×
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

Using 5VDC sensor as analog input

Using 5VDC sensor as analog input

Using 5VDC sensor as analog input

(OP)
I would like to use a relative humidity sensor which operates on 5 Volts DC, and has a linear voltage output of 0.75v to 3.75v based on %RH.

1.  What's the best/least expensive way to supply the sensor with 5 VDC?

2.  Can the PLC interpret the input voltage if the sensor is powered from a separate source?  If so, how?  Could this be accomplished by "grounding" the neutral of the PLC power supply, to the negative of the 5 VDC, so that both have the same reference?

Nic Van Engen
Electrical Technician

RE: Using 5VDC sensor as analog input

1) Depends on what is natively available already.

2) Yes you just tie the two grounds together so the sensor and the PLC are working from the same reference.

Keith Cress
Flamin Systems, Inc.- http://www.flaminsystems.com

RE: Using 5VDC sensor as analog input

How much current does the sensor require? If it is less than a few hundred mA you could hang one of the 78x05 series regulators off the 24V PLC supply.

RE: Using 5VDC sensor as analog input

Hiya-

Just a quickie to expand upon ScottyUK's fine suggestion.

Well, not JUST a 7805ish regulator.  A dropping resistor
to bring the input voltage down to a "reasonable" level
under max. current draw (think like 8VDC some regulators
drop out at 7VDC in), a couple of bypass caps. (0.01 uF)
would be nice too.  A heat sink might be nice too.

Alternatively, you could go with a "wall wart" power
supply available from many surplus houses if you want.
I've seen them in my local "junk shop" places.  Sometimes
it's just easier to use something "found".  Most wall
wart and "brick" supplies have their ratings stamped on
the case.  You might even have something around the
place already.  

I guess that what I'm saying is that even if you do
send the broken electrical/electronic device to the
recycle process, it might be worthwhile to keep the
power supply assoicated with it.

I've got a few 5VDC 1A "brick" supplies that came from
old HP probes that were customer returns.  They come
in handy to be sure.

  Cheers,

   Rich S.

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