What's the best way to measure wattage?

[captain scruffy]

I have no idea where to start.  It seems like the best idea would be to build a voltage divider and measure the voltage (since I go up to 110V).  But how do I measure the current?  Also, what daq system/setup should I build/buy so that I can read AC voltage?  The daq I'm currently playing with (not mine--so I'll have to buy my own soon) reads DC inputs.

Are there any power meters that anybody recommends that I can directly hook up to my experiment and then have it output to Labview?

All I need to do is measure some temperatures, wattage and I'll probably have a RS-232 input later from a weight scale.

My range:
0-1kW
0-110V
0-10A

[smercurio_fc]

At those voltage and current levels you will need some substantial signal conditioning so you don't blow up your DAQ system. I would suggest calling your local NI sales rep for help with this.

An alternative is to buy a digital wattmeter that has a computer interface, like serial or GPIB. Google should turn up some hits for you. You can also perform a power measurement using a DMM as described in this article.

[johnsold]

I concur that the best approach would be to buy a commercial instrument which can be connected to the computer. It sounds as though you do not have much experience with such measurements. If that is truly the situation, you will get better results more quickly, you and your computer will be safer, and the overall task more likely to succeed, by going with an off the shelf instrument.

Power measurements can be difficult if the loads are reactive or non-linear. Just defining exactly what you mean by "power" can get complicated. The safety issues are significant. If you are not expert in these things, buy equipment designed by the experts so you do not need to re-invent the wheel.

Lynn, P.E., MSEE

[Wayne.C]

I would suggest a watt transducer.  Less $$ than a power insturment.  Readily available with varying amouts of precision depending on your application.  These are designed to output an isolated low level signal that is compatable and safe for your DAQ.  Flex-Core is one company that I know makes such a device.