aquisition

[naj_rit]

how can i use labview for analog signal aqusition and my device is pci 6251

[falkpl]

This is a very general Question.  You need to define exactly what signal you need to acquire (rate, amplitude, duration continious or finite .....) and what you want to do with it.  Start with some of the example code or tutoeials using the daq assistant to get started.

paul

[naj_rit]

Thanks for ur concern,
                but we dont have  a control kit with us ,only the basic ni elvis module.And how much did the control kit cost for u?
in  our case we r planning to feed back the motor back emf as the process varible for close loop speed control.  and could u help us with the implementation of speed control pid using basic labview,especially with the tunig..Atleast share the algorithm and just check out my pid implemented using mathscript written in matlab and help me with the tuning.

Tc=0,01;
C_prop=0;
C_der=0;
C_int=0;
C_der1=0;
C_int1=0;
err0=0;
err1=0;
setpoint=Rif;
err1=err0
C_der1=C_der;
C_int1=C_int;
err0=(setpoint-gradi);
C_prop=(Kp*err0);
C_der=((tau_d/(tau_d+N*Tc))*C_der1)+(((Kp*tau_d*N)/(tau_d+N*Tc))*(err0-err1));
C_int=C_int1+((Kp*Tc)/tau_i)*err1;
equPID=C_prop+C_der+C_int;
if equPID>4.9
   equPID=4.9
  C_int=C_int1
elseif equPID<0.2
   equPID=0.2
   C_int=C_int1
end

[Nathan_R]

Hi naj-rit,

For an analog signal acquisition I would recommend taking a look at some of the included DAQmx example VIs. Specifically the Cont Acq&Graph Voltage-Int Clk.vi may apply to your situation. This VI can be found in LabVIEW by going to theHelp menu and selecting Find Examples.... Once the NI Example Finder is open select Hardware Input and Output»DAQmx»Analog Measurements»Voltage»Cont Acq&Graph Voltage-Int Clk.vi. Some other good resources for learning DAQmx in LabVIEW is the DAQ Getting Started Guide and the Developer Zone article Getting Started with NI-DAQmx: Basic Programming with NI-DAQmx.

The Developer Zone article PID Theory Explained contains a basic explanation of the PID algorithm and tuning theory. I found this article by searching the NI website for “PID tuning”. Also the Wikipedia article on PID controllers has a lot of useful information. Both of these articles explain the Ziegler-Nichols tuning method. Use this method as a starting point to tuning your PID system and then you can fine tune it by hand. The Wikipedia article has a table which explains the effects of increasing each gain parameter.

The PID Control Toolkit includes VIs that do PID control. However, you can create your own PID algorithm in LabVIEW. Another option since you already have PID code in mathscript is to use a mathscipt node in LabVIEW. This will let you run your existing mathscript PID code. If you are unfamiliar with the mathscript node the Developer Zone article Developing Algorithms Using LabVIEW MathScript: Part 1 – The LabVIEW MathScript Node is a good place to start.

Regards,
Nathan

[vijay8388]

hi how to we create a pid using basic vi's without pid toolkit.kindly help.thanks in advance

[Eric_R]

Hi Vijay,

Our PID toolkit was generated from mathematical algorithms that are general knowledge. If you need an example there is one included in LabVIEW 6.0, but the simple PID.vi may not work in current versions of LabVIEW (http://zone.ni.com/devzone/cda/epd/p/id/688). This would serve as a good start however in making your own VI.

Thank you,

Eric Reid