February 2018, Vol. 245, No. 2
TechNotes
Wireless Fire, Gas Detection Solutions
Thinking beyond the wire has become reality for fire and gas detection solutions. A recently successful cost-savings wireless project required multiple open path gas detection (OPGD) monitors, installed at various heights, around a new process unit.
The OPGD system is set up to measure C1-C8 hydrocarbon gases. The wireless signal is transmitted to a wireless wave relayer for alarming and evacuation of the new unit. A control system, located away from the unit excavation, receives the wireless signals from the OPGD for local alarm screens, zoning, data logging and network sharing. There are several steps required for a successful wireless fire and gas detection system.
STEP 1: Environmental Data Analysis
Many questions need to be answered in order to ensure personnel and equipment is kept safe.
Where should the gas detectors be located? How many detectors need to be used? In order to ensure the safety requirement is properly fulfilled, gas detection experts can help provide guidance for sensor placement in many operating facilities by using air dispersion modeling software and other techniques.
Identifying leak sources, wind direction, along with details from the process safety management (PSM) team can provide additional information when determining sensor location.
STEP 2: Evaluate Application
The distances between the OPGD’s transmitters and receivers for this application were over 300 feet. Site conditions made it difficult, and cost prohibitive, to run cables between the OPGDs, alarm bars and controllers in the control room. Therefore, a wireless system for harsh environments was requested.
The system not only needed to be able to handle analog gas information, but also required wireless relay control and large data transmission functions.
R.C. Systems’ wireless radios use frequency hopping spread spectrum (FHSS), client/server in either 900 MHz or 2.4 GHz ranges. FHSS means the radios “hop” between frequencies (902-928 MHz or 2400-2483.5 GHz) many times per second to avoid interference, and increase security. R.C. Systems offers 26 hopping patterns to allow collocating of up to 26 networks within the same area.
STEP 3: Perform Site Survey
So, how reliable is your wireless signal? Is there an easy way to tell? The answer came from the Site Survey Tool (SST). Using the SST to evaluate the wireless signal was a critical step for verifying, and validating, signal strength from detection and alarming areas back to the control room.
To get the wireless signal was not enough; the task was to have the quantitative data to ensure the signal would be strong enough to account for attenuation caused by unknown factors.
Only after reviewing the SST data could we ensure signal strength was well above the optimal requirements of 95% (transmitter to receiver). The SST provided counters, along with both tabulated and trended received signal strength indications (RSSI), to determine signal strength and link integrity for the proposed wireless network.
The SST devices can be supplied with either 900 MHz or 2.4 GHz radio modules for optimal signal coverage. It is important to evaluate sites using the same antennas intended for installation. Longer distances may require Yagi directional antennas, and these should also be used during the site survey.
STEP 4: Install Base Station Controller
Using the web based smart controller, all signals were transmitted back to the control room wirelessly, logged and zoned for ease of monitoring. The wireless controller coordinates the entire wireless network.
Continuously diagnosing the health of all the wireless equipment. The data was transferred on to the plant’s Ethernet network via Modbus/TCP for complete plant surveillance with minimal added costs by using the plant’s already installed network infrastructure, and providing access to system information world-wide via embedded webpage.
STEP 5: Starting Up System
The system simplified installation so significantly that installation took only four working hours. This reduced the cost of installation by 60% over that of a similar wired system.
Driving the next evolution of fire and gas detection will be the integration of wireless technologies such as FHSS. Modern fire and gas systems can now be seamlessly integrated through a secure communication network for data capture, alarming, system diagnostics and process evaluation.
Networking capabilities offer additional layers for monitoring the status of the complete fire and gas detection system. Wireless technology is gaining momentum in many industrial facilities. Technology continues to improve wireless reliability and security. Wireless detection and control systems have emerged as an effective cost-saving solution, providing safety for workers, processes and the environment. P&GJ
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