As written in previous posting, I will design and make a test equipment to measure the thrust of propeller and the motor/engine in aeromodelling parts. This measure will help to design rc model, such as fixed wing and multicopter. Before designing a total airframe, need to know first the characteristics of the motor/engine and matching propeller size. I used the load cell with specifications was written on this posting. My load cell is 15Kg of full scale with output voltage about 2mV/V. I used the amplifier capable to gained up to 1000x with source 5V for load cell reference voltage. This mean will give output about 10mV in full scale of 15Kg load.
How to a simple calibrate ?
Since I do not have the standard weight of high-priced, this way is simple to use a digital scale which has an accuracy of about 0.1gram and can measure up to 1Kg. Next, weigh any load with digital scale, record the result. Then move to the load cell and measuring with a digital voltmeter on the load cell amplifier output voltage.
|Photo of digital scale||Photo of Load cell|
|362.2 gram||105.1 Volt|
|528.5 gram||151.8 Volt|
|63.5 gram||19.8 volt|
|275.9 gram||80.7 volt|
|34.1 gram||11.7 volt|
|14.7 gram||6.1 volt|
|30.2 gram||10.6 volt|
|130.2 gram||39.1 volt|
|40.4 gram||13.2 volt|
|101.2 gram||30.7 volt|
Plot data using SCILAB
The commands to plot the datas using SCILAB as follow:
->weight = [362.2,528.5, 63.5,275.9,34.1, 14.7,30.2,130.2, 40.4,101.2] weight = 362.2 528.5 63.5 275.9 34.1 14.7 30.2 130.2 40.4 101.2 ->volt=[105.1,151.8,19.8,80.7,11.7,6.1,10.6,39.1,13.2,30.7] volt = 105.1 151.8 19.8 80.7 11.7 6.1 10.6 39.1 13.2 30.7 ->size(weight) ans = 1. 10. ->size(volt) ans = 1. 10. ->plot(weight,volt,'ro-.') ->xgrid ->title("Loadcell amplifier calibration") ->xlabel("Load (gram)") ->ylabel("Loadcell amplifier output (mV)")
Will result a graph as follow:
How much’s the output voltage of amplifier at zero load ?
On zero load output voltage at zero load is 2.8mV. My amplifier can not adjust to 0.0 volt, because there null offset voltage. On arduino using 10bit adc with 5V ref, will convert into (2.8/5000)*1024 = 0.57344 less than 1, or will known as 0 decimal.
How to calculate voltage per Kg or mV/Kg ?
From the above data, I would find the average value using Microsoft Excel, will be obtained as follows:
So output voltage of amplifier will be: 0.267012014 mV/gram or 267.012014 mV/Kg.
The output amplifier according to specifications from 0 up to 4.3 volts. So that the maximum load that can be read are: 4300/267.012014 = 16.104Kg, near specification of loadcell about 15Kg.
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