reliability by enabling the signals to find the best signal paths to deliver rich diagnostic information about the gas detector. In addition to communicating gas concentration values in PPMs and %LELs, a WirelessHART enabled gas detectors can also transmit information on battery life, temperature and date of last calibration.
In our next and concluding post in the Wireless Gas Monitoring series, we will explore the WirelessHART protocol. Stay tuned!