Three-Position Control; Excess Mixing Valve Temperature; Locking Of Pulses - Siemens RVL470 Basic Documentation

9.3. Three-position control

9.4. Excess mixing valve temperature

9.5. Locking of pulses

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The rate of increase of the flow temperature setpoint can be limited to a maximum. In
that case, the maximum rate of increase of the flow temperature setpoint is the selected
temperature per unit of time (°C per hour).
This function
•
prevents cracking noise in the piping
•
protects objects and construction materials that are sensitive to quick temperature
increases (e.g. antiquities)
•
prevents excessive loads on heat generating equipment
This function can be deactivated (setting ---).
Three-position control operates as weather- or demand-compensated PI flow tempera-
ture control. The flow temperature is controlled through the modulating regulating unit
(slipper or seat valve). Thanks to the I-part, there is no control offset.
The control's positioning commands to the actuator of the regulating unit are fed to the
output relays and indicated by LEDs.
In interconnected plants, an excess mixing valve temperature can be entered on the
RVL470. This is a boost of the heating zone's flow temperature setpoint. The higher
setpoint is delivered to the heat generating equipment as the heat demand signal.
The excess mixing valve temperature can only be set on controllers driving a mixing
valve (controller N2 in the example below, operating line 84).
Example:
w = w + w
N1 N2
N1 Boiler temperature controller (heat generation)
N2 Flow temperature controller (heating zone)
w Setpoint of the boiler temperature controller
N1
w Setpoint of the flow temperature controller
N2
∆w
Excess mixing valve temperature (to be set on controller N2)
If the actuator receives only closing or opening pulses for a period of time equivalent to
five times the actuator running time, all additional pulses delivered by the controller will
be locked, thus reducing the strain on the actuator.
For safety reasons however, the controller delivers pulse in the opposite direction at 10-
minute intervals.
An pulse in the opposite direction negates the pulse lock.
Basic Documentation RVL470
Function block "Three-position actuator heating circuit"
w
N2
w
N2
Siemens Building Technologies
Landis & Staefa Division