Hybrid Control Simplifies Furnace Upgrade
After providing many years of satisfactory service, control systems on 11 integral quench atmosphere furnaces used for steel heat treating and carburizing at a Borg Warner facility in the midwest had become obsolete. Downtime was becoming a problem because the lack of spare parts for the old control system made servicing the furnaces very difficult. Borg Warner wanted to replace the existing controllers with a reliable state-of-the-art system to control important furnace process parameters and to be able to communicate with its central control system.
The existing system (Fig. 1) used a special processing controller to provide profile management and communication with an Intellution™ (Intellution® Inc., Fox-borough, Mass.) supervisory software package. It generated all of the set-point profiles and events for temperature, carbon potential, oil temperature and agitator speed control loops. Logic for parts movement and sequencing was carried out using either a PLC or conventional relay logic.
A main concern in upgrading the system was that the transition to the new system be made as smooth as possible to prevent disruption of the Intellution supervisory software. This meant that the existing systems could never go down while the new system was being installed. Both systems had to function simultaneously on the same operator screens on separate networks.
At the request of Borg Warner, Loy Instrument Inc. (Indianapolis, Ind.) evaluated the situation and recommended Honeywell's HC900 Hybrid Controller, a modular, advanced loop and logic controller, over a PLC alternative. A Windows-based, graphical configuration tool, Hybrid Control Designer, is used for Controller and operator interface configuration. Each HC900 provides eight independent set point programmers with up to 16 event outputs for sequence control functions. Up to 99 set point profiles, each with up to 50 segments, may be stored in controller memory for user selection.
Loy Instrument assumed turnkey project responsibility for the furnace control upgrades. The project scope included supplying all of the network cabling, the installation of the new controls, upgrading to current NFPA standards if needed, startup services and ongoing product support.
Project requirements varied from furnace to furnace. On one furnace, Loy eliminated an existing PLC for logic control using an HC900 remote rack and interposing relays in the logic cabinet. On several furnaces, it was possible to eliminate the existing PLCs and associated programming by performing their logic functions in the HC900.
The first unit was retrofitted with the HC900 in a few days and started up without any problems (Fig. 2). As old units were removed and the new controllers installed, the field terminations were wired in parallel so that the existing controls maintained communication with the Intellution supervisory system. Simultaneously, the new controllers were connected to a new Ethernet network that communicated via TCP to the Intellution supervisory software by means of a separate driver. As each furnace was available for switchover, process values from the new controllers were placed into the vacated locations on the screens. This confirmed that the new controllers displayed the same data as the older controllers. This was a critical step for Borg Warner to facilitate operator acceptance and minimize training requirements. During switchover, furnaces with both new and old controllers were displayed on the same supervisory overview screens validating the seamless integration.
Startup was also simplified by using the online monitoring feature of the Hybrid Control Designer configuration tool. Logic control was done entirely within the HC900 on one furnace. Hybrid Control Designer provides line color changes to monitor and verify proper sequencing of the logic control. This greatly reduced startup and troubleshooting time. Acceptance of the system was almost immediate according to Ron Bryant, supervisor for Borg Warner's heat treat plant. The power and versatility of the HC 900 allowed Borg Warner to simplify and eliminate redundant monitoring hardware while still controlling more equipment than originally expected.
Setpoint profiles screen
After installing an HC900, the software interface to the Intellution supervisory software was carried out. Over many years of operation, the company had created a sophisticated database structure and it was critical that this database be usable with the new controllers. Loy provided the advantage of being able to synchronize the supervisory computer database with the HC900 database while online. This enables Borg Warner to run a set point profile while editing and saving a different profile on both the supervisory system and the HC900 at the same time.
The supervisory system manages 75 profiles per furnace on 11 furnaces. Using material analysis, profiles for each furnace are adjusted so that pieces meet specification, even though the furnaces are not the same dynamically. If the supervisory system is unavailable, the controller is able to run the profiles independently.
Honeywell and Loy also designed an operator interface screen that displays the specific information required for operation of each furnace (Fig. 3). IH