Problems with INA128

[jm4goncalves]

Hi,

im doing a project to school but im having some problems..

my project is a distance transductor with a linear potentiometer, for that i used a wheatsone bridge connected with a amplifier INA128, but the problem is that i don,t have gain in my Vout..

My source in the bridge is 5V, and i use the same 5V to connect in 7-pin, 4-pin is connected to earth as 5-pin..

To change the gain i used an potentiometer (470K) in RG, but every time that i change the value of RG my gain in the Vout dont change..

What im doing wrong??

I will appreciate any help!

Miguel

 

[ericgibbs]

hi Miguel,
Can you post a circuit diagram ,would like to help.

E

EDIT:
One common problem is that +inv and -inv inputs to the INA128 are reversed, so the output signal tries to go below 0V.!

 

[Ian Rogers]

Firstly... Use a new thread ( I have done this for you )..

Secondly... 470k pot is far to large the wheatstone will give you 0 - 20mV ( ish ) An ADC can read 0-5v a gain of 250.... RG around 220 ... I would use a 500 Ω pot.

Oh.. One other thing... I use the 1NA126 This thing doesn't do anything until the signal reaches enough to output .7v... I have to put 2 diodes on the ref pin to jack it up to 1.25v (ish).