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Customer Solutions

A Carburization Furnace Control System

Author(s):

Gregory C. Cala, Ph.D., Data Science Automation, Inc.; Marcela Maldonado, Data Science Automation, Inc.; Ramanathan Varadharajan, Data Science Automation, Inc.

Industry:

Machines/Mechanics

Product:

Compact FieldPoint, FieldPoint, LabVIEW

The Challenge:

Creating a control system to monitor furnace carburization process variables, control furnace temperature, log process variables (PVs) at a user-specified rate, and both annunciate and record alarms with the time of occurrence.

The Solution:

Developing a PC-based automation solution using NI FieldPoint Ethernet controllers and a LabVIEW Datalogging and Supervisory Control (DSC) Module.


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User Interface Status Page

System
Rather than use a PLC to implement the control system for their new carburization furnace, a start-up company required the flexibility provided by National Instruments LabVIEW and the NI LabVIEW Datalogging and Supervisory Control Module. The system allows unmanned 24/7 operation and remote Web-based control. Key features of the system allow postponing alarm notification until after a PV remains in the alarm state for a user-configurable period of time, or going in and out of alarm state a user-configurable number of times.

The purpose of the control system was to control retort and gas preheater temperatures within +/- 1.0 ˚C, and also to be capable of running the heat/soak processes from a recipe file. The design requirements were:

  • The system should address the fact that a typical heat run may run unmanned for several days without interruption. It was very important that the system handle high system component reliability and safety interlocks to protect the retort and costly product material inside it.
  • The system should accept heat and soak process inputs from a recipe file, which the operator may alter during the system operation, if required.
  • The system should include a user interface showing the status of all solenoid valves, process variables, and alarms.
  • The system needs to perform PID closed-loop control for temperature with a scan rate of -1 s.
  • The system should log all process variables at a user-configured rate and generate a text report at the end of a heat run.
  • The system must be capable of logging alarms with time stamps to a text report at the end of a heat run.
  • Each alarm shall be configurable with configurable timers to avoid reporting spurious alarms. In addition, the control system shall report alarms if the frequency of their occurrence exceeds a configurable limit even if they are spurious and intermittent.
  • The system should perform a safe shutdown process in the event of “abort” alarms.
  • The system must provide both manual and automatic operation of the reactor through user interface controls.
  • The control system shall be provided with appropriate security features for allowing and disallowing personnel from making changes to operating parameters.


Creating an Interface to Address Multiple Concerns
Data Science Automation, Inc. (DSA) developed a concise user interface (Figure 1) showing status of all process variables and alarms. When a measured PV goes out of range continuously for a preconfigured time, or when the PV goes out of limits intermittently more than the allowed frequency limits, the system generates an alarm (time delays prevented alarms for temporary disruptions).

We classified alarms in three categories. Level-1 alarms are self-clearing alarms that automatically acknowledged if the PV left the alarm range. Level-2 alarms require operator acknowledgement, and level-3 alarms are “abort” alarms that initiated a safe shutdown process. On the user interface, alarms display next to the PV while the system sounds an audible. We provided operator controls to place the system in automatic or manual operation mode. Also, when the system is in run mode, the operator may place the system into a “hold” or “abort” state.

The control system accepts inputs from a recipe file and populates the user interface controls with the set points when the operator initiates a heat run. Shift supervisors can change these parameters while the system is in “run” mode. The control system also ramps the temperature set points at a specified ramp rate. LabVIEW executes the PID algorithm once a second, and the power controllers vary the power level to the reactor based on the controlled variable output from the PID control algorithm. For reactor safety, the system monitors inlet and outlet furnace temperatures. If their value goes out of the set limits, the system initiates a safe shutdown process (according to level-3 alarm criterion). The control system generates the flow set points at a preconfigured ramp rate, and we wired signals from FieldPoint modules to the mass flow controllers to modulate flow control valves.

The control system also controls two other subprocesses – air delivery and cooling water delivery. The air delivery system ensures adequate air pressure for actuating the flow control and on/off solenoid valves. The cooling water system monitors and controls the water flow around the retort flanges and removed heat from exhaust gases.

Pressure and temperature inside the reactor are monitored continuously and the reactor is shut down whenever those PV values exceed high-high limits. The system monitors process variables for warning pressure and temperature limits. A special “reverse” flow subprocess initiates to determine whether a heat run might be continued without unnecessarily aborting the process. If the “reverse” flow subprocess actions did not yield acceptable results, a shutdown process initiates, protecting the reactor and the valuable product material.

Reliable, Accurate Control, Even in Unmanned Operation
DSA effort produced a fully integrated and automated control system that reliably controls the system and accurately acquires, reports, and records data, while enabling unmanned 24/7 reactor operation. The LabVIEW Datalogging and Supervisory Control Module native functionality, combined with FieldPoint modules, helped DSA implement all design requirements in a reliable, user-friendly control system flexible enough to accommodate future enhancements.

For more information, contact:
Data Science Automation, Inc.
Southpointe Plaza I
400 Southpointe Boulevard
Suite 210, Canonsburg, PA 15317
Phone: (724) 745-8400
Fax: (724) 745-8461