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MPRLS Ported Pressure sensor
Moderators: adafruit_support_bill, adafruit

Please be positive and constructive with your questions and comments.

MPRLS Ported Pressure sensor

by wsquared58 on Mon Aug 12, 2019 7:38 pm

I was wondering how accurate this sensor is for barometric pressure vs some of the other options.
This sensor is appealing to me because I am concerned about moisture getting inside the enclosure and I can bring some tubing outside the enclosure and use a gland to keep it weather tight.

I also have the BME280 but have struggled to figure out a way to have it read accurately without putting some sort of vents in enclosure. Any thoughts on these conformal sprays or epoxies would be appreciated also as I have concerns about keeping the interior of enclosure cool from the Pi 3b+ running.

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Re: MPRLS Ported Pressure sensor

by adafruit_support_bill on Tue Aug 13, 2019 5:55 am

The MPRLS has a range of 0-25 PSI absolute pressure. Since normal atmospheric pressure falls near the middle of that range (~14 PSI), it should work well for barometric pressure measurements.

Conformal coatings are good for protecting electronics from weather, shock and vibration. The down side is that they tend to slow heat dissipation. Although if you search, you can probably find one that is formulated for good thermal properties. The other limitation is that some components (e.g. pressure & humidity sensors) won't work if covered by the coating.

One technique I've used for passive cooling in a sealed enclosure is to cut a large hole in one side of the enclosure and cover the hole outside with a large aluminum plate or heat-sink and seal with silicone. Then mount heat emitting components on the inside - directly to the heat sink.

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Re: MPRLS Ported Pressure sensor

by wsquared58 on Tue Aug 13, 2019 7:42 am

That's a good idea about the plate. Any value in putting a fan on the exterior of the plate? I've seen some vent covers for enclosures that look similar to a dryer vent hood that would protect a fan from direct water intrusion.

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Re: MPRLS Ported Pressure sensor

by adafruit_support_bill on Tue Aug 13, 2019 8:06 am

A fan would increase the cooling capacity. But it is another potential point of failure. And if the fan quits, the shroud would start working against you. You'd want to weigh the cost and/or bulk of a fan & shroud assembly vs just a bigger heat-sink.

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Re: MPRLS Ported Pressure sensor

by millercommamatt on Tue Aug 13, 2019 1:50 pm

For the BME280, you can just run a long string of tubing out from the bottom of your enclosure. Water won't get up that and it will also dampen dynamic pressure perturbations from the wind. So long as your enclosure isn't air tight, the pressure readings will be fine. Condensation is a bit of a worry.

I use BME280s and BMP388s to measure high resolution pressure at 1 Hz for Science™ and I just keep them indoors.

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Re: MPRLS Ported Pressure sensor

by wsquared58 on Tue Aug 13, 2019 3:11 pm

All of this is going to ultimately end up as part of a weather station I'm building for a friend and will be located near Pensacola, FL so high humidity is a given. Everything will be mounted on a pole topped by wind speed, direction and a rain gauge. Hopefully it will stand up to a less than direct hit from a hurricane.

Comparing datasheets the BME is a lot more accurate than the MPRLS so that is a concern. I am assuming that the accuracy is +/- the units of the device rather than % since the data sheets don't explicitly say.
I saw a project on some other electronics oriented site where the person put some tape over the tiny BME port and coated the whole thing with a conformal coating then removed the tape which prompted that part of question.

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Re: MPRLS Ported Pressure sensor

by adafruit_support_bill on Tue Aug 13, 2019 3:22 pm

The accuracy is specified as a percentage of the full-scale span (footnote #5)
So +/- 0.25% of 0-25 PSI is +/- 0.0625 PSI.

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Re: MPRLS Ported Pressure sensor

by wsquared58 on Tue Aug 13, 2019 4:49 pm

Honeywell MPRLS.JPG
Honeywell MPRLS.JPG (41.27 KiB) Viewed 156 times
I see that footnote.
What is the +/- in the attached jpg? That is what I was looking at.

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Re: MPRLS Ported Pressure sensor

by adafruit_support_bill on Tue Aug 13, 2019 5:14 pm

The column header says "%FSS" That means a percentage of the full-scale-span.

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Re: MPRLS Ported Pressure sensor

by wsquared58 on Tue Aug 13, 2019 5:43 pm

I'm not an instrument person but ran a bunch of controls based on temperatures and pressures and have been told that that meant at 25 psi it could be 26.5 on high side and 23.5 on low side and instead of zero it be 1.5 psi on high side and -1.5 on low which would mean it would come off zero late. I'm fine with being dead wrong on that.
Atmospheric pressure runs in a pretty tight band so want the most accurate instrument is all.
I'm used to pressures in the 0 - 2000 psig range and temps as high as 100 - 1000 F and often it was about stability and rate of change vs precision accuracy so this is all new territory.

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Re: MPRLS Ported Pressure sensor

by adafruit_support_bill on Wed Aug 14, 2019 6:20 am

Atmospheric pressure runs in a pretty tight band so want the most accurate instrument is all.


"Accuracy" in sensors is an often misunderstood term. Part of that is because sensor manufacturers often cherry-pick the statistics to make their device look better. It is difficult to directly compare "Accuracy" specs between sensors if they are calculated using different criteria. What is more important that accuracy is precision and repeatability. If you have a precise and repeatable sensor, you can achieve accuracy via calibration.
https://learn.adafruit.com/calibrating-sensors

Honeywell actually does a very good job here at defining what they mean by accuracy and identifying the sources of error on page 3 of the datasheet: https://sensing.honeywell.com/honeywell ... 332628.pdf

For best resolution and accuracy in the atmospheric pressure range, you probably want to choose a sensor designed for that range.

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Re: MPRLS Ported Pressure sensor

by wsquared58 on Wed Aug 14, 2019 10:05 am

Perhaps my terminology was not quite right. Maybe sensitivity is better term.
This is around protecting the electronics from moisture.
Station going to be mostly unattended and a 12 hour drive away.

Started with a BME280 and got to thinking about the FL humidity issue so bought an SHT10 which I can have outside case and use gland to seal that entry. The MPRLS seemed like a good option for capturing atmospheric pressure via the ported sensor and bringing a short section of tubing through another gland.

Record high barometric pressure is 32" Hg = 1084 hPa = 15.7 psia
Record low barometric pressure is 25.9" Hg = 877 hPa = 12.7 psia

That puts the BME280 running at the top end of the scale most always whereas the MPRLS is running closer to mid range.
So which is the more sensitive instrument to run in that narrow band is the question.

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Re: MPRLS Ported Pressure sensor

by adafruit_support_bill on Wed Aug 14, 2019 11:22 am

It is not easy to compare the two directly.

The MPRS starts with a 24 bit raw reading. But after the internal compensation calculations, the manufacturer specified resolution is just 14 bits for the 0.25 to 22.5 PSI range. You are using just 13% of that range, so the effective resolution is down below 12 bits.

The BME has a 20 bit resolution over the 4.35 to 15.95 PSI range. Of that, you are using about 26%, so the effective resolution is about 18 bits. Compensation is performed externally in the library, so there will likely be some loss there.

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Re: MPRLS Ported Pressure sensor

by wsquared58 on Wed Aug 14, 2019 11:33 am

Thanks, I guess since you are way over my head.
Which one would you recommend?

I think the BME280 is semi-broken that I have as the temperature indication on the IO line graph is flatlining at around 80 F and making these step changes that aren't in keeping with the rest of the values.

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Re: MPRLS Ported Pressure sensor

by adafruit_support_bill on Wed Aug 14, 2019 1:17 pm

Which one would you recommend?

For measuring barometric pressures, I'd probably go with the BMP.

I think the BME280 is semi-broken that I have as the temperature indication on the IO line graph is flatlining at around 80 F and making these step changes that aren't in keeping with the rest of the values.

What about the other readings? Do they seem normal?
When did you purchase the sensor?

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