JAN-FEB 2019

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have HART capability, but the I/O for the DCS cannot handle this proto - col, so it is no help at all. Still, there are mechanisms that can capture the HART data externally without affecting the basic performance of the instru - ments. Wired solutions are cumber- some and costly due to the cabling necessary to make the connections and the code written to operate them. The budget and schedule for this proj - ect will not cover such an approach. Applying newer tools: WirelessHART A more recent technology, developed after these devices were installed and operating, is WirelessHART. It can car - ry all the data, including primary and additional variables, diagnostic data, and configuration mechanisms. These instruments have no wireless capabil - ity, but a WirelessHART adapter (figure 2) can be added to send all the infor - mation via a wireless signal without interfering with the basic wired con - INTECH JANUARY/FEBRUARY 2019 15 PROCESS AUTOMATION working just fine, so there is no in- terest in upgrading them. So, what does our IT team do? What does a signal of 17.54 mA even mean? The standard IT tools simply do not apply in this situation, so there is no way to talk to those instruments. What mechanisms are practical or even available to capture data from these five instruments? One possibility emerges: something called a highway addressable remote transmitter, or HART. It is a new one for some technicians, but it means there is a digital signal superimposed on top of the analog signal. Digital sounds more promising than analog, but it is a long way from Ethernet. It is still a different protocol, and there is no mechanism to talk to the instru - ments. Or is there? All the instruments involved here l The instruments are all in place and connected to the distributed control system (DCS) I/O cards, sending their information con - tinuously. l The DCS was installed almost 20 years ago and uses standard dumb analog I/O, meaning all the instru - ments for the project are communi - cating using conventional 4–20 mA current loops. l The DCS has a historian that was added about 10 years ago, and it serves as the main interface for connections to the corporate net - work. However, data streams from these specific instruments are not captured individually. l The historian is not easy to modify, so it is not available to serve as the means to provide data for this project. l The instruments themselves are Figure 3. WirelessHART networks exist side by side with wireless Ethernet, and wired Ethernet can serve as backhaul for the wireless instruments. L5 Internet L4 L3 L2 L1 L0 Corporate network Plant network Area control network DeltaV redundant wireless I/O card Firewalls Root access point(s) Mobility services engine Wireless LAN controller(s) Wireless gateway Mobile workforce Asset tracking Video Redundant wireless field link Wireless sensor networks

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