WXforum.net
Weather Station Hardware => Davis Instruments Weather Stations => Topic started by: jerryg on January 03, 2012, 05:10:50 PM
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I read down in the tech corner thread about replacing the sensor on the davis board when it goes bad and got excited about trying it myself. I have a homebrew dual louver stevenson screen that i use for my davis sensor i removed from the davis shield and i did not need to remount my new sensor on their board. I bought the better speced sensor which is the sht15 and all i needed was a six conductor cable with a connector on one end which i had and a capacitor to decouple the supply voltage which i had, so the sensor cost me 31.56$ shipped and i have it running now on my backup station to see how it compares to my primary station. If everything ages out ok in a few days i will have a more accurate sensor at a third of the cost of the davis sensor. I had a sensor that was potted with clear stuff and i could see the wire colors and where the traces went to on the sht15. One thing the connections on the sensor are very small pads and close together and would be hard for anyone without the proper skill to hook up, but they make a sht75, same sensorl, but mounted on a board with pins to plug into a socket and only cost 5 bucks more. If i did another one i think i would spend the extra dollars and save alot of agony hooking up to the solder pads lol. Will report back in a few days after seeing how it compares to my primary sensor.
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I am also experimenting with temp and humidity sensor replacement. In my case I am testing a long cable, in place of wireless, to give me 24 bit resolution into my PC with low cost 24 bit ADC to USB PC interface.
I think we are all finding how nice it is to understand weather station circuits, to succeed with a better replacement, and to improve weather data quality.
Congratulations to jerryg!
Steve
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This topic also applies to other brand stations as well. I have done the same with a Lacrosse 28xx station, improving it's accuracy using a SHT11 though. You're right about those connections being so tiny and close together! Like doing micro surgery.
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Nice job, jerryg. The prices you have quoted are excellent. Where did you get this stuff? The SHT15 plus breakout is $42 before shipping at Sparkfun. Can you provide a link or two?
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The price i talked about was just for the sensor.It came from the same place. I like the breakout board, alittle pricey but has everything you need for a sensor and still at half price. The board i was looking at just has pins on a pcb board with the sensor, looks like would have to add the 100n cap. Here is the one i was looking at. http://www.newark.com/jsp/search/productdetail.jsp?SKU=18M2988
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Just an added note if anyone needs the pinout connections for the rj plug and the sensor i have it written down and will be glad to post it.
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On the soldering issue...I have a Weller WP25 ( I like a hot iron) and Weller tips are available (on EBay) that are needle sharp and quite long compared to standard tips.
I use a magnifying head set (2x, 3x, 10x, 25x like a jeweler uses) needle soldering tips to solder this type of board - it is now much easier. No mater your age and vision, 5 to 10 x really helps. I actually use 25x to check for the mistakes (like tiny bridges) I make at 5x!
I did not realize how much 10x helped until I soldered an SOIC op amp onto a SOIC board. I suspect the boards you are discussing are about the same size and difficulty with trace separation.
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The pads are super small as is the sensor itself. I used a fine tip weller iron and some hair size solder to avoid blobs. I used some hi power reading glasses for the old tired eyeballs lol. So far the sensor is working fine and tracking with my main sensor. We are supposed to get some fog in the early am and i want to see how it looks on the high end. Then when a norther comes in and the humidity drops low will see how it looks on the low end. With the specs being alittle better than the one davis uses should see a small difference, how much is to be seen. If it is just alittle then could save alittle money by getting the 11.
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jerryg -
You were kind enough to offer to post the pinouts and wiring, and I'd appreciate seeing them. A neighbor gave me an old Davis mounting arm with the shield and sensors still attached but the wires had been cut about a foot long, and I'd like to put it to use for water temp.
If that sensor is bad, then I'd go ahead and follow in your steps with the sht11/15 chip.
TIA
Ron.
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jerryg -
You were kind enough to offer to post the pinouts and wiring, and I'd appreciate seeing them.
Ron.
I would appreciate seeing these also. Wonder if this is the "bigger one" mentioned earlier in the posting?
robotshop.com (http://www.robotshop.com/ca/sfe-sht15-humidity-temperature-sensor-1.html)
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I purchased my SHT11s from Newark for $26.94:
http://www.newark.com/sensirion/sht11/humidity-sensor/dp/69C4848
The also have SHT15s for $33.07:
http://www.newark.com/sensirion/sht15/humidity-sensor/dp/18M2986?in_merch=Popular%20Products
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I did not realize how much 10x helped until I soldered an SOIC op amp onto a SOIC board. I suspect the boards you are discussing are about the same size and difficulty with trace separation.
I linked this video (http://www.youtube.com/v/3NN7UGWYmBY) from one of my blog posts a little while ago for soldering fine pitch devices. SOIC is easy with the techniques presented here. I've successfully done TQFP parts with a Radio Shack firestick soldering iron that I bought umpteen years ago. I really need to get myself a magnifier, though.
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Ok here is the how the connector looks, with the front facing you, that being the side without the latch, starting from the left with pin 1 blue 2 yellow 3 green 4 red 5 black 6 white and Davis uses only four of them probably made it a 6 pin connector so it would not fit in any of the other sockets. The green lead is the ground. The yellow lead is the + voltage. The white is the clock. The blue is the i/o data pin. On the sensor lpin1 is green pin2 is blue pin3 is white and pin4 is yellow. You need a 100n capacitor between 1 and 4 on the sensor.
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Question: on a VP2 wireless, with this setup, does this sensor read °F with no further modifications?
Thanks for the info, Doug
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I am not sure what you asked, the sensor will read f or c depending on what you tell the vp2 you want to read.
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I am not sure what you asked, the sensor will read f or c depending on what you tell the vp2 you want to read.
You answered my question. I think I will order one today.
Thanks again, Doug
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Just a follow up on my sensor. I am well pleased with the results so far. The readings are really close to the metars i compare to and comparing it to the sensor i was using. I am still waiting for a strong cold front to come in an lower the humidity down below 20 percent to compare it with the davis sensor. I have 5 davis sensors with my stations and 4 of them top out at 98% and one at 100% to compare to. The thing i notice so far is the 15 readings are really linear, this am we had dense fog and it was showing 99% then 100% and back and forth, then when the humidity went down it decreased at a rate that was the same as the metars and is now showing the same reading. I have to use the slope setting to get davis sensor to read close when the humidity gets low, i have it to offset a -2 around 50% which gets it close. With the 15 i have not had to use the slope setting so far. If you look at the specs on the 11 and 15 you can see the difference. Here is the link to the specs http://www.sparkfun.com/datasheets/Sensors/SHT1x_datasheet.pdf go down to figure 2 the graph chart and look at how the two sensors compare at the high and low end. The temps compare pretty close with the davis speced at 1 degree f and the 15 is speced around .5 degrees f i really did not expect much difference anyway. Maybe davis should offer an option to get the better speced sensor.
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Great work, I can feel another build coming, Cheap replacment T/H senors anyone? I could quite easily do these to the same dimensions as the Davis sensor for use as a direct replacement.
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For anyone thinking of a DIY digital (.166) T/H sensor, it's perhaps worth remembering that most of the issues with the T/H sensor have not been to do with the sensor element itself AFAICS, but with the way that the element is interfaced to and mounted on the daughter board. We're now on Rev J of the .166 T/H sensor, with progressively more and more weatherproofing being added around the sensor element and the board layout itself evolving over the past few years.
For anyone planning to use the sensor in a damp/rainy/windy climate I think that you're going to have to pay equal attention to the mounting details, as Davis are doing, in order to get a T/H sensor that lasts.
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I agree about the weather proofing and i do have the capability to weather proof the connections, but this is just a trial to see how much difference the better speced sensor makes. So far it looks good and even if it lasted only a year or two without weather proofing at the price you could afford to get another one or two. Now if i could just get some low humidity to check the bottom end readings i would be a happy camper lol.
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OTOH, that doesn't explain why we experience so many failures with current sensors along the Pacific coast, and why replacing the SHT11 fixes the problem.
For anyone thinking of a DIY digital (.166) T/H sensor, it's perhaps worth remembering that most of the issues with the T/H sensor have not been to do with the sensor element itself AFAICS, but with the way that the element is interfaced to and mounted on the daughter board. We're now on Rev J of the .166 T/H sensor, with progressively more and more weatherproofing being added around the sensor element and the board layout itself evolving over the past few years.
For anyone planning to use the sensor in a damp/rainy/windy climate I think that you're going to have to pay equal attention to the mounting details, as Davis are doing, in order to get a T/H sensor that lasts.
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OTOH, that doesn't explain why we experience so many failures with current sensors along the Pacific coast, and why replacing the SHT11 fixes the problem.
What do you mean by 'current' sensors though? Are you including rev 'I' and rev 'J' in that? (The letter should usually be shown as the final character on the label on the daughter board eg 7346.166J). My experience is that I and especially J seem to be lasting substantially better than some previous revisions, though it is relatively early days as yet for J. I don't have the exact dates to hand, but I think that I possibly came in sometime during the 2009 builds, maybe towards the end of 2009 but really can't remember exactly.
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This is a good discussion.
I have been working with a high quality Honeywell humidity senor for a few weeks now and I can verify your comments about taking care to weather proof the humidity sensor itself - as odd as that sounds.
I am experimenting with the Honeywell HIH humidity sensor series and Honeywell is very specific about the conditions the sensor will experience.
If a sensor is to be exposed directly to water droplets or wet environments, they suggest a very special "covered" version which resists water droplets but still measures air or other gas humidity. Obviously the sensors can not be sealed but the problem of wet (industrial) environments are very difficult to monitor for humidity without permanently damaging or at least changing the output of the sensor by getting the actual sensor surface wet!!!
It is the technology of the "cover" that is tricky.
The HIH series has an analog output which happens to interest me. The HIH series must be digitized to work with most weather stations.
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For what it worth: I just built a steveson screen for my wireless VP2. Got everything mounted this past weekend. As I was doing this I also needed to replace the fan that came with the kit which was 2 years old. I did this with a $12 40mm(1.57") 12 volt case fan from Newegg . I hooked this up to a 9 volt dc adapter and it is purring like a kitten 24/7 now. To finally get to the point of this saga....I am also going to build the temp/humidity sensor which is being discussed here. I got to thinking there has got to be a better way to extend the current sensor than cutting the wires. Went to the local Radio Shack. They did not have a 6 wire RJ11 cable but they did have a 6 wire inline connector just like the 4 wire connector that comes with the Davis anemometer extension cable. I found an IT guy who had the cable, a straight through 6 wire RJ11 6' cable. After I got everything mounted, I unplugged the sensor cable, plugged in the connector and 6' cable, both the temp and humidity came back to the exact same reading, to the tenth. So for $8 for the connector and $5 for the cable I have now extended the cable length and will only need a PC board RJ11 connector and will be able to build the new sensor and never cut a cable.
Doug
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Well i finally got a strong cold front in that dropped the humidity low enough for a comparison of the two sensors. I have 3 davis sensors and the homemade sensor in the same screen side by side so i could get a comparison with the same conditions. This is not scientific just eyeball comparison watching on wu site and the two metars that i am between. One metar is 8 miles nw and the other is 12 se of me so get a good idea of the humidity when they are both reading the same. I was surprised how close the 3 davis sensors track each other. The temps of all sensors where withing a tenth or two of each other. All my davis sensors top out at 98% and the new one at 100%. I had a period where the hum. was holding around 75% for some time and they all showed that reading which is the normal calibration point for the sensors. When the humidity went up they all tracked about the same until around 90% when the new sensor slowly went up as the fog moved in and the davis sensors started to fall slowly behind. Just to show how dense the fog was my rain gauged showed .02 inches of rain from condensation on the gauge, really really wet stuff lol. When the davis got up to 96 the new sensor showed 98 and then went to 99 while it took longer for the davis to get to 97 and the new was on 100 for sometime before the davis topped out at 98. Going the other way from 75 they all tracked close until in the low 40s then the davis started to fall behind until the new was at 19 and the davis were at 21 to 22. I can offset the low end difference with weather displays slope adjustment for humidity by setting it at -1 it works pretty close from one end to the other except at 90 percent then it takes awhile for things to even out. I am well pleased with the new sensor and the davis sensors with the correction.
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No i just did a general comparison, nothing complex, as to how they read compared to each other. I have them all uploading to wu and could watch them as they changed and i looked at the info on wu to see how they did over a long period of time. Just something to do to pass the time being retired i have time to do this kind of thing lol.
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No i just did a general comparison, nothing complex, as to how they read compared to each other. I have them all uploading to wu and could watch them as they changed and i looked at the info on wu to see how they did over a long period of time. Just something to do to pass the time being retired i have time to do this kind of thing lol.
Another visual way to compare between stations is have the stations you want to compare with all upload to CWOP. Then, pick the station you want to use as the reference and open it's page on CWOP. Click on 'findu' , 'Quality Control Graphs for (station name)'. At the bottom click to select the other stations you want to compare to then 'Add to Charts'. You will get an overlay of all the temps, humidity, Dew pt., pressures, wind. I use this to keep an eye on things daily.
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Yes that would work pretty well. I was just curious how the better speced sensor was compared to the one davis uses. I do not know why all the ones i have top out at 98, i guess at that humidity it is wet lol. I could just check the show 100 box in wd. For the most part the sensors are just fine, well within specs. I just needed to satisfy my curiosity. I am going to leave the homemade sensor on my main site because i like how it seems to follow the metars closely. I ordered the 75 sensor that is already mounted on a board with the capacitor on board and the filter housing that goes on the sensor, i might have to make it fit the 75 board but will try it anyway. The cover will help keep dust and stuff out of the sensor. It will be another little fun project.
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Got the sht75 in today plus i ordered the sf-1 filter which is a plastic housing with a filter screen that fits over the sensor to keep dust, bugs and water drops out. The 75 is alot easier to work with if you are building a spare sensor rather than replacing one on the Davis board. The sensor will not fit neatly into the filter which is made for a larger square board so i cut a notch in the bottom of the filter so the 75 fit neatly in the housing and sealed it. Then i soldered the cable leads to the pins carefully bending one up and one down etc. so they would not touch. Then i put the sensor in an old temp/hum housing i had from an old station. I have it running now and looks real good comparing to the other sensors. I like the filter, makes it easy to mount and seal the sensor plus keeps all the gunk out. Now i will let it age for awhile and compare the readings with the other sensors to see how it ages if at all. It only took me about a half hour to assemble the sensor, the only thing will be how long will it last outside without all the potting that Davis does. I had some of the os sensors outside for years without any corrosion problems and they were not sealed so hope that is a good omen.
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Would this work on a VP1?
Thanks!
Edit 2/5/2012
I think I answered my own question
(http://img.photobucket.com/albums/v155/AVMan86/VP1Temp.jpg)
This is the Vantage Pro 1 temp / humidity sensor (the the protective cover taken off), and it is defiantly not an SHT11
Any idea on what it actually is? If I could find that white sensor (marked Y421 on the plastic) I could easily swap it out when it dies. I have 5 of these things around Gloucester, MA (a lot of salt and wind) and it would be nice to fix it myself when they die.
Edit Later 2/5/12
Found out the white thing is the humidity sensor, and the blue thing is the temp sensor. I pulled the white thing and the humidity read 100%, which also means if someone has a station reading 100% it could simply be a bad connection to the humidity sensor.
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Well its time for an update on my experiments with the 15 sensor. In my stevenson screen i have mounted side by side three sensors, one is a 15 i built and put in an old sensor housing with no dust screen, the second is a sparkfun breakout board with the 15 on it and the sf1 dust filter, the third is a 15 mounted on a davis sensor board that went bad. I have been doing some comparisons since we have been having alot of dense fog lately and all three sensors show 100 percent when dense fog is happening. The thing i noticed most is the sensor with the davis screen on it had a pretty long lag time before the humidity started to drop and rise when the other two where tracking each other pretty close. This am it was foggy again and the two sensors that track showed 90% while the Davis showed 94% so i removed the screen from the Davis and by the time i got into the house it was showing 90% also and has been tracking with the other two just fine. So it seems to me the dust cover causes a pretty good lag time on the Davis sensor, it does catch up with the other two when the humidity stabilizes some. The temps are real good and track withing a couple of tenths of each other. I have a regular davis sensor in a daytime fars housing that i modified to run on ac so i could run it at night and with the fan running it did not have the lag time that the non fars davis sensor has. It looks to me like the Davis sensor is better at tracking the temp/hum with the fan pulling air over it all the time. The lag time when the fog is dense is because we get dense fog when the wind is not blowing are is very low mph and the sensor is not getting the air movement it needs. We are due a cold front in tonight and the humidity is supposed to get down low and i can compare them on the low side for a change lol. \:D/
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From that single report (and of course with common sense, regardless of that report), a FARS tends to improve average accuracy and decrease response time of sensors.
...translation: a FARS is really necessary if you want accurate realtime data. Agree?
Exactly what do you mean by "accurate data"?
Exactly what do you mean by "realtime data"?
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...translation: a FARS is really necessary if you want accurate realtime data. Agree?
If your weather site has continuous winds faster than about 2-3 mph, then the FARS probably isn't necessary for the various Davis non-FARS radiation shields. I've come to this conclusion after checking various Davis spec sheets and personal experience with Davis units.
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I have not said much here, but I follow these discussions daily.
I have multiple stations, an old Davis Vantage, a new Vantage View, and a precision sensor system I am building myself as a calibration unit.
I have experimented with and without fan aspiration for months and I am a STRONG advocate of sensor aspiration. Each sensor, assuming all to be fairly well calibrated, has its own response time to show air readings so it is simply a matter exposing the sensor the real air temperature as quickly as possible without exposing the sensors to sunlight or rain.
To the extent of a sensor's isolation from sunlight and rain, it's readings are delayed. The delay depends on how long it takes the outside air to get to the sensor. I have seen as much as 20 minutes difference in a daily high temperature reading from two good sensors, depending on the shielding, aspiration, and and/or wind.
Good isolation from direct sun and rain is important for accurate temperature and humidity measurements but blowing outside air over the sensor, with a fan, is even better.
I am now experimenting with a simple 2 inch 12 VDC, 1.5 watt computer fan mounted on edge inside my old Davis Vantage Pro and it works very well and gives a nearly simultaneous reading compared to a fast calibration thermometer outside the Davis unit (but in the shade).
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I liked the results of a fars unit so i broke down and ordered the parts to convert my Davis over to a 24 hr fars. I got all the parts from Archer Trading Post. I got the 24 hr solar panel, two 2300 mah batteries the covers and o rings plugs Archer now has the battery clips with wires that fit into the empty battery housings on the daytime fars. I got the power control board also. The control board is not very complex, it charges the batteries through a blocking diode and a 50 ohm current limiting resistor. The fan has three leads, the black is battery neg. The center red lead goes thru a 10 ohm resistor to battery plus and the outside red lead goes directly to the solar panel plus. With the batteries being in parallel it gives you alot of run time. The hardest part was mounting the panel to the top of the screen, the screws that come with the daytime fars are too long so had to cut off about three quarter inch. The rain gauge base has its own 3 holes to mount spacers in to set the assembly back aways so as not to shield the fan solar panel. I found some spacers in my goodie box that worked and i have it online now to do some comparisons with my other sensor housings. I think Davis ought to sell a kit for this mod instead of pieces.
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I think Davis ought to sell a kit for this mod instead of pieces.
Jerry, I think they did once. The 7755 Solar-Powered Fan-Asperated Radiation Shield looks to be nearly identical to the 24-Hr FARS although I haven't compared the measurements. It does have the inner wind tunnel tube (sensor chamber) that is shielded from radiation and directs air flow across the sensors which a converted daytime FARS doesn't have.
http://www.davisnet.com/product_documents/weather/manuals/07395-084_IM_07750_7755.pdf
http://www.davisnet.com/product_documents/weather/spec_sheets/7755_spec.pdf
Differences that I've noted from the current 24-hr FARS are the sensors, possibly the hardware and the arrangement of it that attaches to the rain collector base, and the lack of a wiring-pass-through hole in the solar panel.
It may be that an old 7755 if still for sale someplace on the internet, might be a better 24-hr FARS than a conversion job.
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I saw that and could not find any for sell i used the manual to help see how the wiring was set up. So i guess making do is the only way to get there if you did not buy the 24 hr to start with. I am set up now to compare it with my stevenson screen and the daytime fars as well as the nonfars shield. Should be interesting to see how it all shakes out.
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Here is one still "offered" for sale: http://www.wxbureau.com/files/7755.html; however, I think that may be a ghost website that is residing on a web server well past its expiration date.
It looks like it died circa 2004. It would be neat if they they are still in operation and still had 7755s in stock.
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How do you know when the original factory supplied sensor is beginning to fail?
Is there a loss of linearity? Failure to reach max of 100%, or a narrowed range?
Can the humidity function fail or be imprecise and the temp still ok and track other thermometers?
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I am far from an expert on this stuff but i can tell you from experience that mine was reading ok and then the next time i looked it had dropped 50% below what it was but the temperature was correct. The readings were all over the place but the temp always read right. I think the humidity can go bad with the temp being ok but if the temp goes bad it will cause the humidity to read wrong. Maybe someone else can explain it better.
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Thanks Jerry,
I have just brought my Davis Pro back on line after being quiet since last summer, and watching it compared to my other stations that track pretty close to one another and drat, I see that my humidity is 50% on the Davis while the others are 78 to 81%....
Grrr, maybe I'll be reading this thread a lot closer than I was to see what my options to get back to being more accurate.
I appreciate all the enthusiasm the contributors have here.
Dale
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I finally got some info on the 24 hr shield and was surprised that it has a number that is 6153s, s is for shield i would think, it is a replacement for the 6153 shield and does not include the sensor. I was looking on Archer Trading Post site and there was one showing as new for March and he had one in stock so i jumped on it and it is comming ups. I did not think you could get a shield by itself. I searched the part on Google and can not find it. Maybe with the interest people have shown in upgrading to the 24 hr fars they are going to put them out there for retrofit. From the picture it looks like all you have to do is mount the rain base on top. Might need some screws that are shorter, will find out and post here when got it up and running.
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jerryg The guy that owns ATP is an electrical engineer, I think he is putting those fan shields together himself for sale. Saw the need and has the parts....make the sale....VERY GOOD idea for those that didn't and now want one. I don't think the price is too bad either.
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Frankly that is a very good price on that 24-hr FARS conversion kit! A daytime only kit is ~$100.
jerryg, ATP is now showing zero units in stock though. I wonder if you got the only one they had and how long it will take to restock?
Also I wonder if ATP is making these parts available by disassembling complete units and then selling the component parts?
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I know i saw there was only one in stock and after my order i could not find any info showing. It is due here next Tuesday and as far as how it came to be it was listed with a Davis part number so will just wait and see. The daytime fars i converted to 24 hr has been working pretty good and am looking forward to comparing the two.
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d_l Check out the site, www.archertradingpost.com/atp, he has the parts in stock to make these so I don't think he's taking good packages apart.
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I would not think he is making them from parts because the 24 hr assembly is different than the daytime fars conversion parts. The sensor chamber on the 24hr goes down the center of 7 of the plates with the holes in them and is open at the bottom with a screen on it. I have never seen parts for this anywhere.
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Disassembling a complete unit and selling it as parts could be price advantageous to a merchant if he can get all the parts sold. Everyone knows that it costs far more to buy the individual parts and build an ISS than buying a complete unit.
Disassembling complete units would be especially profitable if there was some component that is desired by many customers and not available any where else. A retro fit 24-hr FARS fits that description.
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Just got of the phone with ryan and that is what he did. He parted out all the stuff and sold the shield. He said he will have one for sale from time to time when he has the parts sold, can not break up the whole iss without losing his shirt lol. So i guess it will be luck of the draw if you want one or maybe call or email him and get on a list if he has one. I do not see why Davis does not sell the shield to retrofit the standard to 24 hr. Either they buy the iss as a complete unit and do not have the shield set up separate or they do not want the general public messing around with the change out and getting poor results and then bad mouthing the product because they did something wrong. I know there are alot of technical people on here and would have no problem retrofitting one but then again there are alot of people who could break an anvil too lol. :lol: :lol: :lol:
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OK OK, I stand corrected, can't be right all/any of the time. I just figured that with the parts he stocks and his knowledge that it was 'his' configuration.
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I got the shield in the other day and it was very easy to change out. All i had to do was remove the top plates of the shield to get to the fan and remove it so i could get the sensor board out and snap the temp/hum sensor on it, then i just slide the board back in place, routed the cable like it showed and reassembled it. It took about 10 minutes to do. I do not know why Davis doen not sell a retrofit. It would be even easier if it came with the sensor already installed. All you would have to do is mount it to the rain base with the shorter screws and pull out two plastic tabs to active the nicad batteries. You could keep the old sensor for a spare. It works just fine and i compared it to the daytime fars that i converted to 24 hr and the converted shield compares pretty close. I also compared the daytime fars and was not too impressed with the results. The fan starts running after the sun has been up a couple of hours because the sun has to hit the solar panel to get it running and does not have enough umph with just daylight showing. It stops running just before the sun goes down. You have to have the 24 hr solar panel to make the fars work right. The fan runs when daylight breaks. The fan only helps during the day when the wind it light. The 24 hr fars works good at night when the wind lays and you get a more consistant changing of humidity and temp. The daytime fars lags behind on that score as does my stevenson screen. They both catch up after some time and the temp and hum readings have slowed down later at night.
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In case anyone wants to convert their shield to 24hr Archer Trading Post has two showing on his site for sale.
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This is an update to my old topic. Sloweather posted in a new topic a couple days ago about getting the sht15 for 10 bucks which is alot cheaper than buying a new one. I ordered 5 sensors with 7 bucks postage and it took 4 days for them to show up in the mail box. I removed one from the flex strip and soldered connection wires to the sensor and then soldered my connection cable to the wires. I hooked it up to my spare iss and it worked fine except the temp was showing 1.2 degrees higher than my calibration thermometer. The only time i hooked up the sensors before was on the Davis or a breakout board that had the .1 ufd decoupling capacitor on board, so i got a ceramic cap and put across the vcc to ground and the temp came down to the correct value. The cap has to be connected for the sensor to be correct on temp. I have it outside in a shield and it is working just fine. So for ten bucks and a little work the sensor can be repaired with the better speced sht15. Thanks to Sloweather for the link. http://www.allelectronics.com/make-a-store/item/THS-15/TEMPERATURE/HUMIDITY-SENSOR-SMD-ON-RIBBON/1.html
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So what is the final consensus? Does the VP2 use the SHT11 or SHT15? The VP2 specs I saw looked closer to the SHT15.
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The vp2 uses the sht11 which has slightly poorer specs on the high and low end of humidiy performance.
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The chips are identical in footprint, appearance, and pinout. They are likely made on the same line at the same time, and sorted into 11s or 15s at testing.
Unsolder your SHT11, solder in the SHT15. That's what I do when I repair ISS sensor assemblies.
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Hey SLOweather i am curious as to how you found these sensors for such a great price. They list them wrong as ths15 instead of sht15 so would not show up on a search. Was it real genius or just dumb luck :lol: ?
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It's been a while, so I'm not quite sure. I get their paper catalog so I might have seen it there.
Hey SLOweather i am curious as to how you found these sensors for such a great price. They list them wrong as ths15 instead of sht15 so would not show up on a search. Was it real genius or just dumb luck :lol: ?
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The vp2 uses the sht11 which has slightly poorer specs on the high and low end of humidiy performance.
The VP2 temp sensor spec chart seems to correspond more with the SHT15 to me based on these charts...
VP2 (scroll to near the bottom)
http://www.davisnet.com/product_documents/weather/spec_sheets/6152_62_53_63_SS.pdf
SHTx
https://www.sparkfun.com/datasheets/Sensors/SHT1x_datasheet.pdf
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The vp2 uses the sht11 which has slightly poorer specs on the high and low end of humidiy performance.
The VP2 temp sensor spec chart seems to correspond more with the SHT15 to me based on these charts...
VP2 (scroll to near the bottom)
http://www.davisnet.com/product_documents/weather/spec_sheets/6152_62_53_63_SS.pdf
SHTx
https://www.sparkfun.com/datasheets/Sensors/SHT1x_datasheet.pdf
It is an SHT11. See here. (http://madscientistlabs.blogspot.ca/2011/02/busy-weekend-coming-up.html)
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It is an SHT11. See here. (http://madscientistlabs.blogspot.ca/2011/02/busy-weekend-coming-up.html)
Without a doubt it is an SHT11. I don't think the specs have changed since the older analog sensors were being used...
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Would this work on a VP1?
Thanks!
Edit 2/5/2012
I think I answered my own question
(http://img.photobucket.com/albums/v155/AVMan86/VP1Temp.jpg)
This is the Vantage Pro 1 temp / humidity sensor (the the protective cover taken off), and it is defiantly not an SHT11
Any idea on what it actually is? If I could find that white sensor (marked Y421 on the plastic) I could easily swap it out when it dies. I have 5 of these things around Gloucester, MA (a lot of salt and wind) and it would be nice to fix it myself when they die.
Edit Later 2/5/12
Found out the white thing is the humidity sensor, and the blue thing is the temp sensor. I pulled the white thing and the humidity read 100%, which also means if someone has a station reading 100% it could simply be a bad connection to the humidity sensor.
Interesting.
Just performed my annual maintenance on the ISS and it turns out my VP2 temp/hum sensor is this one also. This was sent to me from Davis after my previous sensor failed. If its for the VP1, it seems to be working just fine in my VP2. Now I have an SHT15 lying around waiting for a breakout to solder it to.
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I am not familiar with the vp1 sensor but believe it is an analog set up. Looking at the picture it looks like there are two holes where a standard humidity sensor would go. It also looks like it has the traces for an sht chip with two holes for a .1 cap. It would be interesting to ohm out the traces and see if the leads go to the right pins on the plug, if so you could remove the temp sensor and solder the sht on the board.
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I bought an SHT75 to replace my aging sht11 temp/hum sensor in my VP2. Also bought some 4 socket connectors and the sf1 filter. Below are photos of my finished product. I glued the connector and wiring in place. Once the glue set I soldered the connections very carefully as the pins are very fragile with very little clearance between them. I then used silicone making sure to fully seal all connections to protect them from moisture. The silicone also helps adhere everything the to plastic piece that slides into the FARS. This way if I need to replace the sensor I can simply take the old one out and plug the new one in. For the SF1 filter i carefully cut a small notch to accommodate the neck of the sensor. With the sensor in the filter I attached the filter to some backing make from an old temp/hum module pcb board. I cut a hole in the backing (not shown) and covered that using a cutout of the old filter that came with the original Davis sensor. This was done to try to improve airflow. I just finished it this morning, plugged the new sensor in and it seems to be working beautifully. I will post on sensor performance in a couple of days.
If I do another project like this I will find a way to make the potting (silicone) look better. Perhaps using some electronic potting epoxy will be easier to work with. In a few months I will look things over to see how the silicone and connections are holding up to weathering.
(http://i1283.photobucket.com/albums/a541/hwcorder/3e45f213-1620-4af3-8a30-42eb6c51f11c_zps6fe233e7.jpg?t=1374331766) (http://i1283.photobucket.com/albums/a541/hwcorder/65cfc613-7a1b-4f25-85ec-d402e62097f5_zps9827b89a.jpg?t=1374331699)
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Does anybody know if this sensor will work on an old Davis WeatherMonitor II?
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Does anybody know if this sensor will work on an old Davis WeatherMonitor II?
No it won't. WMII used the older type of 'analogue' T/H sensor.
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I'd sure like to have an SHT15 or SHT75 in my VP2. Much as I hate to wreck a new board, I was thinking of buying a Davis 7346.166 temp/hum sensor from Archer and replace the sensor. That board would go in the VP2 and the board that comes out of the VP2 would go in a wireless temp station to add hum sensing to that.
After reading posts above from hwcorder and jerryg, it seems that maybe the board could be built from scratch with the SHT75, a .1 ufd capacitor, possibly the SF1 filter cap which I understand would require modification and a cable with RJ? connector.
Is there more to the board than that, or would that work for a new board w/o the $89 cost of the Davis board as a foundation?
I realize it probably needs to mount to a small pc board for mounting in the FARS and potting & sealing concerns need to be addressed.
For right now I'm just wondering whether to order the board from Archer, or start a grocery list to build from scratch. I haven't physically seen the sensor board, and prefer to build the new board and then do the swap.
Thanks,
Ken
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The sht75 comes mounted on a board with the .1 on it and has four pins to plug into a socket. The filter will fit over the sensor but you do have to cut a little notch in it to fit right. I soldered my cable leads directly to the pins and sealed the connections with some electrical sealant and secured it in the shield with the black cable clamp which holds it just fine. I used the same sealant to secure the filter to the board. Has been working just fine.
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Have any of you had any noticeable changes in readings since going from the SHT11 to the SHT15/75? Any side-by-side comparisons?
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jerryg,
Thanks - that helps. I think I'll go ahead and order an SHT75 and the filter cap. I've been trying to find a socket to make future replacement 'plug and play' with a little dielectric grease. Haven't been successful so far. I'm mainly looking at Newark because they have the sensor in stock.
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Temperature wise they compare pretty good, we do not get extreme changes in temp down here in s.e. texas. Where i notice the real difference is the humidity on the low end is alot better. With the 11 when we had a cold front come through and drop the humidity down to 10 or 15 percent my 11 would run 4 to 5 percent higher and with the 15 it came within 1 to 2 percent. I just like having the better speced sensor because i can lol. I have compared the sensors in the same shield with 2 vp2s uplinking to wu and watching the consoles and other than the low end humidity readings they compare fairly well. Mostly i replaced them on 2 davis boards because they died and why not use the better one. I like to experiment with the weather gear, right now i am comparing the 24hr fars with my homemade pvc tubing shield and a modified dfars. I made some mods to the dfars and for the last week it has been working better than the 24hr fars as far as temp goes.
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I thought i would do an update to this post with the latest info i have come up with. I have tried all kinds of mountings to make a diy sensor and have probably made 30 of them lol. My final and best solution for those who can solder and work with small parts, plus the sensors lower the lag time of the Davis sensors because it gets rid of the big board and filter that Davis uses. I ordered 10 sht 11 sensors from a company in China off of ebay for 8 bucks each with free shipping. I also ordered 10 smd breakout boards for 50 cents each which are just a little larger than the sensor itself and i got the sf1 filter that fits the sht11 from Newark. I had alot of cable an rj connectors on hand plus salvaged .1 decoupling caps from old boards. The total cost of a sensor is about 11 dollars and when comparing my sensor to Davis the temp and humidity lag time is cut down alot. The boards and sensors arrived in about 3 weeks from order, not too bad. As far as mounting the sensors i just let the sensor hang loose in the middle of the 24 hr fars chamber, works fine. For the regular shield i soldered acouple of wires off of the unused solder holes and made a loop on the end so it could be screwed down on the mounting holes, worked fine. The main thing is i made 10 sensors for less than the best price of one Davis sensor.
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Bumping this because it was my motivation to switch my temp/hum over to the SHT75...
I had the SHT75 lying around for almost a year. I finally got the time to solder a 4-pin connector to an old temp/hum cord I had lying around. I lathered it up with some silicone conformal coating and then plugged the SHT75 into the socket.
I didn't have a lot of daylight to play with, but I wanted to test it anyways. The end result is I'm beyond impressed. The response is miles ahead of my old Davis temp/hum sensor. I have a 9V-12V fan in my FARS and I'm getting a lot of movement on the readings...even at night. One thing I didn't expect was for the sensor to report all tenth temp values...even in degF. The Davis sensor I had installed was one of the older analog ones and it skipped some values...i.e. 66.9,67.1,67.3,67.4,67.6, etc. This one reports all missing values in between. Obviously that's not overly important considering the accuracy of the sensor, but it always annoyed me that some values were skipped. I'm not sure if the Davis SHT11 ones skip any or not.
The only thing I didn't have time for tonight was to install a SF1 filter. The more I thought about it, the more I wondered if I could bypass the sensor filter and instead purchase an equivalent filter to install at the opening of my FARS. The SF1 specs state that the filter material is PTFE with polyester scrim. Has anyone ever tried anything like that? I'd assume I have enough torque and CFMs on my fan at 12V to pull plenty of air through a filter at the bottom of my FARS.
Just curious what you all think,
Brian
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I thought about doing the same thing but changed my mine. The reason being is i took the bug screen off of my fars because our humidity at night generally runs in the mid to upper nineties most of the time and my hum. readings took some time to drop in the am and i found that the screen was holding moisture, like the screen on a window does when the wind blows through it and the humidity is high it runs down the screen. I haven't had any bug problems with the screen off anyway. I figured if i did it it would be like having a wet cloth on the opening. I guess if you live in a low humidity place it might work out ok.
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Some reverse engineering:
This sensor, pre nov 2005, has the following malfunctions.
The HR sensor is bad.
Some trougholes are broken (corrosion)
Somebody know the capacitance from the sensor in good condition?
Last picture is a replacement board with TH sensor Sensirion SHT15.
Regards,
Ruud
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It's been a little over a week now with the SHT75. A few obs...
The response time with the 12V fan is insane. I use wxlink for my software with 1-min archive intervals and sometimes notice a 2-3F swing (0-1F more typical) between the highest and lowest temp for that minute. With the old Davis sensor I actually run an error about 1.5F cooler than MADIS during the daytime. Now I see some spikes in temp that put me close to the MADIS highs. At night the "jumps" are less extreme.
The problem is I'm not sure how "real" the high spikes are. My ISS is mounted on a basic tripod with a pipe at about 2m with no obstructions or objects around. I'm wondering if the response is so great that the sensor is able to measure occasional, but brief, bursts of warmth coming from the tripod or mast. The other sensor had enough thermal mass to miss these 30-60 second spikes. I don't think it's a sensor issue because it seems to perform well otherwise.
I'm going to experiment with another siting arrangement and would like some advice. The goal is to give the ISS free space around the air intake. I was leaning toward concreting an 8-10ft galvanized post into the ground about 2.5-3ft. Then put a T at the top with a 3-4ft arm made out of more galvanized pipe. At the end of the arm add another elbow with 6" of pipe aiming downward that the ISS U-bolts can attach to. I'd like some recommendations on what pipe diameter I should use to prevent any shaking of the ISS.
I was planning on using the galvanized pipe anyways for a Maxbotix snow depth sensor that I have so I could just incorporate the ISS into that. Then I can slide the Maxbotix temp probe (for speed of sound extimates) right into the FARS as well.
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I think re-sitting your ISS is a waste of time. I put in my 12V fan in about 4 months ago and became to realize that the temp spikes are a part of actual temperature reality, not sitting problems. Undulations of heat occur, especially in the day, and Davis does not use an "averaging algorithim". With your fan pulling in so much air, the temp you see, is the temp it is. Your tripod has nothing to do with it. Enjoy your accuracy.
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Oh trust me...I've seen the raw 1-min ASOS obs in action and know how real the fluctuations can be. Some of my spikes seem "extra large" though. Heck, maybe they're legit. As I said before, I'm going to be putting up a pole/arm anyways for the Maxbotix MB7554 so I figured I'd incorporate the ISS into it as well. In other words, I'm going to do it anyways. ;) Do you think 2" diam would be steady enough?
I've attached a couple of graphs. All use a 1-min archive interval. Do you guys see similar behavior?
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I archive at 5 minutes so mine's not as "spikey" as yours but looks typical. After the move, please let us know the results as I'm betting on no change in behavior.
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In reference to the earlier post by dendrite (http://www.wxforum.net/index.php?topic=14175.msg264235#msg264235) and some earlier ones in this thread, I'd like to know... Are some T/H sensors analog and some digital? I think I read somewhere that the ISS (or some of them) are able to detect whether the sensor is analog or digital, is that correct? I'd like to know more about this. How can one know which is which, when did they change over, is the accuracy of the analog ones good and do they drift over time? I have a 2 year old VP2 with a much older sensor in it from my previous VP2 which I got in early 2008. I've checked it and it's accurate but I'm curious. I've never had the filter cover off to look at any of them. Also, in my earlier VP2 the sensor board was mounted "upside down" (filter cap pointing down) on the next to lowest plastic disc (no FARS) on hollow standoffs with screws going through them into the disc, but on the newer one it was on the small diameter insulator disc which is mounted to the uppermost shield disc, directly under the rain collector (it is now where it was on the earlier VP2 however, which I think is a better place for it, away from all that black plastic). Any comments on that? I find it interesting that they made these changes.
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In reference to the earlier post by dendrite (http://www.wxforum.net/index.php?topic=14175.msg264235#msg264235) and some earlier ones in this thread, I'd like to know... Are some T/H sensors analog and some digital? I think I read somewhere that the ISS (or some of them) are able to detect whether the sensor is analog or digital, is that correct? I'd like to know more about this. How can one know which is which, when did they change over, is the accuracy of the analog ones good and do they drift over time? I have a 2 year old VP2 with a much older sensor in it from my previous VP2 which I got in early 2008. I've checked it and it's accurate but I'm curious. I've never had the filter cover off to look at any of them. Also, in my earlier VP2 the sensor board was mounted "upside down" (filter cap pointing down) on the next to lowest plastic disc (no FARS) on hollow standoffs with screws going through them into the disc, but on the newer one it was on the small diameter insulator disc which is mounted to the uppermost shield disc, directly under the rain collector (it is now where it was on the earlier VP2 however, which I think is a better place for it, away from all that black plastic). Any comments on that? I find it interesting that they made these changes.
Firstly, why would you have a 2 year old VP2 with a 7 year old sensor in it? :?
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In reference to the earlier post by dendrite (http://www.wxforum.net/index.php?topic=14175.msg264235#msg264235) and some earlier ones in this thread, I'd like to know... Are some T/H sensors analog and some digital? I think I read somewhere that the ISS (or some of them) are able to detect whether the sensor is analog or digital, is that correct? I'd like to know more about this. How can one know which is which, when did they change over, is the accuracy of the analog ones good and do they drift over time? I have a 2 year old VP2 with a much older sensor in it from my previous VP2 which I got in early 2008. I've checked it and it's accurate but I'm curious. I've never had the filter cover off to look at any of them. Also, in my earlier VP2 the sensor board was mounted "upside down" (filter cap pointing down) on the next to lowest plastic disc (no FARS) on hollow standoffs with screws going through them into the disc, but on the newer one it was on the small diameter insulator disc which is mounted to the uppermost shield disc, directly under the rain collector (it is now where it was on the earlier VP2 however, which I think is a better place for it, away from all that black plastic). Any comments on that? I find it interesting that they made these changes.
Firstly, why would you have a 2 year old VP2 with a 7 year old sensor in it? :?
Because the original sensor was suspect. Now secondly, on to my questions?
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In reference to the earlier post by dendrite (http://www.wxforum.net/index.php?topic=14175.msg264235#msg264235) and some earlier ones in this thread, I'd like to know... Are some T/H sensors analog and some digital? I think I read somewhere that the ISS (or some of them) are able to detect whether the sensor is analog or digital, is that correct? I'd like to know more about this. How can one know which is which, when did they change over, is the accuracy of the analog ones good and do they drift over time? I have a 2 year old VP2 with a much older sensor in it from my previous VP2 which I got in early 2008. I've checked it and it's accurate but I'm curious. I've never had the filter cover off to look at any of them. Also, in my earlier VP2 the sensor board was mounted "upside down" (filter cap pointing down) on the next to lowest plastic disc (no FARS) on hollow standoffs with screws going through them into the disc, but on the newer one it was on the small diameter insulator disc which is mounted to the uppermost shield disc, directly under the rain collector (it is now where it was on the earlier VP2 however, which I think is a better place for it, away from all that black plastic). Any comments on that? I find it interesting that they made these changes.
Firstly, why would you have a 2 year old VP2 with a 7 year old sensor in it? :?
Because the original sensor was suspect. Now secondly, on to my questions?
Yes, sir!
No, analog will not work with digital.
Can't tell you how to tell the difference between the two, I know others will.
IIRC the sensor was moved to the bottom to help with corrosion.
Saying your 7 year old sensor is accurate (of course depending on your definition) is dubious at best. I and others speak from experience.
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In reference to the earlier post by dendrite (http://www.wxforum.net/index.php?topic=14175.msg264235#msg264235) and some earlier ones in this thread, I'd like to know... Are some T/H sensors analog and some digital? I think I read somewhere that the ISS (or some of them) are able to detect whether the sensor is analog or digital, is that correct? I'd like to know more about this. How can one know which is which, when did they change over, is the accuracy of the analog ones good and do they drift over time? I have a 2 year old VP2 with a much older sensor in it from my previous VP2 which I got in early 2008. I've checked it and it's accurate but I'm curious. I've never had the filter cover off to look at any of them. Also, in my earlier VP2 the sensor board was mounted "upside down" (filter cap pointing down) on the next to lowest plastic disc (no FARS) on hollow standoffs with screws going through them into the disc, but on the newer one it was on the small diameter insulator disc which is mounted to the uppermost shield disc, directly under the rain collector (it is now where it was on the earlier VP2 however, which I think is a better place for it, away from all that black plastic). Any comments on that? I find it interesting that they made these changes.
Firstly, why would you have a 2 year old VP2 with a 7 year old sensor in it? :?
Because the original sensor was suspect. Now secondly, on to my questions?
Yes, sir!
No, analog will not work with digital.
Can't tell you how to tell the difference between the two, I know others will.
IIRC the sensor was moved to the bottom to help with corrosion.
Saying your 7 year old sensor is accurate (of course depending on your definition) is dubious at best. I and others speak from experience.
In this particular case my 7 year old sensor is accurate. I have checked it. I pressed it into service after the original one began to misbehave. I'm not asking any of these questions for any reason other than to satisfy my curiosity.
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Any T/H sensor post 2005 will be digital. If you were ever to find an analogue T/H (very unlikely) then yes the SIM board should be able to autosense and read data from it OK. Different positions within the shield have been tried for the T/H sensor - it's not really a big deal whichever option you find.
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Has anyone noted that Sensiron seem to have various revisions of their SHT11/15/75 sensors. It seems that older ones use a slightly different formula to convert the raw RH% data to a real world reading than newer ones.
Since the conversion goes on in software - this is probably in the Davis console. Say you were to replace the Davis original SHT11 with a SHT15 or SHT75 - or even simply replace your original SHT11 with a new SHT11 but with a different revision number the RH% figures may be calculated incorrectly.
So far I have found two different formulas - and as far as I can tell the change happened around 2011. So if you have a Davis older than 2011 and replace the sensor the RH% will be calculated differently. I don't think it is a great difference but it is a definite difference.
EDIT: I have just done some calculations and it seems, that although I am correct, there will be a difference, it will be negligible at all readings up to around 95%RH after which a new sensor will output raw data that will be calculated a little low. For example raw data that should be calculated at 100% will actually report as 98% (97.7% actually) - so, in all, no big deal.
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Has anyone noted that Sensiron seem to have various revisions of their SHT11/15/75 sensors.
Adrian, I raised this on the other thread about the new SHT31 based sensors, where older ISS boards need a 0.5C offset. From the spec sheet it seems to me that it uses a completely different formula to do the conversion, so I'm not sure how it works - but it does so I must me misreading something. :?
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I have an SHT15 that I purchased earlier this year from Ryan at SI that maxed out frequently at 98% during the late winter, but it did hit 99% once. And this is with a console/ISS from late 2006.
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... it uses a completely different formula to do the conversion, so I'm not sure how it works - but it does so I must me misreading something. :?
Hi Mark,
Yes, the formula is different (actually, if you look, its just the constants). I put both into a spreadsheet and fed some representative raw figures in. Both produce similar results until you get to a raw figure (circa 3100) that produces results in the high 90% range whereupon the results diverge for the same input. Its not a biggie thinking about it. Most solid state hygrometers are flaky in the high 90s anyway so this additional cause of error makes not a lot of difference.
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Correction: Mark, When I said "If you look, its just the constants", I was referring to the formulas between the revisions of the SHT1x or SHT7x sensors, which indeed do use similar formulas but with different constants. I read your comment in the other thread and see you are talking about different formulas between SHT1x/7x and the SHT31. So we are talking cross purposes. Sorry.
So, indeed, goodness knows how it works. There must be some further conversion going on somewhere. I note the SHT31 is i2c but the SHT1x/7x are serial so the electronics must be different. The SHT35, for example couldn't just be plugged in as a direct replacement (chip swap) - at least, unless, by some clever design, the SHT31 can "understand" serial as well as i2c. The datasheet doesn't mention it though.
Edit: Just realised I really need to read all of that other thread :-)
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I always thought the data out of the sensor was the same with any changes made internal in the sensor chip. I have two 15 sensors bought this year running on two 2008 consoles and iss's and they both show 100 percent in dense fog and right now both are showing 99 percent along with the 31 i am running on my main unit. I thought that the formula was an internal correction so that any changes in the sensor would not change the accuracy if used in an older unit, what ever that might be. Davis is not the only user of this series or sensors. Just a thought.
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Hi Jerryg. Talking about the SHT1x/7x sensors, when they are asked for a RH reading, they return a number in the range (roughly) 100 to 3300. You have to put this through a software conversion routine of your own (e.g. the Davis firmware) to convert to a number 0-100RH%.
The temperature is simpler (and I haven't read it up in detail so I can't talk about it authoritatively). I believe it outputs the temperature directly but you can adjust it in your own software if you like to take account of the voltage you are feeding the SHTxx. I think.
Regarding calibration, the sensors are calibrated at the factory and each one (or each batch - if they only check by the batch. I think they calibrate each one) has been calibrated to output its raw data the same as next one (or next batch).
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It just doesn't make sense that the sensor would not output some preset info so that when changing out a sensor in an existing system it would be inaccurate because of an internal change. Also is the data from the sensor read at the iss and sent to the console correctly or does the console convert the info? Real confusing stuff, like i said i have two 15 reading fine but i also have several sensor i built myself that top out at 98 percent. I have an iss that was made in 2015 with the rest 2011 are earlier and all my consoles are 2010 or earlier, so makes me wonder.
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I'm afraid is that way though. At least for RH%. Before (approximately) 2011, for the SHT1x/7x you had to use one formula to convert the raw data to RH% and since then you have to use a different formula. The two formulas give the same output figure (or as close as a gnat's whisker) for most of the range but in the high 90s the outputs differ by 1 or 2 percent.
As I said above though, it hardly matters as all RH devices get pretty flakey as RH approaches 100% and most software has a setting that says something like "Treat 98% and above as 100%".
The conversion is done in firmware - it has to be - either in the console or in the ISS transmitter, I don't know which.
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I find it confusing that they would make a change that would introduce an error on the high end if you changed to a newer sensor. I reread some specs on the humidity calibration and it said the sensor is compared to a chilled mirror and the correction factor is programmed into the sensor. Well to ease my blown mind i emailed the manufacturer and asked if there would be and error by changing out an old sensor with a new one. Hope i get an answer back because my 2 15 sensors are reading ok on old gear.
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I got a reply to my email today and the correction factor was put in place in 2008. The correction needs to be entered into the users software. So it would seem that any Davis gear would have the correction made to it manufactured from that year on. That's good news assuming Davis made the correction update to their software. With the correction a newer sensor would read about 1% high around 65% range and above 90% would read 1 to 2% low. He said this is still within the 2% error range.
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In blundering about the internet, I found a Chinese company, http://www.sonbest.com/en/product/8000/236.html (http://www.sonbest.com/en/product/8000/236.html), that makes a soil moisture sensor using Sensirion T/RH sensors. The entire assembly can be placed into the soil as the sensor is covered with a sintered metal shield. There is a note in the write up about using this sensor as a T/RH sensor. Certainly, if this entire sensor can be buried, then condensation while it is in the open air should not be a problem.
I found this type of sensor on eBay and Adafruit. One version even comes with an RJ-45 connector. Has anyone tried to use this on a Davis VP2? I'm curious as to the results as I need to place a T/RH sensor only a few feet above the water surface of a lake.
I bought an SHT75 to replace my aging sht11 temp/hum sensor in my VP2. Also bought some 4 socket connectors and the sf1 filter. Below are photos of my finished product. I glued the connector and wiring in place. Once the glue set I soldered the connections very carefully as the pins are very fragile with very little clearance between them. I then used silicone making sure to fully seal all connections to protect them from moisture. The silicone also helps adhere everything the to plastic piece that slides into the FARS. This way if I need to replace the sensor I can simply take the old one out and plug the new one in. For the SF1 filter i carefully cut a small notch to accommodate the neck of the sensor. With the sensor in the filter I attached the filter to some backing make from an old temp/hum module pcb board. I cut a hole in the backing (not shown) and covered that using a cutout of the old filter that came with the original Davis sensor. This was done to try to improve airflow. I just finished it this morning, plugged the new sensor in and it seems to be working beautifully. I will post on sensor performance in a couple of days.
If I do another project like this I will find a way to make the potting (silicone) look better. Perhaps using some electronic potting epoxy will be easier to work with. In a few months I will look things over to see how the silicone and connections are holding up to weathering.
(http://i1283.photobucket.com/albums/a541/hwcorder/3e45f213-1620-4af3-8a30-42eb6c51f11c_zps6fe233e7.jpg?t=1374331766) (http://i1283.photobucket.com/albums/a541/hwcorder/65cfc613-7a1b-4f25-85ec-d402e62097f5_zps9827b89a.jpg?t=1374331699)
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The temp sensor on my 2009 VP2 just packed up (the humidity reading had failed earlier). I have an unused Davis soil temp/moisture probe (no. 6470) and I am wondering is there any way I can press this into service to give me air temp & humidity? If not, which replacement is easiest to put in for somebody with limited soldering skills (SHT15/SHT75 or other)?
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The 6470 is strictly a temp. sensor, NO humidity. The way prices are now for any of the T/H sensors at Scaled Instruments, ought to just buy a whole new one and be done with it.....just my two-bits.............
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Thanks for clarifying that, it is so long since I got it I had forgotten the 6470 was temp only! I looked at the Scaled Instruments site and they are listing a newer T/H sensor module which appears to be complete i.e. it can be fitted without any mods. It costs $58 (including postage to Ireland). It is a bit expensive but the apparent simplicity of the installation is attractive.
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ecobuild check your PM