Current limitation and indication

[MrEmbedded]

Hi all!
I currently work with electrical muscle stimulation and need some advice on electrical safety and indications.
I will be working with opto-couplers with an output of maximum 40 mA, I therefore need an electrical component that indicates if the current is higher than the maximum allowed, as an AD converter but with current instead of voltage. Does anyone have any suggestions for such a component?
The second problem I have is similar but I need to know if the current that passes through a conductor is too small (below a given amount of current). Any suggestions for this application?
Kind regards,
mr_embedded

 

[MacGyverS2000]

I need to know if the current that passes through a conductor is too small (below a given amount of current).

A current sense amplifier and an ADC would get you what you need here.



Dan - Owner

http://www.Hi-TecDesigns.com

 

[VEBill]

"...an AD converter but with current instead of voltage..."

V=I*R

To measure current, typically a low value resistor is placed in series and the voltage ganerated across the resistor is measured. There are other solutions, but this is the most typical.

The series resistor has to be large enough value (ohms) to generate a measureable voltage (including attention to the magnitude of the LSb [Least Significant bit] for your AD), and it has to be small enough value so as to not drop too much voltage.

Once you can measure the current, then the measurement will indicate if it's too high or too low. For the low end measurements, you really need to consider the LSb issue mentioned above.


PS: If this is being used on live humans, then there are many very serious safety implications to consider.

 

[dbaird]

Take a look at:

http://www.redlion.net/Products/Groups/DCVolt/PAXD/Docs/04024.pdf

David Baird

Sr Controls Designer
EET degree.
Journeyman Electrician.

 

[DPolak]

HI.

Where do you need to measure this current? on the output side of opto?
Do you need to go thru isolation barier with your current reading.
Block diagram or partial schematic will help.
If your DSP is on the "input side" of opto, and you need to measure current on "output side" of opto - this will not be as easy as one resistor.
More details please, then "we" may help...

thx

 

[MrEmbedded]

First of all! Thank you guys for your help.

DPolak: The current will be measured on the "output"-side I will try to post a schematic next week for further details.

Cheers!