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Piotrkurak wrote:

Check and Switch the wires on the TC's? If the control device uses common ground one backwards wired set will bollox up the whole mess.

exer31337 wrote: I've done that several times. (Switch wires)

RECOMMENDATIONS FOR BEST CIRCUIT PERFORMANCE
Input Filter
A low-pass filter before the input of the AD849x is strongly recommended (see Figure 29),
especially when operating in an electrically noisy environment.
Long thermocouple leads can function as an excellent antenna and pick up many unwanted signals.
The filter should be set to a low corner frequency that still allows the input signal to pass through undiminished.
The primary purpose of the filter is to remove RF signals, which, if allowed to reach the AD849x,
can be rectified and appear as temperature fluctuations.

renatoa wrote:

The real cure to this is to playback using a power profile, not temperature, which is the most inconsistent thing in the whole process.

Bhante wrote:


Switching several times raises warning lights!! There are only two possible connections, one correct and one incorrect, so you shouldn't have to swith and forth several times unless you have serious confusion over your wiring? If the withing is correct, warming the probe tip with your finger should increase temperature, the opposite if it is wrong.

There are several issues that can arise from thermocouple measurement. The measured voltages are very tiny, and can easily be drowned by external signals.

1) What is the quality of the probe? Cheap low-quality probes may have an unreliable and intermittent ground connection between probe and sheath, and/or a connection where they are supposed to be insulated.

2) Do you have an elderly fridge or freezer or air-con in the neighbourhood? Using a TC4 I have found they are highly susceptible to radio interference, especially from a fridge turning on or off. An old fridge is hugely worse than a new one, although certain new ones can also cause problems sometimes. I have at times had problems with sudden program crashes due to this interference, causing the monitor program to hang. If you have this problem you may find looping the thermocouple wire through a ferric suppressor bead may help somewhat (one full turn), but the most effective solution is to buy a new fridge, or at least turn it off during the roast.

3) If you have a computer connected via USB cable you may have a ground loop problem between roaster power supply and computer power supply, so it's best to use the notebook with its power supply disconnected. A notebook power supply may cause a large degree of random noise on the RoR signal. Using a good quality probe with an insulated tip you shoud not have this problem (at least with the TC4). Conrad Electronics provide some excellent 1.5mm probes made by B+B Thermo which are very reliable, a few of which are quite low cost, and very well suited to coffee roasting. A separate power supply for the Arduino is potentially also a cause; if you are using a wireless link, try and power the arduino from the same supply as the electronics powering the roaster, which should reduce the risks of ground loops.

4) Putting a large resistor or small capacitor between each of the thermal contacts and ground can reduce grounding problems. Later versions of the TC4 have contacts for installing either resistors (version 4??) or capacitors (version 5??) but these are usually left unpopulated by default - I would recommend installing them. I think the capacitor is preferable to the resistor, but I cannot say that authoritatively.

renatoa wrote:

They should be both, else the filtering effect will be reduced colse to not existing.
Attached is a typical TC input filtering scheme, excerpted from a TC amplifier good practice/usage notes



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Piotrkurak wrote:

Do the probes work properly when held together such that the shafts/cover touch each other?

Common grounds will make you look like my cartoon profile