Typically, this could be two parallel internal dart valves or the external Dual eDART.The DVC intelligently splits the single 4-20mA signal into two signals. These signals are fed to each positioner of the valve pair.
The DVC simplifies the control of dual valves as no special PLC modification need to be made in order to operate a dual valve configuration. To the PLC the two valves are then treated as one valve. The control loop can still be tuned using classic PID controllers. The DVC often leads to improved control as the two valves are prevented from interacting with each other.
Mode of Operation
The Input signal represents the desired Cv as a percentage of the total Cv (both valves fully open). The Primary is set, based on the relative size of the two valves, to achieve the desired Cv. If the Primary is outside the Range, the Secondary ramps until the Primary is approximately 50%. The primary range, secondary step speed and size, are all customisable. However, these programmable parameters require the optional eDart re-programming unit.
Features of Dual Valve Controller (DVC) - eDart
- The Master and Slave output can be reversed periodically if the application requires this to prevent sanding in certain situations
- The time between reversals and the time to complete a reversal is programmable to prevent any surges to the plant
- The DVC will produce a calibration certificate, including serial number, and date for each calibration
- One DVC can drive another DVC to control a third valve if required
Installation of Dual Valve Controller (DVC) - eDart
The DVC requires a 4-20mA signal and 24 VDC. Optionally, 240VAC power can be used.
The input signal is isolated fromthe power supply.A demonstration program is available in order to visualise the response of the signal splitter.
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