Shop OBEX P1 Docs P2 Docs Learn Events
IR for reading objects temperature — Parallax Forums

IR for reading objects temperature

ellizardellizard Posts: 106
edited 2007-02-24 20:13 in General Discussion
HI people,

I'm looking for a non touch system to read temperature of an object,
I'm thinking at using an IR fototransistor, with it's sensible area aimed at the object.

It's this feasible?

any idea?

Regards
Stefano

Comments

  • Beau SchwabeBeau Schwabe Posts: 6,571
    edited 2007-02-24 10:40
    Stefano,

    Forest Mimms has an example of doing this using the reflector from a flashlight and substituting the bulb with an IR phototransistor.

    If I remember right, the circuit actually used two IR phototransistors configured in a whetstone bridge where the local or ambient
    temperature was used as a reference to calculate the remote temperature based on the result of an Op-Amp output.

    ▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
    Beau Schwabe

    IC Layout Engineer
    Parallax, Inc.
  • ellizardellizard Posts: 106
    edited 2007-02-24 10:59
    HI Beau,

    Thanks for the prompt reply,

    Any more links?
    I have no access to Mimms book and a search on the net gave me only references to the book

    Regards
    Stefano
  • Beau SchwabeBeau Schwabe Posts: 6,571
    edited 2007-02-24 18:25
    Stefano,

    I was going from memory, I'll see if I can find something...

    Edit


    There are a few links here that use a thermister as the sensing element rather than a IR photo transistor in a wheatstone (whetstone?) bridge configuration.

    www.thinking.com.tw/db/pdf/ntc/Application.pdf
    www.bbc.co.uk/scotland/education/bitesize/higher/physics/elect/analogue3_rev.shtml
    www.selcoproducts.com/PDF/ntc_pdf/ntc_appl_notes.pdf


    As far as focusing IR radiation, this can be done in a similar way that you would focus visible light.

    www.glolab.com/focusdevices/focus.html


    Note: Something I might point out. Most wheatstone (whetstone?) bridge configurations don't account for any local ambient temperature that might affect the
    temperature reading. A simple way to compensate for this is to use two sensors, one in the top and one in the bottom leg of the bridge and allow only
    one sensor to be exposed or focused to the remote IR interference you want to measure..

    ▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
    Beau Schwabe

    IC Layout Engineer
    Parallax, Inc.

    Post Edited (Beau Schwabe (Parallax)) : 2/24/2007 7:55:29 PM GMT
  • FranklinFranklin Posts: 4,747
    edited 2007-02-24 20:13
    Take a look at www.melexis.com one of their devices was used in an article in the Feb 2005 Circuit Cellar magazine.

    ▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
    - Stephen
Sign In or Register to comment.