Using a Barometric pressure sensor indoors

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Using a Barometric pressure sensor indoors

Postby Graham Webster » 2012 Sep 12, 18:44

I want to buy an electronic barometric pressure sensor and use it indoors. I particularly like the barometric pressure sensor from Young, http://www.campbellsci.co.uk/index.cfm?id=119
I'd rather locate the sensor inside my house because the accuracy is highest, the temperature is stable at room temperature and strong winds/gusts are minimised. I don't have an AWS (yet).
I want to use a serial connection RS_232. How do I go about sampling and logging pressure from this device using my laptop with windows 7? Do I need a datalogger? How do I power the sensor? AC or battery? Is there online software?

In this modern era of electronic devices, is there still a place for the simple Kew pattern mercury barometer? I do enjoy reading traditional instruments. Russell Scientific still make them.

Cheers
Graham.
Graham Webster
 
Posts: 9
Joined: 2012 Sep 04, 17:11
Location: Baintown, Fife. 125m asl. Firth of Forth, 3km to south-east. Hill, 205m asl 1km to NNW.

Re: Using a Barometric pressure sensor indoors

Postby Stephen Burt » 2012 Sep 12, 21:59

I'd recommend you buy a logger. Rather expensive for just the one sensor of course, but you can always add other sensors as time goes on. The logger software will take care of all the polling and logging intervals, which otherwise you'll have to set up yourself. You'll also have to keep the laptop permanently connected and switched on (you can't allow the disk to drop into sleep mode, or you'll lose data), although you could use a netbook or even a Raspberry Pi to handle that, provided you're comfortable with the interface programming that would be required. A logger you can power from a battery and connect to the PC only when you need to, or automatically (say) every hour, while some loggers will piggyback power to sensors too.

There's lots of choice, from sub £100 to £1000 plus. At the risk of sounding like a plug - well, why not! - there's a whole chapter on choosing and using dataloggers in my new book.

I still have the mercury barometer we were given as a wedding present 29 years ago, and still read it occasionally as a calibration check. They are getting harder to find since legislation has outlawed mercury-based instruments. It's also rather tiresome to read it every minute 24x7, which an electronic sensor+logger combination does rather well! Very useful for fine detail in sharp fronts, squalls and thunderstorms, etc.

SB
-----
Stratfield Mortimer, Berkshire - central southern England
51.4°N, 1.0°W, 60 m AMSL, station grade A - AAAA47R
Records commenced here 1987 - local records available back to 1862
The Weather Observer's Handbook: www.measuringtheweather.com
Stephen Burt
 
Posts: 247
Joined: 2011 Dec 02, 19:36
Location: Stratfield Mortimer, Berkshire; a well-exposed rural site, 10 km SW of Reading

Re: Using a Barometric pressure sensor indoors

Postby Graham Webster » 2012 Sep 14, 18:40

Stephen-I have your new book and I've read up to the chapter on metadata.

Maybe I should go for the Vaisala PTB330. It is a high quality pressure sensor and datalogger all in one. You can order it with AC power ideal for using indoors. Other options include; USB connections for downloading data to PC for analysis in Excel, serial DB9 for continuous connection to PC, class A or B sensor-A has 0.01mb resolution and 0.1mb accuracy and class B, 0.1mb res and 0.2mb accuracy. I think the class B is sufficient for my needs. It will cost £1500, about the same as datalogger + pressure sensor or even a new mercury barometer.

Speaking of mercury barometers..Stephen, have you ever had your one calibrated by the NPL or UKAS? In 29 years, what condition is the mercury in? Have you had any trouble with air bubbles or defective vaccuum? The reason I ask is because I would quite like one.
Graham Webster
 
Posts: 9
Joined: 2012 Sep 04, 17:11
Location: Baintown, Fife. 125m asl. Firth of Forth, 3km to south-east. Hill, 205m asl 1km to NNW.

Re: Using a Barometric pressure sensor indoors

Postby Stephen Burt » 2012 Sep 16, 09:47

Answering Graham's question regarding pressure sensors and loggers ...

The first thing I'd say is that there is no need to fork out anything like £1500 to obtain a continuous record of barometric pressure with a precision of 0.1 mbar and accuracy within 0.2 mbar. The suggested equipment is a point solution of high accuracy, ideal where that's the only element under consideration, and where high accuracy and reliability for that one element are essential - at an airport, for example. For an amateur-level system, and in my experience, point solutions (single element sensor/logger combinations) are more difficult to maintain and integrate with other data sources.

What would I suggest? I'm always reluctant to recommend systems, as everyone's needs tend to be slightly different, but I have found the pressure sensor in the Davis AWSs to be as good as much more expensive dedicated pressure sensors - see my dowloadable review of the Davis Vantage Pro2 AWS on www.measuringtheweather.com/equipment-reviews, for example. I installed my first Davis AWS in 1993, and the pressure sensors on all units have been of a similar high level of accuracy (obviously once they have been accurately set to the correct altitude, and then checked regularly against the synoptic pressure field to reduce the drift that tends to happen with all pressure sensors). I currently run both a Vantage Pro2 and a Vantage Vue, comparing both against my professional-spec multi-sensor system based around two Campbell Scientific loggers. (The pressure sensor is the same in both Davis AWSs.) I'm three months into a 12 month comparison trial of the Vantage Vue for John Dann of Prodata systems, and I'm planning to publish an interim review on my website in due course.

A Vantage Vue will set you back about £400, including Weatherlink and datalogger, and a VP2 around £700 - less than half the price of the dedicated pressure sensor quoted, and great value even if you decide not to install or use any of the other sensors (wind, temperature, rainfall etc). If pressure is the only requirement, you could turn off these sensors, or just regard their readings as a bonus.

Alternatively, for around the £1500 quoted, invest in a Campbell logger (CR1000), interface cable and a Setra pressure sensor - I've used a Setra unit as my main pressure sensor for almost 5 years now. This will give the flexibility to add a couple of dozen extra sensors at a later stage (temperature, wind direction/speed, tipping bucket raingaguge, etc) and allow 1 minute logging capability, if required. The logger should last many years - my first CS logger has been in continuous use since 2001 with hardly a glitch.

This is an independent recommendation - I don't have any vested interest in any equipment manufacturer or resellers.

As regards mercury barometers - yes, mine has its original NPL certificate. I check its calibration twice per year against the synoptic field, using the method outlined in my book; I do it at the same time as my other pressure sensors. The drift on a mercury barometer is normally imperceptible, of course. I've never had any problem with 'dirty mercury' or defective vacuuum, but it is well looked-after and in a clean non-smoking environment. I don't use it all that much these days, but I would not want to part with it (even apart from the fact that it was a wedding present of course).

The only trouble I've ever had with it was when we moved house in 1998. Our removals firm wanted a big insurance premium to move it, so since we were only moving within the village I decided to do it myself. They need to be transported upside-down, of course. Unfortunately, it was broken during the 2 minute drive to our new (and current) house. Fortunately I'd wrapped it up carefully in plastic sheeting just in case of any damage, and it was just as well as mercury was EVERYWHERE! I did manage to get it repaired, but it cost me around £600 as I recall. In hindsight, better to have paid the insurance premium and let professional movers take that risk. I'm not sure whether they would these days though with additional health and safety regulations around mercury instruments.

I do know of someone who has a high-quality Fortin mercury barometer they might be willing to sell, so if you're interested drop me a PM or e-mail and I can ask if they are still considering selling it.

SB
-----
Stratfield Mortimer, Berkshire - central southern England
51.4°N, 1.0°W, 60 m AMSL, station grade A - AAAA47R
Records commenced here 1987 - local records available back to 1862
The Weather Observer's Handbook: www.measuringtheweather.com
Stephen Burt
 
Posts: 247
Joined: 2011 Dec 02, 19:36
Location: Stratfield Mortimer, Berkshire; a well-exposed rural site, 10 km SW of Reading


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