2 Expansion Options
Page 10 Mk8 MM Expansion Features Installation and Set-Up Guide 04.09.2016
Exp
Option
Default Range Description
13 50 Feedwater Control Proportional Band
The proportional band is set as a percentage between the control point and
first low where the PID control will make corrections to the feedwater going
to the boiler to maintain the control point. The feedwater control will act on
servomotor or VSD depending on how expansion option 2. The control
point represents 0% and first low represents 100%, so it is possible to set
the feedwater control proportional band to a water level below the first
low. If the water level is outside of the proportional band, then the
feedwater servomotor will remain fully open.
0 Disabled
1 – 200 1% - 200%
14 20 Feedwater Control Integral Time
The integral element in the feedwater control will make corrections to the
feedwater via the servomotor or VSD, depending on expansion option 2.
For a slower response, increase the integral time. For a quicker response in
critical steam applications to avoid the water level reaching first low,
decrease the integral time. However if overshoot occurs and the water level
rises to above the control point and this is not desired, then the derivative
element will need to be enabled, see expansion option 15.
0 Disabled
1 – 1000 Seconds
15 0 Feedwater Control Derivative Time
The derivative element in the feedwater control is suitable for applications
requiring a quick response but the water level should not rise too high
above the control point. For example, if the burner is set to stop firing at
high water in expansion option 9 and high water is commissioned not too
far above from control point, then overshoot is undesirable in a critical
steam application, as the burner would stop firing.
0 Disabled
1 – 1000 Seconds
16 900 Feedwater Servo Open Angle
The feedwater servomotor closed position is set by zeroing the
potentiometer in commissioning mode. As default the servomotor is set as
fully open, however this setting can be decreased to shorten the
operational movement range of the servomotor.
100 – 900 10.0
O
– 90.0
O
17 0 Pump Bypass Operation
The pump bypass (terminal TB) will turn on at the switch point set as a % of
the open range of the valve, and will turn off at an offset from the switch
point, set as the bypass hysteresis, see expansion options 18 and 19.
However if the pump is turned off, then the pump bypass will also be turned
off. For setting 1, the pump bypass hysteresis is below the switch point, so
the pump bypass will turn off at an offset below the switch point. For setting
2, the pump bypass hysteresis is above the switch point, so the pump
bypass will turn off at an offset above the switch point.
0 Pump bypass disabled
1 Pump bypass on above switch point
2 Pump bypass on below switch point
18 20 Pump Bypass Switch Point
The bump bypass switch point is set as a percentage of the valve open
range set in expansion option 16.
5 – 95 5% - 95%
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