×
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

PT100 circuit with limited temperature range

PT100 circuit with limited temperature range

PT100 circuit with limited temperature range

(OP)
Hi all,

I'm trying to design a PT100 circuit to range 10degrees to 50degrees into a 0-5V signal. The resistance at 10degrees is 103.9Ohms and at 50degrees is 119.4Ohms, so I need to get a signal out of my board of around 0V when resistance is 103.9Ohms and around 5V when resistance is 119.4Ohms.

I've tried simple circuits like voltage dividers, and op-amp circuits, but I'm running into trouble due to the small difference in the range of resistance I require. Would anyone be able to advise, or direct me to someone who can?

Many thanks,

Ross

RE: PT100 circuit with limited temperature range

Scrap the RTD immediately!  Wrong approach.

Use any of these instead.
LM35
LM34
LM61
LM60
LM335
LM19

They're linear. They cost a fraction of what an RTD costs.  They put out high level signals, unlike RTDs. You can get versions that are C or F if you care.  They need NO highly complex calculations nor even lookup tables.

 

Keith Cress
kcress - http://www.flaminsystems.com

RE: PT100 circuit with limited temperature range

Depends on the environment - electromagnetically hostile places aren't great for an IC to be embedded. More info!
  

----------------------------------
  
If we learn from our mistakes I'm getting a great education!
 

RE: PT100 circuit with limited temperature range

True, but the RTD will need some chips as well, and running long cables will degrade the RTD performance anyway.  While many of ill-effects of long runs can be compensated, they add complexity and decrease the overall performance.

TTFN

FAQ731-376: Eng-Tips.com Forum Policies

RE: PT100 circuit with limited temperature range

Seems we're talking to ourselves as the poster hasn't bothered to join in the discussion.

Keith Cress
kcress - http://www.flaminsystems.com

RE: PT100 circuit with limited temperature range

(OP)
Yes, I'm really sorry about delay in getting back.

Thank you very much for all the replies.  I think the best way forward is to do as itsmoked said and ditch the resistance device and use IC type sensors.  Having looked at some of the datasheets, the 10mV/degC can be easily amplified into the range I want.

Thanks all!

RE: PT100 circuit with limited temperature range

Thanks for coming back banjohamster.

Unless there is some special specific reason you pretty must always want to grab for those devices in the temperature realm they're good for.

Keith Cress
kcress - http://www.flaminsystems.com

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