The blending controller can operate in PRESET, ON-OFF (manual) and RELEASE mode of operation. The latest mode allows for easier tuning of the control loop.
The main and process flows are used to determine the net volume flow. The operator can view the ratio of totals as well as the ratio of flowrates.
The control of the process flow is via a digital control valve. The flowrate deadband and control responsiveness can be adjusted to reduce wear on valves.
Blend Point Location.
The controller caters for blending points before and after the main flowmeter. The process flow is a ratio of the net (combined) flow (o-80% range).
Ratio% = —————- × 100
During the delivery the ratio setpoint is modified to cater for the flush volume:
SP ratio (mod.) = P ratio —————-
Preset – Flush