Using K-type thermocouple to measure human body temperature

Question

Is there anything I need to he aware of when using K-type thermocouples?

I got the idea by touching the probe. I can get a reading when measuring temperature for 30 seconds using a DMM. A commercial electronic thermometer needs around minutes for the same result.

This gave me an idea to make a device which will use K-type thermocouple to quickly measure temperature. On the other hand if it was so simple to measure temperature, why don't the commercial thermometers produce their result faster.

I have a feeling that I'm missing something important here.

So my question is: Are there any non-obvious problems I could face when using a K-type thermocouple to measure measure human body temperature?

Answer 1

These themocouples have a tiny spot weld between two thin wires to make the active sensor element, which results in a very low thermal mass. Hence they change temperature quickly, which is the same thing as reacting to temperature changes quickly. As soon as you mount them in a larger substrate or coating (eg to provide a sterile insulation, to prevent breakage, to electrically isolate) you increase the thermal mass, so you have to wait longer for stabilisation.

Answer 2

Thermocouples are not stable enough to measure human body temperature (you want 0.05C accuracy there). It only gives about 1-2C long-term stability.

Platinum PT100/1000 RTD ones are much more suitable and way way more procise.

When you have this extra-accuracy, you can measure target temperature while ovserving how it's rising by extrapolating... This would allow some 1-5sec measurement.

The only way to be faster - IR sensors.

Answer 3

The use of thermocouples is not an easy task if you want to achieve high accurracy (that you need to measure the human body temperature). You also have to measure the temperature of the plug that connects the thermo couple to the DMM because this plug also generates a thermo voltage. To get the right temperature that you measure with the thermo couple you have to consider the thermo valtage generated by the plug.

I think you would go better with a PT-100 or PT-1000.