Temperature monitoring for curing cycle

Carbon fiber tube curing process, we are working at, needs to go through several stages. First one is to hold temperature on 70C for ~3hrs, followed by another 1.5h on 140C. To be able to achieve that, we needed to put together some sort of thermostat which would drive our heater.

Discussing this problem all around, Richard suggested to build our own and provided list of parts needed.

So we got ourselves one MAX6675 K-type Thermocouple Temperature Sensor 0-600 Degrees Module Arduino – mainly to grab its signal amplifier.

Followed by AU Heat-resistant K Type Stainless Steel Thermocouple Sensor Probe Meter (1m) as it comes with pretty impressive operating temperature range: -100 – 700°C.

Both packages arrived quickly (days).

It took Seb to hook it up to one his Arduino.

Sebi provided me with a code, claiming that that’s just a copy & paste from some thermocouple example. I am putting it here for reference, while all credits go to Adafruit guys.

// this example is public domain. enjoy!
// https://learn.adafruit.com/thermocouple/

#include "max6675.h"

int thermoDO = 4;
int thermoCS = 5;
int thermoCLK = 6;

MAX6675 thermocouple(thermoCLK, thermoCS, thermoDO);

void setup() {
  Serial.begin(9600);

  Serial.println("MAX6675 test");
  // wait for MAX chip to stabilize
  delay(500);
}

void loop() {
  // basic readout test, just print the current temp

  Serial.println(thermocouple.readCelsius());

  // For the MAX6675 to update, you must delay AT LEAST 250ms between reads!
  delay(1000);
}

Finally we took a tiny video to see it all working together – showing data from Seb’s Arduino being received by a plotter on his laptop responding nicely to temperature changes.

Afterwards we did some attempts to hook it up with Richard’s MosFETs to drive our heating coil, but that didn’t work out well, so keeping it for another post as there is quite a live discussion running around it right now.

Also there is a question of an actual driving of our heater as it will certainly react with some delay following the hysteresis curve, but that’s for another day as well.

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