A key part of the Industrial Internet of Things is the sensors that provide the measurements that feed decisions and actions. At the Emerson Exchange conference in Austin, Emerson’s Cheng Vue presented, When the Heat is On, Control with Wireless. His abstract:
Many measurement challenges exist when monitoring high temperature assets such as arc furnaces. These challenges include high temperature, moving platforms, and high electromagnetic interference (EMI). Many steel mills use these points for control where their only solution was shutting the furnace down and replacing wires often. By implementing an Emerson Wireless technology, the case study customer was able to reduce or eliminate all of these measurement challenges, resulting in greatly reduced maintenance costs while providing additional throughput.
Cheng opened describing a scrap steel mill process which had extreme temperatures up to 3000 degF with ambient temperatures of 140 degF and high electromagnetic interference. He showed a video of an electric arc furnace process that heats steel scraps by an electrical arc. The molten steel is then removed with a ladle process. The process is performed in batches.
On average temperature sensors had 60 feet of wiring to the junction box and then 300 feet from the junction box to the control system. These cables were exposed to the 140 degF ambient temperature.
The temperature sensors are monitoring for hot spots and potential runaway temperatures. The temperatures monitor the burners to help prevent burner failures. The loop controls the electrical energy going to the electrical arc probes to control the temperatures.
Challenges included inaccurate measurements from EMF interference on temperature sensor wiring, wire degradation from heat, rewiring up failure of wiring and downtime of the process during these maintenance activities.
The solution for these challenges was to use wireless temperature transmitters. The transmitters for a mesh network to provide data back to the control system. Rosemount 648 wireless transmitters provided 1 and 2 second updates required for the control strategies. Rosemount 848T transmitter devices were used to collect the sensor data which can take in up to 4 inputs and transmit the values wirelessly back to the gateway. The sensors connected to the 848 provided 4 second update rates.
Dog houses were used to protect the 848T transmitters to protect molten slag from splashing on the device. The back of the dog house is open to provide the wireless antenna a path to connect with other devices to form the mesh network.
Using wireless devices, wiring was minimized just from the sensors to the transmitters. These were ultimately eliminated when they changed over from the 848T to the 648 transmitters. This also helped to mitigate the electromagnetic interference with the elimination of wires. For this application robustness is everything given the harshness of the environment.
In financial terms, additional throughput in the tens of millions was possible. Reduced unscheduled downtime also amounted to a 20% gain. Cost savings from reduced maintenance costs measured in the hundreds of thousands of dollars.
