A WirelessHart temperature control helps a styrene injection-molding company avoid wasted material.

Figure 1. The tanks and the facility are designed in such a way that it is nearly impossible to remove the solid mass from the tanks.


A styrene injection-molding company that makes a makes a range of parts for the automotive industry faced a challenge. Each of the molded parts consisted of a different recipe of molding compound ingredients. Each recipe was stored in a tank in a warehouse that is classified as Class I, Division 1. The warehouse housed approximately 14 different storage tanks for different clients.

Orders and volumes fluctuate, and sometimes these compounds are not used for months. Yet if these tanks are not checked or used frequently, the chemicals in the molding compound can start a chain reaction that, over a period of time, can cause the temperature to increase and the compound to solidify. In fact, the injection-molding company had several tanks where the contents turned into a solid mass within the tank.

To make matters worse, the tanks and the facility are designed in such a way that it was nearly impossible to remove the solid mass from the tanks. The only other option was to remove the warehouse roof and physically remove the tanks from the facility. In all practicality, the tanks and all of the compound would have to be scrapped.

To eliminate this potential problem, the company wanted to install a system that would efficiently monitor the tank temperatures and provide an alert whenever a temperature increase was detected. Unfortunately, previous expansions had cluttered the existing facility with cable trays, conduit and other assorted equipment. The company did not have the room to run new wires or conduit. Instead, they wanted a system that was easy to install and expand. In short, the molding company was interested in incorporating a wireless technology that could meet their requirements.

Figure 2. In addition to a self-contained wireless temperature sensor, the selected system includes a wireless gateway with Modbus outputs.

To solve their problem, the molder needed a control system that would work in a process plant that housed 14 tanks divided between two offsetting rooms. Additionally, the tanks have a fair amount of distance between them. The system had to be able to work in a room cluttered with a large amount of metal objects and receive the wireless information, and the gateway must be located outside of the actual Class, I Division 1, area. Finally, the control system had to be a robust, reliable, long-lasting and cost-effective wireless network. The molder chose WirelessHart technology.

After evaluating their options, the molder approached a control system manufacturer for a solution that included only one thermocouple per tank. The control system also included one wireless temperature monitor to oversee a pair of tanks to help eliminate long thermocouple cable runs. This system setup also would provide a good mesh network. Additionally, the system would be intrinsically safe, meeting the Class I, Division 1, requirements.

In addition to a self-contained WirelessHart temperature sensor, the system includes a compatible wireless gateway with Modbus outputs. The gateway is mounted together with a paperless data recorder in a Division 2 area outside of the tank storage facility. The antenna is mounted in the hazardous area and feeds the data to the gateway. The recorder pulls information from the gateway, records the data, and stores it.

Now, historical information is readily available. Another feature of the gateway is that it enables instant access to the data via web interface. Plant personnel can be sitting in a control room, in another area of the plant, or even in their own living room, and log on to the website. From there, they can quickly access the live data and monitor the temperatures in all of the tanks via the gateway’s local web server. Any change in temperature is easily identified and documented.

Additionally, the injection-molding company was interested in replacing certain transmitters on a few of the storage tanks. With WirelessHart adapters, they could easily add these transmitters without interrupting the process, simplifying expansion.

Figure 3. A recorder pulls information from the gateway, records the data and stores it. The gateway also enables instant access to the data via a web interface.

For this styrene injection-molding company, WirelessHart technology made a lot of sense. It enabled easier access into the tank area for the required temperature data, and it eliminated a great deal of additional wiring and control clutter. With the wireless solution, they eliminate the need for long cable runs, piping and conduit installations, and the related shutdowns during installation as well as the cost of the wiring itself.

Since the monitoring system has been in place, personnel can concentrate on other tasks rather than monitor tank temperatures of unused recipes. The wireless system is set up with alarm outputs notifying personnel of any temperature changes. And, should the injection molder expand the storage facility in the future, the additional tanks can be brought into the current control scheme virtually wire free - all thanks to WirelessHart.

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