controll electric fan in base of the temperature

[pollon]

hi i'm new in this world and i want to controll two electric fan with my compact daq by using the temperatures of two termocouples. can anyone help me

[NathanT]

Hello pollon,
    I first recommend that you first don't think about the actual coding, but rather just plan out what you want the application to do.  Will both fans respond in the same manner?  What type of control loop do you want to have?  How fast does your control system need to react?  Who will be the end user of the system?  Does the setpoint need to be adjustable?  What about the control algorithm parameters?

After you have answered most of those questions and any others that come up in regards to the desgin requirements, you should then define the requirements for your hardware interface.  Do you know what type of thermocouple you have?  Have you considered using multiple thermocouples to get a better idea of the temperature in a larger volume?  How do your fans need to be controlled, PWM, Analog Level, digital commands, etc?  Any compelling reason that you are using two fans?

After those additional questions have been answered, I recommend that you search ni.com and google for some of the following terms: temperature, control, loop, fan, PID theory, etc.

A search for "temperature fan control" yielded NI Ready-to-Run Controls Starter Kit as the second search result.

Good luck with your project,

NathanT

[pollon]

Hello Nathan,
   First of all i'll like to thank you for the interst, anyway i have a very big problem because it's my first time i try to program something.
we just buyed Labview 8.5 and a NI cDaq 9172 with four modules: NI 9211 for the thermocouples, the NI 9263 for output voltage, the NI 9481
(i think a relay module) for controlling our two DC electric fans, and NI 9215 for input voltage.
 i have to controll the fans with a limit temperature gaved me by the thermocouples. when the temperature of one thermocouple reaches a known
temperature one fan must stop and the over must start, and so on. we have to make a cycle.
the controll may be a while loop and the reaction must be immediately. I'll be the only person to use this system and the setpoint needs to be
adjustable if possible.
we use thermocouples type k with the NI 9211, and each fan has it's thermocouple to controll it. we need to use two fans because our project was
made this way.
Thank very much for your help and your time.
 Paul Hanga

[NathanT]

Hello pollon,
      I am glad to hear that you are using a Compact DAQ.  Did you have a chance to search for "temperature, control, loop, fan, PID theory, etc"?  There are some great resources on ni.com and the web in general.  I recommend that you get the separate parts of your application working (temperature acquisition, fan control, prototype the user interface, draw out the control loop, etc) before trying to integrate it all.  "Immediate" is a relative term that should be further defined based on the sampling rate of the thermocouples and performance of the fans.  Can you vary the speed of your fans, or are they on/off only?

Cheers,

NathanT



Message Edited by NathanT on 04-01-2008 08:38 AM

[pollon]

Hio Nathan, glad to hear from you! right now i can acquisit temperatures and control my fans like stop-start (the speed fan can be controlled but it will be another problem for me and right now i'm very messed. the only thing i can do right now is to stop a fan and start the over with the result of only one thermocouple. i'll try to do the things like you described me.

Thank you Paul.

[NathanT]

Hello Paul,  
       It is good to hear that you can acquire data and do basic control of the fan based on that data.  Now what you need to do it is further refine your control logic and then put it in a loop with some timing.  For example:

If   Temp1>50 turn on Fan1
Else turn off Fan1
And so on......

This sounds like a controls class project, so you can also probably refer to your class notes, teaching assitants, professor, or search ni.com and the rest of the web.

Cheers,

NathanT

[pollon]

Hi Nathan! i tried to do the same thing tou told me using a greater or equal block and a select case putting inside a daq assistant with the on/off function of the 9481 relay! is it right? Thanks a lot. Bye 

[NathanT]

Hey Paul,
        That sounds like it would work, but you will probably want to refine your logic as you learn more about the behavior of the system.  Shift registers are great to use in control loops.

Cheers,

NathanT

[pollon]

Hi Nathan, thanks for the tip. do you understand well what i right, because my english right know it's a little bit low.

 right know my boss wants me to export datafrom the cDAQ (three termocouples) to an excel sheet. how can i do that? i want to use labView 8.5 and not signal express

[Albert.Geven]

Writing data to an excel file is made easy when you trick excel.
Write the data to file with "Write To Spreadsheet File" from the file i/O tab.
Look what the list separator in your regional settings is and use that one as the separator character in the vi.
if you use the extension .cvs you can read this with excel by just double clicking the file.