thermocouple to control temperature via plc

Hey guys I just started automating my room and am trying to get some help for how to wire a thermocouple to my plc and then scale the output to temperature. What Im looking for is if I can connect the thermocouple directly to the plc's analog input or if I need to do some interfacing to get proper readings. Please let me know if you have and info on this topic

danksmoker77 said:

Hey guys I just started automating my room and am trying to get some help for how to wire a thermocouple to my plc and then scale the output to temperature. What Im looking for is if I can connect the thermocouple directly to the plc's analog input or if I need to do some interfacing to get proper readings. Please let me know if you have and info on this topic

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Hey Dank, to do this you will need add-ons for your make of PLC. They are like temperature controllers. You normally have space for 2 separate thermocouples per unit. Each unit needs a 24v and 0v. If using it to bring on heat/fans then you will need some solid state relays. Can you rewrite the PLC program to suit?

Do you have a screen you can link in to? You could program this with your PLC to do everything from turning on extracts, lights and fans, climate control and if you are using DWC you could even hoop up a PH meter with PH up/down which would constantly be monitored and kept perfect.

It would be a lot of work but you could make it so you could set up and then come back 3 months later to some serious BUD

A thermocuple is a junction of dissimilar metals. It actually produces a minute voltage varying on the actual temp. It needs to be amplified and conditioned. Not to mention cold junction compensated if you want accuracy. You can use a single chip (AD595) to amplify it. It even does cold junction compensation. Or as previously stated, get a thermocouple module for the rack. A RTD (resistive temperature device) module will NOT work with a thermocouple; its for a thermistor.

For anyone interested here is a link that provides a kit for temperature control. This will give you the ad595 amp/conditioner, printed circuit board and terminal for connections. This is prefect for integrating to plc or pic.

http://store.makerbot.com/thermocouple-sensor-v1-0-kit.html

boy that chip went up in price Think I bought mine for like $5 in onsies twosies a few years back.

guess it went up a little. I found it for around 6-7 bucks. But i was feelin froggy and found that kit with pcb so i bought it.

danksmoker77 said:

guess it went up a little. I found it for around 6-7 bucks. But i was feelin froggy and found that kit with pcb so i bought it.

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I just did a quick search of my typical suppliers, and found a $12-$18 a pop.

(feel sad that I moved to an area where there is no walk in house to get parts)
I can make PCBs here on sight, but rather not.