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Load Cell Amplifier AD620

Question asked by afnan on Mar 15, 2013
Latest reply on Mar 15, 2013 by ScottH

Hello

I know AD620 is an old part but it is available at my place . I intend to develop a Load Cell amplifier. Load cell is 2mV/V. I am planing to use AD620 for it. Following are my calculations

 

Excitation Voltage for Load Cell = 5V

Full Scale for load of 140 kg = 2mV X 5V = 10mV

Gain = Vout/Vin = 5000mV/10mv = 500

From formula of Rg we calculate it to be 98.99 Ohm


I have worked on Following schematic

 

 

Capture.PNG

What is the problem?

1. If i do not attach Ref with anything the voltage at pin 6 is 1.9 Volts (no load on load cell)

2. the max voltage is reached at 6 mv Input. even gain calculation is done. But we have added 100 Ohm resistance.

3. Is there any difference between AD620AN, AD620AR and AD620ANZ ?

4. In some circuits i see that at sense + and sense - sometimes before feeding these to operational amplifiers some resistance is added. what is the purpose of adding these keeping in mind the voltage is already in mV

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