20
3.4 Other features
An additional filter can be selected to increase the damping effect for turbulent conditions.
A test function provides the operator with a diagnostic feature. Inputs can be measured
and outputs can be set from the front panel.
To prevent unwanted or inadvertent changes being made, all commissioning parameters
are protected with a pass code. The commissioning Engineer can change this.
The product can communicate via an infra-red link between adjacent controllers (Spirax Sarco
Products only) - see Section 7 'Communications'.
3.5 Typical applications
Two element control (Figures 9 and 10)
When a sudden increase in steam demand occurs, boiler pressure will drop, and the steam
bubbles in the water will expand. This causes the water level to rise, and the feedwater
valve to close. Although the measured level of water has increased, the mass of water will
be decreasing, requiring the feedwater valve to open. A two element control system (probe /
controller and steam flowmeter) uses the output from the steam flowmeter to alter the control
action and prevent the valve closing, by increasing the Set Point.
Fig. 9 Two element control - electric valve
OK
LC2650
100
50
0
%
SP
PV
AL
Steam meter
Level probe
Motorised KE / EL valve
(with feedback potentiometer)
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