What pressure sensors are you using to gather digital gas pressure data?

Discuss roast levels and profiles for espresso, equipment for roasting coffee.

#1: Post by jpbbden »

What sensors are people using to get gas pressure data into Artisan and Cropster?

I'm looking to upgrade my roaster's gas gauge to something with digital output (a transmitting gauge or a pressure transducer) and am having a bear of a time selecting a product. I'm using a small roaster with a 7 inch H2O (1.7 kPa) gas supply pressure requirement and have been looking at sensors in the 0-10in H2O range.

Most of the offerings I'm seeing in that range are differential pressure sensors that can be made to read gauge pressure by only connecting the high side to the gas line and referencing the low side to atmosphere.

I've seen posts here mentioning using an Extech 755 to do a gas pressure reading that can be output over USB. I contacted Teledyne FLIR (their parent company) about this and got the following reply:
Upon checking with our team, I was able to confirm that unfortunately, model HD755 is designed to be used with air and gasses. Natural gas is combustible. As model HD755 is not intrinsically safe it should not be used with combustible gases.

We apologize for the inconvenience.

Best regards,

Jose Aular
Technical Support Specialist
Teledyne FLIR
Dwyer also suggested that something intrinsically safe would be a requirement.

Application engineers from other manufacturers (Wika, Setra, others) have suggested that sensors (single-ended and differential) can be used with natural gas if they're not in an environment where an intrinsically safe rating (for example ATEX certification) is demanded provided that the parts of the sensor in contact with the gas are natural gas compatible (Stainless Steels, ceramic, etc.).

My risk management brain says that even worst-case accidental ignition of 1kPa gas coming out of a very small orifice wouldn't be catastrophic if someone was standing right there, but I'm not an engineer. :)

If you're willing to share, I'd love to hear your experiences with specific products for recording gas pressure.




#2: Post by aabud »

Subscribed and interested... I looked at this a few months ago and, as you mention, couldn't find a digital gauge that was ok for propane. I ended up circumventing the lack of a digital gauge by manually callibrating my "digital" valve to an analog gauge (e.g. so I know a certain angle of rotation on my digital valve equates to a certain KPA... a couple of callibration points and I can do math to set the valve to any KPA).

It's a pain to have to callibrate for each roasting session, however, so I haven't given up on a digital gauge.

One idea I was going to experiment with (haven't gotten around to it yet), was to build my own digital gauge out of an analog gauge, micro-camera, and a micro processor.... have the micro processor interpret the needle via an image and output the digital value.

But a native digital pressure gauge for natural gas/propane would be ideal...

jpbbden (original poster)

#3: Post by jpbbden (original poster) »

@aabud -- There are a handful of projects out there where people have used OpenCV to read analog gauges and that looks pretty promising if the gauge is well-scaled to pressure ranges and precise enough to allow good angular resolution.

The specific product recommendations made to me by vendor sales engineers were all on the spendy side when they use intrinsically safe equipment:

Dwyer recommended either the Series 3100D for a gauge/transmitter solution, or the Series 2010 Magnehelic gauge combined with the 608 Series transmitter. This solution has a price tag in the $850-$1200 USD range.

SensorsONE recommended the DMK351 at $500 USD. It would benefit from being paired with an analog gauge.

Wika thought their A-10 series would work and the price is a (relatively) more palatable $150-$200 USD. At my pressures the accuracy isn't high enough, but it might make a good option for someone operating a higher gas pressures.

The Setra engineer seemed confident to recommend the 267 series products with NPT ports for natural gas if an intrinsically safe certification wasn't required. New, these can get expensive but the surplus/aftermarket is bustling with these units on eBay.

All of these still need additional hardware to get either a 4-20mA or 0-10VDC output into software, but there are cheap solutions such as Phidgets (or DIY resistors to Arduinos) provided the ADC is at sufficient resolution. I think the Phidget VINT hubs are upsampled to 16-bits.

I think I was hoping there would be a ~$125 USD solution on the sensor end, but maybe the lower pressures are making things expensive...


#4: Post by aabud »

Those Setra ones look like they would be workable for me, if I can catch one with the right range on eBay. I think my setup maxes out at around 5 to 6kpa (never run a roast yet with it over 4kpa, so I'm kinda guessing on the top end).


#5: Post by aabud »

Oh, I also have one of these (https://www.amazon.com/gp/product/B07KJHRPLG) that I was going to experiment with. As the range is 10psi.. . which is about 10 times too big for what I think I need... I assume the accuracy would not be sufficient, but as I have it, thought it might be useful learning tool. Again... unsure on the safety implications of using this with propane in a supervised outdoor environment.

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#6: Post by okmed » replying to aabud »

1% accuracy over 10psi doesn't seem sensitive enough for your use (5kpa) (1% of 10psi = 0.1psi = 0.7kpa = plus or minus 14%)


#7: Post by aabud » replying to okmed »

Yes - agreed... probably not worth the bother. Should probably wait for something to surface on ebay in the <$50 price range that has the right range/accuracy.

Team HB

#8: Post by ira »

Connecting the pressure might be a challenge, but there are likely some things here that might works perfectly in the $100 range.

https://www.mouser.com/datasheet/2/187/ ... 649586.pdf


jpbbden (original poster)

#9: Post by jpbbden (original poster) »

@ira, I hadn't thought about Honeywell -- that's a good suggestion.

There was nothing in that datasheet's wetted parts that seemed incompatible with natural gas. I reached out to their technical sales department to see what they had to say -- will report back what I hear.


Team HB

#10: Post by ira »

And it claims useful for adjusting burners on the data sheet.