- Mon Apr 10, 2017 12:59 pm
#64806
Hi
I am currently building a reflow oven and bought a Thermocouple Type K with a MAX6675 on AliExpress.
As I wanted to calibrate the sensor I put it in boiling water together with a pt1000 high precision thermometer.
The pt1000 showed 98.3C as I would expect at my elevation above sealevel.
But the Thermocouple showed me 141C, which is totally off. At room temperature they are nearly identical.
I suspect that this thermocouple is not of type K but of type J or E. I am using the simple MAX6675 library which is available in the arduino IDE (via Eclipse).
I have searched for some time now and I cant find any source which gives me a conversion formula for converting different TC type values.
The only formula I found was this one for converting K to J:
JTemp = 1E-15*x^6 - 4E-12*x^5 + 2E-09*x^4 - 7E-07*x^3 + 1E-05*x^2 + 0.7696*x + 0.3797
But the value was still too high (111C). So I think it is of type E, but where can I found a formula to convert the values.
I could calculate from the direct reading in the MAX6675 class, but with which value?
(In the MAX6675 class the read value is multiplied by 0.25 for the Celsius value, dont know where this value comes from ?).
Is there maybe an easier way to calibrate it via a formula and value at freezing point and boiling point of water ??
Any hints would be appreciated!
thanks in advance
regards
Erich
I am currently building a reflow oven and bought a Thermocouple Type K with a MAX6675 on AliExpress.
As I wanted to calibrate the sensor I put it in boiling water together with a pt1000 high precision thermometer.
The pt1000 showed 98.3C as I would expect at my elevation above sealevel.
But the Thermocouple showed me 141C, which is totally off. At room temperature they are nearly identical.
I suspect that this thermocouple is not of type K but of type J or E. I am using the simple MAX6675 library which is available in the arduino IDE (via Eclipse).
I have searched for some time now and I cant find any source which gives me a conversion formula for converting different TC type values.
The only formula I found was this one for converting K to J:
JTemp = 1E-15*x^6 - 4E-12*x^5 + 2E-09*x^4 - 7E-07*x^3 + 1E-05*x^2 + 0.7696*x + 0.3797
But the value was still too high (111C). So I think it is of type E, but where can I found a formula to convert the values.
I could calculate from the direct reading in the MAX6675 class, but with which value?
(In the MAX6675 class the read value is multiplied by 0.25 for the Celsius value, dont know where this value comes from ?).
Is there maybe an easier way to calibrate it via a formula and value at freezing point and boiling point of water ??
Any hints would be appreciated!
thanks in advance
regards
Erich
