heat control with PLC

[hapetter]

Hi.
I like to do heat control in a house with a PLC. I want to control a termostat lets say for flor heat. I want to set power/temperature setpoint and read temperature to/from PLC.

In general I want similar functionality as EIB/KNX but it is to expensive and I try to do it without this system.

Any suggestion to a termostat og a way of doing this with a PLC? I use Beckhoff PLC and I/O components.

Thanks!

Best Regards
Hans Pettersson

 

[Manglemender]

Sounds like a good project.

I'm not sure what EIB/KNX is but have a think about this.

You need: 1) Something to measure temperature - Thermocouple / RTD to an analogue input 2) Something to set the temperature - HMI / Potentiometer / BCD switches 3) Something to control power to the heaters - SCR.

Program a PID loop with set temperature and act temperature as inputs and a 0-100% output. Take this output value and use it to control the SCR; e.g. if the output is 80% the SCR is on for 4 seconds out of 5, 20% = 1 second out of 5 etc. (Siemens S7 have ready made block to do this - FB43).

Other features that you may wish to considder are: Different setpoints for different times of day? Measure outside temperature to estimate heat loss and pedict power required?

Just some thoughts

Nick

 

[hapetter]

Thanks Nick. I will look into this

 

[Enrico78]

Is there anyone to explain all details of Siemens S7 PID programming? I have Siemens documents but it is really difficult to understand, I believe that there is different method to use it more effective then copy/past from another project..
Thanks in advance..

 

[Manglemender]

I have Siemens documents but it is really difficult to understand,

I've always thought the the documentation for FB41 was very good. have you tried to highlight it in your project and press F1?

The parameter assignment and monitoring tool is also very useful with its real time trend of setpoint, feedback and PID output. This is really useful for monitoring heating loops for Ziegler Nichols analysis etc.

Edit: If you don't like the Siemens blocks or they don't do quite what you wanted, you can always write your own.

Nick