[TRNSYS-users] ON/OFF Differential controller

[Jeff Thornton]

This mailing list is being discontinued and in its place we are implementing a user forum.  Please post your questions on the new forum in the future; www.trnsys.com/community

But to answer your question, the example and the documentation are both consistent.  Start with the tank half full and the controller off.  When the tank indicates it is empty (state = -1) the controller will start filling the tank

Controller turns ON when input 1 - input 2 > upper deadband 

0 - -1 = 1 which is greater than the upper deadband  of 0.9

When the tank indicates it is full (state = 1) the controller will stop filling the tank:

0 - 1 = -1 which is less than the lower deadband of -0.9

You should connect the model to itself so the model can calculate the previous state of the controller correctly.  In some cases you may want the controller to calculate its signal based on the operation of a different controller - in that case you would connect the input of the controller to the status of the other controller (rare).

Jeff/TESS



Sent from my iPhone

> On Jun 18, 2024, at 8:43 AM, saeid mohammadzadeh via TRNSYS-users <trnsys-users at lists.onebuilding.org> wrote:
> 
> 
> Hello everyone, 
> 
> I have a question about the ON/OFF Differential controller in the PVT example in TRNSYS. The tank level indicator is from 1 (full) to -1 (lower) and 0 (in between). 
> In this example, in order to maintain the level in water in the tank, the first value is set to zero; the second value is connected to the level indicator. The upper and lower dead bands are 0.9 and -0.9, respectively. 
> Can somebody please explain this to me? Since it is against what is explained about dead bands in the software. (copied below)
> 
> "The controller is ON if it was previously ON and Th (Input 1) minus T (Input 2) is greater than the lower dead band.  Otherwise the controller is OFF.
> The controller is ON if it was previously OFF and Th (Input 1) minus Tl (Input 2) is greater than the upper dead band.  Otherwise the controller is OFF."
> 
> I have another question, why we should connect ON/OFF Differential controller to itself again?
> 
> Best Regards
> Saeid Bina, Dr. (Eng.)
> -------------------------------------------------
> Akita University
> Graduate school of International Resource Sciences.
> 1-1 Tegata gakuen-machi, Akita 010-8502, Japan
> -------------------------------------------------
> 
> 
> <Screenshot 2024-06-18 134829.png>
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