Circuit to measure difference in temperature on the human body

[zeyad]

i am looking for a circuit to measure difference in temperature (+ or -) on the human body.
the distance is between two thermal sensors is about 5 cm, and the reading range is between 0 -50 Celsius.
i have a circuit but i need to make it more sensible. i was thinking of adding differential amplifier.
any one has got an idea of how to improve that
many thank in advanced

[ArticCynda]

A typical setup for this kind of application would be to use a Wheatstone bridge, and using PTCs or NTC instead of the LM35 in your design.

[zeyad]

hi ArticCynda
thanks for your reply
can you show me please in sketch how to do that
what i am looking for is attached

[zeyad]

hi ArticCynda
is that what you mean?

[ArticCynda]

Yes that is the principle, measuring the voltage between the two sensors directly.

[zeyad]

does this circuit need any amendments ?

[zeyad]

i am stuck with the circuit because i don't know how to connect the temperature sensor because it has 3 pins, and i don't know which one is going to the human body
i will be very grateful if anyone can redraw the circuit for me and i don't know whether the circuit will work or not.
this what i want to create
http://www.autospeed.com/cms/article...art-2&A=111357

[Audioguru]

Are you trying to find a dead part on a human body because it is colder than the alive parts of the body?
Do you think that diabetes or cholesterol will cause poor blood circulation to a part of a human body causing it to be cooler than the warmer parts with good circulation?

[zeyad]

Hi Audioguru
yea i would like to connect the two sensors on both side of the Vertebral column and see if there is a problem in the vertebra itself.
have you got an idea how to reach that?

[Audioguru]

The vertebra is the spine which is bone. If there is a problem with the vertebra (bent to one side maybe) then I do not think it will affect the temperature which is almost the same everywhere since the warm blood circulates.
Maybe a muscle spasm on one side will cause that side to be warmer than the passive other side.

[zeyad]

yes your are right.
when i repair the muscle it will repair the vertebra

[jiripolivka]

In my opinion similar circuits are not suitable to tell the temperature difference correctly. Attaching a temp sensor on human skin is unstable and circuits affected by DC power supply, RF interference etc.,
The best is to use a thermal camera which can generate a temperature pattern from which an experienced doctor can deduce the temperature difference across the observed area as well as the dynamic changes.
Medical thermal cameras are in use for breast temperature observation ,with a good resolution. I would try this approach rather than playing with circuits.

[zeyad]

that is good idea but it won't be easy to detect small area on the back by Medical Thermal Camera
check this link
https://www.youtube.com/watch?v=9rjZ4jK1dwk

[andre_teprom]

I agree with jiripolivka approach, and even add another inconvenience on using standard sensors, which is the fact that contact temperature sensors require some time to the heat spread into the probe, therefore requiring a long time to 'scan' the entire surface of interest.

[zeyad]

that will be very expensive and i am looking for affordable price

[Audioguru]

I went to a free Chiropractic checkup with a new chiropractor. He measured the resistance of my back muscles and some places he pressed harder. Of course the areas he pressed harder had a reduced resistance that he said needed an "adjustment".
He gave those areas a free adjustment which nearly sprained them.
He gave me the largest x-ray I have ever had from the top of my head to the bottom of my feet. My spine was not perfectly straight and he said he could fix it (I had no problem with it) for $1500.
He tried to sell me some of his home-made "remedies" that would cost another fortune.
I never went back to him nor to another Chiropractor.

[andre_teprom]

that will be very expensive and i am looking for affordable price

Ok, don´t need necessarily to be a 2D thermal reader, but just an optical thermometer that is capable of promptly scan the temperature without the delay mentioned above.

[zeyad]

have you got an idea where i can get good and reasonable one?

[andre_teprom]

have you got an idea where i can get good and reasonable one?

I´m not sure if exists some commercial module so that you can order and connect to your circuit or if you have to develop it yourself, but the working principle is based on reading of 2 IR thermal transistors and comparing the result with a table. A cheap microcontroler would be able to handle that.