Jon Danniken wrote:
Winston wrote:

(...)

I've used the Allegro ACS756 in some extremely low impedance
applications where a sense resistor caused power supply
instability.
http://www.allegromicro.com/en/Produ...0756/index.asp

Highly recommended, though you will need to normalize it's
output. (I did that automatically with DAQ gear.)

For seven bucks, it is a great value.

http://search.digikey.com/scripts/DkSearch/dksus.dll?lang=en&site=US&WT.z_homepage_link=hp_go _button&KeyWords=ACS756&x=0&y=0

Ooh, and up to 100 amps, I like that. Curious as to what you mean by
"normalize it's output", though; is this referring to the "typical
application" diagram given in the datasheet

Short version: It is a 'single ended' output without a
negative supply. You need to subtract Vcc/2 from the
output and multiply the result by 25 to arrive at
the real reading.

Long version:
Let's say you power it from 5.0000 V DC.
Zero amperes will be represented by a 2.50 V (or Vcc/2)
reading between output and ground.

An output of 2.54 V would thus indicate a current flow
of +1 A and an output of 2.46 V would indicate a current
flow of -1 A.

2.54 V - 2.50000 V = 0.04 V
0.04 V * 25 = 1.0 A

2.46 V - 2.50000 V = (-0.04 V)
(-0.04 V) * 25 = (-1.0 A)

With the data acquisition gear I used, I sensed the
Vcc going to the device and wrote an equation that
automatically did all the arithmetic for every reading.
The log files all showed the current flow in amperes.

It worked a treat!

If you wanted 'cheap and cheerful', you could put a
precision voltage divider between sensor Vcc and
ground to provide your multimeter a 'virtual ground',
then just mentally multiply the reading you see on
the DMM display by 25 to arrive at real amperes.


--Winston