Soil Resistivity Meter

من طرف Admin* السبت مارس 24, 2018 12:45 am

Soil Resistivity Meter

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Assume Product Limitation
+ The detection / measurement is less than 15 meters
+ Source is square wave alternating current
+ Based on " Wener Method " or " Wener four-point electrode arrangement " or " four electrode probe in the wener configuration "

Block Diagram

Unit Ohm meter
Resistivity is the resistance of unit length of material of unit cross sectional area . It decreases with increases in moisture content of the material until its minimum value is obtained . This minimum resistivity value is the resistivity of the material .

Square Wave Generator Circuit

Plan an experiment using DC , Direct Current

Soil Resistivity Meter 12053108_1002860333091480_412940764_n

a )

Soil Resistivity Meter 12047712_1002860346424812_1247270644_n

b)

Soil Resistivity Meter 12092776_1002860359758144_1367366036_n

c)

Figure above a ) , b ) , and c ) show the plan setup . Here is the plan , the aim for this first test is to test whether the reading is stable or not . That all , so we minimize the setup just to read the voltage and current . This is just the plan , we will come with a proper paper after finishing this experiment using DC and not AC .

Formula

You may ask what we need to place for 's' and 'd' . 's' stand for spacing between probe while 'd' stand for depth of the probe .

Figure above is a good reference . 's' and 'd' can be any value .

Soil Resistivity Meter 12092776_1002860359758144_1367366036_n%2B-%2BCopy

The precaution is if "s > 20 d" , then we can ignore d . Just like figure above .

Soil Resistivity Meter 12092776_1002860359758144_1367366036_n%2B-%2BCopy%2B%25282%2529

If "s < 20 d" , then we need to take 'd' into calculation . Just like figure above .

Experiment

Soil Resistivity Meter 12047290_1002866653090848_1894569868_n

Figure above show experiment being conduct using probe of 4cm depth and 4cm spacing . The DC voltage use is set to 20V . The upper screen on the power supply show a DC voltage while the lower screen on the power supply show a DC current .

The plan is to take a reading more than 5 reading with interval of 5 minutes . If you notice that the current reading on the power supply show 0 ampere . So we assume that the reading is below 10mA . The power supply current reading is only able to read two decimal place which mean it is only capable to read current more than 10mA . The SANWA multimeter show the voltage reading of two middle probe .

Figure above show the full result obtain.

Soil Resistivity Meter 12166819_1003303319713848_1601184409_n

Figure above show the full result obtain for another set of experiment with some minor change on parameter .

Reading current using multimeter 1
As we know that above power supply can read maximum of 10mA . Hence we need a multimeter set to ammeter in order to read current less than 10mA .

So here is he multimeter . First we need to do some calibration in order to make sure that the ammeter if functioning well .

We convert the multimeter to a sketch . So now we have a on paper multimeter . Easy to explain . Set the rotated to 20m dcA . This mean that the maximum current will be read by the multimeter is 20mA .

Soil Resistivity Meter 12167089_1003304106380436_1055126393_n

The 'A---' symbol mean that the current to be measure is in DC .

Ok , so here is the setup . Power supply is set to 5V and current limiter is set to maximum.

Resistor Explanation
Now we will move to resistor .

Theoretically , we have this resistor . I will take this resistor and measure it real value using multimeter which is set to ohm-meter .

After check the real value using multimeter , i now have this exact value of resistor . Then the second question is what mean by 1/4 watt . 1/4 watt is the maximum rated of the resistor .

Soil Resistivity Meter 12048470_1003309296379917_1845508499_n

What is mean by maximum rate . In short , if exceed 1/4 watt of power , the resistor can no longer retain the value of 463 ohm and may get hot or burn because of excess heat .

To use this resistor , we must maintain the power to below 1/4 watt . From the calculation below ,we cannot allow current more than 23mA to pass through this resistor .

Simplification of Circuit Sketch to Schematic

Ok , again here is the setup .

Simplify the circuit by changing the sketch ammeter to ammeter symbol .

Simplify the circuit by changing the power supply sketch to DC supply symbol .

Simplify the circuit again by integrating the current flow to the wire .

Lastly we have the schematic draw .

Current Analysis

We know that the resistor receive 5V from DC supply .

This is because there is no voltage drop at the ammeter . The ammeter can be model as a short circuit .

Theoretically if we use this setup , we will get a reading of 10.8mA on the ammeter .

Reading current using multimeter 2
Old multimeter seem not work . Here is a new one . Fast check to see whether this multimeter is working on Ammeter mode or not .

Soil Resistivity Meter 12177832_1009231715787675_2024000564_n

Oopppss . Something is wrong . Nothing is coming out at the display .

Soil Resistivity Meter 12188416_1009232235787623_732239245_n

Ahaaa . . . There is no battery . Need to find one in nearer shop and install it inside this meter .

Soil Resistivity Meter 12178240_1009235135787333_943286894_n

Ahaaaa . . . The meter is working now . The meter is in voltmeter mode . DC label on the meter screen represent the current mode as DC Voltmeter mode . Now we try to change the mode to AC Voltmeter mode by pressing the FUNC. button .

Soil Resistivity Meter 12178298_1009235192453994_1802834400_n

No worry at all , it is functioning . Don ' t worry at the 0 . 020 V . That only a noise .

Soil Resistivity Meter 12181797_1009235229120657_597910956_n

Now we change the mode to ohm meter mode . The screen show OL which mean open loop . No resistor to be measured on the probe .

Soil Resistivity Meter 12179778_1009235289120651_1344314713_n

Now we try to measure some resistance by placing it on the probe . No problem at all . Notice that the resistor is rated at 10k ohm with 5% tolerance . This mean that the resistor value is in the range of '+' and '-' 5% from 10k ohm . As expected , the resistor will not read exactly 10k ohm and in the range of 5% from 10k ohm .

Soil Resistivity Meter 12178271_1009238432453670_2113301949_n

Then we will check whether the ammeter mode is functioning or not . Set the mode to DC Ammeter mode .

Soil Resistivity Meter 12177861_1009238509120329_695554473_n

We will setup this schematic.

Soil Resistivity Meter 12179362_1009238655786981_1504011070_n

Into a real setup. Then take the measurement .

Soil Resistivity Meter 12182244_1009238722453641_1923861627_n

Ahaaa . . . The meter read 10.97 ma which is approximately near to the theoretically value . The ammeter mode can be use .

Soil Resistivity circuit

Soil Resistivity Meter 12177712_1009242792453234_887238847_n

Now we will make a soil resistivity setup as above .

Soil Resistivity Meter 12177770_1009242905786556_196286291_n

This is the real setup . We need two multimeter , first multimeter will use as a voltmeter and the another one as a ammeter . Both multimeter will be in DC mode .

Several result
Several result that has been recorded.

Soil Resistivity Meter 12185995_1009245915786255_2045251588_o

Soil Resistivity Meter 12190656_1009246455786201_142473586_o

Draw Table in excel
Now we will transfer the data from paper to excel . The data has been key in to excel as below :

Then we will make up a bit the table in excel by merge some of the table . Compare the result after merger with previous picture . It looks better now .

1 . Go to home
2 . Drag all the data , center the word and data .
3 . Drag the cell that you want to merge , press "Merge & Center" to merge the two cell into one .

Then we will draw a table for the data and digit . Drag all the required data and digit , tright click on it and then choose format cell .

Then we will format the cell accordingly .

1 . Go to Border .
2 . Select colour . Dark gray just nice .
3 . Click outline border to enable it .
4 . Click inside border to enable it .
5 . Press OK to finish it .

Now the table look just nice .

Create graph in excel
Now we will create graph in excel .

1 . Go to Insert .

2 . Drag these 4 cell .

3 . Select Scatter graph .

4 . Select Scatter with smooth lines and markers .

Then you will get something like picture below .

Currently we have graphed the 2cm current . Then we need to graph the 2cm voltage , 3cm current , 3cm voltage and so on . . . .

1 . Click on the graph generated .

2 . If you did not click the graph properly , the "Design" will not pop out .

3 . Press "Select Data" icon .

4 . Then , "Select Data Source" window will pop out .

5 . Press Add in order to add another column of data .

After click Add , another window will pop out .

1 . "Edit Series" window will pop out .

2 . Initially , "Series Name" is blank . Click on it .

3 . Click 2cm voltage in order to link "2cm Voltage" cell to "Series Name"

2 . You will notice that the series name will be fill with some address .

1 . Initially , "Series X values" is blank . Click on it .
2 . Click on and Drag down number '1' , '2' and '3' in order to link "Series X values"
1 . You will notice that the "Series X values" will be fill with some address .

Clear the "Series Y values" as picture below .

Then we will add "2cm Voltage" column to "Series Y values" .

1 . Initially , "Series Y values" is blank after previous step . Click on it .
2 . Click on and Drag down number '1.85' , '1.8' and '1.79' in order to link "Series Y values"
1 . You will notice that the "Series Y values" will be fill with some address .

Then press ok . Then using the same step , add the order parameter as picture below .

Now , we will make up the graph it a bit .

Look just nice .
2cm voltage and current were colored by light blue .
3cm voltage and current were colored by purple .
4cm voltage and current were colored by red .

To Be Continue

Update
24 July - Assume Product Limitation , Block diagram , Unit Ohm Meter , Square Wave Generator Circuit

11 Oct - Plan an experiment using DC , Direct Current , Formula , Experiment
12 Oct - Reading current using multimeter , Resistor Explanation , Simplification of Circuit Sketch to Schematic , Current Analysis
26 Oct - Reading current using multimeter 2 , Soil Resistivity circuit , Several result
2 Nov - Draw table in excel , create graph in excel

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