Looking at the Groove board schematics, it shows that the voltage for the MICS6814 heating and reference is always 3.3V (provided by the ETA3401). The heater serial resistor setup is taken from MICS6814 data sheet and the resistor values have been tried to adjust for the 3.3V. HOWEVER this results is a too low voltage for VhRED and vhNH3.
................. | Typically | 5V supply | 3.3V supply
.................(data sheet)
VhRed ...| 2.4V......... | 2.3V ..........| 1.68V
VhNH3.,.| 2.2V......... | 2V............. | 1.42V
VhOx .....| 1.7V......... | 1.7V.......... | 1.54V
The above voltages have been measured in the working environment as well.
The problem is even bigger looking at the heating power.(p = u2 / r) . The resistance value for each heater is taken from the data sheet as well as the typical power.
Actually the heating power is 50% of the minimum: 71mW for RED and 60 mW for NH3 (MiCS-6814 data sheet, page 3)
The impact is for sure longer heating time, but maybe also the RED and NH3 heaters are not able to reach the necessary temperature and as such providing incorrect results ?
Shouldn't the resistor setup be changed to just have a serial load resistor for each heater separate to the 3.3V (as it is for the ox-heater?)
Looking at the Groove board schematics, it shows that the voltage for the MICS6814 heating and reference is always 3.3V (provided by the ETA3401). The heater serial resistor setup is taken from MICS6814 data sheet and the resistor values have been tried to adjust for the 3.3V. HOWEVER this results is a too low voltage for VhRED and vhNH3. ................. | Typically | 5V supply | 3.3V supply .................(data sheet) VhRed ...| 2.4V......... | 2.3V ..........| 1.68V VhNH3.,.| 2.2V......... | 2V............. | 1.42V VhOx .....| 1.7V......... | 1.7V.......... | 1.54V
The above voltages have been measured in the working environment as well.
The problem is even bigger looking at the heating power.(p = u2 / r) . The resistance value for each heater is taken from the data sheet as well as the typical power.
...................| Typically | 5V supply | 3.3V supply VhRed ...| 76mW..... | 71mW...... | 38mW VhNH3.. | 66mW.... | 55mW....... | 28mW VhOx...... | 43mW.... | 44mW....... | 35mW
Actually the heating power is 50% of the minimum: 71mW for RED and 60 mW for NH3 (MiCS-6814 data sheet, page 3)
The impact is for sure longer heating time, but maybe also the RED and NH3 heaters are not able to reach the necessary temperature and as such providing incorrect results ?
Shouldn't the resistor setup be changed to just have a serial load resistor for each heater separate to the 3.3V (as it is for the ox-heater?)
regards, Paul