The I constant is defined as the time, which brings the I-part of the PI controller to the same value as the P-part. (Unfortunately, this is not the case of my sketch below sorry for that. The P-part and I-part should be of the same height.)
See the behaviour in time for constant controller deviation (setpoint – actual value): in the first moment there is only the P-part (with the P constant set in the UC300 as control deviation at which the valve goes to 100%), then in the course of time the I-part is increasing. This should compensate the inaccurate P controller. In reality, the controller deviation is decreasing in time (because of the increasing “y” value (opening of the valve)), which results in decreasing the P-part and of course the I-part, too, the output curve goes more flat, may hunt several times, and then goes stable to a certain value of combination of P-part and I-part. Something like the red curve below. This is the final and required state of output, until next change of the actual value, etc.
Numerically, the I part is in seconds. For room applications, it is recommended to set it say to 15 to 30 minutes (e.g. 900 to 1800) or even more, depending on the size of the room and the output power of the heating body. Of course if you set it higher, the controller will need more time to reach the final stable position, if you set it too short, it will most probably hunt. The default value is 3600 s, which is high enough for large rooms, with sufficient response at the same time. Please do not set it too low, values like 120 seconds are totally wrong here. (This is suitable for fast processes, such as supply air control at an air handling unit, hot water control in a water heat exchanger, etc.)
If the I constant is set to 0, the I-part is disabled, and the controller acts as a P-controller only. Note that some versions of domat.exe do not allow to set 0 here.
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As part of the expansion of application platforms for the Merbon system, we have established cooperation with the company Wago and launched the stations with the Merbon runtime under the name wall.
Room units with external temperature sensor.
Runtime, or program which runs the application engineered by a programmer, executes the main activity of a PLC. It may be implemented on various hardware platforms. The platforms have different properties, such as processor computing power, operation memory and flash memory size, types and number of serial communication ports, integrated analog and digita inputs / outputs, etc. These properties determine the functionalities which a particular platform is able to support.
In view of the increasing spread of the coronavirus in Europe Messe Frankfurt decided to postpone Light + Building. The fair will now be held in Frankfurt am Main between the middle and end of September 2020.
We would like to invite you to visit our stand at the AMPER 2020 fair, which will take place at the Brno Exhibition Center. As every year, we introduce our product and system news.
On 18 March, Domat will join forces again with the Faculty of Electrical Engineering and Communication in Brno.