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Cold Junction Compensation

A project log for T-962A Reflow Oven Modifications

Modifications to a T-962A reflow oven which turn this cheap oven to a surprisingly effective piece of hardware.

LanceLance 09/29/2020 at 03:190 Comments

Introduction

The cold junction modification adds a temperature sensor to measure the temperature at the board.  The new firmware uses this to correct the temperature readings from the thermocouples and make the heating process more accurate.

Sources

Cold junction compensation page:

https://github.com/UnifiedEngineering/T-962-improvements/wiki

 Unexpected Maker video:

https://youtu.be/HjYqSfLzBKk?t=119

Note that Seon has his oven on the side so he doesn’t have to detach the cables.  However, if you put the top to the left side of oven (as opposed to the right as he has it) the cables reach (at least they did for my oven) and you can leave the oven flat.

Hardware

The temperature sensor I used can be found here:

https://www.digikey.com/product-detail/en/maxim-integrated/DS18B20-/DS18B20--ND/956983

When you read the datasheet it tells you that you need a 4.7kOhm resistor as well.  I used these:

https://www.digikey.com/product-detail/en/yageo/RC0805FR-074K7L/311-4.70KCRCT-ND/730876

If you use a different temperature sensor, make sure it meets the requirements of the new firmware and be sure to check the data sheet for wiring.

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