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Topic: Lambda Control of Oxigen Content in Flue Gas of Pellet Boiler (Read 486 times) previous topic - next topic


You need to have a look at the nerst equation which relates to zirconia probes .
The output is temperature dependant and proportional to the log of the partial pressures of oxygen across the probe.  ( one side usually being 21%). A lot of automotive sensors use an internal heater , which you could drive to a constant resistance . Often with automotive sensors you get an offset voltage caused be heat not being constant across the sensor ( heated up the centre)


A further point is as flue gas temperature is low , there may be little saving due  to running optimally ( there are tables for this)
This for natural gas but it will do :


There is a danger of carbon monoxide production here as the relationship between excess air and complete combustion may well vary .. you might not legally /wisely be able to do this ??


Everybody's got an opinion.

For the temperature I would use a MAX31855 board from eBay.  I believe K type thermocouple is a better choice for a corrosive atmosphere.

Please do not PM me with thread based messages.  If your thoughts are worth responding,  the group should benefit from your insight.


Temperature sensor will be in 10 cm pocket to the middle of the funnel where temperature is highest. So, it will be not exposed to corrosion. Both types of temperature sensors will fit.

Regarding measuring of mV I reviewed also ADS1115 board . It looks to me suitable in differential mode for my purpose. There is also ready arduino function for it.



What you thing for ADS1115 ?


Well, datasheet say that input voltage can be up to 36V but that is in voltage measuring mode. I will use it in current measuring mode for range up to 50mV by removing the shunt resistor as you suggested. However the full range of my sensor is 1V . I want it measure only first 50mV of this 1 V. Will the input sustain 1v in current measuring mode?
According to the data sheet the mV inputs will tolerate even 26V. But after 80mV the ADC is saturated.
You are also free to build a voltage divisor upfront.


Here you have a shield for 80 euros with a wideband lambda sensor. See if it works for you.


Here you have a shield for 80 euros with a wideband lambda sensor. See if it works for you.
Well, I know this solution but it is rather expensive. Minimum set (without power supply) costs 100 EUR. There are ready solutions that are technically better but they are also expnesive  - like thse 2 for example (there are other as well):
My aim is to find chep solution for not more than 30-40 EUR overall , including arduino uno. Control of lambda in pellet boiler does not need such high acuracy like for the car engine. The burnig process in the pellet boiler is naturally varying because the fuel is beeing supplied in portions and burns during the pause. Therefore, the lambda changes in very wide range. That will need integration for 1-2 minutes for measuring the average lambda.
I intend to use old and cheap LSM11 lambda sonde (14 EUR) and 16 bit ADC INA226 (2 EUR) for the purpose , or ADC ADS115. LSM11 does not need so strict control of temperature like LSU 4.9 or latest LSU ADV. It needs just 12 V supply to the heatimh element.
I will probably include also channel for measuring temperature of exhaust gases by MAX6675 and K type sensor (thermocouple). The exhaust gases temperature should not fall below 120 deg.C to avoid condensation in chimney. So the regulation of burning process of pellets is compromise between lambda and temperature of exaust gases. PT500 sendsor will be probably also suitable for this purpose.
The ordered from Aliexpress INA226 and LSM11 sensor came yesterday. I will try them soon.

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