Detecting AC current with a micro controller

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Hi,  I have an application that among other things has to detect the
current of an industrial machine.  Basically the micro controller has
to determine if this machine is idle (drawing low current) or in use.
I do not have to measure exact current use.

Does anyone have suggestions as to how I would do this?

Thanks for any help.

Bradley

Re: Detecting AC current with a micro controller
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A "clamp" amperemeter around one (or more) of the the power supply
lines.  That's a device measuring the current going through a ring by
the magnetic field it generates.

--
Hans-Bernhard Broeker ( snipped-for-privacy@physik.rwth-aachen.de)
Even if all the snow were burnt, ashes would remain.

Re: Detecting AC current with a micro controller
On 11 Nov 2003 18:35:57 GMT, the renowned Hans-Bernhard Broeker

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The "or more" could be a problem. If it's a single-phase device then
the current transformer will output a voltage proportional to the sum
of all the currents going through the toroid. Unless there's a serious
problem with the machine (a ground fault) the current going in equals
the current coming out, so the net is zero output voltage!  

A current transformer can be used for this task. It will provide
isolation. A clamp ammeter is just a current transformer and meter
with a core that can be opened to put around the wire. Be sure to put
a load resistor on the current transformer output or the voltage can
get undesirably high. A Rogowski coil is another possiblility.

Best regards,
Spehro Pefhany
--
"it's the network..."                          "The Journey is the reward"
snipped-for-privacy@interlog.com             Info for manufacturers: http://www.trexon.com
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Re: Detecting AC current with a micro controller


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Current transformer ot optocoupler with LED with current-limited circuit and
phototransistor.

Re: Detecting AC current with a micro controller
You could convert high voltage signal to low with resistors or galvanicaly
isolate it from microcontroller and supply that proportional low voltage
signal
to the microcontroller pin and sample that pin number of times per minute,
and if counted number of samples high were > X then you have power on
that line othervise no power.

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R: Detecting AC current with a micro controller
see www.coilcraft.com for example
current sensor

by

snipped-for-privacy@posting.google.com...
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Re: R: Detecting AC current with a micro controller
Hi
 One should note that the peak current my not be in
phase with the voltage. Using things like a zero-cross
detector to synchronize the processor to the line
my not give a clear current picture if the load
has a lot of reactance. You might need to hunt for
the peak.
Dwight

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Re: Detecting AC current with a micro controller
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Use a hall current sensor from Allegro or LEM or some such.  You'll get
a voltage output (0...5 V, for example) and almost any current range
(up to kA's).  The "downside" is that these sensors are too accurate for
you, but I hope you don't mind.. :-)

  -jm

Re: Detecting AC current with a micro controller

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A company called Solid State Control, SSACI, makes a device
that will do want you want. Yuoe set a trip point and a delay time
and you have a relay contact output.

Check out : http://www.ssac.com/standard/ff-sen.htm

Click on the ECS Series link.

MR
?????




Re: Detecting AC current with a micro controller
Hi, one of those little pics will do this easily.All you need is a current
transformer/bridege rectifier/burden resistor to provide the signal the ad
input of the pic. Then sample continously, store/add/ average enough samples
for your line frequency, even TRMS is not hard to do, compare the result to the
reference value and drive your output bit.

Re: Detecting AC current with a micro controller

    Some 10 years ago I did a self-reporting power meter for a municipal
utility.  This task is not as easy as it seems.

    Not only is there a power factor to confuse but loads aren't necessarily
even a sine function!  Some power controllers use SCR's which chip the
sine into a varying number of degrees, other loads like arc welders have a
huge initial current spike, etc.

    If you want to actually measure power then you'll have to integrate the
actual signals before digitization.  Some of those spikes can be in the
nanosecond and microsecond range, if you can relegate integration to
hardware your computational horsepower requirements become much less
severe.

    Since you don't need exact power just use a current transformer then
full-wave rectify (without diode drops!) and integrate.  That output can
be measured by a slow 8-bit micro with fair accuracy.

On Tue, 11 Nov 2003 09:50:53 -0800, Bradley wrote:

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-- Regards, Albert
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