I need to maintain a temperature profile for my process.Can i use PID control for this application?

[radhika]

Hi all,

I need to maintain a temperature for my process.Can i use PID control vi's for this application?

I have NI-PCI 6023E DAQ board.Should I need any other hardware components???

Any help in this regard is highly appreciated.

Thanks,

radhika

[Conseils]

Absolutely, although you are probably going to need some interface hardware: -
  A temperature sensor (e.g. thermocouple, thermistor, PRT etc.). which may require an interface to the temperature sensor.
  Something to interface from the output to drive the heating system (e.g. a relay driver or zero crossing switching module).

There is no analogue output directly available so unless you fancy building and F/V or a D/A for a counter output you will have to arrange to convert the proportional output into pulse periods (There are a few posts on this in the forum that will help you out with this).

One hardware configuration might be an SC2345 type box with thermocouple and DIO modules in it but you may only have access to an SCB68, so you could build some interface circuiry on the prototype area.

Just an aside, I would suggest that often people use some form of temerature controller and use the P.C. to set, read and control the temperature controller. But it does depend on the applicationt to a large degree.

Good luck.

[radhika]

Hi,

Thanks for your reply.

I do have a temperature sensor and it is read by the DAQ (NI 6023E) .

Also i have a voltage input to the program which has to be controlled in order to control the temperature.

So , I am using a PID , the output of the PID should control the Voltage input so that the temperature is controlled.

Can I give the  voltage input and the temperature  to the PID through the DAQ and  just use one more channel in the DAQ to get the output from the PID.Will that work???

I am not sure why you have mentioned SC2345,SCB68.

Thanks,

radhika

[Conseils]

(if I have understood your response correctly) Your indicated hardware does not appear to have an analogue output channel, so unless you arrange to convert some other output to an analogue value that you indicate is required to controll the process; you won't be able to control the process. But you might use a counter / digital output to generate a PWM output to drive a heater, or a counter to drive a frequency to voltage convertor; to generate a voltage proportional to frequency.

Check out the following examples (I assume LabVIEW 8.X here) search with the term PID.

You can also check out the following for a good background
http://zone.ni.com/devzone/cda/tut/p/id/3782
http://sine.ni.com/apps/utf8/nievn.ni?action=display_offerings_by_event&event_id=14130&event_subtype=WEB_EVENT_DEMAND&site=NIC&l=US
http://zone.ni.com/devzone/cda/epd/p/id/4973
http://digital.ni.com/manuals.nsf/websearch/A25258DF0D3E3CB386256B41000BA9B9

NI Labview PID toolkit manual (this is additional software)
http://digital.ni.com/manuals.nsf/websearch/23880AD630A3C0E386257181007356B0

I asked about the SC2345 or SCB68 as these are excellent interface / connection boxes from NI and these allow conversion (SC2345) or connection to the outside world.

Message Edité par Conseils le 01-17-2007 08:52 PM

[radhika]

Hi,

I have started working on this code.

 The actual application is to control temperature of a chamber using electrical heater.
I am measuring the temperature using a pyrometer and reading this voltage signal thro DAQ NI6023E.Then i need to compare this temperature to set points temperature , and generate an corresponding analog signal (using PID) to control the power of the electrical heater to realize the set points.

The set points are to be entered by the user.
The setpoint temperatures are in the form of clusters.I have attached the profile
My question is ,how to compare the setpoint temperature(in cluster form) with the process temperature in a PID ?

Thanks,

radhika

[Conseils]

Well one way based on your design might be as attached.

I would prefer a state machine as there are likely to be other things going on. But the attached should get you off the ground.

[radhika]

Hi conseils,

Thankyou so much.It helped me a lot.

Thanks

radhika