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Example:
You have a load cell with the specifications given below
Maximum Capacity = 100 lbs
Rated Output = 2 mV/V
Excitation = 10 VDC
Bridge Resistance = 350 ohms
For a default setup with the CSG110 the 0-100 lbs would correspond to 0-10 VDC (or 4-20mA)
Now you would like to have the 0-100lbs (sensor output from 0-2mV/V at 10 VDC excitation) correspond
to 5VDC to 10VDC (CSG110 output) respectively.
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In the problem above we need to move the zero load on the sensor to equal 2.5VDC and the maximum load on the sensor to equal 5VDC.
Thus, our output span needs to be 5 VDC and our zero shift needs to be 5 VDC.
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The equation for calculating the Resistance Needed to shift the zero is below:
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Rz = -Br(abs(Zo) - 0.5E) / (2*Zo)
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Where:
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Rz = Resistance Needed |
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Zo = Zero Offset in Volts |
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E = Excitation Voltage |
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Br = Bridge Resistance of sensor
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We know that Br = 350 ohms from the given info.
We also know that in order to decreas the span from 10 VDC to 5 VDC that we half the Excitation voltage so
E must be 5 VDC. Thus, all we need to calculate is the Zo in
order to utilize the above equation.
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Zo = Zero Shift / *Gain
*Gain = (output of CSG110) / (input of CSG110)
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Thus:
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Gain = (5V * 1000)/(2mV/V * 5V) = 500
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Therefore Zo:
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Zo = Zero Shift / Gain = 5 V / 500 = 0.01 V or 10mV
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Threrfore Rz:
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Rz = -Br(abs(Zo)-0.5E) / (2*Zo) = -350(abs(0.01)-0.5(5V))/(2*0.01) = 43575
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Rz = 43.575K ohm resistor
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