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'[EE]: Nice power factor meter'
2002\05\10@152448 by Peter L. Peres

picon face
Slightly unrelated, I found a clever power factor meter circuit that does
not use a multiplier as such (it uses a switch based modulator instead).
Has anyone built it or anything to add:

http://archives.e-insite.net/archives/ednmag/reg/1994/042894/09di3.htm

This could be turned around to measure power and power factor and it could
use a PIC with 2 A/D channels. All the other parts together minus the
current transformer should cost $5 or less in ones.

Peter

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2002\05\10@203733 by Bob Ammerman

picon face
One obvious and potentially dangerous problem with the circuit referenced
below: there is no burden resistor shown on the current transformer. This
can result in some really nasty high voltages on the terminals of the CT.

Bob Ammerman
RAm Systems

{Original Message removed}

2002\05\11@130128 by Peter L. Peres

picon face
There is a serious mistake in that circuit, it won't work as shown with a
7106. You can't ground COM on a 7106 so you'd have to lift it from ground
and supply decoupling and disconnect the lower switch output from ground
and connect it to COM/REFLO.  This may require an analog buffer (the
fourth opamp in the 324 ?).

You are right, both transformers are undamped. This schematic clearly
represents a concept or idea and not a working circuit. Because of that I
was asking whether someone built it because these 'concepts' that fill
magazine pages have a habit of having hidden flaws that eat lab hours
like nothing else.

Also did anyone build a Hall power meter from scratch ? I plan to make one
as soon as I get hysteresis-less Hall bridges. Why in god's name would
someone put a magnetic field sensitive device on a chip grid that is made
of magnetizable iron. Doohh.

thanks,

Peter

On Fri, 10 May 2002, Bob Ammerman wrote:

>One obvious and potentially dangerous problem with the circuit referenced
>below: there is no burden resistor shown on the current transformer. This
>can result in some really nasty high voltages on the terminals of the CT.
>
>Bob Ammerman
>RAm Systems
>
>{Original Message removed}

2002\05\11@214153 by Spehro Pefhany

picon face
At 08:33 PM 5/10/02 -0400, you wrote:
>One obvious and potentially dangerous problem with the circuit referenced
>below: there is no burden resistor shown on the current transformer. This
>can result in some really nasty high voltages on the terminals of the CT.
>
>Bob Ammerman
>RAm Systems

I was thinking that was an error on the schematic, but perhaps they are
using a ferrite-core CT like those used in SMPS units that self-limits.

Anyone trying this with a typical 100A:5A CT could well find a smouldering
crater where the LM324 used to be.

Best regards,

Spehro Pefhany --"it's the network..."            "The Journey is the reward"
.....speffKILLspamspam@spam@interlog.com             Info for manufacturers: http://www.trexon.com
Embedded software/hardware/analog  Info for designers:  http://www.speff.com
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2002\05\12@012937 by Spehro Pefhany

picon face
At 07:39 PM 5/11/02 +0300, you wrote:
>There is a serious mistake in that circuit, it won't work as shown with a
>7106. You can't ground COM on a 7106

I don't think this is true. The digital ground is generated internally
on the 7106, the analog COMMON is regulated by a current sink regulator
trying to maintain V+ - 2.8V on COMMON, fighting a 10uA pullup. Provided
V+ - GND is > 2.8V there should be no problem.

The author could have made it a lot clearer by stating that the circuit
uses +-5V supplies on all the parts or showing it on the schematic.

Best regards,

Spehro Pefhany --"it's the network..."            "The Journey is the reward"
.....speffKILLspamspam.....interlog.com             Info for manufacturers: http://www.trexon.com
Embedded software/hardware/analog  Info for designers:  http://www.speff.com
9/11 United we Stand

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2002\05\12@154340 by Peter L. Peres

picon face
On Sun, 12 May 2002, Spehro Pefhany wrote:

>At 07:39 PM 5/11/02 +0300, you wrote:
>>There is a serious mistake in that circuit, it won't work as shown with a
>>7106. You can't ground COM on a 7106
>
>I don't think this is true. The digital ground is generated internally
>on the 7106, the analog COMMON is regulated by a current sink regulator
>trying to maintain V+ - 2.8V on COMMON, fighting a 10uA pullup. Provided
>V+ - GND is > 2.8V there should be no problem.
>
>The author could have made it a lot clearer by stating that the circuit
>uses +-5V supplies on all the parts or showing it on the schematic.

I have bad experiences with pulling COM to -VCC on 7106. It works on 7107
(pull to GND, 7107 works on +/-Vcc vs GND). 7106 likes COM 2.5V or more
above -Vcc and there is an entry in the data sheet that seems to say so
obliquely.

After consulting the internal schematic of the 710x it becomes obvious
why. There are conditions where the auto zero cannot cancel the offset if
COM is at GND I think. Anyway this is a very obvious problem with battery
operated 7106 circuits and I've had my share of trouble with it.

I was noticing this as being a sign of this circuit never having been
built and tested.

Peter

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2002\05\12@171155 by Spehro Pefhany

picon face
At 10:54 PM 5/12/02 +0300, you wrote:
>On Sun, 12 May 2002, Spehro Pefhany wrote:
>
> >The author could have made it a lot clearer by stating that the circuit
> >uses +-5V supplies on all the parts or showing it on the schematic.
>
>I have bad experiences with pulling COM to -VCC on 7106. It works on 7107
>(pull to GND, 7107 works on +/-Vcc vs GND). 7106 likes COM 2.5V or more
>above -Vcc and there is an entry in the data sheet that seems to say so
>obliquely.

Yes, well, that's the difference between -V and GND on a dual +/-5V supply.
Referenced to -V on a +/-5V supply, I'm suggesting it be at V- + 5V, rather
than the internally generated V- + 7.2V.

>After consulting the internal schematic of the 710x it becomes obvious
>why. There are conditions where the auto zero cannot cancel the offset if
>COM is at GND I think. Anyway this is a very obvious problem with battery
>operated 7106 circuits and I've had my share of trouble with it.

When the battery supply consists of a single 9V battery there is no
ground, just the internally generated COMMON voltage. You can pull it to
-V without damage, but the chip won't work properly. It should work okay
if you have dual supplies (battery or otherwise).

People who buy 7106 and similar meter modules often have this problem when
they try to use a non-floating supply, I'm sure it has left a bad taste
in many a mouth (and not just from licking the 9V battery).

Best regards,

Spehro Pefhany --"it's the network..."            "The Journey is the reward"
EraseMEspeffspam_OUTspamTakeThisOuTinterlog.com             Info for manufacturers: http://www.trexon.com
Embedded software/hardware/analog  Info for designers:  http://www.speff.com
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2002\05\13@041359 by Alan B. Pearce

face picon face
>Also did anyone build a Hall power meter from scratch ?
>I plan to make one as soon as I get hysteresis-less Hall
>bridges.

Check out the Hall Current transformers from LEM.
http://www.lem.com/

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2002\05\13@094111 by Micro Eng

picon face
ADI makes a nice family of power monitoring chips....shunt or transformer
based.



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2002\05\14@144801 by Peter L. Peres

picon face
On Mon, 13 May 2002, Alan B. Pearce wrote:

>>Also did anyone build a Hall power meter from scratch ?
>>I plan to make one as soon as I get hysteresis-less Hall
>>bridges.
>
>Check out the Hall Current transformers from LEM.
>http://www.lem.com/

Thanks but I'll need to build it from scratch scratch. Bridge, core, etc
etc.

Peter

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