# Digital I/O

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## Current measurement using NI 9227

Hello.

I am using NI cRIO 9012 with I/O modules NI 9472 (DO), NI 9227 (AI current), NI 9225 (AI voltage) in Scan Interface mode. I want to aqcuire current through a resistor using NI 9227 and implement PI control. I think I made the wiring as per the manual of NI 9227 but unable to acquire any measurement.

Im afraid I am making a mistake in connections of the 9227 to the resistor.

Kindly help me. Are there any precautions and necessary steps I need to take while connecting it? Any necessary steps to be taken while using the analog pin in the VI.

Lahari

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## Re: Current measurement using NI 9227

The 9227 needs to be connected in series with the resistor.

What does the rest of your circuit look like?  What is the value of your resistor?  How much current are you trying to put through it?

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## Re: Current measurement using NI 9227

Sir,

I looked back at pages 8 and 9 of the datasheet of NI 9227, from which I see that the current measurement is being done basically by sensing the voltage itself. Also, from the way the wiring is shown in page 8, it did not look that 9227 is connected in series, but it is in shunt; so basically voltage is being sensed and then is being processed for measutring current. Is my understanding correct? In that case, would connecting 9227 in series with resistor be wrong?

As of now my circuit just a simple AC voltage source of 230 V, 50 Hz in series with a 570 ohms resistor, and I want to measure the current through thte resistor.

Since I am using 9227 for the first time, I am trying on this simple circuit. My actual circuit where I want to implement PI control is a dc motor drive. I want to aqcuire armature current of the motor and implement PI control.

Please excuse me if my doubts seem naive.

Thanks

Lahari

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## Re: Current measurement using NI 9227

The 9227 does not measure the voltage across your resistor.  It measures the voltage drop across it own internal current shunt resistor (12mOhm according to the data sheet) that is directly connected between the AI+ and AI- of a channel.  This smaller resistor (the shunt) needs to be in series with your circuit in order to properly measure the current going through your circuit.

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## Re: Current measurement using NI 9227

Sir,

I have connected the NI 9227 module in series with the resistor through which I want to measure the current. I could see the rms measurement perfectly in labview FPGA but in Labview Real TIme the rms measurement shows random values.  I dragged-and-dropped the analog channel pin, placed an rms calclution blick from signal processing, and the values being shown are very random. Also the waveform in the waveform  chart is not sinusoidal in shape but a random one.

Please suggest me as to what could have gone wrong.

Thank you

Lahari

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## Re: Current measurement using NI 9227

Hello guys,

I would like to know if someone can share with me a VI example measuring current with NI 9227, or at least tell me where can I find some information regarding measure current using LabVIEW.

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## Re: Current measurement using NI 9227

According to the datasheet, the impedance is 12 milliohms.

The shunt resistor value is actually 5 milliohms per Jose Esquivel @ NI's Technical Support.

I needed the value to verify that I was within spec of the LEM I was using to measure current.

-Javier

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