RAM 712 KNX
room thermostat for surface-mounted and flush-mounted installation
theben
Version: Dec-10 (subject to change) Page 61 of 65
P-control as temperature control
The P-control response during heating control is as shown in the previous example.
The setpoint temperature (21°C) can never quite be reached.
The permanent control deviation increases as the heat loss increases and decreases as the ambient
temperature decreases.
6.6.3 Response of the PI control
Unlike the pure P-control, the PI-control works dynamically.
With this type of controller, the actuating value remains unchanged, even at a constant deviation.
In the first instant, the PI-control sends the same actuating value as the P-control, although the
longer the setpoint value is not reached, the more this value increases.
This increase is time-controlled over the so-called integrated time.
With this calculation method, the actuating value does not change if the setpoint value and the
actual value are the same.
Our example, therefore, shows equivalent in and outflow.
Notes on temperature control:
Effective control depends on agreement of bandwidth and integrated time with the room to be
heated.
The bandwidth influences the increment of the actuating value change:
Large bandwidth = finer increment on control variable change.
The integrated time influences the response time to temperature changes:
Long integrated time = slow response.
Poor agreement can result in either the setpoint value being exceeded (overshoot) or the control
taking too long to reach the setpoint value.
Usually, the best results are achieved with the standard settings or the settings via system type.
