Hi
what is the best and accurate temperature sensor to measure the human body temperature?
I already try (LM35 and 100kohm NTC thermistrs) but they not too accurate
How accurate do you need?
The LMT87 is specked at +-.3C
omarAlwaadh:
what is the best and accurate temperature sensor to measure the human body temperature?
I already try (LM35 and 100kohm NTC thermistrs) but they not too accurate
Define "accurate".
You can use an accurate analogue sensor, and muck it up with the wrong code.
Or use a simple LM35 with the right code, and calibrate it to 0.01 degrees C.
If you want factory accuracy, use a digital sensor.
Or use this sketch with the LM35, and calibrate yourself.
Leo..
// LM35 temp sensor output connected to analogue input A0
unsigned int total; // A/D readings
float tempC; // Celcius
float tempF; // Fahrenheit
float fudge = 0.001632; // fudge factor for temp calibration | change last one or two digits and re-uplooad
void setup() {
analogReference(INTERNAL); // use the internal ~1.1volt reference | change to (INTERNAL1V1) for a Mega
Serial.begin(9600);
}
void loop() {
// read the sensor
for (int x = 0; x < 64; x++) { // 64(max) analogue readings for averaging
total = total + analogRead(A0); // add each value
}
// temp conversion
tempC = total * fudge;
tempF = tempC * 1.8 + 32; // Celcius to Fahrenheit
Serial.print("The temperature is ");
Serial.print(tempC, 1); // one decimal place
Serial.print(" Celcius ");
Serial.print(tempF, 0); // no decimal places
Serial.println(" Fahrenheit");
total = 0; // reset total
delay(1000); // slows readings
}
consider a higher bit analogue AD converter than the 10bit on the Arduino.
The data sheet offers some means to enhance your circuitry for higher resolution.
Also, familiarize yourself with the multiple components of the term accuracy.
Wawa assumes your chip has little to no hysteresis and has high repeatability and high sensitivity. I believe he is correct in all cases for that particular chip.
if you are just looking at factory specs for chips without any supporting circuitry, you are not taking advantage of all your options. I am not familiar with any that offer much better than +/- 0.5 deg C for the raw chip yet as Wawa pointed out, some work on your part and you can get much higher accuracy.
also, read some of the data sheets from the manufacturers and application notes.
I've used nice digital semiconductor temperature sensors, and they work fine - but often their resolution is poor - only 0.25C or so and the absolute accuracy no better than 1C
You may want better than this.
An ordinary cheap ntc thermistor (eg 10k at 25C) will probably not be very accurate as to it's actual resistance at 25C
- but the characteristic curve eg for a common 3950 type will be - it's built in to the material they're made of.
So calibration is just a matter of measuring the resistance at a known temperature, and putting that value in your code. The source resistor is also not perfectly accurate, so I'd calibrate in the final circuit as built rather than using a meter to just measure the thermistor resistance.
You could always measure both, of course. In that case, since the voltage you get is a ratio, the absolute accuracy of your meter is cancelled out...
Thermistors have the great advantage of having a large change of value for a small temperature change,
ie they're every sensitive - ideal for measuring body temperature within a range of +/- 10C or so.
They also have a low thermal mass - you can get them in 0402 packages from Murata - so they respond quickly.
If you go this way I'd make the source resistance about the same as your expected thermistor resistance in the range of most interest - in your case about 37C. With this value you use the resolution of the A/D to best effect - the curve is steepest there.
regards
Allan
The LM35 with 1.1volt Aref and Arduino's 10-bit A/D has ~1000 A/D values spread over 100 degrees C.
So a display resolution of 0.1C.
With a bit of averaging and calibrating around body temp, it should be better than 0.1C.
At least in a small temp range of room temp to body temp.
Leo..
Just where are you putting this sensor?
KeithRB:
Just where are you putting this sensor?
I don't want to know.....
Hi Leo..
I agree.
Might be painful - or embarrassing - or both.
But the smaller the better... 0402's ??
Allan
My point is that many sensors, especially plastic ones, can not survive being autoclaved, and might have to be disposable.
KeithRB:
Just where are you putting this sensor?
Excellent question, if you are talking medical devices, I would like to have an approved device that is "SAFE" to use in/on the human body.
Have you researched the MEDICAL devices/sensors available.
Thanks.. Tom.... 
I think we need input from the OP before wasting time on thinking about this any more.
Hello,
Is there a temperature sensor can be used to measure human body temperature and it meet medical standards ?
the most sensors i found is batter for measure weather temperature than the body temperature .
The DS18B20 is available in a human-usable package which I imagine would be quite suitable. "Medical standards" is relative term, but a DS18B20 can hardly fail as an under-arm sensor and is certainly accurate enough. I'm sure there are also about 10,000 different models specifically made for medical use, most of which could be pressed into service with an Arduino, and can't be that hard to find. Try Welch-Allyn spare parts desk.
The OP has opened another topic asking the correct question. 8^)
omarAlwaadh:
Hello,Is there a temperature sensor can be used to measure human body temperature and it meet medical standards ?
the most sensors i found is batter for measure weather temperature than the body temperature .
Spare parts for medical instruments are very expensive ... sometimes close to the price of an entire instrument. Depending on your needs, you may find that purchasing an inexpensive medical thermometer such as this and "hacking a cable to a uC" and using temperature probe covers such as this could cut your cost significantly. The assumption of course is that you are not going to make a 1000 of these things.
Ray
PS: I have two of these units laying on the lab bench somewhere ... I found them at one of the "discount/surplus" stores for $1 each.
Please do not cross-post. Threads merged.