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PID temperature control using a relay




I would like to control the temperature of a heating tape using a relay and a PID type controller in labview 2009. The temperature is measured with a K-type thermocouple connected to a NI9211 module. The relay is connected to a NI9481 module. Both modules are inserted in a NI cDAQ-9184. I am looking for the simplest way to perform this operation.



Thank you in advance for your help.





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Message 1 of 5

I do a lot of PID temperature control in LabVIEW to control a variety of heating elements.  I would actually recommend using an external relay for this.  I typically use a proportional output relay (Crydom MCPC1225A) and a NI-9263 AO module. LabVIEW provides a PID output signal to the 9263, which is fed as the control input to the relay.  The relay outputs a % of line voltage that is poroprtional to the control signal.  There are some other ways of doing tempereature control but I have had a lot of success with this one.


Another option:

Use a NI-9472 to drive the control side of an SSR and write LabVIEW code to PID control a duty cycle for the On/Off time of the SSR.  You really should use an SSR (solid state, NOT mechanical relay for this).  Since you will be cycling the relay at high rates a mechanical relay won't be able to keep up and you will wear the contacts over time.  The 9481 has a max switching rate of 1Hz. and is rated for 100,00 cycles under load.  You would exceed this rating quite quickly at this rate under continuous operation.


Message 2 of 5

Thank you for your reply, Dan


The first option using a proportional output relay seems very attractive for our situation. I actually already have a Ni-9263 AO module with one of the channels still available. Do you have an example of VI that I could use?


Thank you again for your help.

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Message 3 of 5

The LabVIEW implementation is quite simple if you have the PID toolkit.  I have attached an image below as an example.  Search for help on the for information about each of the inputs/outputs.  If you don't have access to this toolkit you can either write your own PID algorithm using the  LabVIEW primitives or search around the forums for someone who has shared something that may work for you.




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Message 4 of 5

Thank you Dan. I will try this as soon as I get the proportional SSR. 



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