on/off temperature control through SSR

[nkn5110@psu.edu]

Hi all,

I am trying to create a LabVIEW controller for something that I was recently doing with an Omega temperature controller. The task is this:

Create a simple on/off controller for a heater based on a user-provided temperature setpoint. The physical system consists of a thermocouple, a solid state relay for the on/off control, and a cartridge heater. 

My thought is that I can replace my previous controller with a DAQ, but I am just not sure how to proceed. I can set up the DAQ system to record temperature from the thermocouple, but I get stuck on how to combine that with the SSR and the temperature setpoint. 

Theoretically I would compare current temperature reading from the thermocouple with the temperature setpoint. If temp < setpoint, then the DAQ would output a 5 V signal to the SSR which would activate and close the relay (heater on). If temp > setpoint, then the DAQ would not output anything and the SSR would be open (heater off). 

Physically, I would connect the thermocouple to the DAQ input channels and the SSR wires to the Digital I/O channel. 

Can anyone help me with this? I can provide more information or a drawing if necessary. Thank you!

[santo_13]

You can do it but think twice if this is what you want.

Imagine what would happen if your computer hangs due to a virus or a windows update and the heater is stuck at ON?

Anything that results in catastrophic failure must be hardware controlled and safe guarded instead of through a software.

[nkn5110@psu.edu]

Hi Santhosh,

This isn't a high-risk operation and currently I can simply unplug my heater, or include a remote emergency stop button. I understand that it can be done, but I am more looking for guidance on a way to implement this (namely, at this point, the proper way to output my 5V signal from a DAQ at one condition and no signal at the other).

Thanks,

Natalia

[GerdW]

Hi nkn,

---

nkn5110@psu.edu wrote:

I am more looking for guidance on a way to implement this (namely, at this point, the proper way to output my 5V signal from a DAQ at one condition and no signal at the other).

---

Please rethink your wording!

You don't want to output "no signal" in the "other case", but you want to output 0V!

So your problem reduces to use a Select function to select between 5 and 0 (regarding TRUE/FALSE condition) to output on your AO channel…