Multifunction DAQ

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using SCXI 1520 and 1121 with PXI 6052E

I've got a 4 slot SCXI box reading 1 SCXI-1520 and 3 SCXI-1121's. The signals are multiplexed to a PXI-6052E DAQ card. Please correct any of the following that is wrong:
The 1520 has max input limits of 10V
The 1121 has max input limits of 5V
The 6052 has max input limits of 10V
Now, suppose I set up my 1121's (jumper configurable) for a gain of 1, expecting a max input of 5V on all cards, including the 1520. I setup my analog input in LabView with input limits of 5V. NI-DAQ sees that my 6052 has input limits of 10V, so it sets the gain on the 1520 to 2. The ADC on the 6052E is really only 5V. You get the 10V limits because the card can apply a gain of 0.5 to bring the signal back down to 5V prior to the ADC. Since I'm multiplexing, that means my 1121 signals are also gained at 0.5 by the 6052E card. So now on my 1121's, I've lost half of the ADC range because the 6052 gain was forced to 0.5.
I hope I've got something wrong in there. It is extremely frustrating that NI has chosen not to give the user direct control over the gain settings on the 1520.
Pardon my frustration and thanks for taking the time to help.
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Message 1 of 4

The PXI-6052E uses a separate input range for each channel of the scanlist. In your case, it uses +/-10 V for your SCXI-1520 channels and +/-5 V for your SCXI-1121 channels.

Assuming that you are using DAQmx, you can query what range/gain settings the driver has made or control these settings directly using the properties AI.Rng.High/AI.Rng.Low (for the PXI-6052E) and AI.Gain (for the SCXI modules). These are located in the DAQmx Channel property node under Analog Input -> General Properties -> Advanced -> Range and Analog Input -> General Properties -> Advanced -> Gain. You can use the Active Channels property to specify which channel of the task for which you want to get/set ranges and gains.

Hope this helps,
Brad Keryan
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Message 2 of 4

Thanks for the help. I have not used DAQmx before and I've been avoiding it because I didn't want to deal with the learning curve. If DAQmx gives more direct control over gain settings then maybe it's worth the extra time to get up to speed. I don't know the details of how the 6052 works, but I find it fairly incredible that if I'm scanning a multiplexed signal on a single 6052 channel at 100 kHz or whatever, that it can switch the gain (from 0.5 for 10V inputs to 1 for 5V inputs) on a per-scan basis.


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Message 3 of 4
Hello Jason,

The DAQ device is made to be able to switch the amplifier when multiplexing through channels.  The specifications document has settling times for the amplifier (found here).  You can find the settling time specifications on page 5.

Have a great day.

Jesse O.
Applications Engineering
National Instruments
Jesse O. | National Instruments R&D
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