If you know the exact pressure you need to be at, the easier it is to replicate a roast.

Copy that. It certainly is valid to have tight control over the inputs (gas flow) rather that relying exclusively on feedback from the output (the temperature).

I always went to these guys for sensors and instrumentation, when I was spending OPM (other people's money). They're top notch and I always valued the online resources they offered - lots of information and advice - even if I cheaped out later and went with something else. They give you a good sense of what state-of-the-art is.

I haven't read through all of this, but maybe useful?
http://www.energy.ca.gov/2014publications/CEC-500-2014-104/CEC-500-2014-104.pdf

 

If you know the exact pressure you need to be at, the easier it is to replicate a roast. Yes, the temperature is crucial, but its significantly easy to overshoot if you give just the slightest amount too much gas. The really expensive high-end roasters ($50,00+) have this built in and it makes a huge difference.

I've found loads of sensors out there for air and non-combustible gases, and I've found ones for gas, I just want to make sure I'm getting a sensor that will definitely work with such low pressure. They aren't cheap, so if I buy the wrong one I'm probably screwed.

Figured maybe with all the brains on this site, that someone would be able to give me some guidance.

Rosemont sells a complete line of explosion proof pressure transducers, at least they used to sell them. They had ranges down to a few inches of water column. But I also think that it is controlling the temperature that is what is important And controlling temperature by varying the gas flow is both easier and safer. And it is simple to purchase adequate regulators. 20 years ago my company built and delivered a system that controlled temperature at 200C and the variation was between 199C and 201C. Our customer was both amazed and very pleased. AND, it would hold that range for hours on end, until the test was completed.

 

If the aim is precisely adjust the pressure let it be the same day to day, then probably the cheap solution may be the LPG vehicle pressure regulator. Yet the heating section at metan use is completely unnecessary, to differ fro LPG use, the pressure regulation there is rather precise and calculated on extremely low (few mm/H2O) above till beyound the atmosphere pressure.
So, buy one scraped from vehicle cemetery for some 10 bucks, little bit polish it and use as much want.
For to know an exact pressure value, there may be used just most prost barometer, aneroid, sylphon type manometer, or just even a slopy U-pipe type with water fill. Last at 10% slope may measure so small as sub-milimeter of H2O-column pressures.
Whilst if the electronics was the goal [and Arduino imminently ] then capacitative measure between sylphon plate and added surplus pcb plate copper layer would be rather trustable signal source.

 

There are thermocouples available with millisecond response times, and if one of those were attached to the flame side of the roaster you would see the temperature as it was, with only seconds of delay, plenty fast enough for a tight controller to adjust the gas flow to reduce or increase the heat input. A servo system displayed as it was working would certainly add to the impressiveness of a roasting system. Best part of all is it would not require any computer, so it would be quite reliable.

 

Rosemont sells a complete line of explosion proof pressure transducers, at least they used to sell them.

They are now Emerson Rosemount. The last ones I bought were in the $3500 to $4500 price range but that did include the base manifold. Over the years we used quite a few and the ones installed in the mid to late 60s were still running just fine. They are great, especially the newer programmable versions but they also carry one heck of a price tag.

Ron

 

They are now Emerson Rosemount. The last ones I bought were in the $3500 to $4500 price range but that did include the base manifold. Over the years we used quite a few and the ones installed in the mid to late 60s were still running just fine. They are great, especially the newer programmable versions but they also carry one heck of a price tag.

Ron

EXACTLY! We would use them in industrial machines and while some customers questioned the expense, after a year without needing to re-calibrate the pressure sensors the one customer commented "Now I understand your choice of pressure sensors", since they never needed to adjust them.