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Building Technologies
Boiler sequence controller RMK770
CE1P3132en
HVAC Products
5 General functions, fundamentals
23.04.2009
The actuator running time must be matched to the type of actuator used.
This setting is important for both 3-position and DC 0…10 V actuators.
If in doubt with 3-position actuators, the setting is to be increased since otherwise the
actuator will not optimally operate in the range between 0 and 100% stroke (also refer
to synchronization pulse in subsection 5.7.3 “Control signal”).
The P-band Xp is given in K (Kelvin).
If, after a setpoint step, the control deviation equals the P-band, the valve is readjusted
by 100%.
With a P-band of 40 K and a setpoint change of 5 K, the valve is readjusted by 5 / 40 =
12.5%. Having an actuator with a running time of 150 seconds, this means that it takes
the actuator 18.75 seconds to fully open or close.
If the P-band is increased, the controller responds less intensely to the same control
deviation. With a P-band of 60 K, for example, the actuator only requires 12.5 seconds
to travel to the fully open or fully closed position.
Increasing the P-band Xp means: The control responds more slowly and the tendency
to oscillate is smaller.
This means:
•
The control action is too slow.
Decrease P-band Xp in steps of about 25%
•
The control action is too fast.
Increase P-band Xp in steps of about 25%
The integral action time Tn is given in seconds.
It indicates how long it takes the controller in the event of a constant temperature
deviation to cover the same valve travel as this would be the case with the P-part.
For example, an integral action time of 120 seconds means that in the event of a
control deviation of 5 K in the above example (Xp = 40 K), it takes the mixing valve
120 seconds to travel 2 × 12.5% toward the fully open or fully closed position (12.5%
due to the P-part and 12.5% due to the I-part).
If the integral action time is increased, the control system responds more slowly.
5.7.3 Control
signal
Since the control algorithm uses a stroke model that does not provide control at 0% and
100% respectively, the use of electrothermal actuators is not permitted.
For 3-position control, the actuator’s current position is acquired by a stroke model. As
soon as the stroke model reaches 0% or 100% respectively, a synchronization signal
(continuous on pulse or continuous off pulse for 1.5 times the running time) is delivered
to the actuator, thus making certain it has reached the relevant position.
This synchronization pulse is repeated for 1 minute at 10-minute intervals.
If a position change is called for, the synchronization pulse immediately stops.
5.8 Pump
control
5.8.1
Hours run counter
The number of operating hours of every pump are counted. The counter’s maximum
reading is 99,999 hours. Then, it starts again at 0 hours. In the case of twin pumps, the
number of operating hours of pumps A and B are acquired and displayed separately.
The number of operating hours appear at menu item
Inputs/setpoints
. On the user level,
they can only be viewed, on the service level, they can also be readjusted. It is thus
possible to set the effective number of hours.
Actuator running time
P-band Xp
Example
Basic rule
Integral action time Tn
Electrothermal
actuators
Synchronization
pulse
