Temperature control using PLCs

Hi,

I am thinking about starting a home heating project using a plc but I am not sure about what type of temperature sensors are usually required. The system will just be for splitting the house into different heating zones and controlling the temperature and start up time of the boiler in each zone.
Will analogue i/o cards be required?

Thanks.

 

[abeggmj]

IF you use a thermostat with a dry set of conatacts you can get a way with a Digital input. If you use a thermocouple or an RTD you will need an analog input.

 

[thekoookooo]

Hello,

The simplest kind of temperature sensors are the thermocouples. Those are just two wires twisted together (not just any wires but special metals). Interfacing those to a PLC is easy, you just have to connect the two wires in the back of the controller. One good PLC for temperature applications is made by OMRON. It is pretty compact

and easy to use.

 

[Macbeth]

That is one expensive way to control your house. I assume you already have a controller from some scrap project. So the type of sensor should revolve around the hardware you have. If you only have digital inputs then standard mercury filled temp switches are inexpensive (24Vdc). I you have analog cards you will probably need some type of interface. Such as RTD to 4-20ma. One sensor out there uses 0-1ma (ICTD). For house (HVAC) almost any sensor will work well.

 

[bogdal]

Hi
You didn't tell if you have a boiler in each room. If You have a single boiler, I think it should be more confortable to use thermostate vanes for each room, so you can control individually the temperature. If you have a boiler for eache zone you want to control, I think a simple thermostate for each zone must be the sollution. You must take care on the hyisthresis of each thermostate.

 

[harold2]

If you have analog (0-5,0-10v)inputs you could use LM34 temperature sensors @ $2.50/ea. They have 1mv/Deg F. output and are usable to 300deg. I am using them as sensors in my home Solar heating system & they work very well.

 

[pas0216]

Harold2,

Can you please tell me what PLC you are using? I have a direct logic DO-06DR, and was thinking of using it not only to measure the temperature in several places around my house, but also to control my heater/air conditioner. I would like to use the LM34 as a sensor, but I am unsure how to conect them to my PLC. The PLC I have has 12-24 VDC inputs.

Paul