PT100 circuit with limited temperature range

[banjohamster]

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

 

[MacGyverS2000]

See this thread:

http://www.eng-tips.com/viewthread.cfm?qid=165067&page=1

Dan - Owner

http://www.Hi-TecDesigns.com

 

[itsmoked]

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

 

[ScottyUK]

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!

 

[IRstuff]

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

 

[itsmoked]

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

Keith Cress
kcress -

http://www.flaminsystems.com

 

[banjohamster]

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!

 

[itsmoked]

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