ina125 gain not acurate

[strasni_betmen]

Hi,

I have a load cell setup with ina125 the way datasheet says. Everything works good, but I can't seem to figure out why is output not amplified like formula says.

Formula says: Gain = 4 + (60k/Rg)

My setup:

Rg	Input(mV)	Output(mV)
119 Ohm	0,2	27,3 -> but output should be 101,64
Gain(calculated with forumula
508,202

This means that the amplification is around 136 instead 508.
What could be the reason that I don't get the right amplified output?


Kind regards

 

[FvM]

The specified INA125 offset voltage is in the same order of magnitude as the measured input voltage. To determine the gain of your circuit correctly, you need to measure the output for two different input voltages.

 

[crutschow]

The offset is the output with the inputs grounded. Subtract that value from your measured output with the 2mV input to get the true output gain.