heat control

[hapetter]

Hi.

I like to control an electrical underfloor heating termostat with my PLC (Beckhoff). I like to be able to set setpoint (Temperature) and read flor temperature in the PLC

4-20ma or 0-10V is good, but also any bus signal is fine

However I cant find a sutible termostat for this job. Any suggestion to how this can be done? Dont want to use KNX devices.

Thanks

 

[itsmoked]

KNX?

Keith Cress
kcress -

http://www.flaminsystems.com

 

[hapetter]

KNX or EIB is a bus system. It is often used in building automation on light and heat control. The components are very expensive but they have good functionality. So I try to find a way of controlling the heat without KNX devices.

 

[itsmoked]

Thanks for the lesson.

Umm You question is still not a 100% though. You say you want to control the heat with a PLC but then you say you can't find a thermostat. A thermostat is a temperature controller.

Unless you are talking about a wall box that measures the temperature and provides an adjustment readable by a PLC?


If this is what you're referring to I have not seen anything like it. I will say I have found wall mount housings that look like traditional thermostats. They have little grates in them so the air will pass thru them.

You could get a pot of a value that your PLC can read and use it as a voltage divider that will provide the "setting". Then add whatever temp sensor your PLC can use. RTD, or TC, or ?? Essentially roll your own.

Keith Cress
kcress -

http://www.flaminsystems.com

 

[hapetter]

Ok.

I cant drive big loads from a PLC, so I need a power controller. The PLC is used as a main controller in a distributed control system in house automation. So I found a way of doing this using PLC with I/O's, temperatur sensor and a SCR power controller. Controlling the temperature by a PID block in PLC. The heat element is connected to the SCR

Now I can set temperature setpoint or load in %/max load.

 

[KCRacin]

Your best bet would be to control the temperature with PLC using a Thermocouple input whether this is a single input or a multi.
This brings in the resistance to a card that the PLC can read you do the logic to output a 4-20Ma output to your SCR then using a PID in the PLC you can attain great temperature control.

There is a better solution and that is a temperature controller, West/Partlow makes a T/C input with a 4-20 output, Cheap, easy to program and it has the algorythm for the PID.
I would however use an RTD instead of a thermocouple same readings but you can take an RTD longer distances without having an effect on the reading.

 

[hapetter]

Thanks for good suggestions.

I will go for PLC, Thermocuple, PID, and SCR. I'm using Beckhoff PLC. They have a autotuning PID for temperature control. I want to control temperature from the PLC as it is a part of a bigger building automation system and there is sentralized functions and readings as well.