How to measure current

[kuroshio]

Hi:

We have a DAQmx (6024E) and we want to measure the current from a flowmeter. When I tried to use the example program of LabView, I found that the measured current is much different from the current we got from a voltagemeter directly.

Please help me to figure out HOW TO MEASURE CURRENT with NIDAQmx and LabView. Thanks

Message Edited by kuroshio on 07-11-2005 10:49 AM

Message Edited by kuroshio on 07-11-2005 10:55 AM

[AlanArmstead]

Hello kuroshio,
Current measurements are really just a voltage measurement with V=I*R applied.  Have you tried first measuring a voltage and comparing that to the voltage from your voltmeter?  You could measure the voltage a couple of ways.  I would suggest first using the Measurement & Automation Explorer (MAX) test panels.  Make sure your signal is connected to the correct pins and choose differential as the terminal configuration.  Once you have a correct voltage measurement, then you can use a LabVIEW example from the example finder (Help>>Find Examples) to get started with a current measurement.  In the example finder, you can navigate to Hardware Input and Output>>DAQmx>>Analog Measurements>>Current.  There are a couple examples there for current measurements.  You will have to enter the value of the resistor you are measuring the current through.  Be sure to re-post if you still have problems:)

-Alan A.

[scpbilly]

Dear Alan and all other experts

I am a student and have a concern about current measurement for my graduate project

I am using NI-USB6009 DAQ to measure a current reading

My circuit is here

_________+battery-______________

|                                                           |

|                                                           |

|___-usb6009+___ 10ohm resistor__|

The problem is if I use DAQmx with current measurement, should I key in 10ohm or the input impedance of USB6009 from speciication,144kohm for accurate measuremtnt.

Best regards

scpbilly

[Dennis_Knutson]

Your circuit is not correct. If you want to measure the current through the resistor, place the DAQ board in PARALLEL with it and not in SERIES with it. What you have to remember is that a DAQ board is like a voltmeter. When you get a voltage measurement, use the 10 ohms to calculate the current.