draw bode diagram

[kaush]

Hello,

I have a device which gives 4-20mA AC output and 4-20mA AC input. I have 6036E with voltage to current converter for input and i am reading output directly from the DAQ card.

My requirement is to draw frequency response (bode Diagram) for my device.

Please let me know how to go with this.

Thanks in advance.

[Coq_Rouge]

If you only need amplitude it is very simple. On the input side you apply a know AC excitation. Then you measure the output. Calculate

20*log (output/input). Repeat this for the frequencies you are interested in 

[kaush]

i dont know this card will support AC signal..  😞

and i need both amplitude and phase plot..

 if u have any examples it would be very helpful.

thanks

[Coq_Rouge]

In which frequency range are you interested in? And your Daqcard support AC signals

[kaush]

0 to 20 Hz...  Please let me know if i have to use any extra hardware for this..

Thank you.

[Dennis_Knutson]

You've said that you've only got a voltage to current converter for input. I would assume that you mean you are using that to convert the voltage out of the 6036 and connecting it to the input of the device. You would obviously need to convert the current out of the device to voltage so that the 6036 can measure that. All that you need for that is a resistor.

[Coq_Rouge]

If you have the PCI version the analog out max update rate is 2Khz, and 1Khz for PCMCIA version. But this should be adequate for your measurements. 

[kaush]

@ Dennis.. I guess i can directly read the current output from the device using 6036E..

@coq rouge.. I have PCMCIA version.. But the problem is i don have analog out from the device.. 

i know my question is not at all related to labview,  but if u have any ideas it would be very helpful.

Thanks..

[Coq_Rouge]

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kaush wrote:

@coq rouge.. I have PCMCIA version.. But the problem is i don have analog out from the device.. 

i know my question is not at all related to labview,  but if u have any ideas it would be very helpful.

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If you do not have access to the analog out, for some reason like it is out of order. You have to apply the reference signal with a signal generator or something like it. You can still compare the output/input relation by sampling both the input and output current. But one thing is important. Your DAQ device do not have simultaneous sampling. So a very small constant phase will appear between the two channels

Message Edited by Coq rouge on 06-20-2009 12:39 PM

[kaush]

Hmmm... i am not getting what u r saying.. sorry i forgot to mention that i have got LVDT which is fixed to my device. Can i acquire the LVDT voltage and do something to draw frequency response???