I am currently in a biotech class in which we are building yeast mobiles. Before we constructed our vehicles, we measured the amount of Co2 generated (from fermentation) by using the water displacement method.
My proportions are: 1 gram yeast, .9 dextrose, 25 ml of water. Using these measurements, I have displaced up to 150ml of water.
Is it possible to use a "Double Bubble Airlock" (or generic airlock) with a pressure sensor? (http://www.digikey.com/product-detail/en/MPX4250AP/MPX4250AP-ND/464053) I am looking to measure pressure digitally without the use of additional water beakers. Does my proportion generate enough to get an accurate reading on the pressure sensor? (the sensor cant get wet)
I am looking for some guidance on this topic. Is it feasible? am I on the right track? Any suggestions or help is greatly appreciated!
I doubt measuring fermentation pressure will tell you a great deal apart from a) fermentation has started and b) fermentation has ceased. Basically no gas flows from the fermentation vessel until the pressure exceeds the hydrostatic head of the airlock. So pressure builds until this point. Once the hydrostatic head is exceeded the CO2 flows through the lock to atmosphere and, apart from minor pulses as the lock passes bubbles of gas, the pressure in your fermenter is relatively constant. Once fermentation ceases, no more gas escapes and the pressure diminishes.
I feel that you'd be better trying to measure gas flow rates. You could do this by either using a small gas flow meter or simply by counting the number of gas bubbles passing through your airlock system. If you can approximate bubble volume (you need to assume it is relatively constant) then count bubble rate you will arrive at CO2 volume generated. Since you know the fermentation pressure (airlock hydrostatic head) you can then correct for the reduction in volume due to pressure compression.
To measure bubble size you could set up a simple calibration system whereby you slowly expel a known volume of CO2 through the air lock and count the number of bubbles produced. If the bubble rate is similar to the fermentation bubble rate it would be reasonable to assume bubble sizes are similar.
However, in answer to your specific question : The sensor you illustrate has far too great an operating range to give you any meaningful data. You need a much more sensitive sensor with a range of somewhere in the order of 0 to 8"WG. In other words, the sensor you need should have a range which is slightly more than the hydrostatic depth of your displacement vessel, since this depth is the maximum pressure that will be experienced.
I can't figure out what you're trying to measure. Is the pressure itself significant, or are you actually trying to measure the volume of gas produced?
