search

apollo-ng / picoReflow

Turns a Raspberry Pi into a universal, web enabled Reflow Oven Controller
202 stars 118 forks source link

Wrong Measurement with Max31855 #9

Closed Meister1980 closed 9 years ago

Meister1980 commented 9 years ago

Hello,

I have a problem with PicoReflow. The Temperature measured by PicoReflow & Max31855 is not correct. First i thought that i have a problem with the K-Type Sensor, but then I tested them at work with a Thermocouple calibrator! I tested the Sensors, my thermocouple gauge and the Max31855 (with Picoreflow).

I measured a temperature with picoreflow and it shows 100°C than i measured the same temperature with my calibrated Gauge and it shows 130°C !?

img_20150620_102456

I tested picoReflow with the calibrator and when the calibrator says 225°C, picoreflow shows about 180°C.

I tested this with 3 diffent Max31855 on different boards, everytime the same Problem. I think its a Software Problem.

Can anyone test his Pico and confirm this Problem ? I dont now what to do further ...

Greets, Meister

KammutierSpule commented 9 years ago

You may would like have a look at:

http://www.eevblog.com/forum/projects/max31855-temperature-error/30/

https://translate.google.pt/translate?sl=pt&tl=en&js=y&prev=_t&hl=pt-PT&ie=UTF-8&u=http%3A%2F%2Flusorobotica.com%2Findex.php%3Ftopic%3D7908.msg88928%23msg88928&edit-text=

There are some official faulty batch being selling by major component dealers (eg: mouser, digikey..etc)

Meister1980 commented 9 years ago

Testing with Calibrator :

Calibrator : 25°C picoReflow: 22°C

img_20150620_113824

Calibrator : 100°C picoReflow: 76°C

img_20150620_113910

Calibrator : 225°C picoReflow: 163°C

img_20150620_114015

Calibrator : 350°C picoReflow: 252°C

img_20150620_114111

KammutierSpule commented 9 years ago

Yes it looks like it is a Max31855 faulty batch. I had the same issues while trying to make a reflow oven. In my experience the different was not so big as yours. But the behavior was the same: the more the temperature increases, the more the difference.

Meister1980 commented 9 years ago

Dooooh ! Yes its a faulty Batch ....

2 of the Max31855 I tested where from an order last Year (Mouser). Datecode -> 1352A2 - 23AL The third Max is from this Week from Conrad Electronic, but has the same Date Code :-(

KammutierSpule commented 9 years ago

The maxim IC knows it, probably Mouser/Digikey knows it too.. and still sell it that way :|

chron0 commented 9 years ago

Meh, that's a shame and always happens when you need it the least :/ The modules we got from watterott.com have not had any issues, I've verified the metrics against a reference thermometer during dev/testing. But I had the same issue with a DS1820. As it seems to have been a HW problem, I'll close the ticket if no one raises any objections.