Intrinsically Safe Field Communication

In 2004, the Tianjin Chemical Factory expanded its production capacities with a new plant that produces vinyl chloride monomer (VCM). The production requires controlled temperatures at all times. Too low a temperature would not just lower the reaction speed of the intermediate products, it can also destroy the catalysts.

That is why the Tianjin Chemical Factory uses seven type E thermo elements for temperature measurement in each of the 44 transformation systems in which the addition of hydrogen chloride to acetylene occurs. Including the supply piping, a total of 370 measurements have to be transmitted from the explosion-risk area to the process control level. A task that the project managers could only have completed, in the case of classic point-to-point cabling via interface technology, with high installation costs and major maintenance expenses.

230 V operation for long distances

With a total of six intrinsically safe excom remote I/Os from Turck, the Tianjin Chemical Factory was able to solve the problem efficiently and reliably. The excom stations authorized for use in explosion-risk areas for Zones 1 and 2 are marketed and sold in China by the Turck subsidiary (Tianjin) Sensor Co. Ltd. (TTS) and offered the plant operators in Tianjin a major advantage: They can be installed and operated using either 24 V DC or 230 V AC voltage.

The latter is an enormous advantage primarily with long signal paths compared to other remote I/O stations, which are operated exclusively using 24 VDC. While, in some cases, much larger cable cross-sections have to compensate for the voltage drops that occur due to the longer cable lengths, Turck’s excom I/O solution guarantees a stable power supply even with cable lengths of several hundred meters. This allowed the plant operators in Tianjin to achieve considerable savings on the installation.

“With excom, we were able to reduce the costs for cabling by 40 percent compared to our original plan,” explains Wang Haiwen, an employee in system management. Excom was also particularly user-friendly in case of a potential module defect. The up to 16 I/O modules can be replaced in Zone 1 during continuous operation. Thus, the remote I/Os guarantee increased plant availability in the Tianjin Chemical Factory.

Asset Management with FDT/DTM

In addition to increased availability, hot swapping, and explosion protection, the system makes it possible for operators in China to comprehensively HARD parameterize their field devices via the bus line (Profibus-DP), as well as manage and diagnose using the Field Device Tool (FDT) and Device Type Manager (DTM): Just like the I/O modules, the constantly updated excom DTMs offer a unique modularity that reflects the flexible structure of the overall remote I/O station. With the DTMs, the plant operators at the Tianjin Chemical Factory can manage the diagnosis data for the racks (backplane) just as easily as the data on the I/O modules used or even each individual channel. This allows the plant operators to localize malfunctions in the field faster and reduce expensive downtimes in the production chain.