RAM 712 KNX
room thermostat for surface-mounted and flush-mounted installation
theben
Version: Dec-10 (subject to change) Page 59 of 65
6.6 Temperature control
6.6.1 Introduction
If the RAM 712 is not configured as a switching controller, it can alternatively be configured as a
P or as a PI controller, whereby PI control is preferable.
With the proportional control (P control), the control variable is statically adjusted to the control
deviation.
The proportional integral control (PI control) is far more flexible, i.e. controls more quickly and
more accurately.
To explain the function of both temperature controls, the following example compares the room
to be heated with a vessel.
The filling level of the vessel denotes the room temperature.
The water supply denotes the radiator output.
The heat loss from the room is illustrated by a curve.
In our example, the maximum supply volume is 4 litres per minute and also denotes the
maximum radiator output.
This maximum output is achieved with an actuating value of 100%.
Accordingly, with an actuating value of 50%, only half the water volume, i.e. 2 litres per minute,
would flow into our vessel.
The bandwidth is 4l.
This means that the controller operates at 100% provided the actual value is smaller than, or
equal, to (211 – 41) = 171.
Function:
•
Desired filling volume:
21 litres (= setpoint)
•
From what point should the supply flow gradually be reduced to avoid an overflow? :
4l below the desired filling volume, i.e. at 21l – 41 = 171 (=bandwidth)
•
Original filling volume
15l (=actual value)
•
The loss amounts to 1l/minute
