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Sensor Forum ZTP 135 SR circuit
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Related

ZTP 135 SR circuit

Former Member
Former Member over 13 years ago

I want to have a circuit design and how to use the sensor ZTP 135SR. I  want to apply it to measure human skin temperature and expect the output  to be voltage. I have looked at its datasheet but can not find the  connection schematic. The best I can found is here http://www.thermometrics.com/assets/images/thermopile.pdf but  it does not specify the values (R, C, V). I'm new to electronics, and I  just need a circuit to implement so any help will be welcomed.  Please be specific (like what kind of op amps, or those values), again since I'm a new comer. Many thanks.

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  • Former Member
    0 Former Member over 13 years ago

    did you ever solve your questions on ZTP-135?

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  • Former Member
    0 Former Member over 11 years ago

    Hi, Mark. I see your question dates back more than two years, hope you could solve your doubts in the meanwhile.

    Anyway you can try this: http://portal.fke.utm.my/fkelibrary/files/dhiyafarhanabintiramli/2012/404_DHIYAFARHANABINTIRAMLI2012.pdf

    The circuit used is exactly the same you are referring to.

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  • Former Member
    0 Former Member over 10 years ago

    I have been working with the ZTP 135 SR thermopile for the past couple months and I am having difficulty with the calibration of the thermopile component of the sensor. Resources on circuit design for thermopiles are abundant but the calibration is not and is usually specific to the instrument. This is the only forum I have found speaking about the ZTP 135 SR. @michelangelo coca  I have read that paper and have duplicated its construction. The rest of the reading is broken english and not really helpful for the calibration. I have been able to calibrate the thermistor component using the datasheet resistance measurements at specific temperatures and using the relationship of resistance to temperature. 1/T = A + B*log(R)+C*log(R)^3 where T is the temperature in kelvin and R is the resistance of the thermistor.  The constants A B and C I solved for using simultaneous equations three unknowns on Matlab. The thermopile calibration is more difficult. I cannot seem to get the constants for the equation Vo= k * ( To ^(4-g) - Tamb ^ (4-g)) where Vo is the voltage output of the sensor, To is the object temperature, Tamb is the thermistor reading temperature for the cold junction, k is the proportionality constant and g is a correction to the power law.

         I have used one rail to rail OP amp but have seen that using an additional amplifier for summing is used to add the voltage from the thermistor to the output voltage of the thermopile .  Running this on arduino yun microcontroller thought I could just do this in the program adding the output of thermistor circuit to the output voltage of the thermopile. Any ideas of how to get proper output voltage for the thermopile calibration equation so I can solve for the constants k and g? I can attache circuit diagram and script for arduino if needed.

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  • clem57
    0 clem57 over 10 years ago in reply to Former Member

    Robert Peter Oakes or DAB can you help?

    Thanks,

    Clem

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  • Robert Peter Oakes
    0 Robert Peter Oakes over 10 years ago

    So the math illudes me a bit, it has been a very long time since I had to do that kind of math image

     

    but examining the circuit and assuming it works (It looks like it should), the opamp has a gain of atleast 100 or possible way more in the configuration shown, the thermopile will generate only a small voltage (mV) so the opamp is needed no matter what and the ouput of this should be sent to the micro, in the same way as the origional project did, unless you have a micro that has a gain stage that can amplify over 100* then you must use the op amp as shown int he sample schematic, your micro will nevery have enough resolution to resolve the temperaure without it. And if your doing the op amp, you may as well hook up the thermister as shown too, you can still read the thermistor output but it will automatically compensate for ambient without the micro

     

    the thermistor output range is significantly reduced by limiting its supplied voltage by strapping it across R2 which is in the middle of a resistor divider chain 1K, (R2) 200ohm, 200ohm,  and this configuration is designed to limit the compensation to a similar range as the thermocould will generate I would think.

     

    based on this code shown and the result graphs, the input to the micro is about 1V ish, so you could increase the value of R6 to maybe 200K to increase the gain and improve the overall dynamic range, could even go to perhaps a 470K if your feeding into a 5V controller and the reference is set to the VCC (Default on an UNO), remember the PIC will have been using a different VREF that equates to the 1023 reading so you will have to adjust the value when running on the Yun

     

    the code clearly shows the math involved and would require very little change to get it working from the PIC it was written for, there bot C and to get the LCD working you would just replace it with the approprite library

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  • Former Member
    0 Former Member over 10 years ago in reply to Robert Peter Oakes

    The circuit works fine and I get output to the microcontroller. The problem is that the output is not linear. The data that the thesis above states is a linear correlation between the output voltage and temperature but this cant be for this kind of sensor which needs to be some form of power function. Do you know of anyone that calibrates thermopile sensors? The constant g or gamma from my above equation is an adjustment to the power 4 so must be in a range from 0 to 4 and the k constant I have seen on the order of 10^-4. I large error in the voltage will be significant to the calculation of the Temperature which I would like to be within +- 1 degree Celsius. 

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  • garypty
    0 garypty over 7 years ago in reply to Robert Peter Oakes

    I know this post is more than three years ago, but I have a similar issue. The hyper-link above are broken. Could you kindly show the schematics that you are talking about? Thank you very much!

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  • qaibou
    0 qaibou over 7 years ago in reply to garypty

    Me too, I have the same problem, I can't open them and I don't have enough information about this sensor

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