Setting Aids - Siemens Synco700 RMK770 Documentation Handbook

Setting choices
Setting with the help
of the step response
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Building Technologies
HVAC Products
Operating line
Setp boost mixing valve
Actuator run time
P-band Xp
Integral action time Tn
To enable a mixing circuit to control its flow temperature to the setpoint, it requires a
higher flow temperature on the inlet side. This elevated temperature can be adjusted
separately for each mixing circuit.
In the case of maintained boiler return temperature with mixing valve, this elevated
temperature is not needed. Here, it must be made certain that the minimum boiler tem-
perature will be somewhat higher than the return temperature setpoint.
For all types of control by the mixing valve (maintained boiler temperature control, pri-
mary controller, heating circuit), the same PI mixing valve algorithm is available.
5.7.2

Setting aids

With the help of the P-band (Xp) and the integral action time (Tn), the mixing valve
algorithm can be ideally adapted to the relevant controlled system.
The controller is supplied with the control parameters set to values suited for the major-
ity of controlled systems (typically flow temperature control with a 3-port mixing valve).
In the case of difficult controlled systems (e.g. heating circuit with heat exchanger), the
control parameters must always be matched to the controlled system.
T
A controlled system is usually characterized by the step response. This is explained in
the following example of a mixing heating circuit.
At the point in time t , the actuating device (actuator of mixing valve) shall be opened
o
from 40 % to 80 %. As a result, the flow temperature will increase by ∆x.
Valve position must
Y
∆
change rapidly (manually)
Tu Tg
Tu Delay time
Tg Compensating time
∆x Change of actual value
∆Y Change of valve position
The longer the delay time in relation to the system time constant, the more difficult the
control of the system. If the position of the actuating device is changed and the tem-
perature sensor can only acquire the result of the change after a certain period of time,
control is much more difficult than in the case of fast-acting systems.
Boiler Sequence Controller RMK770
5 General functions, fundamentals
Range
0...50 K
1...600 s
1...100 K
0...600 s
Valve position
Actual value
x
∆
Factory setting
10 K
120 s
48 K
10 s
T
CE1P3132en
01.03.2005