Two-point heating control with analog output (LOGO!)

Hello everyone!

I am new to this forum, tough I am using app examples for some time here at SIEMENS Support.
I have done the LOGO! application example "two-point heating control" , and I understand this principle very well.
But I have tried to make an application that controls heating through analog output (0-10VDC) using this same principle, and it seems I am stuck. Not one function I tried, can take two analog input values, process them, and give an analog output value that i could use with PI controller function.

Attached is the closest I got to that, but not sure if that is ok.

Is there anyone here that already did this kind of app?

Example:
I have a three-way valve on the return pipe of radiator heating system that is mixing the return and flow temperature of the water in the system (mixing is controlled with 0-10V signal).
One analog temperature sensor Pt100 is installed on the flow pipe of the heating system, and one Pt100 is measuring outdoor temperature.
I need to control the flow temperature based on outdoor temperature so that as higher the outdoor temp is, the lower the flow temperature should be. And vice versa, the lower the outdoor is, the higher the flow should be.

Appreciate the help.

Aleksandar

Am I right in assuming that when you describe “example” you actually mean what you described at the beginning?

So I understand that you want to have heating control that is dependent on the outside temperature?
Am I understanding this correctly?

If yes, please provide more information.
Which of the two PT's is the outside temperature?
Which of the two PT's is the flow temperature?
What resolution do you want? 1°C? Or 0.1°C?

How does the mixing valve work?
0 volts is what?
10 volts is what?
5V middle position, so do nothing?

ixo65

Am I right in assuming that when you describe “example” you actually mean what you described at the beginning?

So I understand that you want to have heating control that is dependent on the outside temperature?
Am I understanding this correctly?

If yes, please provide more information.
Which of the two PT's is the outside temperature?
Which of the two PT's is the flow temperature?
What resolution do you want? 1°C? Or 0.1°C?

How does the mixing valve work?
0 volts is what?
10 volts is what?
5V middle position, so do nothing?

 PTs are not important, both are Pt100 or Pt1000. Resolution is also not important.

0-10V is 0-100% valve opening. So 5V would be 50% open valve. Like any other analog 0-10V control.

This is a valve actuator used on site: SAX 61.03U

Question is: what combination of function blocks could be used to get that to work?

The idea is that when an ambient temp is lower, the flow temp should go higher.

The curve for my example should be:

1st point: -15deg Celsius ambient, +70deg Celsius flow;

2nd point: +15deg Celsius ambient, +25deg Celsius flow.

So at every outdoor temperature degree in this range, there is a defined flow temp set point, but it has to be given to PI controller somehow, so the valve actuator can control the flow temperature precisely.

New question published by Otobit is split to a separate thread with the subject Show the curves through virtual display.

Best regards
Jen_Moderator