Convert 4-20 ma signal to voltage and perform FFT Analysis

[jonhelpmejon]

Is it possible to convert a 4-20 ma signal from an accelerometer to a voltage, then perform spectral analysis?

[Jordan F]

Hi

I am interested in learning more about your application.  What type of accelerometer are you using?  To quickly answer your question though, yes, you can acquire a 4-20mA signal from the accelerometer and perform spectral analysis.  However, there some different ways you could go about this.  First of all, what hardware do you currently have?  If you do not have any hardware, there are many different devices that measure acceleration.  What kind of form factor are you interested in (PCI, PXI, USB, etc.)?  I attached a link to some different devices below.

Accelerometer Measurements

http://sine.ni.com/nifn/cds/view/main/p/sn/n25:11/lang/en/nid/1036/ap/daq

You can then scale the current in software to its equivalent voltage value.  If you want to read in a voltage using another data acquisition device, you could use a shunt resistor and measure the voltage across that.     

The next question I have is if you have LabVIEW or are planning on using LabVIEW.  We have some signal processing VIs that are shipped with the LabVIEW Full, Professional, and Dev Suite version that you could use.  What signal processing are you going to perform on your measurement?

In the end, we do have solutions for this type of application but it depends on what hardware you have or are looking for, what software you are interested in, and what exactly what analysis you need to perform.  Any futher information would be extremely helpful! 

Message Edited by Jordan F on 03-05-2009 03:31 PM

[jonhelpmejon]

Thanks Jordan,

I wasn't only looking at  accelerometer 4-20 ma signal, but also any dynamic type of 4-20 ma signal.  I guess the question is there such a thing as a dynamic 4-20 ma signal.  We were told by an engineer that you cannot perform an FFT on any 4-20 ma signal.

[Jordan F]

Hi

An FFT measurement is simply a mathematical equation that is performed in software and you can perform an FFT on a 4-20mA signal if desired.  I am confused on exactly what you need.  National Instruments have modules that measure current such as a 4-20mA signal and also devices that measure voltage.  In software NI provide functions that perform signal processing on incoming data.

[jonhelpmejon]

Sorry Jordan,

Meant to say a usable FFT. The problem is most sensors have a conditioned 4-20ma signal with no bandwidth.  But if I can find a sensor with a dynamic 4-20, It would not be a problem performing a usable FFT.  Sorry about the confusion,  I wasn't sure if there was such a thing as a dynamic 4-20ma signal.  Thanks for your help.