| Electronics > Beginners |
| MAX6675 vs op-amp |
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| shobo:
Hi all, as one of my first projects i want to build myself a soldering station.however i haven't decided to use a MAX6675 module/ic to sense the temperature or use an op-amp. The iron i have is an Atten clone on a hakko. what would be the cons and pros of each method? |
| David Hess:
If you use an operational amplifier, then you will have to add external cold junction compensation in some form or another to use the thermocouple but this is easy enough. The MAX6675 has built in cold junction compensation. If your control loop is going to be analog, then the digital output from the MAX6675 will be inconvenient and something like an LT1025 would be easier to use. |
| shobo:
--- Quote from: David Hess on April 10, 2018, 10:41:44 pm ---If you use an operational amplifier, then you will have to add external cold junction compensation in some form or another to use the thermocouple but this is easy enough. The MAX6675 has built in cold junction compensation. If your control loop is going to be analog, then the digital output from the MAX6675 will be inconvenient and something like an LT1025 would be easier to use. --- End quote --- The control of the will be digital,by using an arduino (arduino mini on perfboard) or ar atmega with the arduino bootloader. The modules are cheap enough to either stuff one in or salvage the IC if i get to etch my own board. |
| David Hess:
--- Quote from: shobo on April 11, 2018, 06:20:22 am ---The control of the will be digital,by using an arduino (arduino mini on perfboard) or ar atmega with the arduino bootloader. The modules are cheap enough to either stuff one in or salvage the IC if i get to etch my own board. --- End quote --- I do not disagree; I was just pointing out that the MAX6675 is only going to be useful with a digital control loop while an analog implementation can work with either. If you are using a microcontroller for the control loop, then another alternative is to implement the cold junction compensation digitally using any temperature sensor. Then you can use any precision operational amplifier. That is what the MAX6675 handles internally for you. So for instance the thermocouple output is amplified and digitized, and an inexpensive silicon temperature sensor like an LM86 located near the thermocouple interface is also digitized to provide the cold junction temperature. Using a thermocouple requires *two* temperature measurements. |
| kazan417:
Actually lm86 are not so cheap, you shoud find cheaper with at least 1 degree precition, to outperform price of chinese produced max6675. Morover it is better to use some cortex microcontrolleer with integrated 12 bit adc instead of 10 bit interated into avr. This way with good precition opamp for about 1 dollar you save money and not loose precition. :-+ |
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