Instrumentation
Fig. 3. John O’Brien, General Manager of FLEXIM Americas. “The meter sends approximately 1000 pulses back a second in 500 pairs.”
new applications for this technology. When we first started this service we were doing straight forward flow measurements. They were basically chemical addition type measurements expressed as GPM or lbs/min. We also did a fair amount of check metering/troubleshooting existing flow meters. We have started to expand our repertoire by now adding heat flow (BTU) type measurements. Our meters are configured for temperature inputs and given the fact that these 601 units are dual channel allows us to measure supplies and returns
simultaneously. This energy meter functionality is starting to pay off. We have never had this ability before and are just now starting to apply it. This is definitely something we will keep out eyes on.” ■
Enter 41 or ✔ at
www.engineerlive.com/epe
Oliver Foth is with FLEXIM GmbH is based in Berlin, Germany.
www.flexim.de
Wireless mesh networking offers end-to-end visibility of process environments
I
DC’s Zigbee wireless products provide simple decentralised wireless mesh networks that enable process manufacturers to improve their control and monitoring procedures, achieving end-to-end visibility of production processes, personnel, logistics and distribution operations.
Wireless has always been considered too unreliable for the replacement of traditional fixed cables in process environments. In addition, most wireless networks do not offer the security, robustness and reliability needed for replacing hard- wired telemetry systems.
ZigBee has the potential to overcome these barriers; the technology having been designed to address the market need for a cost-effective, standards-based wireless network, to operate in
electrically noisy industrial environments; and, typically, for connecting sensors in remote control and monitoring applications.
ZigBee, like Wi-Fi and Bluetooth, operates over the licence - free IEEE802.15, 2.4GHz frequency band. However, whilst Wi-Fi and Bluetooth have been designed for small networks carrying relatively large packets of information, ZigBee is intended for large networks and lower data rates. This is evidenced by the standard one-milliwatt ZigBee chip, which is short range (70-100 m) and relatively slow, only 250Kilobits per second.
Another crucial difference that sets ZigBee apart from other wireless systems is that ZigBee/802.15.4 is a full blown telemetry system in its own right, with the ability to provide wireless
personal area networking (WPAN) ie digital radio connections between computers and related devices, such as sensors. This kind of network eliminates the use of physical data buses. ZigBee cannot be considered for real time control applications requiring deterministic and fast response times; it has a 10 – 15millisecond network latency when routing messages between nodes within the network. However as ZigBee radio transmissions will propagate up to 100m, it’s unlikely a system will require more than one or two message hops, making the system response time adequate for most remote control and monitoring applications. super-frames, for more time critical applications. ■
For more information, visit
www.zig-bee.co.uk www.engineerlive.com 41
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