ChrisATX
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A "cave" environmental chamber, for science!

Mon May 05, 2014 5:18 am

Hi everyone.

I'd like to hear your feedback on some feasibility here. What I need is a monitoring and control system for an environmental control system that turns a chamber into a cave environment.

I'm a scientist who does a lot of work in cave environments, studying their chemistry. What I need is a way to regulate the environment inside a chamber that mimics a cave. Water with a high pCO2 and appropriate levels of calcite saturation will be dripped into the chamber from the top at 1 drop per 30 seconds. This CO2 will off gas out of the water and into the chamber atmosphere. I need either a mess of equipment, or a controller, to do the following:

1) a way to keep the temperature of a small atmosphere of air at a constant 30 C (probe, PID, and some kind of heat source insensitive to elements, as there will be dripping water and 100% humidity).

2) A way to keep the temperature of a reservoir of water at 30 C (waterproof probe, aquarium heater)

3) A way to monitor RH inside the chamber and make sure it stays at ~100%.

4) A way to keep the pCO2 inside the chamber constant through passive ventilation (no fans). Basically, a vent to the chamber that opens more when more off gassing is needed, less when less is needed. I need to keep the chamber at ~500 ppmv. Keep in mind that the water entering the chamber at a rate of 1 drop per 30 seconds will have a pCO2 of >5000 ppmv.

5) A pH probe capable and a way to control a CO2 tank solenoid based on the measured pH.

6) A way to log all of these parameters: temperature, pH in the water, humidity, ppmv CO2 in the chamber.

7) A way to monitor all these parameters by iOS app or remotely through VPN into the University network.

Thanks all! More detail as a come up with it. This is skeletal.

I am a chemist by training, and I work on instruments for a living, but my programming skills are... zero. This would be my first foray into building environmental loggers, etc.

Ideally this would all be OS X compatible.

All help with equipment lists, feasibility, wiring, programming, would be greatly appreciated and properly acknowledged. My goal here is not just to do this and get it done, but to learn it while it's being done. The scientific possibilities of these computers for the type of work I do seem nearly limited only by imagination.
Last edited by ChrisATX on Mon May 05, 2014 5:53 pm, edited 1 time in total.

ChrisATX
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Re: A "cave" environmental chamber, for science!

Mon May 05, 2014 5:51 pm

I guess the easiest place to start would be the heater and temp control/logging.

The chamber is 11" x 5", and cylindrical:

Image

I need a way to maintain the air inside at 30 C. I also need to log the temp inside.

So, first I need to choose a thermocouple or NTD.

Then, I need to choose a heating element. Likely a tubular heater of some sort. The thermocouple obviously needs to be attached to the Raspberry Pi (tutorials? This is where my beginner-itis shines bright). A PID in the Raspberry Pi then controls a relay linking a full power supply and the heating element.

So, I need a 110 VAC relay that will basically work with line voltage, a high quality thermocouple, and PID that will take the input from the thermocouple and tell the relay when to open and close.

I also need to have a recorded log of the temperature inside the chamber.

Parts recommendations, hookup tutorials (I imagine this is an extremely rudimentary task) would all be incredibly appreciated.


ChrisATX
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Re: A "cave" environmental chamber, for science!

Mon May 05, 2014 7:28 pm

This temp probe seems to have more more desirable accuracy (order of magnitude better)

http://media.digikey.com/pdf/Data%20She ... P11493.pdf

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yv1hx
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Re: A "cave" environmental chamber, for science!

Mon May 05, 2014 7:31 pm

ChrisATX, Have you choose a CO2 sensor?

How long will last the data collection experiment? (Days? Months?, years??)

With the raspberry pi you can log any amount of data you need, the only limitation (apart from the budget) is the size of your SD card (and of course the way that you choose to store your figures, a database, plain text file...), also you can program a task that moves your valuable data to another more secure place, like a high availability server already operating in your campus.

For the temperature sensor you can use the DS18B20, (http://www.maximintegrated.com/datashee ... vp/id/2812) this 1-wire sensor can be interfaced directly to the RPi GPIO ports, I guess somewhere is a version with an enclosure ready made so you can put the sensor inside the chamber without compromising the electronic sensor itself.

P.S.
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Re: A "cave" environmental chamber, for science!

Mon May 05, 2014 7:47 pm

ChrisATX wrote:This temp probe seems to have more more desirable accuracy (order of magnitude better)

http://media.digikey.com/pdf/Data%20She ... P11493.pdf
The disavantage of using some analog sensors is the fact you need a suitable ADC (Analog to Digital Converter), the RPi doesn't have any ADC, but this task can be accomplished attaching a external ADC to the SPI or I2C ports.

Depending on the measurement range of the ADC and the electrical characteristics of your analog sensor, you probably need some sort of signal conditioning (a Instrumentation or Operational amplifier).

I offer you other option: http://www.sensirion.com/en/products/hu ... sor-sht15/ I have used this sensor in the past, (but interfacing directly to a PicAXE microncontroller), also, this is the main RH-T sensor of a well know brand of weather station based in California (USA).
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yv1hx
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Re: A "cave" environmental chamber, for science!

Mon May 05, 2014 7:58 pm

ChrisATX wrote:Hi everyone.

...snip ....

5) A pH probe capable and a way to control a CO2 tank solenoid based on the measured pH.

...snip...
Atlas Scientific pH kit:
https://www.sparkfun.com/products/10972
http://atlas-scientific.com/product_pag ... h-kit.html

PS.
I don't have tried this sensor for myself.
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ChrisATX
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Re: A "cave" environmental chamber, for science!

Mon May 05, 2014 8:17 pm

yv1hx wrote:ChrisATX, Have you choose a CO2 sensor?
I was thinking about one of the ambient Cozir VNIR sensors.
How long will last the data collection experiment? (Days? Months?, years??)
Months. We're going to try to grow calcite.
With the raspberry pi you can log any amount of data you need, the only limitation (apart from the budget) is the size of your SD card (and of course the way that you choose to store your figures, a database, plain text file...), also you can program a task that moves your valuable data to another more secure place, like a high availability server already operating in your campus.
Fantastic!
P.S.
I drop you a PM ;)
I saw that! Thank you for your introduction and I deeply and humbly appreciate your help!

ChrisATX
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Re: A "cave" environmental chamber, for science!

Mon May 05, 2014 8:21 pm

yv1hx wrote:[
I offer you other option: http://www.sensirion.com/en/products/hu ... sor-sht15/ I have used this sensor in the past, (but interfacing directly to a PicAXE microncontroller), also, this is the main RH-T sensor of a well know brand of weather station based in California (USA).
Thank you, Marco-Luis. This looks like a great option. The ±0.5°C accuracy is acceptable for our purposes.

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Re: A "cave" environmental chamber, for science!

Tue May 06, 2014 7:06 pm

ChrisATX wrote:
yv1hx wrote:ChrisATX, Have you choose a CO2 sensor?
I was thinking about one of the ambient Cozir VNIR sensors.
As far as I can extract from the Cozir VNIR sensors documents, there is a version with temperature-humidity sensors built-in, (based in the Sensirion SHT21 chip, same family than SHT15), so I would recommend (if your budget allows it!) the Cozir VNIR sensor and a additional RH-T sensor installed inside the chamber for reference.

Also seems the Cozir VNIR sensor have a communication text based protocol, this can simplify to some point the interfacing with your RPi.
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jsobota
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Re: A "cave" environmental chamber, for science!

Sat May 10, 2014 2:18 pm

Guys this is totally awesome! If I could help you with the control and data logging, just let me know. I'm also at the university, specialized in control systems and algorithms. I've written some code to turn RPi and Arduino into a "professional" control and logging device and I have experience in controlling various systems using this mighty duo. The greatest advantage is that all the logging, PID control, etc. runs directly in the RPi.
http://www.youtube.com/watch?v=65jkw4tQJTc

For temperature measurements I recommend Maxim DS18B20 in a waterproof stainless steel body. It can be directly attached to RPi or Arduino, only one 4k7 resistor is needed. Available from Adafruit (http://www.adafruit.com/products/381) or eBay.
For switching 110 VAC I recommend Sainsmart relay board (http://www.sainsmart.com/arduino-pro-mini-2.html) or eBay alternatives.

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Re: A "cave" environmental chamber, for science!

Sat May 10, 2014 5:49 pm

ChrisATX, As possibly you already know, a point of great importance in any long time running experiment is the power supply reliability, your should consider powering the Rasp-Pi, sensor conditioning & control board from a battery operated device capable to withstand enough time to guarantee the operation with temporal AC mains power failures.
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bumblethrift
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Re: A "cave" environmental chamber, for science!

Fri Sep 18, 2015 3:29 am

@ChrisATX

Hi Chris - what configuration of sensors - particularly which co2 sensor - did you go for in the end? And has it been successful, any issues with reliability or corrosion? I'm looking into a similar project but with possible longer term application and in a real cave

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