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Methods on calculating rainfall
Capacitance level switch
Magnetic reed swich
Tiping bucket guage
After doing alot of resarch on which method would be the best to measure rainfall the strain guage was the best option. It was the cheapest and the most available method. A strain gauge is a long length of conductor arranged in a zigzag pattern on a membrane.
When it is stretched, its resistance increases. So our aim is when rain falls into a container we wil be able to measure the difference in resistace to calculate the amount of rain fall.
We managed to get our hands on an old digital weighing scales which we hoped to find some sort of strain guage set up that we could use for our project.
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Got the cover of by undoing clips at each corner
Inside we found a little load cell connected to the electronics with a simple set of leavers transferring the weight from the upper platform to the load cell.
The basic functions of how the scales works as follows
Weight is evenly distributed through the brackets and levers
Long levers are connected to a beam
A stain gauge is bonded on the beam
Deflection of beam causes the change in resistance
Output signal is translated to weight reading on LED display.
Method of how the strain guage/load cell works
The load cell wires are:
Hope fully this wil be the set up of our project
Strain guage - wheatstone bridge - plc - computer
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Once i got the weighing scales apart i started to investigate how the load cell operates,The scales has a 5 vdc input coming from two 3vdc lithunium batterys.Its then regualated down to a 3vdc which is going to the load cell
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CONCULISON WITH STAIN GUAGE
After apply voltage to the strain guage i was getting no change on the output side no matter how much strain i put the guage under. my next move was to try it with a wheatstone bridge again the output was extremely small. At this stage i was after wasting alot of time and i was no further on with my end of the weather station. I informed lads of the situtation and decided it was best to try and come up with another idea.
INTODUCTION TO MY NEXT IDEA
In my work place in ibm we use small pressureisation units alot especially for the chillers for the data centre to keep the flow of cold water circulating the building through various cooling units.If a leak develops on one of the loops the pressure on the pressurisation unit will drop, causing no flow and dropping out the chillers causing serios problems.On the small pressurisation unit there is a high and low limit and is controlled by a simple ball cock so if pressure drops the ball cock will drop which in turn will open a vavle to start filling the small tank.Then when the pressure builds back up and the tank becomes full the ball cock knocks of the water.
This system made me think,the ball cock acts like a float so if i can get some method to guage the float this could be the best way to measure the depth of rain water.
Basically i neesded some sort of switch that when when the float rises it would give me a signal.
A counter system was one method we came up with every time ball cock moved the leaver would activate the read switch and send a voltage to the plc. Problems with calibration down the road so we werent keen on this idea
Another idea was a pully method that when the float rises a pully system would operate and in turn would turn a potentiometer, with its change of resistances through a wheatstone bridge through an opamp with suitable gain we could get a suitalbe voltage to work with
The potentiometer was the way forward but we were complicating things with the pully system and after group disscusion we decided to try and use the leaver on the ball cock to turn the potentiometer. So maybe cross this bridge when it comes.
Notes on potentiometer
A potentiometer is a manually adjustable
. The way this device works is relatively simple. One terminal of the potentiometer is connected to a power source. Another is hooked up to ground (a point with no voltage or resistance and which serves as a neutral reference point), while the third terminal runs across a strip of resistive material. This resistive strip generally has a low resistance at one end; its resistance gradually increases to a maximum resistance at the other end. The third terminal serves as the connection between the power source and ground, and is usually interfaced to the user by means of a knob or lever. The user can adjust the position of the third terminal along the resistive strip in order to manually increase or decrease resistance. By controlling resistance, a potentiometer can determine how much current flows through a circuit. When used to regulate current, the potentiometer is limited by the maximum resistivity of the strip.
BUILDING OF THE INSTRUMENT
The first thing i needed to get was a small tank preferably the same as the tank in presurisation units in ibm,Hopefully the come with a ball cock already hooked up if not will buy seperately.
Had to buy the tank and the ball cock seperately wich came to 15 euro all purchsaes in herbys the local hardware store. My first job was to drill an inch hole in side of tank to install the ball cock. I was then tinking to get a proper flow of water into tank through the vavle on the ball cock i needed some method of collecting and transferring water in a controlled manner into the header tank. This idea would be ideal for measuring rainfall from the gutter of a roof, using the roof to catch the water with the gutter directing the flow of water into my storage tank
This is when I came up with the idea of a second tank to collect the water. Which i reckon didnt need to be the same has a the header tank just somthing to gather the water so it can be piped to the header thank, so had a look round the garage at home and found an old plastic bin.
Which was prefect
depth 16inch length12inch
I drilled an inch hole in the bottom of the bin and got suitable copper fittings from the hardware to connect up a small bit of pipe . Seen as im not to hot at the plumbing my father give me a hand to connect the small bit of copper pipe to the bottom of the bin. I then attached a water hose to the small bit of pipe which will connect into the header tank
My plumbing woulnt be hectic
Once I got this done, I had 2 more problems i needed some sort of an upright to stand the bin on and my 2nd problem is that i need some sort of control on the flow of water going in to the header tank or else i would have serious floods everytime i tested
The control the water i was going to simply use a tap so again I plumbed a tap on to the pipe coming of the ball cock which was tricky.
I needed a bracket of some sort to hold the storage tank(bin) obove the header so that the hose can connect in to the tap.
Had a few ideas, one was to make up timber frame with two shelves, sit the storage tank on top and the header on the bottom but this would take a fair bit of time,money plus had to tink of transportation. My next idea was to make a steel frame with half inch angle iron as i had all the materials and equipment at hand this would be the fastest, cheapest method.
There was of course one snag IM NOT GREAT AT WELDING. Thankfully my father said he would give me a hand.
Instead of putting legs on the frame i decided to use the the top of the header tank to balance the bracket with the storage tank on top. So i cut 4 bits of angle in a square the exact size of the header tank got them welded together, then came of that with 2 uprights.My next move was to cut 4 more bits of angle the same square as the storage tank get them welded together and simple weld that to the 2 uprights.
All the cutting was down with safety in mind
My father busy tacking the frame together
The building of my rain guage is now completed next step is get my potionemeter fitted to a bracket so that it can be operated by the movement
of the ball cock
At this stage i had the idea of having the leaver rising up through the centre so i got a piece of angle iron, welded two small brackets on to the piece
and rivet it down going across the middle of tank as show below. Hopefully get enough movement from the ball cock to operate the potioemoter.
The next step was to solder the connections and then fit potionemoter to the bracket of rain guage
Once i got the pot fitted I then tested my rain guage to see if everything working ok. I got my multimeter and connected to the pot
so i then filled the storage tank full of water and slowly opened the tap. The water started to flow into header tank ball cock started to
rise and I got a change of resisance. So with the results of this my next step is to build a circuit and change the output resistance to
an output voltage using the wheatstone and possible an op amp
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