Measureing high voltages, Voltage divider assistance requested.

[Vr6Fidelity]

I would like to divide a 0-440V signal down to 0-4.4V  So i can measure it in labview.  How do i build this voltage divider so i dont blow up my card? The voltage is from one leg of a 3 phase electric motor to ground.

[Kenn_N]

Vr6Fidelity,

Thanks for contacting National Instruments.  There is certianly more than one way to go about this, but we do have hardware that can handle such voltage.  Our SCXI systems have devices that can read high voltages and in conjunction with an attenuator block you can read up to 1000V AC/DC.  Please review the following devices.

SCXI 1125 8-channel isolation amplifier

SCXI TBX-1316 high-voltage attenuator block

This will give you an idea of what you would need to safely read these high voltages. 

Regards,

[Vr6Fidelity]

Only 5 grand to condition a signal? Awsome.

How about doing it on the terminal block with resistors? Im pretty sure thats in the budget.

I will be using a laptop, PCMCIA card and a CB-68 or SCB-68.

[Kenn_N]

Vr6Fidelity,

Thanks for replying so quickly.  Although there may be more than one way do it, the SCB-68 is not rated for voltages in that range.  The SCB-68 is only rated to take 42V maximum.  The SCXI modules previously suggested is the way we provide as a safe, supported method for voltages in that range.

Regards,

[Vr6Fidelity]

Any thoughts on where to get a stand alone small voltage transformer (attenuator) perhaps?

[AnalogKid2DigitalMan]

I think Signal Transformer makes sensing transformers to step down high voltages. You need to be aware of frequency limitations, the shape of the signal you want to sense (sine, pulse,etc), and impedance matching. Some may distort the signal shape.

Personally, I would strongly suggest you go the route of an isolated measurement- transformer, optical, hall effect, etc not only for the safety of the PC/DAQ, but more importantly the human operating the equipment.

[Vr6Fidelity]

I purchased a fully isolated transformer from CR magnetics