NI9221 Input Gain

[Roumaenski]

Hi there,

i have a simple question about the NI9221 module. I am building a teststand with this module used for measurement of fuel cell data like voltage, current etc. The 60 V are great for the fuel cell stack voltage but at the same time i want to measure a very small voltage signal from an ACS712 (5A) where i get a signal of about 1 V max. The resolution would be low for the current, which is why i'd like to know, if there is a possibility to set different gains for the individual channels of the module. I see in NI MAX for example that one can set the maximum and minimum signal value for each channel of the NI9221 but i am not sure whether this is equal to setting a channel gain. I cant find any information regarding this in the documentation. When looking at the documentation of the module NI9205 i see the

Nominal input ranges

±10 V, ±5 V, ±1 V, ±0.2 V

which makes me beleive the NI9221 only has one gain setting (for 60 V). Am i right?

I assume in this case it would be better to use the NI9205 with individual gain settings for each channel and measure the fuel cell stack voltage with voltage divider via a 10 V channel.

Thank you very much for your help in advance!

Kind regards

Roman

[ZYOng]

Your understanding is correct!

See Setting NI-DAQmx Channel Gain by Min/Max Value or Range High/Low in LabVIEW

[Roumaenski]

Hi ZYOng,

thank you very much for your answer! Honestly i don't understand how the info in your link refers to my problem but i understand from your answer that i ill only be able to measure with an accuracy of 60 V / 4096 = ~0.015 Vwith this module. Good to know...can you (or someone) tell me what the setting of the min and max signal value are used for, when it doesn't set any gain then?

Another problem arose in the mean time: i tried to use the NI9205 module with a NI USB-9162 device (Hi-Speed USB Carrier). Unfortunately MAX wouldn't recognize the NI9205 module - only the NI9162. But when i change the module back to the NI9221, MAX recognizes it and i am able to test, measure, configure etc in MAX and use it in LV. Can't the NI9205 be used with this USB device?

Thanks again for your help in advance!

Kind regards

Roman

[ZYOng · Accepted solution]

can you (or someone) tell me what the setting of the min and max signal value are used for, when it doesn't set any gain then?

It is pretty much useless on a module with a single input range.

Can't the NI9205 be used with this USB device?

Only limited modules are supported in USB-9162. NI-9205 is not one of them.

See C Series Module Not Seen In cDAQ-9172, USB-9162, WLS-9163, or ENET-9163 and NI-DAQmx 19.6 Readme

[santo_13]

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@Roumaenski wrote:

what the setting of the min and max signal value are used for, when it doesn't set any gain then?

So, setting the min, max when creating DAQmx task allows the driver to determine the nearest input range that can accomodate your min and max values. In the case where the device has only one range, it will always choose the same range.