Wireless technology is so much a part of our lives that we use words like Bluetooth and WiFi systems with confidence and familiarity. So why has it taken so long for the chemical industry to take advantage of the benefits a wireless network can offer?
Some things that we can tolerate as consumers — such as signal loss when driving through a tunnel or occasional interference from other wireless networks — are unacceptable at plants. The chemical industry requires reliable and secure transmission of information via a technique that’s easy to set up and flexible enough to adapt to changing conditions. WiFi, Bluetooth and others simply don’t meet these basic requirements. The result is that wireless networking has found a few specialized applications at plants but hasn’t been widely deployed.
The wireless instruments available to date are either proprietary or early pilot developments that only can exist within a single vendor network. However, an open approach is emerging.
Figure 1. At last year’s ISA show WirelessHART effectively linked instruments from multiple vendors.
Figure 2. A plug-in adapter can provide a simple, low cost way to get information from instruments.
In September 2007, the Hart Communication Foundation (HCF), Austin, Texas, released its latest specification, HART 7, which included wireless connectivity. HART 7 provides the chemical industry with a wireless network that can support instruments from multiple vendors in an industrial environment. This WirelessHART specification was demonstrated at last year’s ISA show in Houston, where a multi-vendor network of instruments worked together within the same wireless network connection to asset management applications running on computer workstations (Figure 1).
HART 7 gives plants a real incentive to consider wireless. So, we’ll examine the advantages and typical applications of a wireless instrument network, whether now is the right time to consider a wireless project, and how a WirelessHART instrument network works.
Traditional 4–20-mA field instruments have been using the extremely successful HART protocol to assist during commissioning and scheduled maintenance work; in fact, more than 24 million such instruments have been installed to date. However, some 20 years since HART 5 became available we’re still not making the best use of the remote access HART offers — instrument information remains locked away for the vast majority of users. WirelessHART can provide the key to unlock this information and allow us to install instruments at a very much lower cost.
Retrieving stranded instrument and process information. The vast majority of 4–20-mA instruments installed have no mechanism to allow remote access to the information they hold. If you wish to retrofit a communications path back to an asset management system, then you typically would need to break into the field wiring to insert a HART multiplexer. This poses some risk and cost. The use of a WirelessHART plug-in instrument adapter (Figure 2) offers a more convenient, lower risk and lower cost alternative.