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Last modified by Mengting Qiu on 2024/09/02 17:23
From version 6.1
edited by Mengting Qiu
on 2024/09/02 13:49
Change comment: There is no comment for this version
To version 4.1
edited by Mengting Qiu
on 2024/09/02 11:55
Change comment: There is no comment for this version

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16 16  In some case, the measurement and real value are in different range, but they are both linear, we have to calculate the real value with the measurement we can use a simple Linear Calibration.
17 17  
18 18  
19 -**Example:** we have a water level probe, the measurement range is 0 ~~ 10 meters, and the output is 4~~20mA, this means the when the water level is 0 meter, the output is 4mA, when the water level is 10 meters, the output is 20mA.
19 +Example: we have a water level probe, the measurement range is 0 ~~ 10 meters, and the output is 4~~20mA, this means the when the water level is 0 meter, the output is 4mA, when the water level is 10 meters, the output is 20mA. We can make a coordinate axis as below:
20 20  
21 -We can make a coordinate axis as below:
21 +1. Y axis is the real value, from 0 ~~ 10 meters
22 +1. X axis is the probe output , from 4~~20mA
22 22  
23 -1. (% style="color:blue" %)**Y**(%%) axis is the real value, from 0~~10 meters
24 -1. (% style="color:blue" %)**X**(%%) axis is the probe output , from 4~~20mA
25 25  
26 -We use two points to make the linear line: Point1(x1,y1) = (4,0), Point2(x2,y2)= (20,10).
25 +We use two points to make the linear line: point1(x1,y1) = (4,0), point2(x2,y2)= (20,10). Since the reading is linear, all probe output and real value is on this line, so we can calculate the real value by probe output in two steps:
27 27  
28 -Since the reading is linear, all (% style="color:blue" %)**probe output**(%%) and (% style="color:blue" %)**real value**(%%) is on this line, so we can calculate the real value by probe output in two steps:
27 +Step1: Get k(Slope) for the line: k=(y2-y1)/(x2-x1) = (10-0)/(20-4) =10/16= 0.625
29 29  
30 -* **Step1:** Get (% style="color:blue" %)**k(Slope)**(%%) for the line:
29 +Step2: Get real value (y):
31 31  
32 - k=(y2-y1)/(x2-x1) = (10-0)/(20-4) =10/16= 0.625
33 -
34 -* **Step2:** Get (% style="color:blue" %)**kreal value(y)**(%%):
35 -
36 36  k=(y-y1)/(x-x1)  
37 37  
38 38  ~-~-> y = k*(x-x1)+y1 = 0.625 * (x-4) + 0.
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39 39  
40 40   ~= 0.625 * (x-4)
41 41  
42 -When x=12mA , y=5 meters
37 +When x=12mA , y=5 meters
43 43  
44 44  When x=8mA, y= 2.5 meters
45 45  
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