Nitrox/Trimix & CO analyzer

[estresao]

Hi all,

I've made my own version using similar approach and it's working fine..... actually I'm already using it in my nitrox stick (so far I only blend Nx).

I've got a couple of questions:

- I have my O2 sensors connected directly to the ADS1115, but I've found in some datasheet a load resistance is recommended. In the schematic shared here it seem you guys went for the same approach of no load resistor... have you ever considered using some?

- My implementation reads up to two O2 cells to extend it in near future for He support, but so far, the two O2 values are just displayed as independent O2 values. This is OK for me so far, and it allow me to use both sensor at the same time to test some O2 cells I've given from rebreathers and so on, this way I'm always have one which I know it works properly, and the another under test (or to double check to avoid wrong values when one get wore. OK.... the point is that initially I've tried to connect both to same ADS1115 but I've found there where some interferences affecting the values, so I ended up using two ADS1115, did that happened to you guys? I see in the schematic you are also using two ADS1115 but for different reason.

 

[Steve78]

Hi,
I am also working on my trimix analyzer and found a strange thing related to the ZE07 CO sensor.
I use separate ADS1115 for the O2/He and for CO detection. I use the DAC output of the CO module, 0.4 -2 volts. I calibrate the CO sensor with 100% oxygen, this case it shows about 404 mV / 0ppm. In normal air it goes a bit higher, 408 mV / 1.2 ppm. And it fluctuates between these two values and stabilize at one of them for a few seconds. This case there is no gas flow through the analyzer so it might be saturation of the sensor.
When I connect my trimix tank (I have already used for diving) CO level goes up to 15ppm. If I leave the gas flow through the analyzer it slowly goes down to the original value, 408 mV/1.2 ppm.

Is it a normal behaviour?
Any experince?

 

[bobziuchkovski]

@Steve78 Did you end up figuring this out? I'm also considering CO analyzers and would love to know how well the Winsen sensors work.

@Miyaru Any chance you'd be willing to share how the dive center testing went and how the HE/CO sensors fared for you?

 

[Steve78]

@Steve78 Did you end up figuring this out? I'm also considering CO analyzers and would love to know how well the Winsen sensors work.

@Miyaru Any chance you'd be willing to share how the dive center testing went and how the HE/CO sensors fared for you?

@bobziuchkovski​

I have contacted Winsen and they told me it was a normal behaviour.

This is Iris from Winsen who responsible for US market. From your description, the sensor performance is normal.

 

[VladimirG]

@Steve78 @bobziuchkovski You may also check the input voltage of the ZE07/ZE15. I'm also doing my own O2/He/CO analyzer based on the ideas in this thread and had a few cases of strange behavior of the sensors.

The ZE07's input voltage is 5 to 12V. Initially I powered it from a Liion battery with a step up converter to 5V. Then noticed that if the voltage was slightly lower, e.g. 4.9V, the ZE07 generated higher readouts. Instead of 400mV (0ppm) it read 3-5mV higher, which is not much, but it still corresponds to >0 ppm. I could adjust it by some constant in the code, but this is guesswork.
Instead I tried powering the ZE07 with 8V and got better readings. Now the output is stable around 400.7mV.

And I have a few questions of my own, although it seems the thread and original author are not that active any more

What is the max temperature that the MD61 helium sensor warms up to? I measured it to about 25C when the ambient temp was 15C. I haven't added the temperature sensor yet, but that's the next step.

What voltage do you get from the MD61/MD62 at 100% He? Provided that it is powered with 3.0V and the resistors used are 2k/2k/0.5 Ohm.

Here is the code GitHub - vldgeorgiev/scuba-gas-analyzer: A DIY Trimix and CO scuba gas analyzer

 

[Steve78]

@Steve78 @bobziuchkovski You may also check the input voltage of the ZE07/ZE15. I'm also doing my own O2/He/CO analyzer based on the ideas in this thread and had a few cases of strange behavior of the sensors.

The ZE07's input voltage is 5 to 12V. Initially I powered it from a Liion battery with a step up converter to 5V. Then noticed that if the voltage was slightly lower, e.g. 4.9V, the ZE07 generated higher readouts. Instead of 400mV (0ppm) it read 3-5mV higher, which is not much, but it still corresponds to >0 ppm. I could adjust it by some constant in the code, but this is guesswork.
Instead I tried powering the ZE07 with 8V and got better readings. Now the output is stable around 400.7mV.

And I have a few questions of my own, although it seems the thread and original author are not that active any more

What is the max temperature that the MD61 helium sensor warms up to? I measured it to about 25C when the ambient temp was 15C. I haven't added the temperature sensor yet, but that's the next step.

What voltage do you get from the MD61/MD62 at 100% He? Provided that it is powered with 3.0V and the resistors used are 2k/2k/0.5 Ohm.

Here is the code GitHub - vldgeorgiev/scuba-gas-analyzer: A DIY Trimix and CO scuba gas analyzer

View attachment 864316

My ZE07 is powered by a voltage regulator (5V). It should be stable, I do not think it can drop down to 4.9.

The temperature that an MD61 can reach depends on the boundary conditions. Temperature, humidity, convection coefficient , gas flow...... As the physics work...

The output in 100% He is more than 500mV

 

[sinidive]

Any ideas/experiences with affordable 3.3V CO sensors?

 

[Alastor]

https://it.farnell.com/en-IT/dfrobot/sen0377/gas-sensor-board-3-3v-to-5-5v/dp/3974139?srsltid=AfmBOopvKAv9XoIBz4wmngdXvgX_j0TylosrFCeLlhWeXSex2fqmH_5p

I've no idea how it could be used in you context though.