Modulating level controls - Filter

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4 The optimum level control system Preamplifier housing probe electronics Level probe fitted in protection tube in boiler shell to reduce the effects of turbulence and foaming How the system works The controller receives a water level signal from the level probe. This is compared with the set point in the controller to produce an 'error signal'. Depending on the polarity (+ or -) of the error signal one or other of the control relays in the controller is energised to open or close the modulating feedwater valve. With electrically actuated valves a feedback potentiometer in the modulating valve actuator continuously signals the valve position and the controller continues to energise the actuator until the valve position is proportional to the error signal. In this way proportional level control is achieved. In practice the valve will find a steady position and make small adjustments from time-to-time to maintain the water level. Internal damping of the water level signal and a built-in 'dead-band' prevent over frequent valve movements. Internally or externally mounted controls? The historical development of level controls determined that float operated units mounted in external chambers became the standard. It has been usual to fit a sequencing purge valve to let the steam and water through the connections to keep them clear and to test the alarms. However with the advent of self-monitoring level alarms there is a strong argument for mounting both the level controls and alarms directly in the boiler shell to detect the water where it really matters - above the heated tubes. The Spirax Sarco level probe is suitable for mounting in external chambers or directly in the boiler shell within a protection tube. Adjustable high or low level alarm Adjustable set point Transmitter 100 % Valve closed Adjustable proportional band Valve open Transmitter 0 % Boiler fitted with probes directly mounted in shell
Adjustable transmitter range (typically boiler level gauge glass) LC2200 controller (LC2300 for pneumatically actuated valves) Green LED power on Red LED Test button For remote level signal transmission (optional) Green LED indicates level is above the set point Amber LED indicates level is outside the proportional band Alarm set point adjuster Level set point adjuster Proportional band adjuster Mounting position for probe in Spirax Sarco C2 side chamber with sequencing purge valve Level transmitter 4 - 20 mA to management system or remote indicator Purpose designed boiler feed check valve with soft seat to provide tight shut-off Digital display unit Electrically actuated modulating feedwater valve. Pneumatically actuated valves also available. User benefits Power on Span Zero Span adjust Zero adjust • Modulating system gives steady feedwater flowrate matched to steam demand • Can provide information to management systems • Can be used as direct replacement for old and outdated controls (modulating and on-off) • Three stage level wave filter to maintain a stable signal. • Out of range alarm checks for damage to wiring or probe, or incorrect wiring. • No need to depressurise boiler to change probe electronics 5
Page 1 and 2: Modulating level controls for steam
Page 3: On-off level controls The water lev
Page 7 and 8: Control valves Traditionally most l

Modulating level controls - Filter

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