Current Sampling/Measuring

[Reloadron]

Tomorrow I will try to put something together on the bench. I only have 120 VAC available unless I run a 240 line but working with 120 VAC and at least a 1 KW load I should see something.

All of this is very nice but you have yet to define what sensor(s) you are using for voltage and current?

My power line is 240V AC 60Hz.
My power measuring device in between the line and load.
My load would be 0-10A which means 0-2400watt.

Ron

 

[KeepItSimpleStupid]

I'll throw this out at you too: ADE7953 | Single Phase Multifunction Metering IC with Neutral Current Measurement | Energy Measurement | Analog to Digital Converters | Analog Devices

 

[Pagedown]

yeah, that's exactly I want to do, like the ADE 7953. But the IC itself is still in production, and it is my final year project, if I use a single chip to finish all, it won't mean anything. I'm still deciding my resolution. at least 100mA? Can it be done?

Can I solve all this by using programmable gain?
i.e.
0-1A One stage and set of measurements
1-10A 2nd stage and set of measurements

 

[KeepItSimpleStupid]

I doubt it, because you don't have the luxury to autorange.

This AD9461 | 16-Bit, 130 MSPS A/D Converter | All A/D Converters | Analog to Digital Converters | Analog Devices is way to expensive, but you get the idea. Combine a sample and hold with converter so you CAN sample I & V at the SAME time. Sensors designed for 1 AMP may quickly let out the "magic smoke" when exposed to 10.

Now one converter and a two good sample and holds might work. As others have said, it's difficult to measure power from a VFD.

 

[Pagedown]

I can do autorange with an MCU. External ADC is connected to the MCU via SPI.

 

[cachehiker]

Can it be done?

Fast, accurate, inexpensive. Choose any two.

You have to have fast to measure a switcher. My impression is 100mA wouldn't be too much to ask and still be inexpensive.

Best case we figure we get about ±10 Watt accuracy from a 16-bit system sampling single phase voltage and amperage at its maximum 100 KHz. That's 8 bits lost to isolation, RFI, EMI, aliasing, etc. However, our typical application involves simultaneously sampling and synchronizing the analog data with a couple of digital channels (in software) along with near real time display of the processed data. This mandates slowing the sampling down and degrades our accuracy to about ±25 Watts or about ±1%.

Of course most of this figuring is by the seat of the pants. We don't have a decent reference standard (±0.1% or so) to compare things to unless the engineers from Delta bring their instrumentation along. I wasn't even working on this project when they last did that. The closest thing we have is Fluke 189's and oscilloscopes and some data from a few years back that indicates our data acquisition system is more accurate than the Flukes.

More accurate than that? Hmmmm. Maybe, as a student, you could get one or two of those fast AND accurate chips sampled to you.