Current DC wrong values with USB 6341

[giant_steps]

Hello everyone,

I am having a problems measuring current of a DC motor.

I need to measure with Labview the current of a motor that is working with 14V and 1 Ampere +/-. I need to measure this 1 ampere in Labview, but using a shunt resistance of 10miliohms i am displaying the values that you can see in the attached image that i have.

I am using a USB - 6341 and its only supports 10 volts input analog so i had to make a voltage divisor that i also have in the attached image. For Al1+/Al-) i measuring the voltage. For Al2+/Al2- I am mesuring current.

Could you please help with this. I don´t understand why I can´t measure the correct value.

[rgwagner888]

Please post your LabVIEW code and a better image of your MAX setup.

Kind regards,

Rick Wagner

[ben64]

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@giant_steps wrote:

Hello everyone,

I am having a problems measuring current of a DC motor.

I need to measure with Labview the current of a motor that is working with 14V and 1 Ampere +/-. I need to measure this 1 ampere in Labview, but using a shunt resistance of 10miliohms i am displaying the values that you can see in the attached image that i have.

I am using a USB - 6341 and its only supports 10 volts input analog so i had to make a voltage divisor that i also have in the attached image. For Al1+/Al-) i measuring the voltage. For Al2+/Al2- I am mesuring current.

Could you please help with this. I don´t understand why I can´t measure the correct value.

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What is wrong with the measured value? You are measuring voltage across a shunt resistor so you need to connect AI2-. Your measured value (with AI2- connected) is a noisy signal (which is normal when measuring motor current) with an average value close to 10 mv (absolute), this seems like the expected value for 1A in 10mohms. Just filter or average the output value for a cleaner result.

Ben64

[giant_steps]

My program is very simple. I just connected my DAQAssist with a waveform display to check the value i thought that would be enough. How could i filter or avarage my value to display the correct value of my mesurement?

thank you for your help,

[ben64]

Look at the VIs in the Waveform Measurements palette ( Waveform -> Analog Waveform -> Waveform Measurements). You can use Basic DC-RMS.vi or Avg DC-RMS.vi.

Ben64

[giant_steps]

I did it like you said but this way i don´t get any "wave" and I still "see" amplitudes moving around 0.034 and 0.035.

Is it normal or i am doing something wrong?

thanks ,

Tiago

[ben64]

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@giant_steps wrote:

I did it like you said but this way i don´t get any "wave" and I still "see" amplitudes moving around 0.034 and 0.035.

Is it normal or i am doing something wrong?

thanks ,

Tiago

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Hard to say if your doing something wrong without seeing what you're doing!

Ben64

[giant_steps]

Basicly i did this. :x

Thanks for your help

[ben64]

You're averaging a noisy signal on a few samples (100), try taking more sampling (like 1000) and you will have less amplitude variation.

Ben64

[giant_steps]

Still not working :x I thought that would be much easier to display current :x

Its suppose to get a current around miliampers in labview?