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Author Topic: BlackGlobe Temperature Sensor WBGT index  (Read 701 times)

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Offline MichaelPT

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BlackGlobe Temperature Sensor WBGT index
« on: June 19, 2017, 03:37:08 PM »
Hi

going to make a set of temp sensors calibrating temperature sensors  to each other ,before  mounting  ,adding the black globe ,ambient air temperature ,wet bulb temperature is make by using a glass tube with the temp chip inside then  sealing   both ends then applying a cotton tube over the temperature senser tip ,this  is to keep the wick saturated  using  distilled water

The ambient temperature sensor will be mounted in a glass tube same specification as the wet bulb sensor with out the wet wick

The black globe temperature sensor I am going to use a copper ball and Mount the temperature sensor in side

The BlackGlobe Temperature Sensor for Heat Stress (BlackGlobe) measure  radiant temperature.  This measurement, along with the measurement of  ambient air and wet-bulb temperatures, is used to calculate the wet-bulb globe  temperature (WBGT).  The WBGT index combines the effects of temperature,  humidity, radiant heat, and wind into one single index employed to express  environmental heat stress

Mick
« Last Edit: June 19, 2017, 03:43:13 PM by MichaelPT »

Offline nellyt

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Re: BlackGlobe Temperature Sensor WBGT index
« Reply #1 on: June 27, 2017, 09:47:58 AM »
I am doing the same.
I was however under the impression I just needed to measure the globe temperature and could derive wet bulb temperature from ambient and relative humidity?
Have I missed something?

Offline MichaelPT

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Re: BlackGlobe Temperature Sensor WBGT index
« Reply #2 on: June 30, 2017, 01:42:47 AM »
I am doing the same.
I was however under the impression I just needed to measure the globe temperature and could derive wet bulb temperature from ambient and relative humidity?
Have I missed something?

Yes  you are correct , what sensors are you using?

I like to make my sensors in sets so the data will be coming from only one location
as this set WBGT sensors will be in mounted a 120cm mostly in full sun

Info of my other sensor sets


My weather station is made up from 1 wire modules

I have a 1 wire wet & dry bulb temperature sensor.
Which are mounted in a small Stevenson screen box
With a small fan drawing air across the wet bulb
Box is mounted at 120cm in shade most of the day
In the same box is a set of glass Thermometers Sheathed ordinary wet & dry Met Office pattern (BS692). So I check the 1 wire against the Sheathed wet & dry sensors
http://www.weather-above.com/1wirewetbulb.html   http://www.weather-above.com/Stevenson%20screen%20repair.html


I use a Solar radiation aspirated shield ,with a
HIH-4031 Honeywell Humidity Sensor and a DS18S20 digital thermometer.As main station air temperature & humidity mounted at 144cm in shade most of the day http://www.weather-above.com/solarrdscreen2.html
http://www.weather-above.com/pcbTempHumSolar.html

The new sensor is a DS18S20 mounted in a 6 inch copper ball panted black. This will be mounted in full sun . next to it will be a wet bulb temperature sensor using a DS18S20 mounted in a tube with a wet Cotton Wick in full sun . next to this will be the air temperature with a white shield on top mounted at 120cm  this set of sensors
Will be used to work out the WBGT Index


Mick






Offline nellyt

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Re: BlackGlobe Temperature Sensor WBGT index
« Reply #3 on: July 02, 2017, 03:39:11 AM »
Photos of my plan attached.

I will use the ambient temp and humidity from my radiation shield for the other parameters used to derive WBGT. These are a Hobby Board temperature and humidity = DS18S20 and a Honeywell sensor.
I don't/can't want a true wet bulb temperature using a wick as I will never keep the reservoir topped up! I need something that takes zero maintenance.

Tg is measured using this set up :

  • Building bracket bent at 45degrees
  • Black plastic ball float (about 5inches). This is a prototype using a plastic ball. I also have a copper 6in float to paint black if this prototype is successful. Getting the copper balls is a hassle in New Zealand, this one came from UK. I don't particularly like it. If you have a better source of metal spheres let me know.
  • Short length of uPVC piping (not yet cut to length) to stabilise the ball onto the bracket
  • Ball held in place with a cavity wall/plaster board fixing. This will be inserted into the drilled out mounting point of the ball and hopefully expand inside. Just mounting the ball with a bolt does not seem very stable - I get high winds.
  • Sensor is a 1 wire DS18S20
  • this enters sphere through a cable gland tapped into sphere
  • small metal box plus another cable gland provide a coupling between the sensor and the reset of the stations wiring. This means the sensor can be replaced without major rebuild
  • My current unresolved item is how to keep sensor in the middle of the sphere. I am thinking there will be a hollow plastic or metal tube between the metal box through the two cable glands and half way into sphere. The probe will then be slide down this tube from inside the metal box. I have not resolved what to use here. It needs to be UV stable and low diameter, with an ID to take the sensor and firm enough to not sag when it gets very hot inside the sphere. Metal may be the only option but not sure on the conduction implications. I may just sleeve it in plastic over the short distance it is exposed to the atmosphere[/li/
How are you resolving getting the sensor into the center of the sphere ?
« Last Edit: July 02, 2017, 03:42:02 AM by nellyt »

Offline MichaelPT

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Re: BlackGlobe Temperature Sensor WBGT index
« Reply #4 on: July 02, 2017, 10:06:16 PM »
Photos of my plan attached.

I will use the ambient temp and humidity from my radiation shield for the other parameters used to derive WBGT. These are a Hobby Board temperature and humidity = DS18S20 and a Honeywell sensor.
I don't/can't want a true wet bulb temperature using a wick as I will never keep the reservoir topped up! I need something that takes zero maintenance.

Tg is measured using this set up :

  • Building bracket bent at 45degrees
  • Black plastic ball float (about 5inches). This is a prototype using a plastic ball. I also have a copper 6in float to paint black if this prototype is successful. Getting the copper balls is a hassle in New Zealand, this one came from UK. I don't particularly like it. If you have a better source of metal spheres let me know.
  • Short length of uPVC piping (not yet cut to length) to stabilise the ball onto the bracket
  • Ball held in place with a cavity wall/plaster board fixing. This will be inserted into the drilled out mounting point of the ball and hopefully expand inside. Just mounting the ball with a bolt does not seem very stable - I get high winds.
  • Sensor is a 1 wire DS18S20
  • this enters sphere through a cable gland tapped into sphere
  • small metal box plus another cable gland provide a coupling between the sensor and the reset of the stations wiring. This means the sensor can be replaced without major rebuild
  • My current unresolved item is how to keep sensor in the middle of the sphere. I am thinking there will be a hollow plastic or metal tube between the metal box through the two cable glands and half way into sphere. The probe will then be slide down this tube from inside the metal box. I have not resolved what to use here. It needs to be UV stable and low diameter, with an ID to take the sensor and firm enough to not sag when it gets very hot inside the sphere. Metal may be the only option but not sure on the conduction implications. I may just sleeve it in plastic over the short distance it is exposed to the atmosphere[/li/
How are you resolving getting the sensor into the center of the sphere ?

Hi

Using  the same copper float  , I drilled a 5mm  hole in the copper ball.  I found a brass fitting which a cable gland can be screwed into it after cleaning around the hole I placed the brass fitting over the top and soldered in place

I then made a temperature probe using a  DS18S20 component after soldering the wires I thread it through a heat resistant plastic tube then sealed the top of the tube and over the component soldering joint a rubber compound which they use to make seals in refrigerators and also used in very hot environments I ordered the liquid rubber from China cost about 1.99  including delivery I've used the existing fitting to Mount the ball to a bracket I'm using a very long Bolt which is locked in place with a locking nut

If I'm ok sometime tomorrow I will take some pictures and post them

 I ordered the copper ball float from eBay
Mick

Offline nellyt

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Re: BlackGlobe Temperature Sensor WBGT index
« Reply #5 on: July 02, 2017, 10:57:49 PM »
Any idea what type thread the bolt is into the bottom of the ball? I dont think it is metric ?

Offline niko

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Re: BlackGlobe Temperature Sensor WBGT index
« Reply #6 on: July 02, 2017, 11:49:47 PM »
Doesn't the ball need to be thermally isolated from the mounting bracket ? (For best results.)

Offline BWX

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Re: BlackGlobe Temperature Sensor WBGT index
« Reply #7 on: July 03, 2017, 05:05:30 AM »
is this the same thing
How will you do the calculations, can WD do it?
« Last Edit: July 03, 2017, 05:38:24 AM by BWX »

Offline MichaelPT

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Re: BlackGlobe Temperature Sensor WBGT index
« Reply #8 on: July 04, 2017, 12:05:14 PM »
Doesn't the ball need to be thermally isolated from the mounting bracket ? (For best results.)

Thanks, I think you are correct it would be better to be isolated from the bracket,

Need a rethink on the mounting

Please see images so far

New bracket the centre bolt is now covered with white plastic to help deflect.


« Last Edit: July 04, 2017, 07:58:17 PM by MichaelPT »

Offline BWX

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Re: BlackGlobe Temperature Sensor WBGT index
« Reply #9 on: July 05, 2017, 05:19:17 AM »
A ceramic washer should suffice on the insulation

Offline nellyt

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Re: BlackGlobe Temperature Sensor WBGT index
« Reply #10 on: July 05, 2017, 11:08:12 PM »
Good point on the insulation.
That will be needed on my implementation between the sphere and bracket if they are touching, or I just make my bit of PVC pipe a fraction longer so that there is no direct contact between sphere and fixing bracket.
It does not though get round the fact that the copper sphere is attached with a metal thread, so that would mean using a plastic screw thread.

I've also realised that my cavity fixings are not going to be outdoor rated so i may just have to use a threaded stud and lock nut.

Potential solution to holding the sensor in the center found at the local tip yesterday.....and old UHF/VHF antenna made of extruded aluminium rod ... just the correct OD for a cable gland and ID for the sensor. Not ideal because its not plastic.

Offline niko

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Re: BlackGlobe Temperature Sensor WBGT index
« Reply #11 on: July 05, 2017, 11:45:37 PM »
Here we can get tubing in glass epoxy, and carbon fiber. You could use the epoxy tubing with a compression connector for both the sensor mount and it's also strong enough for the mount to the bracket.  I think the epoxy tubing is used for kite frames so hobby shops may have it.

What diameter is the ball?


Offline nellyt

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Re: BlackGlobe Temperature Sensor WBGT index
« Reply #12 on: July 06, 2017, 01:34:07 AM »
Sphere is 6"

Yes I can get nylon/epoxy tube it's just a long trip to town look at and select. Maybe this thread will make me do it.

Not sure about the compression fitting...what sort were you meaning, it would need screw into a tapped hole on sphere

Offline niko

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Re: BlackGlobe Temperature Sensor WBGT index
« Reply #13 on: July 06, 2017, 02:14:02 AM »
It will be interesting to see what the response time will be with a 6" ball.

I was thinking of this type of fitting, and soldering it to the ball.

Offline Weather Display

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Re: BlackGlobe Temperature Sensor WBGT index
« Reply #14 on: July 15, 2017, 03:10:23 AM »
I have added this to WD now, see under setup, advanced/misc, latest .zip update