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'[EE] Detection of getting unplugged'
2007\05\10@145009 by alan smith

picon face
Well, I've been trying to solve a particular problem for a few months, sorta on again, off again issues.
 
 Simply put, I need to know when something has been unplugged from a AC socket.  I don't care about how much current its drawing (I do...but I dont need to know), because in some cases it might be a 100mA wall wart and in other cases a 100W power supply.  I just want to know....did it get unplugged.
 
 I've looked at some exotic solutions like power monitor chips but they aren't really designed for this.  I've played with Allegro hall sensors but the sit at 2.5V nominal, and just mimic the AC waveform and yes, with a larger load I can see it but smaller devices do not make a large enoough effect even when I use a simple gain stage op-amp.
 
 Nothing really gives a solution to cover all the ranges.  I need it small, cheap and simple to build.  (think production enviroment).
 
 
 So, any good ideas out there?


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2007\05\10@150138 by PAUL James

picon face

How are you going to monitor this detection method?  

For instance, you could add a pilot lamp of some sort.  If you look at
it and the lamp is out, it's probably unplugged.   Or the other side of
the coin is you would monitor it remotely by some sort of panel or even
a
Video screen.  The solutions offered will necessarily depend on how you
intend to monitor the function.
Will it be a visual check in close proximity to the device that is being
powered.  Or will it need to be monitored remotely?   And if remotely,
how far away, and what is at your disposal in the way of monitoring
equipment?  



Regards,

       
Jim

{Original Message removed}

2007\05\10@151815 by M. Adam Davis

face picon face
Do you need to know when it gets unplugged vs when it is turned off?

For instance a lamp may draw no power but still be plugged in.

If so, a mechanical solution may be your best bet.

-Adam

On 5/10/07, alan smith <spam_OUTmicro_eng2TakeThisOuTspamyahoo.com> wrote:
{Quote hidden}

> -

2007\05\10@152929 by Scott Touchton

flavicon
face
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Optical sensor (look for when something is not blocking a light source)?

Or - toroid, single transistor amp, comparator and an integrator?  Use a
ratio on the toroid to get enough sensitivity for a minimum current?

Or - park a 100mH inductor next to the hot wire, resonate the inductor to
60Hz, envelope detect and use a simple comparator to trigger?



Scott


>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>

 Simply put, I need to know when something has been unplugged from a AC
socket.  I don't care about how much current its drawing (I do...but I dont
need to know), because in some cases it might be a 100mA wall wart and in
other cases a 100W power supply.  I just want to know....did it get
unplugged.
>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>

 




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2007\05\10@162428 by Peiserma

flavicon
face
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.....piclist-bouncesKILLspamspam@spam@mit.edu wrote:
> Or - toroid, single transistor amp, comparator and an
> integrator?  Use a ratio on the toroid to get enough
> sensitivity for a minimum current?


years ago I used a toroidal current transformer for something similar. It was a Bicron EX9PC200 (I'm sure there are others, that's just the one I happened to find at the time). Wind a turn from the AC hot through the toroid, select an appropriate bias resistor, and it gives you a voltage out proprotional to current drawn from the AC source.

The trick would be selecting a combination that lets you reliably detect the entire anticipated current range. It might take two current transformers, one for low ranges, one for higher ranges. Or maybe an op-amp to amplify the low-range into useable results (and also limit the high range) could suffice, especially if you just have to detect if something is drawing power or not. You'll have to determine if this approach is suitable for you, but it sounds feasible.

Production environment i take to mean "use it on a shop floor," in which case cheap should be replaced by reliable.




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2007\05\10@163510 by alan smith

picon face
To answer some of the questions...this is remote with a PIC and an RF link.  PIC detects the event and transmits via the RF link to mother an tattles.  So video is out of the question, or a pilot light.  It has to detect and report.
 
 Optical maybe, but may be  in a dark enviroment to begin with and can't depend on the plug
 size to block.
 
 Torroid or inductor...same issues I am thinking with the hall sensor.  Difficult to the measurment sensitivity over the range.
 
 And, as far as something plugged in and not on...not the case.  Whenever a device is plugged in, it will be on, yet may not be pulling very much current.
 
 Mechanical may be the best.  If I could find a AC recpeticle that the blades touched when the device is unplugged, and opens when the device plugs in.
 

     
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2007\05\10@164934 by Alex Harford

face picon face
On 5/10/07, alan smith <micro_eng2spamKILLspamyahoo.com> wrote:
>   Mechanical may be the best.  If I could find a AC recpeticle that the blades touched when the device is unplugged, and opens when the device plugs in.

Does it need to be instantaneous?  If not, what about some kind of
capacitive sensor near the socket?

2007\05\10@165451 by Peter P.

picon face
Hack: microswitch on side of receptacle, tongue bent in 'L', short side of L
pokes partially into receptacle. This will sense machanically. Alternately drill
hole and have microswitch lever (plastic) protrude into receptacle. Or provide a
cover-like thing that must be moved aside to use a recepacle. None of these
sense the circuit proper.

To sense high and low loads I have used two antiparallel diodes before. These
create 0.5-1V of drop when there is something 'in'. This can be sensed in many
ways, including with a 1:1 transformer (which will not be a current transformer
in this case). The diodes may need heatsinking, but not for low loads (a few
amps will be ok w/o heatsink, the diodes run hot). Shunt the diodes with 0.1uF
25V to avoid parasitics. The voltage that appears on the diodes is almost square
wave and will pass a 1:1 pulse transformer that will not let 50/60Hz through.
The pulse transformer must be coupled with a capacitor to avoid heating the
coil. In theory adding a NTC in parallel with the diodes can increase the load
capacity w/o heatsinking. The NTC will take over more and more current as the
diodes heat up. Of course this needs a lot of testing.

Peter P.


2007\05\10@165822 by Andre Abelian

flavicon
face
Simple solution is to add memory capacitor
http://images.google.com/imgres?imgurl=http://www.suntan.com.hk/product/TS12_Electric_Double_Layer_Capacitor.gif&imgrefurl=http://www.suntan.com.hk/moreinfo.asp&h=193&w=226&sz=23&hl=en&start=2&tbnid=mdx2knkvHBuJeM:&tbnh=92&tbnw=108&prev=/images%3Fq%3Dgold%2Bcapacitor%26gbv%3D2%26svnum%3D10%26hl%3Den%26rlz%3D1T4HPND_en___US210

disconnect 5 v that goes to pic vdd and add shotcky diode then
add above cap to pic side. thru one of pic pin read zero crossing
pulse from your AC. when the power goes off the pic has enough power
to run and detect an error.
If I understood the question right?

Andre Abelian  




{Original Message removed}

2007\05\10@171255 by alan smith

picon face
hmmmm....explain that a little more.  I can stand delay...meaning that even a second of delay.  I'm not really familiar with capacitive sensors

Alex Harford <.....harfordKILLspamspam.....gmail.com> wrote:  On 5/10/07, alan smith wrote:
> Mechanical may be the best. If I could find a AC recpeticle that the blades touched when the device is unplugged, and opens when the device plugs in.

Does it need to be instantaneous? If not, what about some kind of
capacitive sensor near the socket?

2007\05\10@173602 by Richard Prosser

picon face
Or you can detect the electric field from the cable for voltage detection.

Wrap 10-20 turns of hookup wire around the cable (or fit a conductive
sleeve etc.). This will have capacitive coupling to the live conductor
as well as the neutral (and earth conductors if fitted). So you have a
capacitive voltage divider. The capacitance isn't much (100pf or so
?), but the input impedance to the pic pin can be pretty high also.
I've had the setup working with a protection diode to + and grnd and
feeding a ADC input on an atmel micro. Take 10 or so samples over a AC
cycle and the difference between connected and not connected can be
easily detected. (I think I measured the difference between the max &
min of the sampled data with the input biased to midpoint using high
value resistors).

You do need a ground reference for you detector however - unlike the
magnetic/currrent detection systems.

And it won't work on neutral screened cables, but that's an unlikely
requirement.

RP



On 11/05/07, alan smith <EraseMEmicro_eng2spam_OUTspamTakeThisOuTyahoo.com> wrote:
{Quote hidden}

> -

2007\05\10@190832 by Mike Harrison

flavicon
face
On Thu, 10 May 2007 11:50:08 -0700 (PDT), you wrote:

>Well, I've been trying to solve a particular problem for a few months, sorta on again, off again issues.
>  
>  Simply put, I need to know when something has been unplugged from a AC socket.  I don't care about how much current its drawing (I do...but I dont need to know), because in some cases it might be a 100mA wall wart and in other cases a 100W power supply.  I just want to know....did it get unplugged.
>  
>  I've looked at some exotic solutions like power monitor chips but they aren't really designed for this.  I've played with Allegro hall sensors but the sit at 2.5V nominal, and just mimic the AC waveform and yes, with a larger load I can see it but smaller devices do not make a large enoough effect even when I use a simple gain stage op-amp.

Look at GMR sensors - much more sensitive than Hall Effect.

http://www.nve.com/

I've used these in a system which detected on/off when clamped on the outside of a mains cable - not
sure how well it would work down at lower currents but definitely way better than Hall effect

2007\05\10@192009 by Gerhard Fiedler

picon face
alan smith wrote:

> And, as far as something plugged in and not on...not the case.  Whenever
> a device is plugged in, it will be on, yet may not be pulling very much
> current.

I think for anything to make sense, you need to specify the minimum current
you want to sense and the maximum current that may flow through the wire.
The possible solutions depend a lot on these two parameters.

Gerhard

2007\05\10@194429 by peter green

flavicon
face
part 1 994 bytes content-type:text/plain; (unknown type 8bit not decoded)

+AD4-   Simply put, I need to know when something has been unplugged
+AD4- from a AC socket.  I don't care about how much current its
+AD4- drawing (I do...but I dont need to know), because in some cases
+AD4- it might be a 100mA wall wart and in other cases a 100W power
+AD4- supply.
you can always put a shunt resistor in and then compare the voltage accross it with a threshold. If we assume its a 20A outlet and that we can tollerate a maximum of 0.5V of volt drop that means we need to use a resistor of 0.025+A6k-. That means at 100ma we have a voltage of 0.00125V accross the resistor. To detect this i'd amplify (use an inverting amplifier design since the input is low voltage but also low impedance) and evelope detect it with an op-amp circuit powered by a transformerless (resistor/capacitor) power supply with its +ACI-ground+ACI- at mains live then feed to an opto-isolator to transfer it to the rest of your system.







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2007\05\10@200026 by Jinx

face picon face
> PIC detects the event and transmits via the RF link to mother and
> tattles.  So video is out of the question, or a pilot light.  It has to
> detect and report

Seeing as you specified 'unplugged' and not 'turned off', a motion
sensor. Clipped or adhesived to the plug or immediate cable

2007\05\11@084446 by M. Adam Davis

face picon face
On 5/10/07, Peter P. <plpeter2006spamspam_OUTyahoo.com> wrote:
> To sense high and low loads I have used two antiparallel diodes before.

This is a great idea.  Just put two diodes antiparallel to each other
in series with the load.  There will be no voltage across them when
there is no current drawn.  Any amount of current draw will place a
1.5v AC square wave across them.  Make sure they can take the load.

If you use diodes with a largish drop (1.8V) then you can drive an LED
in a optoisolator for isolation if needed.  Otherwise use clamping
diodes and a comparator or a one shot (since it'll be pulsing).

AC is considered a nasty, nasty service as-is, so you won't need to
worry about the effects on the power from the slight voltage drop and
"glitch" at zero crossing.

-Adam

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Interested in electronics? Check out the projects at http://ubasics.com

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2007\05\11@095822 by Peter P.

picon face
M. Adam Davis <stienman <at> gmail.com> writes:

> On 5/10/07, Peter P. <plpeter2006 <at> yahoo.com> wrote:
> > To sense high and low loads I have used two antiparallel diodes before.
>
> This is a great idea.  Just put two diodes antiparallel to each other
> in series with the load.  There will be no voltage across them when
> there is no current drawn.  Any amount of current draw will place a
> 1.5v AC square wave across them.  Make sure they can take the load.

Actually you want to use diodes with low drop, i.e. Schottky, and you can,
because they do not need to withstand line voltage. Then by the time 2-3A are
drawn (250-350W in 110V land) they need cooling. The 0.1uF cap across them
removes switching noise and there will be a relatively nice square wave voltage
on them (about 0.8-1.2Vpp). This is not enough to light a LED but something
creative can be built from this starting point.

Peter P.


2007\05\11@102625 by Mike Harrison

flavicon
face
On Fri, 11 May 2007 13:57:59 +0000 (UTC), you wrote:

>M. Adam Davis <stienman <at> gmail.com> writes:
>
>> On 5/10/07, Peter P. <plpeter2006 <at> yahoo.com> wrote:
>> > To sense high and low loads I have used two antiparallel diodes before.
>>
>> This is a great idea.  Just put two diodes antiparallel to each other
>> in series with the load.  There will be no voltage across them when
>> there is no current drawn.  Any amount of current draw will place a
>> 1.5v AC square wave across them.  Make sure they can take the load.
>
>Actually you want to use diodes with low drop, i.e. Schottky, and you can,
>because they do not need to withstand line voltage. Then by the time 2-3A are
>drawn (250-350W in 110V land) they need cooling. The 0.1uF cap across them
>removes switching noise and there will be a relatively nice square wave voltage
>on them (about 0.8-1.2Vpp). This is not enough to light a LED but something
>creative can be built from this starting point.

As it's AC, a simple capacitive charge pump would give enough voltage to drive a LED or
optoisolator.


2007\05\11@105403 by Alex Harford

face picon face
I was thinking something along the lines of sensing if the plug is
near the socket... you might have to filter things a little bit to
avoid triggering when the plug is handled, ie look for a steady state.
There's lots of touch sensitive sensors that could be adapted.

On 5/10/07, alan smith <@spam@micro_eng2KILLspamspamyahoo.com> wrote:
> hmmmm....explain that a little more.  I can stand delay...meaning that even a second of delay.  I'm not really familiar with capacitive sensors
>
> Alex Harford <KILLspamharfordKILLspamspamgmail.com> wrote:  On 5/10/07, alan smith wrote:
> > Mechanical may be the best. If I could find a AC recpeticle that the blades touched when the device is unplugged, and opens when the device plugs in.
>
> Does it need to be instantaneous? If not, what about some kind of
> capacitive sensor near the socket?
> -

2007\05\11@123029 by Peter P.

picon face
Mike Harrison <mike <at> whitewing.co.uk> writes:

> As it's AC, a simple capacitive charge pump would give enough voltage to
> drive a LED or optoisolator.  

Actually, no, because it would require Germanium diodes and would still provide
too little current for an opto. The easy way to sense it was as I said, using a
1:1 (can be other ratio) pulse transformer capacitively coupled. For ordinary
diodes something like this should work:

      +---C0---+
      |        |
A o----+-A-D1-K-+----o
      |        |
      +-K-D2-A-+
      |        |
      C1       R1
      |        |
      +-A-D3-K-+
      |        |
      +K-LED-A-+

With LED=ir (optocoupler, Vf=1V), D3-Schottky, C1=10uF and R1=5R.
C0=0.1uF, D1+D2 = 1N4001 etc

Peter P.



2007\05\11@140623 by alan smith

picon face
I'll have to look at this and see if it might work.  Some of the other ideas....dont really fit because of the application....details would make sense of it all...but I am under NDA so can't divulge more than the generics.  Suffice to say....the devices under "watch" are not under the control of the client.....yes I know, that raises more questions but...if its outside the box and plug, there is no control.  It all has to be inside behind the plate.
 
 Thanks to all for the suggestions, thats what I like about this group..very diverse populace with lots of good ideas.

"Peter P." <RemoveMEplpeter2006TakeThisOuTspamyahoo.com> wrote:
 Mike Harrison whitewing.co.uk> writes:

> As it's AC, a simple capacitive charge pump would give enough voltage to
> drive a LED or optoisolator.

Actually, no, because it would require Germanium diodes and would still provide
too little current for an opto. The easy way to sense it was as I said, using a
1:1 (can be other ratio) pulse transformer capacitively coupled. For ordinary
diodes something like this should work:

+---C0---+
| |
A o----+-A-D1-K-+----o
| |
+-K-D2-A-+
| |
C1 R1
| |
+-A-D3-K-+
| |
+K-LED-A-+

With LED=ir (optocoupler, Vf=1V), D3-Schottky, C1=10uF and R1=5R.
C0=0.1uF, D1+D2 = 1N4001 etc

Peter P.



2007\05\11@182537 by Jinx

face picon face
> It all has to be inside behind the plate

Kind of an important detail, don't you think ?


2007\05\11@185925 by Peter P.

picon face
Jinx <joecolquitt <at> clear.net.nz> writes:

>
> > It all has to be inside behind the plate
>
> Kind of an important detail, don't you think ?

Better later than never ...

Anyway, neither the circuit I posted nor any other will successfully sense the
'new' SMPSU wall wart type of load, as their quiescent is way too low. Also,
even a switch type sense device will fail to sense a disconnected load if the
user uses an extension piece or cord. The definition of 'unplugged' is too wide
to be useful imho.

Peter P.


2007\05\14@043120 by Alan B. Pearce

face picon face
>The definition of 'unplugged' is too wide to be useful imho.

Well, the more I read this thread, and the more the OP writes, the further
my feeling is that rather than "unplugged" he is looking for "empowered",
and that can be done by simple voltage detection with an opto-isolator.

2007\05\14@045837 by Alan B. Pearce

face picon face
>rather than "unplugged" he is looking for "empowered",

Grrrr flaming spell checker - of course that is supposed to be "unpowered"
not "empowered" ...

2007\05\14@083544 by alan smith

picon face
True...unplugged....unpowered....the crux of the matter is I have control on the source side of the plug and not the device plugged into the wall.  The device could be a wall wart, a regular plug, so size itself may change thus any sort of optic sense can't be employed but I'd love it I could as it stays away from touching the 110VAC.  Wire wrapped around the hot (or return) would be great if this was a custom one-off or home project but this is going to be a mass produced with as little overhead as possible.
 
 I'm leaning toward the anti-parallel diodes approach, driving a optocoupler.

"Alan B. Pearce" <spamBeGoneA.B.PearcespamBeGonespamrl.ac.uk> wrote:
 >The definition of 'unplugged' is too wide to be useful imho.

Well, the more I read this thread, and the more the OP writes, the further
my feeling is that rather than "unplugged" he is looking for "empowered",
and that can be done by simple voltage detection with an opto-isolator.

2007\05\14@091225 by Alan B. Pearce

face picon face
>True...unplugged....unpowered....the crux of the matter is I
>have control on the source side of the plug and not the device
>plugged into the wall.  The device could be a wall wart, a
>regular plug,


Ahh, suddenly the light turns on ... you are wanting to see if a load is
plugged into your supply ...

I would suggest you look at the LEM Minisens devices, neat little hall
effect sensor in an SOIC-8 package, designed for sensing current in PC
tracks or adjacent wires. By adjusting the effective number of turns of
primary around the chip you can adjust the low current sensitivity.

You will probably need to screen the device against electrostatic coupling
from the mains wiring, but that is not impossible.

I phoned the UK representatives when I saw them announced in the local
Electronics Weekly, and got a couple of samples plus one of the evaluation
kits for free.

http://www.lem.com/


2007\05\14@101409 by alan smith

picon face
duh.....Sensirion also makes those, should have thought of it first off...have to find my samples on it.  Lost my contact info it was from a job ago....but thanks for reminding me about that one!

"Alan B. Pearce" <TakeThisOuTA.B.PearceEraseMEspamspam_OUTrl.ac.uk> wrote:  >True...unplugged....unpowered....the crux of the matter is I
>have control on the source side of the plug and not the device
>plugged into the wall. The device could be a wall wart, a
>regular plug,


Ahh, suddenly the light turns on ... you are wanting to see if a load is
plugged into your supply ...

I would suggest you look at the LEM Minisens devices, neat little hall
effect sensor in an SOIC-8 package, designed for sensing current in PC
tracks or adjacent wires. By adjusting the effective number of turns of
primary around the chip you can adjust the low current sensitivity.

You will probably need to screen the device against electrostatic coupling
from the mains wiring, but that is not impossible.

I phoned the UK representatives when I saw them announced in the local
Electronics Weekly, and got a couple of samples plus one of the evaluation
kits for free.

http://www.lem.com/


2007\05\14@105037 by Alan B. Pearce

face picon face
>duh.....Sensirion also makes those,

Oh, do they, I can find only humidity and temperature sensors on their site.
Do you have a reference? Looking for alternatives before I commit to
designing the LEM ones in.

2007\05\14@105046 by Gerhard Fiedler

picon face
alan smith wrote:

> True...unplugged....unpowered....the crux of the matter is I have control
> on the source side of the plug and not the device plugged into the wall.

Still not clear (to me?) whether you want unplugged or unpowered :)

> The device could be a wall wart, a regular plug, so size itself may
> change thus any sort of optic sense can't be employed but I'd love it I
> could as it stays away from touching the 110VAC.  Wire wrapped around
> the hot (or return) would be great if this was a custom one-off or home
> project but this is going to be a mass produced with as little overhead
> as possible.

Are you making the outlet (mechanical portion)? If so, maybe you can add a
switch of the sort they have in audio sockets. Or something optical that
detects when there's something plugged in.

Gerhard

2007\05\14@114134 by William Chops Westfield

face picon face

On May 14, 2007, at 7:50 AM, Alan B. Pearce wrote:

>> duh.....Sensirion also makes those,
>
> Looking for alternatives before I commit to designing the LEM ones in.
>

Allegro micro has some hall-effect based current sensors that I
believe are fully integrated: no fancy PCB design required:

http://www.allegromicro.com/en/Products/Categories/Sensors/
currentsensor.asp

2007\05\16@090642 by alan smith

picon face
I'll need to look thru my old boxes to see if I kept the samples and data sheets....its just where are the boxes.....soon as I can, I'll look for you and let you know.

"Alan B. Pearce" <RemoveMEA.B.PearcespamTakeThisOuTrl.ac.uk> wrote:  >duh.....Sensirion also makes those,

Oh, do they, I can find only humidity and temperature sensors on their site.
Do you have a reference? Looking for alternatives before I commit to
designing the LEM ones in.

2007\05\16@091150 by alan smith

picon face
Thats what I have right now is a hall sensor and that feeds to a small gain stage.  The issue is, for an AC waveform, that the output mimics the AC and rides on a 2.5V (half Vcc) offset.  Its the matter of detecting when a very small current is flowing.  Of course, now the issue is that someone else brought up...the new Cali laws that require SMALL current flows for wall warts (ie...switchers and not just cheap linear warts) the ability to detect them may be even more difficult.  I've convinced my client that this may either have to change in his overall business plans or we may need something more mechanical rather than non-contact electronics.  Its been one of these projects where it sounds so simple on the outset and grows in difficulty during the design stage.
 
 So, for now....I'm leaving in the Allegro hall sensor and op-amp and just see if I can function with that or just....leave that piece out.  Its not the most critical part of the design.

William Chops Westfield <westfwEraseMEspam.....mac.com> wrote:
 
On May 14, 2007, at 7:50 AM, Alan B. Pearce wrote:

>> duh.....Sensirion also makes those,
>
> Looking for alternatives before I commit to designing the LEM ones in.
>

Allegro micro has some hall-effect based current sensors that I
believe are fully integrated: no fancy PCB design required:

http://www.allegromicro.com/en/Products/Categories/Sensors/
currentsensor.asp

2007\05\16@093742 by Alan B. Pearce

face picon face
>I'll need to look thru my old boxes to see if I kept the
>samples and data sheets....its just where are the boxes.....
>soon as I can, I'll look for you and let you know.

OK, appreciate that. Meanwhile I have had a look at the datasheets for the
Allegro Micro ones someone else pointed me at, and they are similar, except
they all contain the "sense wire" as a loop through the device. I like the
LEM ones as you can adjust the sensitivity by putting more "turns" around it
with tracking. I haven't yet figured out if one could do that with the
bottom end Allegro device.

2007\05\16@094251 by Alan B. Pearce

face picon face
>So, for now....I'm leaving in the Allegro hall sensor and
>op-amp and just see if I can function with that or just....
>leave that piece out.  Its not the most critical part of the design.

Another option would be to use a second stage of gain purely for detecting
very small currents, and when that stage saturates (or the output is larger
than some value below saturation) then look at the output of the earlier
stage (I assume this is some form of metering application).

As you are using Allegro devices, how sensitive are they to nearby magnetic
fields? I haven't gone digging in the datasheets and app notes for detailed
info as yet, as this project is still in the incubation stage.

2007\05\16@110744 by Mark Scoville

flavicon
face
I'm jumping in really, really late... sorry.

Have you considered using something like a GFCI type of detector? If what
you are after is an outlet that detects when current is being drawn I would
think using a GFCI type circuit (Only 1 AC line thru the core, of course)
might have some merit.

As I said, late on this one, so if this is totally off the mark (or already
been discussed) then just disregard.

-- Mark

> {Original Message removed}

2007\05\16@153050 by Bob Axtell

face picon face
Alan B. Pearce wrote:
>> So, for now....I'm leaving in the Allegro hall sensor and
>> op-amp and just see if I can function with that or just....
>> leave that piece out.  Its not the most critical part of the design.
>>    
>
> Another option would be to use a second stage of gain purely for detecting
> very small currents, and when that stage saturates (or the output is larger
> than some value below saturation) then look at the output of the earlier
> stage (I assume this is some form of metering application).
>
> As you are using Allegro devices, how sensitive are they to nearby magnetic
> fields? I haven't gone digging in the datasheets and app notes for detailed
> info as yet, as this project is still in the incubation stage.
>
>  
I am using the +/- 50A version current sensor from Allegro. I am very
impressed. I have NOT noticed
any effects from nearby PCB traces or cables placed near it.

I am using it to monitor motor current, and because of the DC motor
driver's pulse controller, I have to
use a RC network to clean up the output, but it really works well.
Priced at about $6 USD.

I only wish there were a smaller version of this, say +/- 5A instead of
50A. Oh well.

--Bob

2007\05\16@183142 by alan smith

picon face
I've thought of that....but not sure how easy that would be to impliment into this particular design but I need to look a little deeper on it

Mark Scoville <EraseMEmscovillespamunicontrolinc.com> wrote:  I'm jumping in really, really late... sorry.

Have you considered using something like a GFCI type of detector? If what
you are after is an outlet that detects when current is being drawn I would
think using a GFCI type circuit (Only 1 AC line thru the core, of course)
might have some merit.

As I said, late on this one, so if this is totally off the mark (or already
been discussed) then just disregard.

-- Mark

> {Original Message removed}

2007\05\16@183325 by alan smith
picon face
I'm not sure how sensitive, but I would guess if there is a strong nearby field, it would affect it.  Next time the Allegro FAE comes around, I'll ask him that.  I
 
 
"Alan B. Pearce" <RemoveMEA.B.PearceEraseMEspamEraseMErl.ac.uk> wrote:
 >So, for now....I'm leaving in the Allegro hall sensor and
>op-amp and just see if I can function with that or just....
>leave that piece out. Its not the most critical part of the design.

Another option would be to use a second stage of gain purely for detecting
very small currents, and when that stage saturates (or the output is larger
than some value below saturation) then look at the output of the earlier
stage (I assume this is some form of metering application).

As you are using Allegro devices, how sensitive are they to nearby magnetic
fields? I haven't gone digging in the datasheets and app notes for detailed
info as yet, as this project is still in the incubation stage.

2007\05\17@002527 by Vasile Surducan

face picon face
Why don't you buy a cheap phase detector and take a look inside?
It need only get close (one cm or so) to the phase wire and it's lighting a LED.
And it's not current dependant.


On 5/10/07, alan smith <RemoveMEmicro_eng2spam_OUTspamKILLspamyahoo.com> wrote:
{Quote hidden}

> -

2007\05\17@040142 by Alan B. Pearce

face picon face
>I only wish there were a smaller version of this, say +/- 5A
>instead of 50A. Oh well.

The ACS712 comes in a 5A version, SO-8 package, without the massive lump of
metal that the other parts have.

2007\05\17@061809 by Vasile Surducan

face picon face
On 5/17/07, Vasile Surducan <RemoveMEpiclist9TakeThisOuTspamspamgmail.com> wrote:
> Why don't you buy a cheap phase detector and take a look inside?
> It need only get close (one cm or so) to the phase wire and it's lighting a LED.
> And it's not current dependant.

http://www.chauvin-arnoux.com/Produit/Famille_detail.asp?idFam=1957&idPole=1

{Quote hidden}

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