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Building Technologies Modular Heating Controller RMH760B CE1P3133en
HVAC Products 5 General functions, fundamentals 05.02.2007
A
B
3131D12
Setpoint
Open pulse
Close pulse
Open pulse
Close pulse
Flow
temp.
A
The control pulses are too long:
Measure the effective valve running time (0…100 % stroke) and enter it. If the pulses
are still too long, increase P-band Xp
B
Several successive relatively short on or off pulses: Increase integral action time Tn
A
B
3131D13
Open pulse
Close pulse
Open pulse
Close pulse
Setpoint
Flow
temp.
A
Difference between the first pulse and the following pulses is small:
Measure the effective actuator running time (0…100 % stroke) and enter it. If the
control performance does not considerably improve: Decrease P-band Xp
B
Long starting pulse followed by many short pulses: Decrease integral action time Tn
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).
It is important to also set the actuator running time with DC 0…10 V actuators. Only this
ensures correct operation of the control system.
The P-band Xp is given in K (Kelvin).
If, after a setpoint step, the control deviation equals the P-band, the valve will be read-
justed by 100 %.
With a P-band of 40 K and a setpoint change of 5 K, the valve will be readjusted by
5 / 40 = 12.5 %. Using an actuator with a running time of 150 seconds, for example, this
means that it takes the actuator 18.75 seconds to fully open or fully close.
If the P-band is increased, the controller will respond less promptly to the same control
deviation. With a P-band of 60 K, for example, the actuator will only require
12.5 seconds to travel to the fully open or fully closed position.
Increase of P-band Xp means: The control responds more slowly and there is less
tendency to oscillate.
This means:
The flow temperature
fluctuates about the
setpoint
Flow temperature ap-
proaches the setpoint only
slowly
Actuator running time
Note
P-band Xp
Example
Basic rule
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