[PSUBS-MAILIST] Optical Oxygen Sensors

Fri Aug 9 08:33:41 EDT 2019

Just heard back from SST sensing (UK) re price & accuracy.
The price is reasonable at GBP 46.85, per unit, but the freight on 3 to NZ is 
GBP 59., which is expensive considering the size & weight. I will see if they 
can put them on a slower boat! 
Had the below response re accuracy...
Hi Alan,

0-300mbar is the ppO2 range.

2% FS is then +/-6mbar ppO2.

O2% = (ppO2 / total pressure) x 100

So, total pressure varies the accuracy of the sensor.

At atmospheric it would be around +/-0.6 O2%

We are currently going the opposite direction for ppm (parts per million). Our intention s to then investigate extended range (%)

Cheers Alan

> On 9/08/2019, at 4:08 PM, Alan via Personal_Submersibles <personal_submersibles at psubs.org> wrote:
> 
> Thanks Jon,
> Some great products there. I had read that I could use a resister & capacitor to
> read analog on the digital pins based on the time it took to charge the capacitor,
> & wasn't too thrilled about going down that path. 
> Was tempted to buy all those items straight away but will hold off a bit until I 
> buy all my sensors. Knowing that I can rely on these options is great though.
> I have requested clarification on whether the optical sensors accuracy is <2%
> error on the range that it measures (0-25%) or on 0-100% O2. If it's on the latter
> then it's not very good, however it was quite accurate in the video I saw so
> hopefully it's <2% on 0-25%.
> I have also asked if they make a product with a wider measuring range.
> Have two price requests in the pipe line & will give an update when the info
> comes in.
> Cheers Alan
> 
> 
> 
>> On 9/08/2019, at 1:05 AM, Jon Wallace via Personal_Submersibles <personal_submersibles at psubs.org> wrote:
>> 
>> Alan, you have a few options.
>> 
>> You can run Processing language on the Raspberry.  The Arduino IDE language is in fact the processing language.  Check out processing.org.  However, you are correct in that the Raspberry is somewhat lacking in communication IO pins and does not have any onboard IO ADC pins.  You can get around the IO limitation by using a multiplexer like https://www.sparkfun.com/products/13906 or https://www.sparkfun.com/products/9056.  You can get around the ADC issue by using an external ADC like https://www.adafruit.com/product/1085 which will talk to the Raspberry via I2C.
>> 
>> Check out Teensy at https://www.pjrc.com/teensy/ which are Arduino compatible in terms of software but have much more muscle power and IO than any of the ardunio boards.  It also has a teensy footprint.  I used Teensy 3.2 for the compass project.  You should look at Teensy 3.5 or 3.6.  Both have 6 serial IO pins, 3 SPI pins, 3 I2C pins, and gobbs of analog pins.  If you use the multiplexers listed above you can expand your IO capacity by factors.  The 3.5 is 120mhz and 5v tolerant, the 3.6 is 180mhz but strictly 3.3v. 
>> 
>> In terms of the sensor, I considered it but it's only a 25% measurement and has about a 2% error full scale.  That still puts it within acceptable use but doesn't provide much overhead on the top end.  It is however price compatible with typical gas sensors and has a much longer expected life of 5 years.
>> 
>> Maybe I'll buy one anyway just to try it out.
>> 
>> Jon
>> 
>> 
>> 
>> 
>> On Thursday, August 8, 2019, 12:03:54 AM EDT, Alan via Personal_Submersibles <personal_submersibles at psubs.org> wrote:
>> 
>> 
>> Hi Jon,
>> I was a bit bamboozled by one products description of code for data transmission
>> & thought it would be easier to just have a voltage or an amperage range to
>> deal with. I don't need the temperature & pressure data as I have other sensors
>> for that. The arduino uno B I have has only one tx rx option; however you prompted
>> me to review things & found that the arduino mega has 3 tx rx ports & so would do 
>> for my 3 sensors. Still considering my options.
>> I am looking to use the arduino & raspberry pi but have been going round in circles
>> a bit. Was learning to program the arduino, then decided no, I need to use the
>> raspberry Pi, so was learning Python for programming that. Now I have found out
>> that the raspberry Pi doesn't have any analog pins & has a small maximum
>> current draw. 
>> Is there an alternative to those two that is a bit more robust?
>> Alan
>>  
>> 
>>> On 8/08/2019, at 2:28 PM, Jon Wallace via Personal_Submersibles <personal_submersibles at psubs.org> wrote:
>>> 
>>> CO2 meter has an RS485b analog model.  But I'm curious, why use voltage instead of serial?
>>> 
>>> Jon
>>> 
>>> 
>>> On Wednesday, August 7, 2019, 09:45:45 PM EDT, Alan via Personal_Submersibles <personal_submersibles at psubs.org> wrote:
>>> 
>>> 
>>> Hi,
>>> I've been reading a bit about the solid state optical oxygen sensors which
>>> have a longer life & are more reliable than traditional galvanic cel ( battery)
>>> type O2 sensors. 
>>> Poseidon developed them for the dive industry & they were hailed as a break
>>> through at the time. There is a company, SST sensing that is marketing them for 
>>> varying applications....https://www.sstsensing.com/optical-oxygen-sensors-key-benefits-and-applications/
>>> Is any one familiar with them? There seems to be a big price difference between
>>> varying brands.
>>> The ones I've seen are calibrated internally for pressure & temperature & transmit 
>>> data rather than a voltage or current reading. I am looking for a cheap option that 
>>> has a current or voltage signal rather than data & I will be using something like a raspberry Pi or Arduino to process the reading.
>>> I am also wanting 3 as in a rebreather to compare readings.
>>> Do they need much of an O2 flow over them or are they ok just being placed 
>>> randomly within the hull?
>>> Cheers Alan
>>> <image1.jpeg>
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>> 
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