Why WireFree: Wireless Gas Detection System Basics and Benefits

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1 Why WireFree: Wireless Gas Detection System Basics and Benefits Anyone who needs gas detection can benefit from using a wireless system. Whether you re just being introduced to the gas detection market, or you re seeking a system upgrade, WireFree is the most innovative gas detection solution. Although traditional wired gas detection has proven to be durable and reliable, installations can be costly and time-consuming. Therefore, in 2005 Otis Instruments began pioneering wireless (WireFree) gas detection products. Seven years later, we confidently offer two generations ( Gen I and Gen II ) of WireFree gas detection systems. Benefits of using WireFree gas detection are: time saving conduit-free setup and maintenance, ease of use and implementation, ability to use multiple receivers, and ability for remote monitoring. Because Wirefree gas detection requires no wiring or conduit, WireFree setup saves time and money by requiring fewer field hands (and non electrician-trained field hands). When setting up a WireFree system, simply mount the units and turn them on. With Otis Instruments WireFree technology, no wires are necessary from the sensor assemblies to the Monitor, or from external power source to the sensor assemblies. With Otis WireFree, internal power is used providing up to 12 months of field-life before battery replacement is necessary. WireFree systems are one of the lowest risk systems on the market. WireFree systems are both safe and dependable. With no wires that could be cut (resulting in damage to the system), there s little room for even the greenest field hand to make a costly mistake. While cost and efficiency are at the forefront of gas detection system decision-making, the most important factor is safety. With WireFree, you can be assured that the gas detection system serving your application will be dependable, with readings that are accurate. When looking for WireFree technology, consider products that are: field adjustable for background gas; addressable to eliminate interference with other systems; and designed to reject EMI and other forms of interference in order to avoid false gas readings. The remote monitoring capabilities that wireless gas detection provides, via radio communication, allows sensor assemblies to be setup throughout a site while the controlling monitor may be setup miles away. Alarms for notification of gas presence at the monitor, as well as at the sensor assemblies, let off-site field hands know that there s danger at the site before entering the premises. Communication Options When considering a WireFree system, there are a few basic setup and communication criteria to consider. Radio frequency options, certification requirements, and the type of antenna most suited for your application, will primarily be dictated by where the system will be setup. 1

2 The radio frequency for your application will depend on several factors, particularly those required by the country in which your system will be setup (either 900 MHz or 2.4 GHz). The two most common options are 900 MHz (up to 7-kilometers line-of-site) and 2.4 GHz (up to 3- kilometers line-of-site). Countries also individually mandate the type of certifications that gas detection equipment being used in their country must have. Commonly, CSA and ATEX are required internationally. Otis Instruments CSA and ATEX certified WireFree sensor assemblies use one of the easiest interfaces on the market. Non-intrusive calibration allows sensor assemblies to remain in the field while being calibrated, because a hand-held magnet triggers menu switches. Sensor assemblies feature a simple three-button interface, and Stand-Alone Assemblies offer on-board relays eliminating the need for a monitor to trigger relays/alarms. Categorized menu options on all WireFree products allow the user to go directly to the option they need to setup or modify. When using a wireless gas detection product, signal strength performance will vary due to: environment and surroundings, including open fields, buildings, trees and landscape, etc.; distance between the sensor assemblies and monitor(s); penetration; antenna type; weather conditions; radio power. For many applications, a standard antenna will suffice either Monopole or Dipole. When standard antennas don t have enough strength, though, high gain options are the answer. High gain options include Yagi (directional) and Omni (360 degrees). Yagi antennas are directional, and are typically used at the sensor site. Figure 1. Yagi Antenna Image Figure 2. Yagi Antenna Signal Diagram Omni antennas are used in 360 degree environments, and are: Typically used at the receiver site Available in 15, 25 or 65 Compatible with a 20 increment extension cable Since High Gain antennas are taller than the average antenna, lighting can sometimes be an issue. To help prevent lighting damage, a lighting surge suppressor is recommended with High Gain antennas. 2

3 Interference Solutions Several selections are required for WireFree system setup, allowing each system to be unique. System setup selections can include: VID # Manufacturer selectable for your application Network ID User-selectable; up to 78 networks Address - User-selectable; up to 255 per network The VID feature is typically only a factory-settable feature that may only be set one time. The VID # cannot be changed or read once it has been set, so the correct value needs to be set initially. This allows networks to be secured. When using a radio with a pre-set VID #, a nearby plant with the same radios as another plant s radio will not see each other. The Network ID must be the same on all radios that need to communicate with each other. If there are separate zones that do not need to be seen on the respective monitors, then the number can be changed to make that possible. Changing the Network ID essentially changes the hop sequence of the radio. If not all radios have the same hop sequence they cannot communicate with each other. Each network needs its own Primary Monitor a monitor from which all sensors receive acknowledgments (that must be present for the sensors to send transmissions). User-settable addresses ensure that each sensor assembly in a network has its own wireless communication path to the receiving monitor. When using multiple sensor assemblies in a single network, all items in the network (sensor assemblies and receivers) will share the same Network ID, while each sensor assembly will have its own address. Multiple Receivers = Network Reliability With WireFree, multiple receivers (that serve similar or different purposes in varying locations) can be used (i.e., Primary and Secondary Monitors). The major difference between Otis Instruments Gen II Primary and Secondary Monitors is that Primary Monitors send acknowledgments to the sensor assemblies. This is useful in that it allows the sensor to have an RSSI (receive signal strength indicator) value. Secondary Monitors receive all transmissions, but do not send acknowledgments. Also unique to this configuration is that the presence of the Primary Monitor is required in order for the Secondary Monitor(s) to function. While this can create a potential dependence on a single node for the radios to function, there are several backup methods that prevent this from occurring. Due to the nature of Otis Instruments radio protocol, it is mandatory for a Primary Monitor to be present to receive transmissions from the sensor assemblies. Setting up an optional Primary/Secondary scenario helps guarantee that there will always be a functioning monitor on your site. Scenarios in which a customer would benefit from having multiple monitors include: The Primary Monitor goes down, and there is a Secondary Monitor in the area All sensor assemblies within range of the Secondary Monitor will now report to that monitor as a Primary Monitor. 3

4 The Primary Monitor goes down, and there are multiple Secondary Monitors Each Secondary Monitor has a random back-off time in which it waits before attempting to become the Primary Monitor. When the first Secondary Monitor finishes its back-off, it checks to see if there is a Primary Monitor, and then becomes the Primary Monitor if none are yet present. The Primary Monitor goes down, a Secondary Monitor takes its place, and the Primary Monitor is restored In this instance, when the Primary Monitor is restored, it will send out a beacon letting the Secondary Monitor know it is functioning again. This will prompt the Secondary Monitor to step down and resume its position as Secondary Monitor. Also, any indicators present on the Secondary Monitor will now be cleared since the Primary Monitor is functioning again. The Primary Monitor goes down, and two Secondary Monitors step up as Primary Monitors because they are out of range of each other This situation is unavoidable, as the Secondary Monitors cannot see each other because they are out of range. This normally takes place if the Primary Monitor is situated in the middle of both Secondary Monitors. In this case, all sensor assemblies in range of one primary Monitor will report to that monitor. If there are any sensor assemblies in range of both monitors, then whichever monitor s beacon is last received by the sensor before it transmits, the sensor will transmit to that monitor. The Secondary Monitor loses communication with the Primary Monitor but the Primary is still on and functioning the Secondary Monitor will periodically step down to look for the original Primary Monitor. If the Secondary Monitor is able to once again see the Primary, then the Secondary will return to being a Secondary Monitor. If it still does not see the Primary, then the Secondary Monitor resumes the place of the Primary.) The Primary Monitor goes down, and two Secondary Monitors step up as Primary Monitors but are in range of each other both New Primaries will continue to check for the presence of the original Primary. Because they will not utilize the same wait period, one New Primary will check before the other. When that New Primary sees the presence of the other, it will step down to act as Secondary Monitor again. Examples of various receivers that may be used individually or collectively are: Industry-certified explosion-proof 32-channel 3-relay wireless relay/alarm monitor (Relayer) Touch-screen data-loggers Touch-screen monitors Message-repeating device for long-distance communication between WireFree sensor assemblies and monitors (WireFree Repeater) Hand-held signal strength meter that shows the status of any WireFree Gen II gas detection device within range (View) 255 channel receiver that works collectively with Otis Gen I and Gen II WireFree sensor assemblies, and a PLC, PC or other compatible monitor (Interface) 4

5 Figure 3. Multi-Receiver WireFree Setup Otis Instruments have been manufacturing gas detection since 1983, WireFree gas detection since Otis WireFree gas detection systems are field-tested, industry certified, and multigenerational. 5