×
INTELLIGENT WORK FORUMS
FOR ENGINEERING PROFESSIONALS

Log In

Come Join Us!

Are you an
Engineering professional?
Join Eng-Tips Forums!
  • Talk With Other Members
  • Be Notified Of Responses
    To Your Posts
  • Keyword Search
  • One-Click Access To Your
    Favorite Forums
  • Automated Signatures
    On Your Posts
  • Best Of All, It's Free!
  • Students Click Here

*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.

Students Click Here

Jobs

Current limitation and indication

Current limitation and indication

Current limitation and indication

(OP)
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
 

RE: Current limitation and indication

Quote (MrEmbedded):

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

RE: Current limitation and indication

"...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.

 

RE: Current limitation and indication

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

RE: Current limitation and indication

(OP)
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!

Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

Red Flag Submitted

Thank you for helping keep Eng-Tips Forums free from inappropriate posts.
The Eng-Tips staff will check this out and take appropriate action.

Reply To This Thread

Posting in the Eng-Tips forums is a member-only feature.

Click Here to join Eng-Tips and talk with other members!


Resources