Accurate thermocouple amplifier recommendation?

Dear All,

I am working on a project, where I am using thermocouple amplifier Max6675 with my K type sensor.
I bought my Max6676 from alibaba, so I am using a cheap and maybe not so accurate item. The heatsensor is produced by Omron, so it is maybe the best sensor by my level,it has to be good.

I am using an arduino nano(at this moment) for interpreting the data from Max6675 and I am experiencing variable temperature values, but the condition around the sensor and amplifier did not changed.
For example: I measure from 21 to 24 degree Celsius in my room, and I know that K type sensors have just 2-3 degree accurate, but between unchanged environment it is not acceptable for me. The measured values has to be the same, when the circumstances did not changed. Or am I wrong?

I measure the heat in every second, after I make an average from the 60 sec info, and experience this jumping (between 21-24 degree) in the average value. I think something is not accurate enough.

The project what I am developing will manage a cooking system, that is why I am not able to accept this jump between unchanged conditions.

Maybe I have to buy a more expensive amplifier. Could somebody recommend my an other type amplifier, what could be more accurate?

I am thinking about adafruit MAX31855 breakout board because of the manufacturer, but maybe somebody have experience in this topic and could recommend me something else, or can encourage my to buy an adafruit.

many thanks in advanced
Miklos

You might check the raw numbers going into that average to see if there are any outliers caused by bad reads.

I've been using the Adafruit MAX31855K breakout modules with type K thermocouples. Generally I go for the cheapo Chinese stuff but in this application I thought it was worthwhile to make sure I had a high quality product. At that time, Adafruit's price on the MAX31855K module was fairly competitive with the Chinese modules. Now I see you can get the Chinese 3.3 V minimal breakouts for super cheap! Even the clones of the Adafruit module are significantly cheaper.

Many months after I bought those modules from Adafruit, I got an email. They had investigated reports of problems with some of their modules and tracked it down to some chips that the manufacturer of the MAX31855K had screwed up on, but not bothered to tell anyone about. They told me which date codes were affected. It turned out some of my modules were bad ones (luckily they were backups I had never used). They replaced them simply on my word that mine had the affected date codes, no returns required. Do you think I would have gotten that level of customer service from a Chinese seller?

I have checked the measured data to see the bad reads, but the values do not contains any huge pick what could disturb my average value. thermocouple with omron sensor provide values from 19-to 22 degree the noname Chinese sensor provide 26-28. (they are next to each other, between similar conditions so the accuracy is a big question, but I can believe in omron, temperature can be around 22. )

Based your experience Adafruit more expensive price maybe give some additional support or hopefully a better manufactuere value.

When you dealt with your project you did not experienced any value changes between unchanged environment?

As you can see I get from the Chinese sensor higher values than the reality. I am able to modify the date in my arduino code, but when the gap between reality and measured data does not change in a linear way, than I will make wrong values with my static correction. Am I able to setup or customize my sensor in Max6675 class or somehow/somewere?

thanks

I read out the values in every second:

20:33:30 22/9/18
thermocouple 1 value in degree celsius: 27
thermocouple 2 value in degree celsius: 21
20:33:31 22/9/18
thermocouple 1 value in degree celsius: 27
thermocouple 2 value in degree celsius: 22
20:33:32 22/9/18
thermocouple 1 value in degree celsius: 27
thermocouple 2 value in degree celsius: 22
20:33:33 22/9/18
thermocouple 1 value in degree celsius: 27
thermocouple 2 value in degree celsius: 22
20:33:34 22/9/18
thermocouple 1 value in degree celsius: 27
thermocouple 2 value in degree celsius: 21
20:33:35 22/9/18
thermocouple 1 value in degree celsius: 27
thermocouple 2 value in degree celsius: 21
20:33:36 22/9/18
thermocouple 1 value in degree celsius: 27
thermocouple 2 value in degree celsius: 21
20:33:37 22/9/18
thermocouple 1 value in degree celsius: 27
thermocouple 2 value in degree celsius: 21
20:33:38 22/9/18
thermocouple 1 value in degree celsius: 27
thermocouple 2 value in degree celsius: 21
20:33:40 22/9/18
thermocouple 1 value in degree celsius: 26
thermocouple 2 value in degree celsius: 21
20:33:41 22/9/18
thermocouple 1 value in degree celsius: 28
thermocouple 2 value in degree celsius: 21
20:33:42 22/9/18
thermocouple 1 value in degree celsius: 27
thermocouple 2 value in degree celsius: 21
20:33:43 22/9/18
thermocouple 1 value in degree celsius: 27
thermocouple 2 value in degree celsius: 21
20:33:44 22/9/18
thermocouple 1 value in degree celsius: 27
thermocouple 2 value in degree celsius: 19
20:33:45 22/9/18
thermocouple 1 value in degree celsius: 28
thermocouple 2 value in degree celsius: 21
20:33:46 22/9/18
thermocouple 1 value in degree celsius: 27
thermocouple 2 value in degree celsius: 21
20:33:47 22/9/18
thermocouple 1 value in degree celsius: 27
thermocouple 2 value in degree celsius: 21
20:33:49 22/9/18
thermocouple 1 value in degree celsius: 27
thermocouple 2 value in degree celsius: 21
20:33:50 22/9/18
thermocouple 1 value in degree celsius: 27
thermocouple 2 value in degree celsius: 21
20:33:51 22/9/18
thermocouple 1 value in degree celsius: 27
thermocouple 2 value in degree celsius: 22
20:33:52 22/9/18
thermocouple 1 value in degree celsius: 27
thermocouple 2 value in degree celsius: 21
20:33:53 22/9/18
thermocouple 1 value in degree celsius: 27
thermocouple 2 value in degree celsius: 19

It is strongly recommended to add a 10nF/0.01mF ceramic surface-mount capacitor, placed across the T+ and T- pins, to filter noise on the thermocouple lines.

library - GitHub - enjoyneering/MAX6675: Arduino library for 12-bit MAX6675 K-thermocouple to digital conver

thanks, I will try, and give feedback.