NI-4461 stackable Outputs?

[ed_Z]

Are the analog output channels as a NI-PXI-4461 stackable so that 10 Volts + 10 Volts = 20 Volts?

If I had a quantity of 3 NI-PXI-4461 boards could I make a signal that is 20 Volts + 20 Volts + 20 Volts = 60 Volts?

[johnr4]

Hello ed_Z,

What is the current that you are wanting?  Each module has a maximum power that it can output so as long as your requirement is equal to or less than the 160 mW (16mA) requirements, then this should work (depending on how you design the circuit).  Keep in mind the minimum working resistance is 600 ohms.

Thanks,

[ed_Z]

John,

I am interested in using the outputs of the NI-4461 for calibration testing of the inputs of other NI DSA boards such as the AIs of the NI-4461 and NI-4498.  

I am not sure if I read the specification sheet correctly. 

The resistances of the NI DSA Boards seem to be 50 Ohms in the psuedo-differential configuration and the resistances are

The resistances of the NI DSA Boards seem to be   1 MOhms in the differential configuration. 

So would I will need to add a large resistor at least 1 MOhm for doing a calibration in the psuedo-differential configuration?

Ed

[johnr4]

Hi ed_Z,

In the 446X Specifications, it states that the input configuration whether differential or psuedodifferential will have 50 ohm impedance.  What is the frequency of the signal you are sending?  Also, what is your overall application?  It sounds like you are just generating a signal and reading it back in.  Is there anything else you are doing in the process?  If you are at a lower frequency, impedance matching isn't as critical as at higher frequencies, but it still is something to consider.  Regardless, you will have to put a 600 ohm resistor in the line and will likely want to read back in on the differential mode.  I believe that the psuedodifferential mode is just doing software scaling, and does not actually have a 1Mohm impedance.

Thanks,

[ed_Z]

John,

The basic idea is to check the various NI DSA boards to make sure they are working correctly.

teh application of interst is verifying the boards for acoustical noise and audiometry measurements. 

In this process, we produce a signal then just read the signal back. 

Ideally I would like to be able to produce up to a 42.4 volt amplitude sinusoid with frequencies varying from 20 Hz to 20 kHz, since we are interested in the complete audiometric frequency range.   

The 42.4 volt output will require stacking five NI-4461 output channels. 

So I understand that each source output channel on the 4461 will need a 600 Ohm Resistor when stacking the voltages.  Also using the differential configuration will yied better results. 

Thanks for your help,

Edward Zechmann

[johnr4]

Hi Edward,

No problem, I am happy to help.  Have a great day!

Thanks,

[johnr4]

Hello Edward,

I did a little more digging and it appears that the 4461 is not stackable since it does not have the channel to channel isolation.  I would recommend another device that is capable of the 42.4V requirement that can be stacked, like the 4322.  Please let me know if you have any additional questions.

Thanks,

[ed_Z · Accepted solution]

John,

Do the NI-4322 in the voltage mode need 850 Ohm resistors or larger across each of the channels?

Resistance= 16.83 Volts max / 20 mAmps max = 841.50 Ohms

http://www.ni.com/pdf/manuals/375956b.pdf

Ed

[johnr4 · Accepted solution]

Hi Edward,

When cascading in voltage mode you will want to put the voltage channels in series with the necessary load.  The diagram is shown on pages 10 and 11 here:

http://www.ni.com/pdf/manuals/373754a.pdf#page=10

If you are wanting the voltage to be 42.4V with 20mA current, you will need a resistance of 2120 Ohms I believe.  

Thanks,