High voltage!

[jeff_scharpf]

Hi,

This is really an electrical question so I hope this isn't the wrong place to post.

I'm just wondering if anyone here has any experience measuring line voltage (120VAC or 230VAC) using the cRIO or other high speed data acq. systems.

I am trying to figure out a way to step the line voltage down to a safe level without a transformer, minimal loss of frequency content, so it can be read into a high speed analog input.

I thought of a voltage divider but not sure if that's safe.

Any ideas?

[preston_johnson]

Today, the best solution is to use www.lem.com, for voltage and current transducers.  They offer some high frequency devices, so as to not loose freqency content.  Many of the power quality instruments and power quality analyzers uses probes from lem, and from fluke. 

You may be able to put together a voltage divider, just make sure you have plenty of spacing between your leads so as not to arc.  This is what is done in the SCXI-1316 and SCXI 1327 terminal blocks for high voltage applications. 

We are interested in your feedback and are studying the requirements for similar SCXI modules in cRIO. 

[jeff_scharpf]

Thanks for the reply Preston.

I'm familiar with LEM, but most of their sensors produce a voltage out (dc value representing an rms value). I will check them out though.

In the meantime, I noticed that there is a 250V continous isolation on the 9215 card that I'm using, (2300V withstand).

So, I'm going to try to build a voltage divider for the voltage sense and use a shunt for the current. I put the shunt on the neutral side so that the potiential for a higher voltage is minimal. The voltage divider is just a 11K in series with a 500 ohm resistor right across the line.

I think this should be ok.

If I can create this power analyzer using the cRIO I can save my company alot of money.

I will also check LEM.

Thanks again for your help.

[SergKr]

Hi Jeff,
We used cRIO 9215 to measure HV/HC  with LEM sensors. It works fine and have good bandwidth. Today it's the best one we could find. We regularly use them in our HV PXI test systems. But, LEM sensors are mostly suitable to be connected to transformer and could not be connected to capacitor HV divider, because of LEM has low input impedance and needs about 20ma of current  from the measured source. Just keep in mind. We had to use precizion HV resistors divider in this case, or custom designed isolation preamplifiers. If you'll need details, e-mail to colleague of mine Mike (mike@acs-inc.ru). He'll be back from business trip in the middle of the next week.

[jeff_scharpf]

Sergey,
Thanks for the response. Yes I would like to learn more about what you did. I am trying to do the same thing.

I will write to your colleage.

Best Regards,

Jeff