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Pt1000 amplified for arduino

Discussion in 'Microcontrollers, Programming and IoT' started by Kvdeurzen, Jan 13, 2014.

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  1. Kvdeurzen

    Kvdeurzen

    3
    0
    Jan 13, 2014
    Hi all,

    First I've got to admit I'm new to this forum and am not schooled in electronics, please forgive me if the following is a Noob question or in case I could have found theanswer elsewhere (I haven't been able to findit).

    I'm trying build a brewing vessel for beer. I'm controlling my heating element with an Arduino through an Arduino. For temperature sensing I'm converting my setup to rely on a pt1000. The problem is that I willneed to amplify the signal to get a reliable accuracy. For this I think i need to employ opamp's. Currently I'm trying to figure out a circuitthat would work, but haven't been able tofindsomething workable online.

    As far as I've understood I should use a differential amplifier. I've drawn a circuit with a differential amplifier, where I try to make to make V1 equal to V2 when the PT1000 is at its lowest (C=0, V2 = 1/2 Vcc). The amplification would than be, R3/R2. However if I than attach Vout to an analog input I'm receiving a static value (analogin = 174-175).

    I'm using an LM358n as the opamp. R1 = R3 = 330. R2 = 82. A= 330/82 =4.

    Does anyone know what I'm doing wrong?
     

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    Last edited: Jan 13, 2014
  2. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    25,271
    2,718
    Jan 21, 2010
    Firstly, you're clearly from Australia because that diagram looks upside-down to me.

    Secondly if you're using a platinum temperature probe, you should have a low current flowing through it to reduce self-heating.

    removing R3 (both of them!) will make this into a comparator.

    Your second R3, the one going to the negative supply rail is incorrect. It should go to your 0V reference. Once you've done this, increasing the R3 in the feedback lop will increase the gain and thus the voltage swing with temperature. You may have to adjust the voltage divider or the fixed resistor in series with the platinum sensor to get a sensible "0" point.
     
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