maximum sampling frequency I can use

[pascal2007]

Hi,

I am measuring the turbulent flow in jet with the hot wire.

I use for this a National Instruments SCXI signal conditioning (containing a SCXI 1000 chassis, an 8-channel simultaneous-sampling differential amplifier module SCXI 1140 and a shielded terminal block with BNC connectors SCXI 1305).

Question: What is the maximum sampling frequency I can use for the measurements? Or the maximum frequency allowed by the SCXI 1140?

Thank you in advance

 

[Corby_B]

Hello pascal2007!

Thanks for your post and questions about SCXI!

The max scan rate is determined by the communicating module you are using. Are you using a DAQ board or the USB-SCXI 1600 to communicate with your PC?

Let me know if this helps you with your application!

Cheers!

Corby_B

http://www.ni.com/support 

[pascal2007]

thank you for your replay,

I am using a 16-Analog-Input Multifunction DAQ card PCI-6052E (333 kS/s, 16-Bit) .

Is this mean, the maximum sampling frequency I can use is 333 kHz?

thanks for your time

[Corby_B]

Hello pascal2007!

Thanks for the response. Yes you are correct that your Max sample rate is 33kS/s at 16 bits. One thing to keep in mind is is that this is for 1 channel. So if you add channels to your acquisition then your sampling rate per channel will go down. So for instance is you are bringing in data on 10 channels divide your sampling rate by 10 to get the rate for each channel.

Let us know if this helps and good luck on your applications!

Cheers!

Corby_B

http://www.ni.com/support 

[pascal2007]

Hi, I have another question:

My instruments:

I am using for my application a National Instruments SCXI signal conditioning (containing a SCXI 1000 chassis, an 8-channel simultaneous-sampling differential amplifier module SCXI 1140 and a shielded terminal block with BNC connectors SCXI 1305).

I am using a 16-Analog-Input Multifunction DAQ card PCI-6052E (333 kS/s, 16-Bit).

My application:

I am measuring the turbulent flow in jet with the hot wire. The signal is between 0 and 3 volts. I am using 1 channel.

I want to cut of the frequency above 50 kHz in the signal conditioning SCXI-1140, or before it goes to the DAQ.

Question: How I can filter the signal in the SCXI-1140? Or between the SCXI-1140 and the DAQ?

Thank you in advance.

[Corby_B]

Hello pascal2007,

Thanks for your post back!

I see that you need to do some filtering in your application. So the SCXI-1140 was designed to have different gain settings and not specific for filtering. You could go with the 1141 that has a programmable filter setting between 10 and 25k but that will not get you to your 50KHz that you need. So even though your signal may contain these frequencies that you do not desire you can always filter these out in software using functions on the "signal processing" functions palette. There is also an express filter VI in the express palette that can be used to filter in software. 

There is always the option of creating your own analog filter circuit but I would recommend doing this before any of your NI hardware. There is digital communication data sent between the SCXI chassis and your DAQ board so I would not recommend filtering there.

Let me know if any of this helps you with your application!

Cheers!

Corby_B

[pascal2007]

Hello,

Do the 16-Analog-Input Multifunction DAQ card PCI-6052E (333 kS/s, 16-Bit) has an internal filter? From the manual they explain that it does not have  a "Programmable Input Filters".  If it has an internal filter, is this mean, if I sample at 20 KHz, it will cut all frequency above 20 kHz? Because if it is the case, that's mean I don'thave aliasing problem in my signal.

Thank you for your help

[Corby_B]

Hello pascal2007,

Thanks for the post back. So the board you have (PCI-6052E) is an E-series board. The M-Series boards (62XX) have this low pass filter and on some of them you do have to option to enable the filter. See the M-series manual on page 4-4 linked here. Is this the manual that you were referring to on your previous post? Un fortunately the E-series boards do not have lowpass filter functionalities. So if you send a signal that is above your sampling rate there is a potential for aliasing. We do have the M-series 628X boards or our DSA board that have lowpass filter functionalities that may be useful for your application.

NI PCI-6289

Dynamic Signal Acquisition

 Let me know if this information assists! 

Cheers!

Corby_B