Author Topic: How to make a black globe sensor  (Read 996 times)

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Offline Michaelpt

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How to make a black globe sensor
« on: July 15, 2017, 08:26:26 PM »
Hi

Made a black  globe sensor plus a wet & dry bulb using 1 wire temperature sensors

This is  to work out WBGT

This has been added to wd software  to work out the Calculation

http://www.weather-above.com/blackball%20sensor.html

http://www.weather-above.com/1wirewetbulb.html

Made a Robust outdoor sheath pattern  thermometers Mod.
http://www.weather-above.com/glassscreentemp.html

Mick  :-)


 
weather-above weather station consists of a  1 wire system ,sky ir cloud temperature ,UV,solar home made modules , live data seismic instrument there is  lot of information on modified sensors,  and 1wire projects pleased  sign my guestbook

Mmichael Parry-Thomas
http://www.weather-above.com/wxgraphic/wxgraphic.php

Online SLOweather

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Re: How to make a black globe sensor
« Reply #1 on: July 31, 2017, 06:02:51 PM »
Thanks, Michaelpt! I have enough Davis sensors and inputs available to try this, and I just ordered a 6" copper sphere.

Online SLOweather

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Re: How to make a black globe sensor
« Reply #2 on: August 02, 2017, 12:27:12 PM »
My 6" copper ball float arrived yesterday.



It's a shame to paint it black, and would look really cool all polished up. 3 halves would make an interesting yard ornament wind feature.

Offline Michaelpt

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Re: How to make a black globe sensor
« Reply #3 on: August 04, 2017, 04:41:39 PM »
My 6" copper ball float arrived yesterday.



It's a shame to paint it black, and would look really cool all polished up. 3 halves would make an interesting yard ornament wind feature.

Yes I think it would make an amazing  Wind feature .Weather display now has a custom tag for the WBGT

Just updated my site with the custom tag Fingers crossed it should update automatically probably will need to refresh the page I think the data updates every five minutes

http://www.weather-above.com/extra%20temperature%20sensors.html
weather-above weather station consists of a  1 wire system ,sky ir cloud temperature ,UV,solar home made modules , live data seismic instrument there is  lot of information on modified sensors,  and 1wire projects pleased  sign my guestbook

Mmichael Parry-Thomas
http://www.weather-above.com/wxgraphic/wxgraphic.php

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Re: How to make a black globe sensor
« Reply #4 on: August 07, 2017, 02:57:28 PM »
OK. My black globe sensor is complete except for a mount. Here are a few details and photos for anyone wanting to make one or compare my construction to Michaelpt's.

I made mine to use a Davis temperature probe. I used a 14" NPT brass pipe cap, a 14" NPT brass male hose barb, some 1/4" brass hobby tubing, a 4-40 stainless machine screw, and a 1/4-20 brass adjusting nut I found in the junk box.

Like Michaelpt, I drilled out the pipe cap to pass the probe and soldered it to the sphere. In order to hold it in place, I screwed it down with a self-drilling machine screw and a washer:



After it was soldered, I removed the screw and washer and drilled out the sphere through the cap.

I made a holder for the probe out of the hose barb, sawing off the barb and drilling it out to just pass the brass tubing. Then I drilled and tapped a 4-40 set screw hole through one of the hex flats.



The probe assembly is made from the brass tubing and the brass adjusting nut.

Hint: The temperature sensor is supposed to be in the middle of the sphere. I dry fit the Davis sensor through the full length tubing. You'll have to cut off the phone jack on the end of the cable, and either splice it or crimp on a new connector later. Save the original connector so you can get the colors right if you are crimping a new one on. I screwed the holder into the cap, and slid the probe and tube in until it hit the far side of the sphere and marked the tube where it exited the holder fitting. Then, since it's a 6" sphere, half way is 3" up the tube from there. I marked that.

I drilled out the nut (now it's a stop) to pass the tubing, cut the tubing to allow about a half inch beyond the stop and soldered the 2 together at the previously marked "halfway" mark, ensuring that the threads pointed the right way. :)

I used the tips of a pair of needle nose pliers to debur and slightly flare both ends of the tube. Be careful not to flare the "inside" end so much that it won't pass through the holder. (Don't ask how I know this...)



Then I slid the temperature probe cable through the tube assembly and secured the probe and the exiting cable with 5 minute epoxy.



While that set, I painted the sphere and set it up for testing.





Next, a mount and building a Davis Wet Bulb sensor. I already have a wet bulb cobbled up for calculations. It's a heck of a lot easier than trying to calculate theoretical wet bulb from other data. :)

« Last Edit: August 07, 2017, 03:00:09 PM by SLOweather »

Online SLOweather

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Re: How to make a black globe sensor
« Reply #5 on: August 07, 2017, 03:06:31 PM »
BTW, a commercial black globe sensor seems to cost $365USD and up on line...
« Last Edit: August 07, 2017, 03:08:42 PM by SLOweather »

Offline Bashy

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Kind regards
Bashy

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Re: How to make a black globe sensor
« Reply #7 on: August 08, 2017, 09:45:27 AM »
At 70mm diameter, it's a little less than half the size of a standard 150mm/6" black globe. It's also aluminum, rather than copper, but I don't suppose that would matter much.


Is this any different?

https://www.labfacility.com/radiation-pendulum-temperature-sensor.html?gclid=Cj0KCQjwn6DMBRC0ARIsAHZtCeOIYWcEGgRZwy5krk5PZKpOvYlseTJcBYPPIFNwIej5Iq2YRy7HTZ8aAtjfEALw_wcB

Offline Michaelpt

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Re: How to make a black globe sensor
« Reply #8 on: August 08, 2017, 10:53:40 AM »
OK. My black globe sensor is complete except for a mount. Here are a few details and photos for anyone wanting to make one or compare my construction to Michaelpt's.

I made mine to use a Davis temperature probe. I used a 14" NPT brass pipe cap, a 14" NPT brass male hose barb, some 1/4" brass hobby tubing, a 4-40 stainless machine screw, and a 1/4-20 brass adjusting nut I found in the junk box.

Like Michaelpt, I drilled out the pipe cap to pass the probe and soldered it to the sphere. In order to hold it in place, I screwed it down with a self-drilling machine screw and a washer:



After it was soldered, I removed the screw and washer and drilled out the sphere through the cap.

I made a holder for the probe out of the hose barb, sawing off the barb and drilling it out to just pass the brass tubing. Then I drilled and tapped a 4-40 set screw hole through one of the hex flats.



The probe assembly is made from the brass tubing and the brass adjusting nut.

Hint: The temperature sensor is supposed to be in the middle of the sphere. I dry fit the Davis sensor through the full length tubing. You'll have to cut off the phone jack on the end of the cable, and either splice it or crimp on a new connector later. Save the original connector so you can get the colors right if you are crimping a new one on. I screwed the holder into the cap, and slid the probe and tube in until it hit the far side of the sphere and marked the tube where it exited the holder fitting. Then, since it's a 6" sphere, half way is 3" up the tube from there. I marked that.

I drilled out the nut (now it's a stop) to pass the tubing, cut the tubing to allow about a half inch beyond the stop and soldered the 2 together at the previously marked "halfway" mark, ensuring that the threads pointed the right way. :)

I used the tips of a pair of needle nose pliers to debur and slightly flare both ends of the tube. Be careful not to flare the "inside" end so much that it won't pass through the holder. (Don't ask how I know this...)



Then I slid the temperature probe cable through the tube assembly and secured the probe and the exiting cable with 5 minute epoxy.



While that set, I painted the sphere and set it up for testing.





Next, a mount and building a Davis Wet Bulb sensor. I already have a wet bulb cobbled up for calculations. It's a heck of a lot easier than trying to calculate theoretical wet bulb from other data. :)



Your probe assembly is amazing , I prefer to use the wet and dry bulb to work out humidity compared to a electronic humidity sensor
But that's just my preference

mick
weather-above weather station consists of a  1 wire system ,sky ir cloud temperature ,UV,solar home made modules , live data seismic instrument there is  lot of information on modified sensors,  and 1wire projects pleased  sign my guestbook

Mmichael Parry-Thomas
http://www.weather-above.com/wxgraphic/wxgraphic.php

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Re: How to make a black globe sensor
« Reply #9 on: August 08, 2017, 03:26:47 PM »
Your probe assembly is amazing , I prefer to use the wet and dry bulb to work out humidity compared to a electronic humidity sensor
But that's just my preference

mick

Thanks!

Here it is mounted on a 1/4-20 bolt and a PVC pipe sleeve.



Back in '09 I made an experimental Davis based wet bulb/dry bulb psychrometer and wrote it up in this topic. It worked OK, except, the Davis temperature probes are sent in full degrees, and a one degree difference in one of the temperatures can make a rather large difference in RH.

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Re: How to make a black globe sensor
« Reply #10 on: August 09, 2017, 05:42:59 PM »
From https://www.designingbuildings.co.uk/wiki/Globe_temperature

Quote
The standard sphere has a diameter of 150 mm. Other sizes do exist, but the smaller the diameter of the globe, the greater the effect of convection on the temperature recorded.

At 70mm diameter, it's a little less than half the size of a standard 150mm/6" black globe. It's also aluminum, rather than copper, but I don't suppose that would matter much.


Is this any different?

https://www.labfacility.com/radiation-pendulum-temperature-sensor.html?gclid=Cj0KCQjwn6DMBRC0ARIsAHZtCeOIYWcEGgRZwy5krk5PZKpOvYlseTJcBYPPIFNwIej5Iq2YRy7HTZ8aAtjfEALw_wcB

Online SLOweather

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Re: How to make a black globe sensor
« Reply #11 on: August 09, 2017, 06:19:47 PM »
Here is today's graph of the black globe temperature,



10 min average wind speed'



and solar insolation.



You can get a feel for how wind and sun affect the globe temperature.

Offline Bashy

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Re: How to make a black globe sensor
« Reply #12 on: August 10, 2017, 12:30:06 AM »
Also, copper is a better heat exchange than the aluminium, shame, could have had a ready made,

I notice it says the standard sphere, not, the official sphere? I struggles yesterday to find any Met Office specs for the globe :/
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Offline Michaelpt

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Re: How to make a black globe sensor
« Reply #13 on: August 10, 2017, 09:07:27 PM »
Also, copper is a better heat exchange than the aluminium, shame, could have had a ready made,

I notice it says the standard sphere, not, the official sphere? I struggles yesterday to find any Met Office specs for the globe :/



Some info about standards

https://en.m.wikipedia.org/wiki/Mean_radiant_temperature
The MRT can be measured using a black-globe thermometer. The black-globe thermometer consists of a black globe in the center of which is placed a temperature sensor such as the bulb of a mercury thermometer, a thermocouple or a resistance probe. The globe can in theory have any diameter but as the formulae used in the calculation of the mean radiant temperature depend on the diameter of the globe, a diameter of 0.15 metres (5.9 in), specified for use with these formulae, is generally recommended. The smaller the diameter of the globe, the greater the effect of the air temperature and air velocity, thus causing a reduction in the accuracy of the measurement of the mean radiant temperature. So that the external surface of the globe absorbs the radiation from the walls of the enclosure, the surface of the globe shall be darkened, either by the means of an electro-chemical coating or, more generally, by means of a layer of matte black paint. [1] This thermometer actually measures the globe temperature (GT), tending towards thermal balance under the effect of convection and radiation coming from the different heat sources in the enclosure. Thanks to this principle, knowing GT allows the mean radiant temperature MRT to be determined.[1]According to ISO 7726 Standard, the equation that is used most frequently (forced convection) is the following:

Mick
weather-above weather station consists of a  1 wire system ,sky ir cloud temperature ,UV,solar home made modules , live data seismic instrument there is  lot of information on modified sensors,  and 1wire projects pleased  sign my guestbook

Mmichael Parry-Thomas
http://www.weather-above.com/wxgraphic/wxgraphic.php

Offline Bashy

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Re: How to make a black globe sensor
« Reply #14 on: August 11, 2017, 01:24:41 AM »
Thanks Mick, that'll do it :)
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Bashy

Offline nellyt

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Re: How to make a black globe sensor
« Reply #15 on: October 04, 2017, 03:47:18 AM »
...and here is mine.
The sphere is a plastic ball float from a farm shop which is a fraction of the cost of a metal one.
I know the globe is meant to be metal .... this one is a prototype, I have a copper sphere also which I may make so I can compare plastic vs metal.

Mechanically very stable because of the two mounting points at 45 degrees.
A UNC bolt into the ball fitting is then used with the lock nut to pull the globe back onto the short length of white plastic pipe. This gives a rock solid attachment improved further with the plastic tube between the box and center of the ball, this holds the sensor (1 wire DS18S20) in the middle of the globe and adds another axis of mechanical stability. Probe can be withdrawn and replaced via tube if needed.

Daily plot attached
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