# Building an Electrical Circuit to Monitor Pressure

1. Nov 29, 2011

### tarheelchem

I need to build a circuit to do the following:

I am making some wine at home and need to monitor the process. During the fermentation process CO2 is produced so I need to monitor the pressure in the system and provide for a pressure release (back to 1.1 atm.) if the pressure gets too high (> 1.4 atm.). I also need to track the rate of pressure increase to determine if something is going wrong with the fermentation process. If the pressure is increasing > 0.01atm./hour for more than 5 hoursthe system needs to shut down by permanently opening the pressure release valve and turning on a red warning light. Finally, I need to determine when the wine is done (17% EtOH). I have a sensor to detect %EtOHwith an output of 1V/1% EtOH. When the EtOH concentration is at the correct level, a green light should be turned on and the pressure release valve permanently opened.

Any ideas?

2. Nov 30, 2011

### dlgoff

3. Nov 30, 2011

### sophiecentaur

I think I'd be inclined to use a manometer of the right height (which is basically what the normal breather / bubbler things are - but with no proper calibration or set pressure values) and an optical method for sensing the level of the liquid in the manometer. You could count the number of the times the pressure builds up and is released as the optical sensor operates, giving the total volume of CO2 produced - which I guess is what you want to know. I am interested in the significance of the actual CO2 pressure. Is it a factor in fermentation rate?

There are a number of pressure sensors (cheap spares) which are used to set the water levels in Washing Machines and Dishwashers. Could that be a solution? (perhaps the pressure you want is too high for that, though.)

Last edited: Nov 30, 2011
4. Nov 30, 2011

### AlephZero

That woud be about 13 feet, for a water manometer

FWIW these seem very high pressures for home winemaking. Usually, you use an airlock to stop anything getting in from the atmosphere, but the internal pressure is atmospheric.

5. Nov 30, 2011

### sophiecentaur

No worse than the domestic water system. Any plumbing device can take much more pressure than that.
I would also be interested in the whys and wherefores of such high pressure.

6. Nov 30, 2011

### dlgoff

I'm actually a "don't reinvent the wheel" type of guy and prefer to do integration when making monitor/control systems. But I see your point too; keep it simple.

I'm curious about the pressure significance in the process too. I can think of a couple reasons he might want to do this. To collect good data to get the best wine consistently or he's just nerdy like most of us here and wants to play. Which ever. More power to him.