[Siemens LOGO!] How can I improve valve control in Siemens LOGO! when the temperature changes?

Hello,

I have a Siemens LOGO! controller, along with a 3-wire solenoid valve (open/close) with limit switches.

I also have two sensors: one measuring the room temperature and one measuring the radiator temperature.

Ultimately, the programme will be more complex, but that’s for later. For now, I’d like to maintain a set temperature based on the sensor measuring the room temperature.
I’ve written a programme that makes the valve operate in steps. It sort of works, but the way it is, if the temperature exceeds a certain threshold, the same action always takes place. This happens because the programme is flawed in that it ‘doesn’t know’ whether the temperature is falling or rising, so when a given threshold is reached and the condition is met, the same action always takes place.


Example:
from 21’ it rose to 22’: the valve closes by one step.
From 23’ it dropped to 22’: the valve also closes by one step.

Ideally (in my opinion), the programme should check whether the temperature has changed from the previous reading and then carry out the relevant action.
But I’m not sure if that’s possible. I’m not very familiar with Logo Soft Comfort

Thank you in advance for your help; if this post is unclear, I’ll try to explain it in more detail.

Kind regards.

Hello
I can’t remember the LOGO itself, but I think the algorithm can be easily fixed. Use hysteresis. Assuming you want to reach a temperature of 22 degrees, open the valve at 21 degrees and close it at 23 degrees. This will also prevent the valve from constantly opening and closing when the temperature fluctuates around the set point.