Smart sensors have been around for a long time, but when combined with wireless capabilities, the sky’s the limit.

If you are anticipating a wireless future, you can easily spend $6,000 or more for an intelligent sensor capable of preventing and withstanding an explosion, but you probably don’t need to spend that much. Instead you can choose from self-contained wireless sensors/transmitters or use wireless RTU (remote terminal unit) and I/O units with a cluster of wired sensors that will tie into the plant network through a gateway device. To have a successful and upgradeable wireless installation, however, you need to know what you want to accomplish, as well as how much your needs will grow.

With the ISA100.11a specifications complete, processors can choose from new ISA100-compatible sensors and gateways or several already existing WirelessHART devices on the market-from low-cost, “hockey-puck” sensors right on up to the $6,000-plus explosion-proof sensor. In addition, several alternative proprietary solutions are available with price tags ranging from a couple hundred dollars for a temperature node to about $2,000 a point for some RTU and remote I/O-based units that let users cluster wired sensors together for transmitting to a remote data collection unit or Ethernet gateway. The new ISA100.11a specification allows for WirelessHART and other protocols (e.g., Modbus TCP) to be “tunneled” through its system components, giving users the option of using these with ISA100-compatible equipment.

If you are planning an intelligent, wireless sensor network, there are some important considerations above and beyond radio frequency (RF) communications theory. This article looks at some of the practical issues in choosing a wireless sensor network. While cellular technology is a long-haul technology supported by several wireless sensor suppliers, it is not covered in this article. Should you need the longer coverage cellular systems provide without an investment in licensed-radio technologies, be sure to ask your sensor/automation supplier about this option.