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probe circuit to measure 230 V(ac) signal using a DAQ USB 6008?

I want to build a circuit to measure a 230V (ac) signal using a DAQ card (+- 10V Analog input). I want to create a software oscilloscope in LabView to measure the signal. If there are any ideas on how to approach this problem it will be greatly appreciated.
Message 1 of 6
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Re: probe circuit to measure 230 V(ac) signal using a DAQ USB 6008?

Where is the signal you are trying to measure coming from? I would think that you could use a relatively simple attenuator circuit (voltage divider depending on power) to bring that singal down to a usable voltage in the ±10V range for the USB-6008. I would also buffer the output of the voltage divider before sending that into the 6008. Depending on where the signal is coming from and how you ground your circuit will determine whether or not you'll want to hook up to the 6008 as single ended or differential, but it will likely be a differential connection.

Once you've figured out the circuitry you need to make the proper connections, I would take a look at one of the LabVIEW example programs to base your application off of. You could start with something like "Cont Acq&Graph Voltage-Int Clk.vi" which you can find in the NI Example Finder.

Chris W

Message 2 of 6
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Re: probe circuit to measure 230 V(ac) signal using a DAQ USB 6008?

What frequency range?

I would use a step down or signal conditioning isolation transformer just in case something goes awry, your DAQ card and PC are not exposed to high voltage.

-AK2DM

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"It’s the questions that drive us.”
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Message 3 of 6
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Re: probe circuit to measure 230 V(ac) signal using a DAQ USB 6008?

The signal I want to read in is a 230V ac signal which is phase controlled by a triac circuit. The frequency is between 45 and 50 Hz dependant on the mains. I think the current supplied is between 1A and 2A.
Message 4 of 6
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Re: probe circuit to measure 230 V(ac) signal using a DAQ USB 6008?

Since you cut the 'phase' of your main power, you can (will) have frequencies up 20kHz and more .... so a standard main transformer will not work (unless you want to use it as a filter 😉  ).

A compensated voltage divider 100:1 with a good OP as a buffer is the way I would go. As with a 10:1 scope probe the compensation C trimmer can be set with a square signal.

On the high side use at least 2 resistors in your voltage divider and also use 2 high voltage C in series (if one fail there is still another one that limit the current. 5mm gaps between traces one the PCB should be minimum in the high voltage part. )

If you don't feel comfortable with higher voltages, buy a 100:1 scope probe and build a buffer with a 1M 30pF input impedance (or whatever the scope probe needs).

Greetings from Germany
Henrik

LV since v3.1

“ground” is a convenient fantasy

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Message 5 of 6
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Re: probe circuit to measure 230 V(ac) signal using a DAQ USB 6008?

Thanks a lot. I'm a bit unfimiliar with OP-amp buffers for this type of application, do you maybe have any links or advice on how to build the buffer? Otherwise if I understand you correctly the probe will consist of a voltage divider and the buffer circuit? Is the buffer circuit not maybe going to filter out the signal I want to measure with the capacitors present in the buffer circuit?

Thanks a lot guys...

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