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
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?
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 1 Wire Wet and Dry Bulb SensorUntitled
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 aspirated solar radiation screen temperature humidity solar module
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
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
[li][i]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 ?
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
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.
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.
