Videographic Control System Manages Complex Furnace Operation
Simulating continuous furnace conditions in a batch furnace was a new furnace concept undertaken by Harper International Corp. (Lancaster, N.Y.) in a pilot project that also involved BCS/Sanwal (Tonawanda, N.Y.) and Eurotherm Process Automation. The actual process is proprietary, but the end user wanted to simulate different furnace conditions to establish the aspects of a continuous furnace. Harper built and automated a batch furnace for the customer that simulated a continuous multizone, multisection production furnace. The furnace is capable of achieving very high temperatures in a very short time. The process had to have the capability of changing various physical components and tuning parameters, together with temperature, gas flow and atmosphere composition as needed, which required a versatile, flexible control system. The customer wanted the furnace system controller to have a programmable setpoint with the ability to hold, or "freeze," at any given time, or to hold and then go to a predefined level when certain atmospheric circumstances occurred. The customer also wanted to be able to log data from the batch to a local floppy disc with the ability to incrementally change the file of each batch automatically.
The complexity of control was facilitated using the high-level programming tools and the high level of integration provided by Eurotherm's T800 Visual Supervisor and 2500 I/O. The powerful videographic control system has the capability of a multiloop process controller, data logger, setpoint programmer and has its control algorithms embedded in an HMI touch screen.
The unit has open communications standards, offering Modbus master communications, ProfibusR DP or DPv1, and ALIN (ARCnet local instrument network), which allows both peer-to-peer and wider system communications. The process I/O was interfaced to the controller via the 2500 remote I/O unit having 16 slots communicating via ProfibusR DPv1. For this process, the 2500 I/O is capable of ten thermocouple inputs, nine voltage or milliamp inputs, six analog outputs, eight digital inputs and eight relay outputs.
The 2500 not only provides the I/O, isolation and signal conditioning for the videographic control system, but also provides a flexible and powerful I/O base having on-board fusing and termination of field wiring. The 2500 was only used as I/O in this application. However, it has the capability for a direct carbon probe input with zirconia algorithm for use in carbon-control applications. Total arithmetic operations available include 32 analog and 32 digital toolkit blocks, 16 user values, 8 timers, 8 counters, 8 totalizers and an analog switch.
In addition to the 2500 I/O, the T800 also communicates with two over-temperature units on RS422 Modbus slave and an SCR power controller on RS485 Modbus slave.
All information is brought back through the ALIN network to a SCADA system running Wonderware Factory Suite 7.1R integrated with a dedicated I/O Suitelink driver. Eurotherm SuiteR supports automatic tag creation for the T800 database, standard user interface with online tag browser and a standard SQL alarm database. Both the faceplates and the user interface for the function blocks are predefined.
In the furnace control system, the 2500 provides the I/O for the six control loops selected out of the available 20 control loops in the T800. The six loops include three temperature loops and three flow loops, where one temperature and one flow loop are compensated. The control loops can either function as independent loops with local setpoints or as part of the T800 setpoint profile program running in remote operation. Remote operation is selected as soon as the setpoint profile program is started. The control loops can control either on temperature or on a specified output related to the SCR power.
The points to be locally trended by the control system are a total of 32 analog and digital signals, divided into two trend groups. The data format can either be ASCII or PKD (a special format developed for FDA approved data collection). The unit has a maximum capability of six trend groups of 16 points each, to be trended to a disk using various scan rates for each group. It has a maximum logging speed of ten seconds.
Real-time trends for all the assigned signals are provided in trend screens having historical data access. The amount of time spent scrolling back through memory depends on the number of points trended. In this application, 32 points were trended for 48 hours with a one-second update.
The setpoint programmer was programmed for a ten-segment program having six analog ramp and soak signals and four digital event outputs. Setpoint profiles can be modified and saved through a local standard interface or they can be programmed using a WindowsR-based offline tool and uploaded using floppy, ALIN or a serial connection. Setpoint profile limits are 250 segments having 16 analog signals and 8 digital events spread out and executed using up to four independent time bases. The total number of profiles that can be stored is 25.
Six custom user screens were programmed on the graphic controller to reflect the graphics of the furnace and operation of the controllers. Up to 99 screens are available for HMI functions. Programming is executed through a WindowsR-based user screen editor from Eurotherm.
The unit runs a continuous database to execute the control of the furnace and a sequential or batch database defined by the customer, and can override the outputs of the control loops. The programming is done via Eurotherm's Lintools utility, which provides off-line and on-line tools.
Alarm acknowledgement can be done through the graphical controller or from the SCADA package. There always is a history of alarms in the unit's memory.
For more information: Rob Kambach is product manager, Eurotherm Process Automation, 741-F Miller Dr., Leesburg, VA 20175-8993; tel: 703-443-0000; fax: 703-669-1300; e-mail: rob.kambach@ controls.eurotherm.com.