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Setpoint profiling for PID control

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article image Advanced programming features.

THE Eurotherm 2000 series of precision controllers can now provide advanced PID control with setpoint profiling programs.

This allows a process to be controlled to a specific profile of heating and cooling, such as in annealing, when the metal may need to be heated to 270°C, held, for two hours, then the temperature increased to 320°C in 10 minutes, and held for four hours.

Such a profile could be automatically controlled by the Eurotherm 2000 Series.

The 2400 series controllers are supplied standard with a single eight segment program, but are available with 1 x 16 segment and 4 x 16 segment options.

The high specification 2604 and 2704 are available with up to 50 programs and 500 segments. These controllers can also control up to three individual profiles simultaneously.

The setpoint program is simply generated via the graphical editing software available for the module, or via the front keypad. Each program segment can be set to step to a particular value, dwell or hold at a value or ramp to a value in a set period of time.

The time frame for each segment can also be varied from instant to many hours. Once the program completes its profile, it can be set to stop and hold, restart and complete a preset number of cycles, or continually repeat.

Advanced program features are also provided. If a profile required control to a preset value, and the value was not reached before the segment timeframe was completed, the program can be set to "hold until" the value has been reached, or the product has been at a preset value for a set period of time.

Called "holdback" or "guaranteed soak", this feature is critical for annealing and sterilising.

In addition to holdback, three wait events are also available. The events provide a method of halting the program until an event or series of events is met before continuing. This may be to wait until a tank is full before starting pumps, and adding further product.

In the event of a power failure occurring during a program, the controller can be programmed to recover in various modes, either continue, ramp back to the value at the power failure, to reset, or to check the time against an internal real time clock to determine recovery mode options.

Not only can analog values be controlled, up to 16 digital events can also be activated during each segment. This allows full integration between analog and logic data processing. During each segment, any of the 16 digital outputs can be turned on or off, activating sequences of relays, motors, fan, etc.

All the 2000 Series can be fitted with serial communication cards, for ModBus (RS232, RS422 and RS485), DeviceNet and ProfiBus. This allows the setpoint programs to be activated from higher level control systems such as SCADA or PLC systems. The programs can also be started, stopped and held from using the user interface on the front of the controllers.

The user interface on the 2704 provides a complete trend of the current program status using its 160 x 120 pixel graphical screen. Providing operators with instant access to the current program status.

All models feature a modular design allowing for simple plug in configuration as required, reducing spare back-up and allowing simple future reconfiguration as required.

A universal process and temperature input on all models allows for nine internally stored thermocouple types (J, K, T, L, N, R, S, B & P) plus Pt100 and process inputs such as 4-20mA, 0-20mA, 1-5V or 0-10V dc while another 11 thermocouple are available as factory downloadable inputs.

Advanced PID algorithms to provide stable 'straight line' temperature control. Self-tuning is included on all models to optimise the control performance without the need for specialist knowledge or training.

Dual 4 and 5-digit displays provide the operator interface, the functionality of which can be customised to present only those parameters that an operator needs to see and adjust, while all other parameters are locked under password protection.

Configuration is achieved either via the front-panel interface or by using Eurotherm's "iTools" configuration package running under the Windows 95, 98, 2000, ME, XP or NT operating systems, which can be utilised for all models in the 2000 Series range.

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