MAX31855 K-Type Thermocouple SPI Readings Fluctuate When Touched—Why?

hi all,
In my application i am using k type thermocouple ic which is MAX31855 interfaced with freescale uC through SPI, its works fine but when i touch the thermocouple temperature value will changed randomly i dont know why. kindly help me to solve the issue

Regards,
santhoshkumar.

Hey Santhoshkumar,

Don't you want the temperature to change when you touch it? Your body temperature is different than ambient temperature so of course the value will change.

Or are you talking about when you touch the device itself?


Matt

Hey MATTHEW KENNEY,

Thanks for the reply,What you said is right,its not a problem for changing from ambient temperature to body temperature,Actually this application is used to monitor the zinc bath its minimum temperature is 400 degree and maximum range is nearly 900 degree.Once i dipped the thermocouple into the bath value will oscillate form 350 to 400 degree but the actual temperature is 390.Kindly suggest me to solve the issue.

Thanks & regards,
santhoshkumar.

Do you have have the part number for the external thermocouple that you are using?

Have you tried stabilising the signal by a small capacitor across:
1) the sensor;
2) the input terminals to the system ?

Are you certain the thermocouple you are using is rated for that temperature ?

This may help also:
https://en.wikipedia.org/wiki/Thermocouple#Type_K