Generating 1mv output signal from AO1 using NI 9381 card

[Gundu123]

Hi,

I am using NI 9074 cRIO & NI 9381 IO card, I am trying to generate 1mv signal from the AI port.

1. Programatically i am supplying 1mv to AO port and reading AI port.

2. On the AI port i am getting 22mv without connecting AO port to it .

3. Is there any method to achieve this task.

Please help me in this.Thank you.

[Vijay_J]

First the 9381 card itself is a 12bit card it means resolution is 5/(2^12) = 1.22mv. Theoretically you cannot measure or generate 1mV using this module. 

Second, even though the resolution is 12bit you will have noise over it to check the accuracy of the module from the NI Data sheet.

[Gundu123]

Hi Vijay Thank U.

i agree with you.In my card i am getting 22mv  signal without giving any input signal to it . Is there any way to set the zero voltage at this pin.

I think the pin might be acting as an antenna as it is floating.So how i can avoid this situation.

[Vijay_J]

If it s offset, you can read and subtract in your application. If it is a noise issue then i am not sure. 

[johnsold]

According to the specifications the offset error can be as large as 16 mV depending on calibration and temperature.

Devices with input multiplexers can experience an effect called ghosting which results from capacitances in the input circuitry charging to unknown voltages due to leakage currents from adjacent channel inputs or other internal circuit nodes. Measurements made with the input open or floating do not have any meaning. The manual recommends input source impedances less than 1000 ohms.

As has already been mentioned the resolution is larger than 1 mV. When you combine the offset and gain errors of both the AO and AI channels, in the best case you will not know the output within 11.5 mV and in the worst case the error could be greater than 66 mV.

If you need both 1 mV resolution and 1 mV accuracy, you will need a better device.

Lynn

[Gundu123]

Thank you everyone.According our past conversation i conclude that i need to go for better analog device having 24bit resolution or more.

[Vijay_J]

Hi,

Not only the resolution, it should also have high gain and better measurement range. I mean go for a signal conditioner with 10mV or 100mV range.

16 Bit resolution card will do, but you need a high gain card or signal conditioner.