Ideas for inexpensive True-RMS Metering?
in [Design]
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From: EnigmaPaul on 3 Jul 2010 11:37 Hi Guys, I'm looking for the best ideas for implementing an AC power instrumentation front end for a microcontroller or FPGA. What I need to accomplish is to measure 50-60HZ AC in the range of 120V upwards of 600VAC with about 1% accuracy, TRUE RMS. I need to extract: 1. Voltage 2. Current (via current transformers) 3. Frequency 4. Power Factor 5. Phase difference This needs to work with reasonably distorted waveforms, like what might be found in small generators driven by engines. I also need something that will work for single phase or for 3phase and be scalable to instrument up to two 3-Phase sources. There are a variety of ways to go about this but I'm looking for something that is very flexible and can adapt to a variety of voltage configurations (line to line, or line to neutral) and is very low cost. I would guess that it might be similar to the best practices that would be used in the front end of True RMS DMMs or DAQ cards with AC inputs? I know there are also energy metering chips out there, but they are rather expensive. Thanks for any ideas! PW
From: Winfield Hill on 3 Jul 2010 11:58 EnigmaPaul wrote... > > I'm looking for the best ideas for implementing an AC power > instrumentation front end for a microcontroller or FPGA. > > What I need to accomplish is to measure 50-60HZ AC in the range of > 120V upwards of 600VAC with about 1% accuracy, TRUE RMS. I need to > extract: > > 1. Voltage > 2. Current (via current transformers) > 3. Frequency > 4. Power Factor > 5. Phase difference > > This needs to work with reasonably distorted waveforms, like what > might be found in small generators driven by engines. I also need > something that will work for single phase or for 3phase and be > scalable to instrument up to two 3-Phase sources. Don't waste your time trying second- and third-best solutions. Go to Analog Devices' web site and acquaint yourself with their wide selection. We're featuring the ADE7753 in H&H AoE III, you could start there. 20-pin ssop, $4.61 at DigiKey. It's single phase, but they have more complex 3-phase versions with the same architecture, so what you learn on one is extendable. -- Thanks, - Win
From: Nico Coesel on 3 Jul 2010 13:24 Winfield Hill <Winfield_member(a)newsguy.com> wrote: >EnigmaPaul wrote... >> >> I'm looking for the best ideas for implementing an AC power >> instrumentation front end for a microcontroller or FPGA. >> >> What I need to accomplish is to measure 50-60HZ AC in the range of >> 120V upwards of 600VAC with about 1% accuracy, TRUE RMS. I need to >> extract: >> >> 1. Voltage >> 2. Current (via current transformers) >> 3. Frequency >> 4. Power Factor >> 5. Phase difference >> >> This needs to work with reasonably distorted waveforms, like what >> might be found in small generators driven by engines. I also need >> something that will work for single phase or for 3phase and be >> scalable to instrument up to two 3-Phase sources. > > Don't waste your time trying second- and third-best solutions. > Go to Analog Devices' web site and acquaint yourself with their > wide selection. We're featuring the ADE7753 in H&H AoE III, > you could start there. 20-pin ssop, $4.61 at DigiKey. It's > single phase, but they have more complex 3-phase versions with > the same architecture, so what you learn on one is extendable. Still very expensive. The same amount of $ buys you a complete micro with ADCs. -- Failure does not prove something is impossible, failure simply indicates you are not using the right tools... nico(a)nctdevpuntnl (punt=.) --------------------------------------------------------------
From: krw on 3 Jul 2010 13:28 On Sat, 3 Jul 2010 08:37:38 -0700 (PDT), EnigmaPaul <enigmapaul(a)gmail.com> wrote: >Hi Guys, > >I'm looking for the best ideas for implementing an AC power >instrumentation front end for a microcontroller or FPGA. > >What I need to accomplish is to measure 50-60HZ AC in the range of >120V upwards of 600VAC with about 1% accuracy, TRUE RMS. I need to >extract: > >1. Voltage >2. Current (via current transformers) >3. Frequency >4. Power Factor >5. Phase difference All of these are easy to do except the last one. The waveforms can be pretty ratty and it may be difficult to measure this. Why phase difference? Although in getting the rest I suppose you could calculate this. >This needs to work with reasonably distorted waveforms, like what >might be found in small generators driven by engines. I also need >something that will work for single phase or for 3phase and be >scalable to instrument up to two 3-Phase sources. > >There are a variety of ways to go about this but I'm looking for >something that is very flexible and can adapt to a variety of voltage >configurations (line to line, or line to neutral) and is very low >cost. > >I would guess that it might be similar to the best practices that >would be used in the front end of True RMS DMMs or DAQ cards with AC >inputs? I know there are also energy metering chips out there, but >they are rather expensive. > >Thanks for any ideas! > >PW
From: Paul Keinanen on 3 Jul 2010 15:50
On Sat, 3 Jul 2010 08:37:38 -0700 (PDT), EnigmaPaul <enigmapaul(a)gmail.com> wrote: >Hi Guys, > >I'm looking for the best ideas for implementing an AC power >instrumentation front end for a microcontroller or FPGA. > >What I need to accomplish is to measure 50-60HZ AC in the range of >120V upwards of 600VAC with about 1% accuracy, TRUE RMS. I need to >extract: > >1. Voltage >2. Current (via current transformers) >3. Frequency >4. Power Factor >5. Phase difference > >This needs to work with reasonably distorted waveforms, like what >might be found in small generators driven by engines. I also need >something that will work for single phase or for 3phase and be >scalable to instrument up to two 3-Phase sources. > >There are a variety of ways to go about this but I'm looking for >something that is very flexible and can adapt to a variety of voltage >configurations (line to line, or line to neutral) and is very low >cost. If you are trying to make a globally acceptable product, you may also have to use three voltage transformers (in addition to the current transformers). I am not sure about the current situations, but many countries used 127/220 V three phase systems. Some dropped the 127 V wye option, thus only 3 phase wires are available (no neutral), with 220 V between the phases in delta configuration. |