Hi everybody!
I'm using an INA125 to amplify the output signal of a load cell. The INA125 is single supplied (5V), and I have an ADC that acquires voltage values between 0 and 3.3 V. The lower saturation voltage of the amplifier is 0.3 V so I decided to set an output offset which value is (0.3+3.3)/2=1.8 V in order to acquire both positive and negative values. So I have connected IAref pin of INA to LM317 output which voltage output is 1.8V.
As you can see in the datasheet, INA's output is given by the expression:
V_out = V_offset + G[(v_in+)-(v_in-)] = 1.8 + ....
The problem is that I can't read 1.8V at INA's output when no load is applied (i.e. there is no strain)
First I balance the bridge using a pot (I use an Agilent 34401a to read bridge's output) and then I should expect an output of 1.8V.
When I don't connect gain resistor the output is exactly 1.8V, but when I connect gain resistor the output isn't 1.8 V and it is very unstable. I can assure that wheatstone bridge is balanced (2-3 microvolts) and it drifts 10 microvolts maximum.
I can't explain this behavior. Any help is well-accepted! Thanks a lot!
I'm using an INA125 to amplify the output signal of a load cell. The INA125 is single supplied (5V), and I have an ADC that acquires voltage values between 0 and 3.3 V. The lower saturation voltage of the amplifier is 0.3 V so I decided to set an output offset which value is (0.3+3.3)/2=1.8 V in order to acquire both positive and negative values. So I have connected IAref pin of INA to LM317 output which voltage output is 1.8V.
As you can see in the datasheet, INA's output is given by the expression:
V_out = V_offset + G[(v_in+)-(v_in-)] = 1.8 + ....
The problem is that I can't read 1.8V at INA's output when no load is applied (i.e. there is no strain)
First I balance the bridge using a pot (I use an Agilent 34401a to read bridge's output) and then I should expect an output of 1.8V.
When I don't connect gain resistor the output is exactly 1.8V, but when I connect gain resistor the output isn't 1.8 V and it is very unstable. I can assure that wheatstone bridge is balanced (2-3 microvolts) and it drifts 10 microvolts maximum.
I can't explain this behavior. Any help is well-accepted! Thanks a lot!
