Problem with an IC - AD621

[djalli]

I use AD621 to amplify with gain 10 by connecting pins 1 and 8 and the output is slightly different. Instead of getting 3volts for 300mV 100Hz input I get 3.9volts.
Is something wrong I am doing here?
Vcc=6volts.

Is any better version of AD621? I use it because of CMMR is over 95dB.
thanks.

 

[Hughes]

May be the connection between pins 1 and 8 has a resistance.

 

[djalli]

May be the connection between pins 1 and 8 has a resistance.

sorry I forgot. connecting pins 1-8 makes the gain 100. I do not have them connected.
There is else something wrong.

 

[H_u_n_t_e_r]

...from analog device ad621 data sheet page 15

GROUNDING
Since the AD621 output voltage is developed with respect to the
potential on the reference terminal, it can solve many grounding
problems by simply tying the REF pin to the appropriate
“local ground.”