We have purchased some AD620BR instrumentation amplifier but we found that the
measured gain is different from the one given in the datasheet (i.e. G=1
(49.4k/RG)). We are using a resistor of RG=5.6K but we have a gain of about 2.
Furthermore, when we use a resistor of RG=inf (not connected) we found a gain
of 0.8 instead 1 !!
How many devices have you tested?
How are you measuring the gain? Please send circuit diagram and description of
your test setup.
The gain accuracy on the AD for unity gain is production tested to 0.02% over
temperature and this parameter is a guaranteed maximum.
If you are measuring gain different to the datasheet spec, the most likely
cause is that the part is damaged (so try a handful of devices) or that
measurement set up is not correct. While it is not impossible, it is highly
unlikely that parts have been supplied to you outside of spec.
If you have checked a number of devices and checked your measurement setup and
are still convinced that the parts are outside spec, please get back to me and
I will review your application and/ or we can organise a further analysis.