×
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

Signal Aquisition/Signal monitoring

Signal Aquisition/Signal monitoring

Signal Aquisition/Signal monitoring

(OP)
I am curious if anyone has any good ideas where I can get a "high voltage" input analog multiplexer/demultiplexer.  Preferably the device would be 16:1 (I could live with 8:1).  I am looking for a voltage input range of 0 to 100VDC.  Thus far it has been a quest for the holy grail.
Any input would be most appreciated.
Thank you.

RE: Signal Aquisition/Signal monitoring

What resolution do you need?

RE: Signal Aquisition/Signal monitoring

(OP)
Hmm...
Resolution.  I don't quite understand what you mean.
As far as the signal integrity through the MUX, it is not a big concern.  The smallest voltage I will probably see is about 1-5VDC.  It is the larger voltages I am concerned about.

RE: Signal Aquisition/Signal monitoring

scale it down and if needed scale it up again.

RE: Signal Aquisition/Signal monitoring

That high a voltage requires either:
>  scaling, as mentioned above
>  relays
>  DIY mux using high voltage Mosfets

TTFN

RE: Signal Aquisition/Signal monitoring

Hi, you can use opto isolators to do this.

RE: Signal Aquisition/Signal monitoring

(OP)
Thank you all mindful engrs!!!!!

I have thought about all you have proposed.
Of course in the real world, we have to think about cost.
I should have mentioned earlier that my goal was to measure 128 channels.  16:1 or 8:1 MUX/DEMUX would work as cascading them together but I needed the advice on the "seed".  Imagine scaling down the 128 lines before it got to the MUX/DEMUX.  That is a lot of components if I were to multiply by 128. : )
Photo-MOSFET relays are a god send but they are expensive, not only in cost, but real estate on a PCB.

Thank you for all your thoughts.
If you think of anything more please contact ASAP!

RE: Signal Aquisition/Signal monitoring

Like it or not, you're going to have to scale down each input. However, all this takes is a pair of resistors on each input. This will take up a lot less room than relays or high voltage mosfets. That's because, even if you multiplexed at the high voltage, you're going to have to scale down after the switch anyway as you will not be able to find a 100V input ADC anyway. The only real kicker here is the accuracy you need. If you need better than 1%, you're going to have to buy more expensive resistors, select them or add trim pots.

RE: Signal Aquisition/Signal monitoring

The relay solution is probably the easiest to implement.   You can get Opto SSR's in SOP packages to minimize your board space.  I would recommend looking at the 400V telecom relays, they are overkill voltage wise, but the high volumes keep the price of those relays low.  NEC makes some good ones.

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