RAM 712 KNX
room thermostat for surface-mounted and flush-mounted installation
theben
Version: Dec-10 (subject to change) Page 60 of 65
6.6.2 Response of the P-control
Max. 4l/Min.
Bandbreite
Sollwert
Istwert
17l
21l
15l
Verluste
1l/Min
A filling volume of 15l gives rise to a control deviation of 211 – 151 = 61
As our actual value lies outside the bandwidth, the control will operate the flow rate at 100%
i.e. at 4l / minute
The supply quantity (control variable) is calculated from the control deviation
(setpoint value – actual value) and the bandwidth.
Control variable = (control deviation / bandwidth) x 100
The table below shows the response and therefore also the limits of the P-control
Table 36
Filling level
Control variable Supply
Loss
Increase in filling
level
15l
100%
4 l/min
1 l/min
3 l/min
19l
50%
2 l/min
1 l/min
20l
25%
1 l/min
0 l/min
The last line indicates that the filling level cannot increase any further, because the inflow only
allows the same amount of water to flow in as flows out through loss.
The result is a permanent control deviation of 11 and the setpoint value can never be reached.
If the loss was 1l higher, the permanent control deviation would increase by the same amount and
the filling level would never exceed the 19l mark.
In a room this would mean that the control deviation increases with a decreasing outside
temperature.
