PIR pyrometer sensor as temperature sensor for liquid

Dep

RRF with Duet board is used for photopolymer printer. Resin vat heating - infrared.

Is it possible to connect any pyrometer sensor to measure liquid at a distance (resin)?

What can you advise for this?

dc42

@dep do you have a particular sensor in mind? Perhaps something like one of these https://uk.farnell.com/w/c/sensors-transducers/sensors/temperature-sensors/infrared-temperature-sensors/prl/results?sort=P_PRICE ?

Dep

Hi @dc42. I can use any sensor that is the easiest to connect.

The task is to measure the temperature of the resin in the vat. The distance is not large - 10 - 15 centimeters. Accuracy is also not needed great - about 1 degree will be enough.

dc42

@dep which Duet are you using? Please include the revision number.

Dep

@dc42

Now I have Duet 3 (the inscription on the sticker is D3MB6HC v1.01 WD43001).
In general, I planned to purchase Duet 3 Mini 5+ for further work.

dc42

@dep there are various types of thermopile-type pyrometer sensors available. Some include lenses to achieve a narrow field of view. Some provide a direct output either via I2C or another protocol, while others provide just the output of the thermopile plus a thermistor to read the sensor temperature. Some have a filter for detecting a particular gas; I expect you would need to avoid those.

Here are some possible options:

Use one of the sensors that provide a I2C output. I2C signals are very prone to picking up capacitive interference. So the pyrometer would need to be mounted fairly close to the main board, and the cable would need to be kept away form stepper motor cables.

Unfortunately the current Duet 3 MB6HC does not support I2C in hardware (the next version will), although it would be possible to convert the board to support it by soldering a resistor or wire link on top of one of the resistors on the board. Revisions 1.01 and later of Duet 3 Mini boards do have hardware support for I2C.

RepRapFirmware for Duet 3 and 3 Mini does not yet support I2C but we expect to add this functionality in RRF 3.5.

In order to support a sensor using I2C, a new sensor type would need to be added to RRF.

Use one of the basic sensors with a thermopile output and a thermistor. If the thermopile output is large enough then it could be fed directly into an analog input configured as a Linear Analog Sensor; otherwise use an op-amp to amplify it. The thermistor can be read as normal. To get an accurate temperature, the thermistor temperature will need to be added to the temperature difference provided by the thermopile. This could perhaps be done by having the daemon.g file adjust the linear analog sensor parameters as the thermistor temperature changes.
Use an Arduino or similar to read one of the above types of pyrometer, and output a voltage proportional to temperature, that can be read by a Linear Analog sensor on the Duet.

Dep

@dc42 Thanks for the detailed answer!

This option seems to me the best. Soldering to the board is no problem if you say what exactly needs to be soldered. Also the question is when will support be released in RRF. We are not in a hurry, but if it happens in a year, then this option will not suit.
This method is very interesting! But I think it's hard to implement.
We can do this, I thought about it. But this is an extra processor, I would not want to complicate it.

In general, the first method is the most interesting!

Dep

@dc42 I purchased MLX90614 sensors for experimentation. Maybe you have a beta version of the RRF software to try to connect?