berger.h
Member level 5
I'm looking for a way to measure the amount of gas flowing so that it is small and cheap.
Gradually I ended up at MAF or Thermo Anemometer.
According to my experience, the heated platinum wire has a problem with impurities on its surface, plus I would have to solve how to assign the wire to the electrodes.
That's why I was interested in the solution with heated transistors
Any as this
her id schematics with my notes
How it works in my opinion
Let's leave aside the basic principle of depletion of Q1 and comparison of Q1 = Q2
If Q1 = Q2 and the system is balanced (gas does not flow)
Output 7 LM393 F is Hi
Q7 is close
Q3 is close
Q6 is Open
C1 is fuil charged
If Q1 != Q2 the system is not balanced (gas does flow and cools Q1)
Output 7 LM393 F is Lo
Q7 is Open
Q3 is Open and mae additional cuurent in Q1
Q6 is Close
C1 is disharage
On C1 is saw
And system meke 800us current puls to Q1 and min 200us pause between pulses
the number of pulses is then a function of the flow rate with the maximum frequency being 1000Hz
If so
I can only take Q1 and Q2 with R2 + R1 a Q3 for generating current pulses take some small cheap MCU with integrated comparator
for exmple STM32L011x3 in TSSOP14 and Q1 Q2 connet to internl comparator, and Q3 drive using PWM.
Am I much out?
If not have
several questions
Technically I would need to measure the gas flowing 1/4" pipe speed 0-15m/s
Physically brass T Pipe Fitting Q1 STO23 in center of flow, Q2 either in the measuring inlet or in direct contact with the brass fitting thanks to the use of the MCU, an NTP thermistor could also be placed in the measuring input and the gas temperature could be measured.
1. The 2N4401 is exceptional for this type of use, that it is used so long and I have to use it in SMD MMBT4401 or does it matter and can I use BC817-40 for example?
2. Location Q2 . Do you see how it is more convenient to use it so that it is not drained by gas but rather isolated from the body of the fitting, or is it more suitable to have contact with the body of the fitting and take the temperature of the cells of the fitting as a reference?
3. The use of a processor brings much greater variability in the control and calibration of results. If you have any ideas, I'll welcome him
Gradually I ended up at MAF or Thermo Anemometer.
According to my experience, the heated platinum wire has a problem with impurities on its surface, plus I would have to solve how to assign the wire to the electrodes.
That's why I was interested in the solution with heated transistors
Any as this
her id schematics with my notes
How it works in my opinion
Let's leave aside the basic principle of depletion of Q1 and comparison of Q1 = Q2
If Q1 = Q2 and the system is balanced (gas does not flow)
Output 7 LM393 F is Hi
Q7 is close
Q3 is close
Q6 is Open
C1 is fuil charged
If Q1 != Q2 the system is not balanced (gas does flow and cools Q1)
Output 7 LM393 F is Lo
Q7 is Open
Q3 is Open and mae additional cuurent in Q1
Q6 is Close
C1 is disharage
On C1 is saw
And system meke 800us current puls to Q1 and min 200us pause between pulses
the number of pulses is then a function of the flow rate with the maximum frequency being 1000Hz
If so
I can only take Q1 and Q2 with R2 + R1 a Q3 for generating current pulses take some small cheap MCU with integrated comparator
for exmple STM32L011x3 in TSSOP14 and Q1 Q2 connet to internl comparator, and Q3 drive using PWM.
Am I much out?
If not have
several questions
Technically I would need to measure the gas flowing 1/4" pipe speed 0-15m/s
Physically brass T Pipe Fitting Q1 STO23 in center of flow, Q2 either in the measuring inlet or in direct contact with the brass fitting thanks to the use of the MCU, an NTP thermistor could also be placed in the measuring input and the gas temperature could be measured.
1. The 2N4401 is exceptional for this type of use, that it is used so long and I have to use it in SMD MMBT4401 or does it matter and can I use BC817-40 for example?
2. Location Q2 . Do you see how it is more convenient to use it so that it is not drained by gas but rather isolated from the body of the fitting, or is it more suitable to have contact with the body of the fitting and take the temperature of the cells of the fitting as a reference?
3. The use of a processor brings much greater variability in the control and calibration of results. If you have any ideas, I'll welcome him