EbV Product documentation THETA NORM/UNIT
8-32
Note: The adjustment time can be determined through the Ziegler-Nichols method. The
mixer is closed, initially, and the heat generator is taken to the maximum temperature
for the heating circuit concerned. As soon as half of all consumers at the circuit to be
measured have been opened, the mixer is fully opened from cold condition (= room
temperature) by means of the Relay Test function. The characteristic heat-up curve,
i.e. the temperature development over time following this action, shows an inflection
point. The crossing of the tangent through that point and the time axis is the delay
time. This value multiplied by the factor 3.3 is the optimum integral action time for this
heating circuit.
Example: Step response function (surface heating)
In the example illustrated to the right the mixer circuit
temperature reaches the level of the heat generator
temperature after about 17 minutes, with the mixer fully
opened.
The curve tangent through the inflection point indicates a
delay time of 5 minutes.
The resulting optimum adjustment time (Tv x 3.3) is approx.
16.5 min (setting: 17)
8.2.3.3 Sample time Ta
The sample time is a controller setting that defines the time interval between two subsequent actuator
pulses when a deviation is detected. Shorter sample times result in finer adjustment.
8.2.3.4 Actuator Running Time
This function allows adjusting the actuator, with regard to its finite running time, to the control characteristics,
meaning that actuators with different running times (e.g. 1 min, 2 min, 4 min) react to the same deviation
by readjusting by the same amount through adapting the action times. The integral action time Tn remains
unchanged in this. However, care must be taken that the latter must always exceed the running time of the
respective actuator. If necessary, actuators with other running times should be used.
Temperature (°C)
Inflection tangent
Inflection point
Delay time Tv
min
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