Fieldbus Part 2

Earlier, we mentioned that AS-i wasn’t appropriate for IS applications. Therefore, another solution was sought for the discrete devices in the electrically classified space. An IS implementation with FISCO and an IS solution were envisioned for the discrete devices. We tried to keep host controller cabinets in safe-area spaces, and only allow I/O subsystems in process spaces. IS remote I/O was installed in the process space to interface to low-power solenoid operators for valve actuators, valve-position limit switches, rupture-disk indicators and transfer-panel proximity switches. The remote I/O modules are intrinsically safe, but the communications (Profibus-DP) to each are not. Profibus-DP can’t be implemented intrinsically safe, even though it’s a non-incendive design. Our experience with fieldbus shows there are some fieldbus devices that lend themselves nicely to biopharma applications. A few instruments can illustrate this point. The first is the Rosemount 848T temperature transmitter, which also allows for other input types besides RTD and thermocouple. Steam-in-place (SIP) is a common process in biopharmaceutical facilities for sterilizing process vessels and piping. SIP is usually automated, with multiple temperature elements at various low-point condensate drains, and usually has five to eight temperature elements per vessel. In the case of a bioreactor, the temperature element count can approach 30 or more. In the early design stages of our cell-culture facility, there was some concern about how to handle the many RTD inputs with a bus system. Certainly, a Foundation fieldbus transmitter for each input would be unwieldy from a construction standpoint, not to mention the cost. Fortunately, 848T allows up to eight inputs per instrument, which reduces the device count. We also use this device to convert conventional 4-20 mA/DC devices to Foundation fieldbus. Likewise, Micromotion mass flowmeters are used extensively in our facility, such as on chromatography skids. From one fieldbus connection to the