A "cave" environmental chamber, for science!

[system]

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 (I promise! check my profile ) 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 an Arduino 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 for the type of work I do seem nearly limited only by imagination.

[system]

I'm a scientist (I promise! check my profile smiley ) who does a lot of work in cave environments,

In other words, a bonafide CAVE MAN ? XD

but my programming skills are... zero

In other words, a typical Newbie... XD

[system]

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)

These two may be problematic unless you can guarantee the temp for BOTH will NOT INCREASE, eliminating the need for the ability to cool either one. If not, you may need to design a cooling system that circulates air slowly through PVC pipes to an ice
bath where the air enters the bottom , rises to the top of the ice bath and out the exhaust vent above the sealed chiller enclosure
(lexan) and back to the CAVE via a small PWM speed controlled computer cooling fan that turns off an on by a PID running the chiller based on feedback from the CAVE. Conversely, the heating of the cave would need a similar PID and possibly heating coils.

[system]

raschemmel:

I'm a scientist (I promise! check my profile smiley ) who does a lot of work in cave environments,

In other words, a bonafide CAVE MAN ? XD

I've been called worse

but my programming skills are... zero

In other words, a typical Newbie... XD

I've been called worse

Actually, I work a bit in Matlab, but that's about it. As far as this type of coding, no clue.

I also have a lot of experience culturing corals, orchids, etc. so I'm good with mechanical things, and building artificial environments.

[system]

raschemmel:

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)

These two may be problematic unless you can guarantee the temp for BOTH will NOT INCREASE, eliminating the need for the ability to cool either one. If not, you may need to design a cooling system that circulates air slowly through PVC pipes to an ice
bath where the air enters the bottom , rises to the top of the ice bath and out the exhaust vent above the sealed chiller enclosure
(lexan) and back to the CAVE via a small PWM speed controlled computer cooling fan that turns off an on by a PID running the chiller based on feedback from the CAVE. Conversely, the heating of the cave would need a similar PID and possibly heating coils.

The reservoir and the chamber atmosphere will be too completely different modules. The reservoir contains the CO2 reactor for dissolving limestone and providing soil water pCO2 end members for the water going to the "cave" chamber. The only thing the reservoir provides to the cave chamber is a drip of water.

Also, just for more info, the setup will be indoors, so no need to worrying about cooling below ambient, as this is meant to simulate tropical caves.

[system]

And I imagine something like thermostated water circulating through a wort chiller style set of copper coils in the chamber would be ideal.

[system]

He said he doesn't need chilling.

[mrburnette]

Respectfully,
You need to start with a spreadsheet that translate requirements, priorities, 1st choice sensor, 2nd choice sensor, Voltage, current,calculated Watts/power, comm protocol, etc.

Power dissipation is important for sensors in the environment as the heat must be neutralized.
Protocol may be anything from DC to SPI to I2C to Rs232 to serial TTL, etc.

Two schools of thought:

• every sensor buffered and protocol translated before assimilation
• connection to main uC/MPU and translated internally

Consider that sensors drive input to the PID algorithm, my preference is that every sensor be independent and addressable. Selecting this approach leads to a black-box traditional design effort, allows building "working spares" and simplifies troubleshooting.

Most Arduinos are 8-bit machines and while they may easily handle a few sensors, they have internal limitations in SRAM; for example, UNO only has 2K total RAM. Most utilize software floating point, the ARM based DUE being the exception.

The most minimum Arduino is the single uC, a $2 Atmel328P. Running at 8MHz on internal oscillator, it can easily handle any single sensor... Serial, I2C, SPI.... Yes, it could handle many sensors, but Arduino supports no threading model w/o using a RTOS and if one wished to use an Arduino as a "hub device" then I would design around an RTOS.

For aggregating the sensors, I would move away from Arduino an suggest a RaspberryPi or other computer on a board. An Arduino Due is hardware capable but an RPi is better supported and runs Linux which will make interfacing to the Apple OSX easier. RPi can easily thread so running the PID algorithms is a natural. Ideally, using a MacBook would even be better! But, RPi is inexpensive and less likely to grow legs and run away.

Good luck, sounds like a fun project. Get the spreadsheet started.

Ray

[system]

raschemmel:
He said he doesn't need chilling.

Hahah, that was me. By wort chiller I simply meant a wound copper spiral. Warmer thermostated water can be pumped through to keep the tank heated.

[mrburnette]

ChrisATX:

raschemmel:
He said he doesn't need chilling.

Hahah, that was me. By wort chiller I simply meant a wound copper spiral. Warmer thermostated water can be pumped through to keep the tank heated.

A TEC would make an ideal temp device since the H/C function is DC controllable. Multiple devices could be used to provide redundancy ... Working at 33% - 40% capacity, plenty if safety overhead - just stagger power, 3 supplies distributed via blocking diodes provide ample overhead and redundancy.

[system]

Thanks mrburnette.

It will take me a bit to do the background research to follow your post 100%.

My brother, a software engineer, also recommended either a Netduino or Raspberry Pi.

Cozir makes an integrated all in one Humidity/Temp/VNIR CO2 sensor that would be perfect. I need to find out what kind of device would be controlled by it to allow changes in ventilation of excess CO2 from the chamber.

CozIR®-A 2,000ppm CO2 + RH/T Sensor

DHT22 temperature-humidity sensor + extras

[system]

mrburnette:

ChrisATX:

raschemmel:
He said he doesn't need chilling.

Hahah, that was me. By wort chiller I simply meant a wound copper spiral. Warmer thermostated water can be pumped through to keep the tank heated.

A TEC would make an ideal temp device since the H/C function is DC controllable. Multiple devices could be used to provide redundancy ... Working at 33% - 40% capacity, plenty if safety overhead - just stagger power, 3 supplies distributed via blocking diodes provide ample overhead and redundancy.

Hmmm. I do like TECs. Nice idea.

[system]

Looks promising:

Using CO2Meter.com Sensors with Raspberry Pi

[mrburnette]

ChrisATX:
Thanks mrburnette.
It will take me a bit to do the background research to follow your post 100%.
consider it homework
My brother, a software engineer, also recommended either a Netduino or Raspberry Pi.
Bro is smart
Cozir makes an integrated all in one Humidity/Temp/VNIR CO2 sensor that would be perfect. I need to find out what kind of device would be controlled by it to allow changes in ventilation of excess CO2 from the chamber.
CozIR®-A 2,000ppm CO2 + RH/T Sensor | CO2Meter.com
Accuracy: ±50 ppm ± 3% of reading

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.

This will require a serious eye based upon chamber volume and permissible venting and humidity fluctuations. Modeling will be required.

DHT22 temperature-humidity sensor + extras : ID 385 : Adafruit Industries, Unique & fun DIY electronics and kits

Cheap. If you source one, do so from one of the "big" houses that can provide tracking to true source of manufacturing.

General note from my college research days in the lab: buy many sensors, test and "map" each for archives. Match and serialize all sensors to be utilized... Put lot under controls. Do same for interface modules, mate repair parts to sensors and bulk test, record. Select deployment sensors from spare stock. Any significant PID issues should be mapped into software from day #1. Results header should always spit out serial numbers of sensors used at any present time... This will allow for validation of sensors in the data stream!

Better yet, use XML for data passing.

[system]

Cheap. If you source one, do so from one of the "big" houses that can provide tracking to true source of manufacturing.

Yeah. Many many options in the temp area though. Some of the instruments I work with are K-type, some are RTD...

[mrburnette]

ChrisATX:

Cheap. If you source one, do so from one of the "big" houses that can provide tracking to true source of manufacturing.

Yeah. Many many options in the temp area though. Some of the instruments I work with are K-type, some are RTD...

Yep, instrumentation amps, etc. Been there with engine exhaust monitoring with thermocouples.

You know this, but procurement always raises hell when you have to purchase numerically beyond your initial requirement and your only excuse is to support the lifespan of the project and any extensions of same. But, amass not just parts, rather assembled and profiled and calibrated assemblies. Grad students come and go and continuity must be designed into the project. The environment hardware is collectively expensive but data becomes increasingly valuable as more is collected... Restarting an experiment ovrr may require tossing out the old datasets... Now, that would be expensive!

[system]

This sounds like an ideal application for a PLC and industrial controls rather than hobby grade equipment. Assuming the data is what is important I'd prefer sensors and controls that are calibrated and NIST traceable so that I'd never be called into question the validity of the data. Ladder logic programming is going to be easier for the next guy to adapt and troubleshoot because it is more widely understood by non-programmers who typically can support the hardware and unlike an arduino the program can be retreived from the controller if for some reason the original copy is misplaced or destroyed.

The downside would be cost, although inexpensive components can be found on Ebay or from discount distributors like AutomationDirect.com the initial capital expense is going to be higher, but I believe the long term costs will be equal or lower compared to using an arduino.

[system]

Right now this is a pilot experiment, and in this capacity there is the need to keep costs low and, hence, my attempt to build a control system (keeps costs low and I learn stuff, which I really love). If the chamber works correctly (we are essentially trying to grow a stalagmite), the pilot/proof of concept data can be used to justify spending much more. The old scientific catch 22... Need money to get data; need data to get money. Right now the idea is to make the monitoring and post-experiment chemical analyses an honors project for undergraduates.

I just need a road map for fundamentals.

[zoomkat]

Right now this is a pilot experiment, and in this capacity there is the need to keep costs low and, hence, my attempt to build a control system (keeps costs low and I learn stuff, which I really love).

I suggest you get an old junk refrigerator to use as your insulated box (or build an insulated box). In the box you will need a large mass with good heat transfer to maintain stable temperatures. Maybe put a large container of water in the bottom of the box with an with some aluminum fins in the water sticking out of the water into the air for good heat transfer. Modify a aquarium heater such that the heater is in the water container and the thermostat section is in the box air section. The humidity should stay at ~100%. Just inside the box use a clear barrier (Plexiglas or clear plastic film) so the box door can be opened for observation without interacting with the atmosphere in the box.