Re : USB DAQ 6363 measurement bad with several channels

[bourdel]

Hi All,

We are using NI DAQ USB 6363 for current measurement in differential mode.

1/

When using one channel, measurement can be done up to 2Msamples/s.

But when using 2 to 16 channels, average measurements are wrong when sampling is over 10ksamples / s / channel !

FYI, Current signal is around 1 to 10 mA with 0.1ohm resistor, so signal measurement is noisy

I suppose it's due to input multiplexer before PGIA who can't sample higher ?

What is specification limits for this product?

2/

I want to use pythom script to run current measurement in remote

Which Python library do you advice to control USB-6363 DAQ? ( i found ctype on google)

Thanks

Laurent

[Antonin_G.]

Hi Laurent,

How many channels are you using for your application ? Only 2 or more ? 

Moreover for your Python script, you can use the ctypes FFI package to control your DAQ board. The link below will help you to understand the package through tutorials,... : 

How Can I Call DAQmx C Functions in Python?

Regards,

[bourdel]

Hi Antonin,

Thanks for your answer.

For measurement, following testcase we run, we can use up to 16 channels.

But sampling problem appears when we activate at least 2 channels

I use LabView signal express to do current measurement

If needs, i can send snapshot

Regards,

Laurent

[Antonin_G.]

Hi,

Yes please, it could maybe help me to go further.

Thanks

[bourdel]

Hi Antonin,

I made some screenshot showing problem I explained:

I use a waveform generator to output sinusoidal signal at 1hz with ~5mV offset.

1/

When I configure SignalExpress with sample to read=20k, Rate=1M, 1 channel

average is 5,12mA

2/

When I configure SignalExpress with sample to read=20k, Rate=1M, 2 channels

average is 5,62mA

=>So 0.5mA higher when I add a second channel

=> Not Good

3/

When I configure SignalExpress with sample to read=2k, Rate=100k, 2 channels

average is 5,12mA

=>By decreasing rate from 1M to 100k with 2 channels, I have same result that case 1/

So it seems that with more than one channel, we can't use max sample rate possible ?

I will send snapshot by mail

Thanks

Laurent

[Antonin_G.]

Hi Laurent, 

I encourage you to attach the files on your post, it will be easier for you and us 😉 

Regards,

[bourdel]

Antonin,

With snapshot

I saved also seproj config files but I can't attach them in this thread, I can send to your mail if needed

1/

When I configure SignalExpress with sample to read=20k, Rate=1M, 1 channel

average is 5,12855mA

2/

When I configure SignalExpress with sample to read=20k, Rate=1M, 2 channels (second channel not displayed,but configured)

average is 5,62893mA

=>So 0.5mA higher when I add a second channel

=> Not Good

 

3/

When I configure SignalExpress with sample to read=2k, Rate=100k, 2 channels (second channel not displayed,but configured)

average is 5,12211mA

=>By decreasing rate from 1M to 100k with 2 channels, I have same result that case 1/

[Antonin_G.]

Hi Laurent, 

Do you observe the same behaviour with MAX when you look into the tests panels for analog input ?

Regards,

[bourdel]

Hi Antonin,

I use averaging function on SignalExpress, i think it's not possible with MAX tool?

Regards,

Laurent

[Antonin_G.]

Oups you're right, I meant with LabVIEW (or another programming language) ? Or are you only using SignalExpress for your project ?

Regards,