Re: [time-nuts] Weather/units question for European members
On May 23, 2014, at 11:12 PM, Mark Sims hol...@hotmail.com wrote: The nice thing about measuring temperature via sonic measurements is that the measurements are unaffected by solar heating of the apparatus... it does not need to be in the shade. I stumbled on this paper a while back when I was investigating a similar idea: Wen-Yuan Tsai et al, An ultrasonic air temperature measurement system with self-correction function for humidity, 2005 Meas. Sci. Technol. 16 548 http://iopscience.iop.org/0957-0233/16/2/030 It uses both time of flight and phase measurements. Since this is for rocketry, note that RockSim (a commercial package for simulating the trajectory of a model rocket flight) lets you choose a variety of units for windspeed and barometric pressure. I've used meters per second and hectoPascals with the kids I mentor on rocketry. One funny thing about weather measurements is that the data that NOAA reports is not what it would seem. The standard ASOS data (which is what NOAA reports in its local current conditions) includes barometric pressure in inches of mercury and in hectoPascals. It turns out that neither is the actual barometric pressure. First, both are compensated to sea level, so they are not reporting the station pressure. Next, the in.Hg measurement is actually altimeter setting, which is the value which, if set in the Kollsman window of a standard aviation mechanical altimeter located at the ASOS site, will cause the altimeter to indicate the height above sea level of the ASOS site. So it's really not related to sea-level barometric pressure in any direct way; it's not compensated for temperature nor for humidity, etc. It's just based on the standard atmospheric model as used by the standard aviation altimeter. There is a straightforward way to derive station pressure from the altimeter setting, so it's not entirely useless if you are not an aviator. Finally, if you try to compare the reported in.Hg barometric pressure versus the reported hPa barometric pressure, you will often find that the two values are not related by the standard conversion factor from in.Hg to hPa. That is because the ASOS hPa value is actually the average of the current station pressure, corrected to sea level (I don't know what factors are included in that correction), and the sea level corrected station pressure from 12 hours previous. This averaging is to correct for the diurnal variation in station pressure resulting from solar heating. Without this correction, the weather fronts would oscillate back and forth on the weather map with a 24 hour period. So unless you are drawing weather maps, the ASOS hPa value is useless. So, when RockSim asks the user to input barometric pressure, exactly which one does it mean? Note that it also asks for the height above sea level of the launch site. Does it take altimeter setting and assume that it is measured at the height above sea level of the launch site, derive the station pressure from that, and then apply a temperature and humidity compensated version of the standard atmospheric model to calculate the air density profile for the simulated rocket flight? What if the station height above sea level isn't the same as the launch site above sea level? Does it even take any of these complications into account, and just assume that the number you enter for barometric pressure is the station pressure at the launch site? If so, note that most folks just enter the barometric pressure number reported by the local weather forecast. This is one of the dangers of relying on closed-source programs for science and engineering; you can't tell what it's really calculating. It seems like what is the barometric pressure should be a simple question, but it turns out to be quite subtle. Best regards, -Steve -- Steve Byan steveb...@me.com Littleton, MA 01460 -- Steve Byan steveb...@me.com Littleton, MA 01460 ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
[time-nuts] Weather/units question for European members
I ran across this very issue when trying to calibrate my barometer chip against the NWS station located less than two miles away. Their numbers for millibars and inches of mercury do not agree. I sent them an email and asked what was going on. They said their instruments read out in millibars (to three decimal places) The reported value is converted to sea level pressure and reported to two decimal places. They are also converted to inches of mercury for their reports. Only problem is their conversion constant is NOT the proper value. They consistently report around 0.02 too high. I reported this back to them, but have received no further responses. Note that the conversion between true pressure readings and sea level pressure involves an equation with about a fifth power/root (depending upon the direction of the conversion) so it can be quite sensitive to true chip calibration. The pressure chip that I am using (MP5611) is factory calibrated and has calibration constants stored on-chip (the Bosch BMP085 and BMP180 chips also do this), but the soldering process can affect the chip so you need to do some final calibration. The MP5611 can detect the air pressure change seen by raising the chip less than 6 inches... Relevance of temperature/humidity/pressure sensors to time-nuttery? We all know the comparatively massive effects of temperature on our equipment. But humidity and air pressure also affect them in many subtle and not-so-subtle ways. I'll post some recommendations/observations on various sensor chips in a while. - One funny thing about weather measurements is that the data that NOAA reports is not what it would seem. The standard ASOS data (which is what NOAA reports in its local current conditions) includes barometric pressure in inches of mercury and in hectoPascals. It turns out that neither is the actual barometric pressure. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Weather/units question for European members
atmospheric pressure taken for a weather observation is measured in millibars and respresents the barometric pressure at ground level at that location. If the instrument is located somewhere besides ground level it will be corrected to ground level. The value given in inches of mercury is that barometric pressure corrected to sea level and converted to inches of mercury. This is the altimeter setting and will be used by aircraft to adjust their altimeter so that when on the ground the altimeter will read the height of the aircraft above sea level, in other words the ground elevation on which the aircraft is sitting. This means there is no direct comparison between the pressure given in millibars and that given in inches of mercury (altimeter setting) unless the altimeter setting is corrected to the same height above sea level at which the atmospheric pressure was measured. The Altimeter setting in Europe is not the same. There the altimeter setting is such that the aircraft's altimeter reads ZERO when on the ground. Two miles away is pretty close but can make a difference as can a difference in ground elevation but it sounds like you are taking ground elevation into account already. cheers, Graham ve3gtc On 2014-05-25 23:06, Mark Sims wrote: I ran across this very issue when trying to calibrate my barometer chip against the NWS station located less than two miles away. Their numbers for millibars and inches of mercury do not agree. I sent them an email and asked what was going on. They said their instruments read out in millibars (to three decimal places) The reported value is converted to sea level pressure and reported to two decimal places. They are also converted to inches of mercury for their reports. Only problem is their conversion constant is NOT the proper value. They consistently report around 0.02 too high. I reported this back to them, but have received no further responses. Note that the conversion between true pressure readings and sea level pressure involves an equation with about a fifth power/root (depending upon the direction of the conversion) so it can be quite sensitive to true chip calibration. The pressure chip that I am using (MP5611) is factory calibrated and has calibration constants stored on-chip (the Bosch BMP085 and BMP180 chips also do this), but the soldering process can affect the chip so you need to do some final calibration. The MP5611 can detect the air pressure change seen by raising the chip less than 6 inches... Relevance of temperature/humidity/pressure sensors to time-nuttery? We all know the comparatively massive effects of temperature on our equipment. But humidity and air pressure also affect them in many subtle and not-so-subtle ways. I'll post some recommendations/observations on various sensor chips in a while. - One funny thing about weather measurements is that the data that NOAA reports is not what it would seem. The standard ASOS data (which is what NOAA reports in its local current conditions) includes barometric pressure in inches of mercury and in hectoPascals. It turns out that neither is the actual barometric pressure. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Weather/units question for European members
Here in the US, most people who really care about wind speed think knots. For causal use to the general public them it's MPH. If you want to be esoteric use the Beaufort Wind Scale It is actually still used because it can be estimated from looking at the water. It is easy to learn to tell a 2, 3 ,4 just by looking On Fri, May 23, 2014 at 9:21 PM, David J Taylor david-tay...@blueyonder.co.uk wrote: I am building a weather sensor that includes a ultrasonic anemometer to measure wind speed, direction, and air temperature. It uses 4 cheap ($1 each) HC-SR04 ultrasonic rangefinder modules that output a pulse width proportional to the time of flight of the sound signal (topic is time nut related since it simultaneously measures the speed of sound in 4 directions to a pretty good accuracy/resolution using a cheap-ass microprocessor - ATMEGA328 (like and Arduino)... and does so without using any counter-timer channels). Now the question... I would like it to be able to output data in imperial or metric units. In what units is the typical wind speed reported (meters/sec, km/hour, ?). Also air pressure (millibars/hectopascals/pascals/?). == Mark, m/s and hPa are often used, but not exclusively. Cheers, David -- SatSignal Software - Quality software written to your requirements Web: http://www.satsignal.eu Email: david-tay...@blueyonder.co.uk ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. -- Chris Albertson Redondo Beach, California ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Weather/units question for European members
In message blu170-w517a3e7d32e32be4c3d3a4ce...@phx.gbl, Mark Sims writes: I am building a weather sensor that includes a ultrasonic anemometer Now the question... I would like it to be able to output data in imperial or metric units. In what units is the typical wind speed reported (meters/sec, km/hour, ?). Also air pressure (millibars/hectopascals/pascals/?). Whatever you do, use SI units internally and make it an option for the user to get those. Convert from SI to whatever the user wants in their local cultural geograpy. PS: In Denmark we use the SI units: Meter per second and hectopascal. See for instance: http://www.dmi.dk/vejr/til-lands/regionaludsigten/vssjaelland/ -- Poul-Henning Kamp | UNIX since Zilog Zeus 3.20 p...@freebsd.org | TCP/IP since RFC 956 FreeBSD committer | BSD since 4.3-tahoe Never attribute to malice what can adequately be explained by incompetence. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Weather/units question for European members
Hi Mark, I second Paul Henning, here in Europe we use officially the SI standard, does mean m/s and hPa! Privately used other units are another thing like km/h or units Beaufort and mb (millibar), but not official. If possible use always the international SI units and as personal choice km/h, hPa and millibar are anyway same numbers. Regards Arnold Am 24.05.2014 03:16, schrieb Mark Sims: I am building a weather sensor that includes a ultrasonic anemometer to measure wind speed, direction, and air temperature. It uses 4 cheap ($1 each) HC-SR04 ultrasonic rangefinder modules that output a pulse width proportional to the time of flight of the sound signal (topic is time nut related since it simultaneously measures the speed of sound in 4 directions to a pretty good accuracy/resolution using a cheap-ass microprocessor - ATMEGA328 (like and Arduino)... and does so wbbithout using any counter-timer channels). Now the question... I would like it to be able to output data in imperial or metric units. In what units is the typical wind speed reported (meters/sec, km/hour, ?). Also air pressure (millibars/hectopascals/pascals/?). ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Weather/units question for European members
Hello, Wind speed usually in meters/sec (when used for scientific data) or km/h (used in the news, so the people can compare with car speed ;) ) Pressure in millibars. Meteorologist also usually refers to hectopascals, but it is more for representing something at a given altitude (for example, winds at 700hPa) than for managing pressure data. Temperature in ºC Precipitation in liters/squared meter or millimeters (it is a 1:1 equivalence) Best regards, Javier On 24/05/2014 3:16, Mark Sims wrote: I am building a weather sensor that includes a ultrasonic anemometer to measure wind speed, direction, and air temperature. It uses 4 cheap ($1 each) HC-SR04 ultrasonic rangefinder modules that output a pulse width proportional to the time of flight of the sound signal (topic is time nut related since it simultaneously measures the speed of sound in 4 directions to a pretty good accuracy/resolution using a cheap-ass microprocessor - ATMEGA328 (like and Arduino)... and does so without using any counter-timer channels). Now the question... I would like it to be able to output data in imperial or metric units. In what units is the typical wind speed reported (meters/sec, km/hour, ?). Also air pressure (millibars/hectopascals/pascals/?). ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Weather/units question for European members
hektopascal is pseudo-SI form, as it is a compromize between the old milibar and propper SI unit of Pascal with suitable prefix 1 mbar = 1 hPa, but since we have normal pressure at 1013 mbar we should write it as 101,3 kPa but not 1013 hPa if we is to follow SI all the way. Temperature in C is really not strict SI, but accepted. m/s for windspeeds is the proper unit, while km/h is only used when explaining high windspeeds. Cheers, Magnus On 05/24/2014 02:01 PM, Javier Herrero wrote: Hello, Wind speed usually in meters/sec (when used for scientific data) or km/h (used in the news, so the people can compare with car speed ;) ) Pressure in millibars. Meteorologist also usually refers to hectopascals, but it is more for representing something at a given altitude (for example, winds at 700hPa) than for managing pressure data. Temperature in ºC Precipitation in liters/squared meter or millimeters (it is a 1:1 equivalence) Best regards, Javier On 24/05/2014 3:16, Mark Sims wrote: I am building a weather sensor that includes a ultrasonic anemometer to measure wind speed, direction, and air temperature. It uses 4 cheap ($1 each) HC-SR04 ultrasonic rangefinder modules that output a pulse width proportional to the time of flight of the sound signal (topic is time nut related since it simultaneously measures the speed of sound in 4 directions to a pretty good accuracy/resolution using a cheap-ass microprocessor - ATMEGA328 (like and Arduino)... and does so without using any counter-timer channels). Now the question... I would like it to be able to output data in imperial or metric units. In what units is the typical wind speed reported (meters/sec, km/hour, ?). Also air pressure (millibars/hectopascals/pascals/?). ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Weather/units question for European members
Here in Canada, for many years we have officially used km/hr and kilopascals (kPa) for all reporting (both civil and aviation). These units are now easily understood by the general population. Personally, for pressure I preferred hectopascals but over the years even I have adapted to the official unit. Sounds like you have a really neat project. ... Martin VE3OAT ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Weather/units question for European members
Hi Mark: The key benefit of an ultrasonic wind speed/direction sensor is that it can detect very slow wind speeds. My Peet Bros. system does not start telling me anything until the speed is a few MPH. http://www.prc68.com/I/UltimeterWeatherStation.shtml But all the weather stations I've seen don't tell you if the wind is backing or veering and how fast that's going on. This is critical for forecasting. It would be possible to have a graphical display the would be like looking down on a smoke stack with the smoke trail showing the history of wind direction. See the Sager Weather Caster book for more on that. http://www.prc68.com/I/Weather.shtml Have Fun, Brooke Clarke http://www.PRC68.com http://www.end2partygovernment.com/2012Issues.html http://www.prc68.com/I/DietNutrition.html Mark Sims wrote: I am building a weather sensor that includes a ultrasonic anemometer to measure wind speed, direction, and air temperature. It uses 4 cheap ($1 each) HC-SR04 ultrasonic rangefinder modules that output a pulse width proportional to the time of flight of the sound signal (topic is time nut related since it simultaneously measures the speed of sound in 4 directions to a pretty good accuracy/resolution using a cheap-ass microprocessor - ATMEGA328 (like and Arduino)... and does so without using any counter-timer channels). Now the question... I would like it to be able to output data in imperial or metric units. In what units is the typical wind speed reported (meters/sec, km/hour, ?). Also air pressure (millibars/hectopascals/pascals/?). ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
[time-nuts] Weather/units question for European members
I am building a weather sensor that includes a ultrasonic anemometer to measure wind speed, direction, and air temperature. It uses 4 cheap ($1 each) HC-SR04 ultrasonic rangefinder modules that output a pulse width proportional to the time of flight of the sound signal (topic is time nut related since it simultaneously measures the speed of sound in 4 directions to a pretty good accuracy/resolution using a cheap-ass microprocessor - ATMEGA328 (like and Arduino)... and does so without using any counter-timer channels). Now the question... I would like it to be able to output data in imperial or metric units. In what units is the typical wind speed reported (meters/sec, km/hour, ?). Also air pressure (millibars/hectopascals/pascals/?). ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Weather/units question for European members
For civilian use, Miles/hour and inches Hg. Aviation and marine would be knots and inches Hg. Tom - Original Message - From: Mark Sims hol...@hotmail.com To: time-nuts@febo.com Sent: Friday, May 23, 2014 9:16 PM Subject: [time-nuts] Weather/units question for European members I am building a weather sensor that includes a ultrasonic anemometer to measure wind speed, direction, and air temperature. It uses 4 cheap ($1 each) HC-SR04 ultrasonic rangefinder modules that output a pulse width proportional to the time of flight of the sound signal (topic is time nut related since it simultaneously measures the speed of sound in 4 directions to a pretty good accuracy/resolution using a cheap-ass microprocessor - ATMEGA328 (like and Arduino)... and does so without using any counter-timer channels). Now the question... I would like it to be able to output data in imperial or metric units. In what units is the typical wind speed reported (meters/sec, km/hour, ?). Also air pressure (millibars/hectopascals/pascals/?). ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Weather/units question for European members
Mark I think wind speed is also in Bueforts. Pretty sure thats misspelled. Regards On Fri, May 23, 2014 at 9:16 PM, Mark Sims hol...@hotmail.com wrote: I am building a weather sensor that includes a ultrasonic anemometer to measure wind speed, direction, and air temperature. It uses 4 cheap ($1 each) HC-SR04 ultrasonic rangefinder modules that output a pulse width proportional to the time of flight of the sound signal (topic is time nut related since it simultaneously measures the speed of sound in 4 directions to a pretty good accuracy/resolution using a cheap-ass microprocessor - ATMEGA328 (like and Arduino)... and does so without using any counter-timer channels). Now the question... I would like it to be able to output data in imperial or metric units. In what units is the typical wind speed reported (meters/sec, km/hour, ?). Also air pressure (millibars/hectopascals/pascals/?). ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Weather/units question for European members
Hi Mark I have been running an older Davis VantagePro station for the last fifteen years. It gives either miles per hour or meters per second. Air pressure in either inches or millimeters of Mercury as well as hectoPascals One note - wind direction is opposite from what you might think. A West wind blows to the East -- it is coming __from__ the West. The project sounds like a fun hack -- I would be curious as to the resolution you achieve with these modules. Dave -Original Message- From: time-nuts-boun...@febo.com [mailto:time-nuts-boun...@febo.com] On Behalf Of Mark Sims Sent: Friday, May 23, 2014 18:17 To: time-nuts@febo.com Subject: [time-nuts] Weather/units question for European members I am building a weather sensor that includes a ultrasonic anemometer to measure wind speed, direction, and air temperature. It uses 4 cheap ($1 each) HC-SR04 ultrasonic rangefinder modules that output a pulse width proportional to the time of flight of the sound signal (topic is time nut related since it simultaneously measures the speed of sound in 4 directions to a pretty good accuracy/resolution using a cheap-ass microprocessor - ATMEGA328 (like and Arduino)... and does so without using any counter-timer channels). Now the question... I would like it to be able to output data in imperial or metric units. In what units is the typical wind speed reported (meters/sec, km/hour, ?). Also air pressure (millibars/hectopascals/pascals/?). ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Weather/units question for European members
Beaufort scale Mark I think wind speed is also in Bueforts. Pretty sure thats misspelled. Regards ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Weather/units question for European members
I have a crappy Chinese-made handheld propeller anemometer. I'm not in Europe but FWIW the output can be selected as: m/s, km/h, ft/min, knots or mph. So, the first two of those seem to be likely metric choices. Your method sounds interesting. Would you be willing to share any details about how you are using the ultrasonic modules? Do they just point out into open space or is there something more involved? Was there a reference that got you started on this idea? On 5/23/2014 6:16 PM, Mark Sims wrote: I am building a weather sensor that includes a ultrasonic anemometer to measure wind speed, direction, and air temperature. It uses 4 cheap ($1 each) HC-SR04 ultrasonic rangefinder modules that output a pulse width proportional to the time of flight of the sound signal (topic is time nut related since it simultaneously measures the speed of sound in 4 directions to a pretty good accuracy/resolution using a cheap-ass microprocessor - ATMEGA328 (like and Arduino)... and does so without using any counter-timer channels). Now the question... I would like it to be able to output data in imperial or metric units. In what units is the typical wind speed reported (meters/sec, km/hour, ?). Also air pressure (millibars/hectopascals/pascals/?). ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
[time-nuts] Weather/units question for European members
The project sounds like a fun hack -- I would be curious as to the resolution you achieve with these modules.--- The best description on the net about building a sonic anemometer is one by Hardy Lau:http://www.technik.dhbw-ravensburg.de/~lau/ultrasonic-anemometer.html I have also built one that I call the Cheap Ass Sonic Anemometer It is part of a portable weather sensor for use at launches of large model rockets (some reach over 100,000 feet). It is built out of very inexpensive, off-the-shelf components. The only wiring involved is hooking power, ground, clock, and data lines to small off-the-shelf circuit boards (mostly from China off of Ebay). I did lay out a custom circuit board so I don't even have to do that. A commercial sonic anememeter can set you back $5000. It uses 4 HC-SR04 ultrasonic distance sensors ($1 each!) as the wind sensors. These are small modules that you drive with a 10 microsecond ping signal and they output a pulse width dependent upon the distance to an object. I use two modules facing each other on each axis and fire them in pairs. Instead of picking up an echo, they receive the ping from the opposite module. You can fire them around 30 times per second. I use an $5 ATMEGA328 chip based CPU board (you could use an Arduino) to measure the pulses and calculate the wind direction, speed, and temperature. I was originally using a more powerful processor (ATMEGA128) that has two 16 bit counters with input capture capability to measure the pulses with 65 nanosecond resolution, but to make the device more accessible for other people to build, I switched to the ATMEGA328 and time the pulses in software to around 1 microsecond resolution. I was measuring all four directions at the same time, but started seeing some cross-axis interference with some of the SR04 modules and switched to simultaneously measuring the N-S and S-N times followed 3 milliseconds later by the E-W and W-E times. Surprisingly the downgraded pulse measurement capability did not affect the results to any significant degree. The structure is built out of 1 inch inside diameter PVC plumbing pipe and couplers/caps... around $5 total. The ultrasonic sensors are spaced around 0.65 meters. The D/L ratio is around 20. The larger the D/L ratio, the smaller the errors caused by the structure interfering with wind flow. The device also contains a 10 degree-of-freedom inertial measurement unit board ($11) that is used as a tilt compensated magnetic compass and highly accurate barometer. It also has a DHT-22 humidity sensor ($5) and compensates the sound measurements for humidity and air pressure (which can be quite high a high temperatures and humidity levels). With the compass measurements you can deploy the sensor in any orientation and it adjusts the wind readings for however it is aligned. Also, you can buy the IMU boards for less than the price of the pressure sensor alone! The software auto-detects and supports 5 different pressure sensors, 4 different accelerometers, and the popular HMC5883 magnetometer chip (also used in the popular ST LSM303 integrated magnetometer/accelerometer. It also has an AS3935 based lightning sensor board ($20)... but they don't seem to work very well. I live next to a golf course that has an elaborate lightning warning system and the AS3935 has never triggered even though the golf course waring sirens have gone off several times. It also has a UV light sensor ($13 from Sparkfun) for reporting a UV index. I get temperature measurements with around 0.5 degree F accuracy and 0.25 F noise (averaging readings over 3 seconds). I am still characterizing the wind speed/direction measurements, but they seem to agree quite well with a cup/vane anemometer... basically if your temperature results are accurate your wind measurements will be spot on. The nice thing about measuring temperature via sonic measurements is that the measurements are unaffected by solar heating of the apparatus... it does not need to be in the shade. Also ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Weather/units question for European members
I am building a weather sensor that includes a ultrasonic anemometer to measure wind speed, direction, and air temperature. It uses 4 cheap ($1 each) HC-SR04 ultrasonic rangefinder modules that output a pulse width proportional to the time of flight of the sound signal (topic is time nut related since it simultaneously measures the speed of sound in 4 directions to a pretty good accuracy/resolution using a cheap-ass microprocessor - ATMEGA328 (like and Arduino)... and does so without using any counter-timer channels). Now the question... I would like it to be able to output data in imperial or metric units. In what units is the typical wind speed reported (meters/sec, km/hour, ?). Also air pressure (millibars/hectopascals/pascals/?). == Mark, m/s and hPa are often used, but not exclusively. Cheers, David -- SatSignal Software - Quality software written to your requirements Web: http://www.satsignal.eu Email: david-tay...@blueyonder.co.uk ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Weather/units question for European members
On Saturday, May 24, 2014, David J Taylor david-tay...@blueyonder.co.uk wrote: Now the question... I would like it to be able to output data in imperial or metric units. In what units is the typical wind speed reported (meters/sec, km/hour, ?). Also air pressure (millibars/hectopascals/ pascals/?). In the US wind speed is in MPH (civil) or knots (aviation or marine). Atmospheric pressure is in inches of mercury (US) or millibars. I have seen wind speed in m/s in Europe. -- Brian Lloyd Lloyd Aviation 706 Flightline Drive Spring Branch, TX 78070 br...@lloyd.com +1.916.877.5067 ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Weather/units question for European members
On Sat, 24 May 2014 01:16:32 +, Mark Sims wrote: Now the question... I would like it to be able to output data in imperial or metric units. In what units is the typical wind speed reported (meters/sec, km/hour, ?). Also air pressure (millibars/hectopascals/pascals/?). Our weather channel is reporting windspeed in meter/sec , and on rare occations km/h. But Second-meter seems to be the standard here in DK CFO ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Weather/units question for European members
There is a great sonic anemometer in: An inexpensive sonic anemometer for eddy correlation G.S.Campbell and M.H.Unsworth, (1979), Journal of Applied Meteorology Vol 18, August 1979, Pp. 1072-1077. This unit uses 4000 CMOS, a LM301A and two cheap ultrasonic transducers. It operates a phase-locked loop and alternately uses the sensors for transmitter and receiver, swapping ends at about 74 Hz, to get a two way signal. This method cancels most errors. It has temperature and velocity outputs. cheers, Neville Michie On 24/05/2014, at 11:16 AM, Mark Sims wrote: I am building a weather sensor that includes a ultrasonic anemometer to measure wind speed, direction, and air temperature. It uses 4 cheap ($1 each) HC-SR04 ultrasonic rangefinder modules that output a pulse width proportional to the time of flight of the sound signal (topic is time nut related since it simultaneously measures the speed of sound in 4 directions to a pretty good accuracy/resolution using a cheap-ass microprocessor - ATMEGA328 (like and Arduino)... and does so without using any counter-timer channels). Now the question... I would like it to be able to output data in imperial or metric units. In what units is the typical wind speed reported (meters/sec, km/hour, ?). Also air pressure (millibars/hectopascals/pascals/?). ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
