Hi, I am trying to design some sort of system for measuring level of sawdust/wood in my stove. This very hard environment, so it is not simple for me. I mean high temp., thick metal tank.
I was thinking about maybe some combinations of sensors like temperature, ultrasound, timer (predictions). Basically what I want is to get an alert when stove is going to be empty soon and needs to be filled again.
I burn coal in my stove but I have never thought about a system to warn when more fuel is needed - normal procedure is that I feel too cold to continue typing here
So I suggest you get a temperature sensor and collect data over a few days to see if there is a useful and usable pattern. A nice Arduino project would be to log the temperature every 5 minutes. It may be sufficient to monitor the temperature near the stove if you don't have a high temperature sensor.
the inside is dirty. cresote will burn and coat any type of optical sensor.
heat is not a good indication.
if you put in wet wood, the fire will stay cool and the sap will pop until the wood dries, then the temperature will soar. this is often about half the burn time.
dry wood will burn hot and faster, putting out more BTU into the room. wet wood lets too much of the heat up the chimney as moisture.
weight of the fireplace would only change sightly with ash building up, you could calculate for that.
to start a fire you must have 3 logs. the three form an oven, as the wood burns the radiant heat is projected onto the other logs. the inside cavity will expand and the fire will cool a bit, then once the wood falls into the cavity, it will burn hot again, then start to die.
if you want an automatic log feeder, I have some ideas, a home-brew plan but need a welder, torch or plasma cutter....
Some mechanical device projecting down into the hopper - just a steel rod with a 'flag' welded on the end. Then a small motor which can only just turn the stirrer when it's hanging in the air. When the fuel level is surrounding the stirrer, it can't turn. Put a rotation sensor (switch, optical, hall effect whatever) on the shaft where it is outside the hopper.
Measuring exhaut gas temperature, there are ready made senors for that)
Barometric pressure inside the combustion chamber. Combustion in a stove creates underpressue. Sensor can be places at air intake where temperature is low)
Temperature gradient on the outside of combustion chamber
My automated pellet furnace uses a LDR to detect flames.
Weighing seems a bit problematic because the environment inside the combustion chamber. You can weight the whole stove but that means that the relative weight difference would be small and thus difficult to establish.
To clarify things up - it is simple stove, no automatic filling. Got to use shovel
Important is fact, like someone noticed, that time of burning varies - wet/dry, wood/sawdust.
There is old non-electronic thermometer but I can install electronic. Of course not inside stove. Actually nothing inside will survive long. Also there is relatively easy access to incoming air (with mechanical regulation). Outcoming air is problematic. I believe there is pressure sensor in water circuit but I cant check it soon.
gremmlin:
To clarify things up - it is simple stove, no automatic filling. Got to use shovel
Get a cheap LM335 or LM35 temperature sensor. Mount it (say) 15 cms from the side of the stove near the top.
Collect data for a few days.
Study the data.
Review your options.
A type K thermocouple and MAX31850 (1-wire max 1800°C), MAX31855(SPI max 1800°C), MAX6675(SPI max 1024°C) might work, place it just after the stove in the smoke outlet.
The temp will vary due to moisture and gaps.
Next a broad spectrum lambda, will cost a bit but can benefit with less fuel consumption when a almost perfect combustion is possible.
The oxygen level will rise fast then fuel is out.
If its possible to adjust the gas/air mix with a servo or stepper motor through the process its a win win for you and the environment.
To get clean burn you will have reach 850°C or more in fire or just after.
This will not work with a ordinary lambda probe from a car, the specification does not match wood burning and it must be heated or placed there it is 600°C to work.
A lambda for race purpose can work and they usually have multiple outputs like analog, serial and digital at the same time.