A guide to using Samovar to control an autoclave.
Working temperature.
For autoclaves it is in the range of 110-120 degrees. The difference seems small, but it is critical for some kinds of products. Vegetables can be preserved even at 110 degrees. Fish needs 115, and meat needs a full 120 degrees.
In fact, Samovar's work with an autoclave comes down to one thing: using the voltage regulator to control heating and, as a result, the temperature inside.
A possible problem is choosing a good-quality DS18B20 sensor.
According to the specification this sensor works up to 125°C, but in real life far from every one works normally at 120°C. It may happen that sensors work wonderfully in distillation and rectification, and fail when used in an autoclave.
Practical tip.
It is recommended to make the sensor yourself, buying several DS18B20 chips from a well-known store from a supplier with good reviews. The chance of making a good-quality sensor yourself that withstands operation at 120 degrees is much higher than of buying a ready-made one. Ready-made sensors often fail at elevated temperatures. When making it, it is important to provide a thermal interface between the sensor and the surface of the sleeve. For this it is convenient to use a neutral heat-resistant sealant. Do not use an acidic sealant: it will corrode the wire. You can use hot-melt thermal glue, but if something happens to the sensor, thermal glue is much harder to remove.
Important: the inside of the autoclave sleeve where we place the sensor must also be filled with a thermal interface. Glycerin is the most convenient for this.
To work with an autoclave, switch to the "Beer" («Пиво») mode.
1. Check:
Settings («Настройки») / Temperature («Температура») / "Boiler sensor address" («Адрес датчика в кубе»). Make sure the address of the correct sensor is set here.
2. Settings / Beer («Пиво»).
Leave the "Brewing order" («Варочный порядок») at All-in-one / BIAB: in this option heating is regulated by the boiler sensor. HERMS and RIMS control the temperature by the water and column section sensors and are not suitable for an autoclave.
"Regulator voltage/power in temperature holding mode: ___ v («Напр./мощность регулятора в режиме поддержания темп.: ___ v»)." This parameter needs to be tuned and the value chosen for your equipment. It is the minimum voltage/power that is enough for the autoclave temperature to keep rising after boosting is switched off. By default boosting is switched off when the temperature is 1 degree below the one set in the program (this can be changed in the file Samovar_ini.h
, the line #define HEAT_DELTA 1). For that one degree, the autoclave should keep heating slowly with the voltage/power value set in this field. To start, you can set 100 volts.
3. Program.
We use the malt mashing program. Here we set the temperature and the time to hold this temperature.
These values may change slightly depending on the products being prepared. The classic is 120 degrees for one hour. Set the PAUSE («ПАУЗА») mode, temperature 120 degrees, time 60 minutes.
Practice has shown that the chance of damaging jars and of products boiling over is lower if you heat to 120 degrees not as fast as possible in boost mode, but gradually, roughly over half an hour, for example in "steps" at 105, 110 and 115 degrees with a hold of 3 - 5 minutes each.
The result is this program:
P;105;4;0^0^0^0;0
P;110;4;0^0^0^0;0
P;115;4;0^0^0^0;0
P;120;60;0^0^0^0;0
The last field of the line is the number of the sensor by which the temperature is held: 0 is the boiler sensor. The device field 0^0^0^0 means that the stirrer and the pump are not used in the line.
Safety.
To ensure safety you can use the following methods:
- Use a bimetallic thermostat KSD9700 (NO - normally open) rated 55-70°, installed near the autoclave's emergency valve.
Connect the thermostat outputs in parallel with Samovar's emergency button (applying a logical one to ALARM_BTN_PIN: D35 for the DEVKIT board, D48 for the ESP32-S3; the firmware must be built with the emergency button, that is the Samovar_alarm_button environment or #define USE_ALARM_BTN). When steam is released, Samovar will tell the regulator to turn heating off.
- Replace (or modify yourself) the pressure gauge with an electric contact one set for a maximum pressure of 0.25 MPa and use its contacts to connect in parallel with Samovar's emergency button.
- Connect to the emergency valve a unit that provides additional protection by means of a contactor or an RCD. If steam breaks through, Samovar will switch off, and so will the heating.
The setup is finished; press the "Turn on heating" («Включить нагрев») button and enjoy the automatic process until it ends.
When the process ends, Samovar will tell the regulator to turn heating off. Wait for the autoclave to cool down and take out the finished product.
Note.
The temperature and pressure in an autoclave are directly related. As heating increases, so does the pressure. Accordingly, the temperature regime can be calculated and checked from the working pressure and vice versa.
For example, for an autoclave to reach a temperature of 120 degrees, excess pressure is required.
There are tables of temperature versus pressure on the internet. You can use them quite well, taking into account the correction for your location.
