Measuring High Voltages

[andrew_JKTA]

Hi,

I am trying to measure the voltage across appliances connected to the mains but I currently have a PCI-6024E DAQ board which can only read voltages in the range of -10V to 10V. Is there some external circuitry I could add to the board to allow it to be able to read voltages in the range of -300V to 300V. Buying a new DAQ board is not an option at the moment.

Any ideas?

Thanks very much.

Andrew

[K C]

Hi Andrew,

Can't you use a transformer of let say 5VAC output. It is cheap and safe !

[andrew_JKTA]

ok, thanks, would that significantly reduce the resolution

also, can my DAQ board measure AC signals? does the -10V to 10V range refer to AC or DC?

[K C]

Neither (or both), just like it says; from -10 to +10 referenced to the signal ground of your DAQ board.

So yes, you can measure AC as long as the top value stays below the 10V. The top value of a 5V transformer is below the 9V.

[Rich_Silley_NIUK]

Hi

Can I please highlight a couple of things to take into consideration if using a transformer to step down the voltage to fall within the input range of our DAQ cards. A transformer's output is floating, so you will need a resistor from both + and - (because it's AC) to ground. Something like a 10 kOhms should work fine and not distort the signal. A bigger concern is power spiking. When you disconnect an inductor you get a massive power spike on the output so you have to be very careful as any damage caused by this will not be covered under warantee. You should have some type of external protection circuitry to prevent harming the board.

Hope this helps and if you have any more queries please post here.