USB 6008_Lab View Power Monitor

[Power Monitoring and control unit]

Hi,

I'm doing a project on Power Monitoring Unit. Here I measure the line voltage and current and display it in the computer using the NI USB 6008 unit.

So I'm giving two signals corresponds to the line voltage and current. Then use Lab View to calculate the power and power factor.

I bought the USB 6008 unit and finding it difficult connect this hard ware to the Lab View software. I need to use the Lab view, not signal express.

If you guys can give me a solution for this, it's greatly appreciated,

Cheers,

Milinda

[Dennis_Knutson]

'Difficult' is not much of a description.

You have the DAQ Assistant as well as numerous example programs (Help>Find Examples). Plenty of solutions there. What exactly have you tried and what exactly are the problems you are having?

[aeastet]

Did you install the DaxMX Drivers and Measurement and Automation DVD that came with your USB-6008? This would keep you from connecting easily. If you did can you open measurement and automation explorer and see the device installed? Can you do a self test and does it pass.

Measurement and Automation Explorer (should be on your desktop)

Self test

[Power Monitoring and control unit]

Thanks guys for your replies,

Yes, I have done the self test in Measurements and Automation. Even the test panels are working properly.

USB 6008 DAQ hardware can be detected by Measurements and Automation and Lab VIEW Signal Express.

But it's not detected by the Lab VIEW 2010 Student Version or Lab VIEW 8.6. 

E.g.: When I open a new project in Lab VIEW, when I click on 'Project' --> New  --> Targets and Devices , ISB 6008 doesn't appear there.

So I can't Use the hardware to acquire an Input signal.

This is my problem.

It would be greatly appreciated, if someone could help me to overcome this issue.

Cheers,

Milinda

[Dennis_Knutson]

It's not supposed to show up there.

Try the DAQmx Getting Started tutorial. It should explain a lot such as the DAQ Assistant.

[Power Monitoring and control unit]

Thanks for the help and suggestions.

It's working in Lab VIEW 2009 student version as it's shown in the help videos.

But it doesn't work with the Lab View 2010 student version which came with the NI hardware.

Is there a setting or Plug-in that I have to add to Lab View..?

Cheers,

Milinda

[Power Monitoring and control unit]

Hi,

There is another problem that came to me when calculating the Power Factor.

NI USB 6008 measures voltage inputs only.

So, when I calculate the power, I have to measure Voltage and the line current.

For the Voltage input signal, I can use a small transformer to step down the Voltage to an acceptable range with the DAQ. (230 V to 6V)

For the Current input signal, 1) I can use a shunt resistor and measure the voltage difference across it and input it to the DAQ

                                      or 2) I can use the small Current Transformer and a burden resistor get a voltage difference across the burden

                                               Resistor and input it to the DAQ.

If i measure the power of a resistive load, Voltage and Current signal will overlap and gives no difference.

If i measure the power of an inductive or capacitive load, there is a lag or lead between Voltage and Current signal.

My question is, when it's an inductive load, which current input method will display the difference between voltage and current signal?

Note: Power Factor - Angle difference between Voltage and current signal.

Cheers,

Milinda

[Dennis_Knutson]

The main thing is installing the latest version of DAQmx.

[Power Monitoring and control unit]

Hi,

I tested the Digital I\O pots of the NI USB 6008 Unit.

In the manual, it says that it gives out 8.5mA and 5V.

When i testes it, It's giving out 5V but current is very less than 8.5 mA. I tested the output voltages and currents by running it in Measurements and Automation.

How come this happen...?

If i run it in the Lavb View, and set and Digital Out put, will i get the recommended current...?

What could be the reason to get less current...?

Thanks

[Kev1823]

Hi Milinda,

for your current input signal you would need to be build a potential divider circuit for option 1, otherwise you would just be measuring the 230V across the shunt resistor.

I would recommend using the second option, especially if you plan on long-term testing, as the transformer will produce less heating effect than using simply a shunt resistor or potential divider circuit.

Therefore, I'd recommend CT for current signal (with shunt resistor to convert to voltage input to DAQ) and VT for voltage signal. Read both input signals and plot them together on the same graph to see the differences. You will need to think about how to implement the logic to find the phase angle (theta) between the two signals, from which you can calculate your PF...where PF = Cos (theta)

Oh, and having read you last post, you would be using the analogue inputs not the digital ports.

Hope that helps.

Regards,

Kevin