EUROTHERM ’S 2704 hybrid controller is now available with a ratio flow control function block for control of flow and dosing applications in chemical dosing, water treatment, chlorination, mixing vessels, waste incinerators and general ratio control.
It uses an inbuilt ratio function to control a process variable at a setpoint which is calculated as a proportion of the main input. The ratio setpoint determines the proportion of the lead value to be used as the actual control setpoint. The ratio setpoint can be applied as either a greater or a fraction to the (lead) input. A typical application is in a mixing vessel where in order to achieve the correct mix of product, inputs 1 and 2 need to be maintained at a constant ratio.
When the control loop is placed in manual or ratio control is deselected, setpoint tracking is used to recalculate the setpoint from the actual achieved ratio. This ensures bumpless transfer between modes. If the input from the lead process probe fails the working setpoint of the loop will remain at its current value.
The 2704 ratio function block maintains the relationship between two variables and provides for ratio setpoint tracking and ratio setpoint trim. It also automatically calculates the actual measured ratio which is then available to be displayed on the controller front panel. Up to three individual ratio control loops can be controlled by a single 2704, with alarming for up to 20 digital outputs and 20 switched inputs available via the add-on I/O expander. Additional flow information can be obtained such as totalised flow, flow time, and integrated totalised output pulse rate using the internal maths functions blocks.
The 1/4 DIN Panel mounting 2704 features a 120 x 160 pixel electro-luminescent HMI display on which all the process information can be presented in an easily understood graphical format, simplifying configuration and operation. Eight customisable user pages allow for hundreds of parameters to be monitored and viewed by the operators. The user interface is menu driven via the display and seven front panel keys, providing extreme flexibility and ease of operation.
The 2704 is a multifunction controller/programmer available in a single, dual or three-loop format. It is designed for demanding, high-accuracy multi-loop control applications such as furnace and kiln control, environmental chambers and a wide range of critical batch production processes in the chemical, brewing, pharmaceutical and plastics industries.
Two plug-in communication slots provide communications options. Modbus serial, Modbus TCP/IP, DeviceNet and Profibus provide opportunities for local, plant wide and worldwide system integration. A block read for the most commonly used values minimises network traffic and speeds up response. Any number of controllers can be monitored locally, or remotely over the internet.
It is provided with a range of application blocks including advanced maths, logic, timers, totaliser and counters plus monitoring functions for max, min and averaging of inputs. The setpoint programmer offers 600 individual program segments that can be allocated to any of the 60 programs. A standard real time clock ensures that regular or routine actions can be triggered at a particular time.
The instrument incorporates a self-correcting input circuit to maintain calibration accuracy. Configuration is achieved either via a front-panel interface or by using Eurotherm's iTools configuration/datalogging/mini SCADA package running under the Windows operating systems.