Re: Current Sensor
 

ACS750 see my previous post.

Appears FRC doc had error- 150uF shown as an output filtering.
(seemed logical for the 2kHz PWM square wave noise)

Allegro doesn't recommend such a large filter.

The 150uF tantalum may rather have been intended to filter the +5V power !!
(I received no replies to that post question)

Tantalum capacitor polarity can be safely verified using a bench power supply
current limited to a few mA.
Set PS to 6V.
No harm if Cap backwards.
If Backwards the voltage just goes down to a volt or so at the current limit.
(if there were no current limit tantalum caps can explode like a fire cracker
which is dangerous. (less drastic, cap gets warm to hot, degradiing cap)
If you must use a full lexan shield and will need a lot higher voltage
to force a very high current)
Correct cap orientation, the voltage spikes momentarily resting at 6v, 0 mA.

No bench supply ?
Simulate one.
Using your 5V power source of choice, (RC +5v max is ~1A limited by 7805?)
place a current limit resistor in series with the Cap.
(Rlimit =5v/1mA(.001A) =5k ohms)
Place DMM across Cap., place Cap in both directions)


I'm using 274 ohms in series with ACSout to 150uF for filtering
(~125mS = 3 time constant)
and additional Cap(s) for +5V supply filtering at the sensors.

ACS750 = 20mV output for each Amp sensed.

0A = 2.500V out (ratio, i.e. 1/2 of +5.00 v supply)

Positive current sensed: 2.500 + 20mV/A (512 counts + ...)
Negative current sensed: 2.500V - 20mV/A (512 counts - ....)

Analog scale factor: 5v/1024 counts = 4.88mV/count
Analog zero: 2.5V=512 counts = 0 A
then +-20mV/4.88mV/count per amp sensed analog measurement

+1A = 512counts + (20mV/4.88mV/Count=) + ~4 counts = 516 counts
-1A = 512counts + (20mV/4.88mV/Count=) - ~4 counts = 508 counts

The PWM cables do fit the ACS PCB
though a bit of finess is necessary.

Use of the PWM male crimped pin & housing is advisable for effective strain relief.
Solder the male PWM pins into the outside PCB row.
Using the male PWM connector effects an effective wire strain relief
from vibration, frequent moving/testing/etc.

Direct soldered wires require separate strain relief to avoid wire breaking where the stranded wire becomes stiff with solder.

I'll send/post pictures if requested.

Dale.Hall@ngc.com

Re: Current Sensor
 

I would be obliged if you could post that. I am interested to see what you have to recommend. Our team just cut the male ends off and directly soldered the PWM cables to the PCB.

Re: Current Sensor <cabling/picts>
 

Hay4man & all
Here are pictures of PWM male end
pressed fully into the outer 3 holes of the current sensor PCB
bent flat onto the PCB for firm cementing
then soldered.

The stranded wire crimped PWM connections provide a good strain relief.

If the stranded wires are soldered directly to the PCB
it is important to anchor them
else movement will cause breakage at the stiff solder joint.

A stranded wire joint is vibration resistant if crimped (multi wire suspension)
but when soldered turns into a solid wire joint not preferred for
vibration/movement prone areas, like cars,
cause solid joints are prone to crack and break easily.

Bottom
[IMG]F:\Robotics\2004\75AcurrentHallSensor\P1210044Curr 75Asensor1bott.JPG[/IMG]

Top
[IMG]F:\Robotics\2004\75AcurrentHallSensor\P1210043Curr 75Asensor1top.JPG[/IMG]

picts may not have inserted (my 1st try I did copy/paste below & attach files)
(& they didn't show up in preview) so
email me & I'll send send them direct.

& plse instruct how to insert .jpgs from local HD into posts....
(or to preview replies ?? preview appeared to only be of orig post)

Dale.Hall@ngc.com

Re: Current Sensor <cabling/picts>
 

Dale,
It looks pretty good. Nice job on the insulation wrapper. This is not well stated in the docs, all teams should remember to adequately insulate the board. A big piece of heatshrink works very well.